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Discussion in 'GT4 Tuning' started by Scaff, Mar 18, 2005.
Reply to a post in another thread, moved here as its a more accurate place to discuss the subject (i.e. its about braking)
I don't know of any figures published on the web, but can certainly state my own experiences from testing, brake lock seriously increases stopping distances.
What I can do is post up details from Going Faster (the manual of the Skip Barber racing school) in regard to it, but that will have to wait until tomorrow.
I do have to ask why you are asking?
Is it simply out of interest or a belief that locked stopping distances are not greater than threshold braking?
Because if its the latter you have already answered the question yourself
"aka - rotating tires turn cars, locked ones do not."
Because rotating tyres also stop cars (as long as the are rotating slower than the car is travelling), locked ones don't (well not anywhere near as well).
I will however post up the Skip Barber info tomorrow.
This should be of interest in the mean time
Do I need to sit and think about this? No, not at all.
And (although I have already posted this)
Cars slow down because the tyres are rotating at a slower rate than they would normally be for the speed the car is travelling at (they are travelling slower than the car is), in the same way that they accelerate due to tyres rotating at a faster rate than the car is travelling. If a tyre stops rotating you get immediate tyre lock-up, and big problems.
The exact percentage that these speeds can differ by (in both acceleration and deceleration) is referred to as the Slip Percentage and will vary from tyre to tyre, and to a lesser degree the same tyre type will vary from car to car. Its the principal reason why the single biggest factor in potential stopping distances is the tyre/road interface.
I suggest that its not me that needs to sit and think about that for a moment.
You seem to have read it and not taken it on-board
And now from above
You will struggle to find exact stopping distances for lock-up, because from a braking point of view its totally the wrong thing to do, threshold braking (which technically ABS does for you) is the correct thing to do and braking figures for this is of far more use when comparing car to car.
Why in your example figures above do you once again suggest that in a non ABS equipped car that stopping distances for a car with locked tyres are shorter than one with no lock-up (i.e. threshold breaking)? This is simply not the case. I did ask the question
..which you have not answered, but do once again seem to be saying.
What you are suggesting does not hold with the laws of physics, a car with locked tyres will take longer to stop that one braking on the threshold. Please stop suggesting otherwise.
Now in your Viper example you say that the magazines braking figures compare an 03 and 02 Viper (which would be 3rd generation and 2nd generation I believe), however the only details I can find on the web close to this are from Motortrend, who state
Link - http://www.motortrend.com/roadtests/coupe/112_0306_2003_dodge_viper_srt_10/
Now that could be any previous version of the Viper, and despite you previously saying
even a quick look at the 2nd generation to 3rd generation cars shows some very significant changes in all the areas you have mentioned (and more particularly to the wheelbase, front & rear track, length and height), including at least three changes in tyre size during the 2nd generation cars life and a change in the actual OE tyre between the 2nd and 3rd generation cars!!! And that's without knowing any information about changes to the suspension set-up and/or brake balance.
The reduction in braking distance is very impressive, but certainly can be attributed to a wide range of different factors between the 2003 car and previous RT/10's.
you win scaff.
by posting breathlessly long posts, and reposting some more, not understanding/misquoting, every argument with you becomes more than I can bear.
you're real problem?
you snipped the part where I specified 02
275 - Front / 335 - Rear
275 - Front / 345 - Rear
BOTH - same kind of tire
you left out the nearly identical weight dist.
While I'm SURE the track/wheelbase had MASSIVE effects on the braking, are you being so blatently ignorant to assume 1% weight dist, along with slight differences in wheelspacing accounts for 80 ft?
Isnt it magical that the braking distances never got better the whiole way through the Viper's existance, until ABS was introduced?
Are you suggesting ABS doesnt stop cars faster?
but then why do race drivers prefer no ABS?
P.S. Physics do not allow tires to turn at a slower rate without losing SOME grip. and they then therefore do not have full traction. There is a thresehold, it's just not what you seem to think it is. It's the difference between a little past the limits, and a lot.
Tires moving faster than car = burnout
Tires moving slower = lock-up
now understand there are different levels of tire spin and lock.
This is what I found that may or may not help better understanding of braking, from rscnet.org.
Vehicle Dynamics for Racing Games
By Ted Zuvich
I think because brake coeffecient vs slip curve can change at the different car speed, it make the sophistication of ABS important. If ABS only tuned for spesific speed, then at above or bellow those speed, the ABS not optimal. A sophisticated ABS would make tire slipage in max braking coeffecient range at any speed, load, road condition, etc.
I think GT4 ABS is not properly tuned, since using max BBC make braking worse. If GT4 ABS is properly tuned, even with max BBC, it can maintain maximum braking coeffecient at any speed. Maybe to make tuning more interesting (harder) .
"A couple of months ago, Alpine posted some pacejka coefficients and other tyre information in the High Gear Racer Physics forum (this thread). I've copied over the meaty bits of the thread and edited out the chat.
This data is apparently from a Michelin tyre test rig, and Alpine says that the tests were done 12 years ago.
First up, a series of measurements that are NOT pacejka coefficients but which are interesting and relevant..... SI units are used throughout, and the italics indicate the values for which I don't have a clue what's being measured. The unknown words (caou, etc) are in French "shorthand" "
rolling effort = rolling resistance?
First off part of your problem comes from looking at this as an argument (you seem to have a habbet of wanting to argue), secondly please let me know exactly what I have not understood or misquoted.
In regard to post 542 above, I simply inserted the quotes to provide background to anyone coming across this thread without any prioir knowledge of the original thread (as this is a far more suitable thread). If however you are refering to my posts in general, well its a subject that requires explination and I would rather provide documented and sourced information, if this takes space then I make no apology. No one is being forced to read it.
No I did not snip it at all, go back and actually read what I posted.
I said that while you stated that you had read an article stating the braking distance change was between the '02 and '03 model cars, I could not find any article that suggested this at all. Rather the only source I could find (which I linked to) stated the difference was between the '03 and "previous RT/10s".
Now that’s quite different to your claim, so please provide a source for your '02 to '03 claim and stop mis-quoting me.
Why are you acknowledging that some of these factors (track and wheel base) can have a massive effect, and then dismissing others and saying they could not (in part) account for this reduction?
In addition weight distribution is an important factor, but certainly not the whole story as far as load transfer (an important secondary factor is stopping distances), as a significant lowering of a car’s Centre of Gravity would also have a massive impact. This is incidentally not a figure I can find for any generation of the car, yet could play a major role in its performance (as it does in the case of the BMW M3 vs the M3 CSL).
I'm saying that a combination of these factors (with the addition of some you will not find published, such as brake bias and CoG) could have this effect on stopping distance.
Its also quite interesting to note that it would seem that the Viper got ABS before '03.
Source - http://autos.msn.com/research/vip/overview.aspx?year=2001&make=Dodge&model=Viper
and from a piece on the '03 model.
Source - http://www.edmunds.com/news/autoshows/articles/45676/page017.html
Source - http://www.answers.com/topic/dodge-viper
Now while the MSN piece is refering to the Coupe it does state that the 2002 model year car featured ABS, and the Edmunds article about the '03 car says that it will feature an uprated version of the (and I quote) "current four-wheel disc ABS system", which would seem to also be saying that the final versions of the '02 car already featured ABS. Now it may well have been an option, but it would apear that it was avaliable, and possiably as early as the 2001 model year.
ABS does not reduce a cars potential stopping distance (but for many drivers it will stop the car faster than they could), I have quite clearly and repeatedly said this.
Source - http://www.tc.gc.ca/roadsafety/tp/tp13082/abs2_e.htm#stop
Source - http://www.donpalmer.co.uk/cchandbook/managegrip.htm
And just in case you don’t know who Don Palmer is - http://www.donpalmer.co.uk/
As far as racing driver’s thoughts on ABS I have already posted the following from former racing driver and current instructor Ross Bentley.
As far as a preference most racing drivers don’t even get that luxury as the vast majority of racing series do not allow ABS to be used as part of the series regulations.
Physics most certainly does allow tyres to turn at a slower (or faster rate or develop slip angles) and increase grip.
Tyres develop tractive forces (grip) as slip percentages and/or angles increase, up to certain point (the threshold) after which they reduce, often very quickly. This is clearly described in every book and work I have ever read/studied/taught on the subject.
Skip Barber covers this here
It is also covered in the following piece on slip angles
Source - http://www.donpalmer.co.uk/cchandbook/modelgrip.htm
Its also worth mentioning that the post above by Suchayo also says exactly the same thing.
If however you really want the physics on it then here we go
The above is an extract from The Physics of Racing by Brian Beckman Phd, the full piece with all of the physics involved can be found here http://www.miata.net/sport/Physics/Part21.html
Tyres spinning = 100% Slip Percentage under acceleration
Tyres Locked = 100% Slip Percentage under deceleration
What occurs up to the tyres slip percentage is an increase in the available tractive forces (grip) and what occurs after it is a reduction in the available tractive forces (grip) often a very rapid loss towards total lock or spin.
I understand these concepts very well (I have taught them for a wide range of manufacturers), and have clearly illustrated them with quotes and links to informed and credible sources both on the web and in print.
okay, now you're telling me Viper's came with ABS before 2003?
Since clearly sarcasm is completley lost on you, and you can't comprehend the simplist of posts, I'll try even simpler.
What was the best motor trend stopping distance published for a 96-02 Dodge Viper RT/10, or GTS?
Now, what's the average stopping distance of a base family coupe?
NO actually I'm not. Three seperate source that I have provided links too have all clearly stated that the Viper came with ABS before the '03 model year and possiably as early as 2001.
That is not me saying it at all, as however you have not been able to provide any form of proof of your claim I am at present far more inclined to believe these three (and there are more) sources.
Now can you please provided details of the article you have mentioned that states the '03 car has a much shorter stopping distance than the '02 model. After all I provided a source for the stated quote of the different stopping distances being between the .03 and 'previous RT/10s.
And what sarcasm would that be exactly? Because I see little evidence of it in any of your posts, all I see are unsubstansiated claims.
Getting slightly off topic with this now are we not?
I don't believe I have claimed to be able to provide these figures or commented on them at all.
What I have come across however is yet another source that disputes your no ABS prior to '03.
Source - http://www.autoworld.com/apps/news/FullStory.asp?id=601
So either every source of this info is wrong or you are?
You also appear to have ignored the vast bulk of my post with regard to ABS and Slip Percentages/Angles & Grip.
that's weird.... the 2002 I drove locked the tires up, and kept skidding at full lock-up until I let off the brakes.... hmmmmm...?
musta been malfunctioning somehow....
Really? no way! <--- (sarcasm)
I know you did'nt.
so now we only have to acknowledge what we state we want to beforehand?
ok, than stop mentioning slip angles, and most everything you're 100 meter page entails, as I havent mentioned most of it.
The POINT, since you did'nt bother, is 160ft 60-0 is WORSE than the average family coupe, and that was the BEST 60-0 distance I saw for the Viper before the introduction of ABS in 2003
So, why does the sports car with massive tires, and brakes, have such a horrible stopping distance? why can't it slow down as fast as heavier, unsporty vehicles?
guess you answered you're own question here huh?
unless I said something regarding slip angles, and went into detail on those things?????...............??
I just realized the beauty of your position, Scaff.
By arguing differences with unknown consequences, and posting thousands of numbers of which only the obsessed or insane would read, you are relying on ignorance, as you know very well that no one can translate the stopping differences cause by .04% weight distrobution, and .7in track (no, these numbers are for illistrative purposes), and therefore, by using this unguided speculation as a basis for the car suddenly stopping 60 or 80 ft shorter, however much satisfies you, you can't really be proven wrong, because no matter how slight the differences are, they DO exist.
So instead of focusing on the 20 total mm of rubber difference, and almost identical critical factors, you would rather take slight differences, and exploit them as though this makes the car's braking oh-so drastically different.
The reality? The differences in the car's braking are 90% contributed to these things: Weight - Tires - ABS System - Brake system
If you disagree with that, I feel bad for you, and retract all my previous statements.
I don't recall stating that there was an article stating the differences between '02's and '03's directly. if I did Show me. otherwise, shut up about it already, it'd only further prove your misquotes.
secondly, I don't recall you stating different stopping distances, simply that the '03 stops 80ft shorter from 100mph
thirdly, what is a .03? did you perhaps, mean '03? the buttons arent side-by-side ya know.
I DO recall saying the '02's stopped in 160ft from 60 not 100
I DO recall saying the '03's stopped in 100 from 60 not 100
so yes, if you mean I posted different distances from 60, you are right.
if you mean you argued (i'm sorry, debated, since the differences are huge), but if you mean you retorted with 100-0 distances, you would, again be right. however, I fail to see the relevance in regard, given I quoted different speed distances.
You see, the problem with looking up old road tests online, is that they rarely show exact numbers, and therefore you cannot use them for exact numbers.
However, if you would like, ask me for my address, and send me postage money, and I will personally mail you 2 of my old Motor Trend's, or R&T's, whichever the results are in. And you can even keep the mags!
And you have based youre statements about when ABS was fitted to the Viper on this!!!
I thats your idea of sarcasm dont give up the day job.
However In regard to slip angles, etc that I have mentioned in my posts I quite frankly do not care if you have not mentioned it before.
Im going to be rather blunt here, if you dont want or like a detailed explanation of a subject then quite simply do not post up opinion as if it were fact and make sure you actually know what you are saying is actually correct before you do so.
I actually think the main reason you dislike my posts is because every single one of your factual statements about braking I have proven to be incorrect.
And how do you expect me to answer than without using the terms I have been for the last few posts.
The answer is the same as the fact that a Range Rover will stop quicker than a Lotus Elise.
You want to know the answer, then read all of this thread.
You did say something regarding all of this, when you questioned my point about rotating tyres slowing cars and L4Ss post, and then claimed that ABS reduces stopping distances and claimed that non-ABS cars would stop quicker with locked tyres. You opened the floodgates yourself however by claiming to know the physics involved.
All these claims require an answer and if you feel uncomfortable with that or the manner of the answer then dont make statements you cant back up.
Lets look at these one at a time.
Weight Of minor importance in determining stopping distances, it has no real significance. Load transfer on the other hand does, it is however a secondary effect.
Tyres Quite agree on this one, it is the prime determining factor in a cars stopping distance. The tyre road interface determines the shortest possible stopping distance, any other factor will either allow this potential to be maximised or increase the distance taken.
ABS Has no effect on a cars shortest possible stopping distance, as I have already illustrated. May allow some drivers to maximise the cars potential, but it can not increase grip and there-fore cant reduce stopping distances.
Brake System Massively complex and can cause significant increases in stopping distance if not set-up or maintained well (particularly in the area of brake bias), can not reduce stopping distances below that provided by the tyre grip for the same reasons as ABS.
If you dont agree with any of the above, then please dont feel sorry for me, simply explain exactly why I am wrong (and Skip Barber, etc are as well). I also dont mean just say I am wrong, explain why.
As far as only the obsessive or insane being interested in my posts, well each to there own. I would however point out that those insane obsessive people with an interest in this kind of detail include those who design and engineer cars, work in motorsport or the industry as a whole, race engineers and drivers. Quite a list, you see anyone seriously interested in driving or racing will want to know this, quite evident in the fact that most of the sources I have quoted are racing drivers or instructors.
As for these factors not being able to be calculated, pure nonsense, working in the industry I know full well that they can be calculated and often are.
The charge I find most insulting is that I am relying on peoples ignorance! Please, you are the one posting with no explanation or reference; I have posted clear links that explain exactly what I am saying.
You original quote on the subject was
Now while you do not say that it comes from a particular magazine article, it certainly suggests that. You also did not even provide a speed figure for the 03 Viper.
In addition the statement I made in regard to this was simply that ABS would not account for the difference, a point which is now rather clear as both the 02 and 03 car would it appears have actually had ABS.
I have a better idea, why not just scan them or take a digital photo and then post the images up here.
I have extracted the following bit
Are you aware of the irony of posting a comment like that and including a spelling error in it, its arent not arent. That before we even get onto the simply huge number of spelling errors that inhabit youre posts.
I would however question exactly why you wanted to bring it up? Seems rather silly to pick on a single typo, when you are far from a colossus in the area of grammar.
Either malfunctioned or deactivated ABS.
The Dodge Viper has four wheel disc antilock brakes standard since 2001.
//edit: official source by DaimlerChrylser Corporation:
(follow the link to "History" and scroll to 2001):
Firsthand experiance is now a bad source of information????
Actually, all of you're numbers posted have not been translated into what they account for in real life driving terms.
They're simply numbers right now.
If that's true, than the Lotus either has A. Horrible brakes. B. (more likely) something I've been claiming for a looooong time. Most foreign automakers put inadaquetly sized tires on many of their "sports" coupes, and/or sportscars
There are no floodgates, we're on the internet.
The "floodgates" need to remember that when a tire is moving slower than an automobile it is attached to, it IS slipping.
If a vehicle is moving at 70mph, and the tires are only moving at 60, please, in real world terms, tell me how it is NOT slipping.
it may be going faster than zero, and is not fully locked, but it is slipping.
No. Weight is absolutley crucial.
You see that highlighted part? without weight, it can't happen.
Plus, weight has the exact same effect on braking as it does accelerating.
It makes tires harder to spin, and lock-up. This extra resistence makes lock-up and tires spin more effective at moving the car than a lighter car. This is overidden by the extra momentum the car has, (or doesnt have) all the extra weight keeps pushing the car harder than a lighter car, causeing more tire wear along with it.
Remember, heavier cars almost always have larger wheels/tires, and therefore, it may sometimes seem like the weight has less consequence then it does.
It is not the "prime determining factor"
put 4 drums on a car with the best tires.
make a car weigh 40 tons, with the best tires. (see bigrig)
Put shoddy pads on a car and feel the fade from 100-0
Make brake pads so weak they can't lock the tires up.
No, tires are no more important than any of the other factors I mentioned, it just seems like it on sportscars, because they all have the required equipment to do the other jobs.
CAN have effect on stopping distance.
What if the ABS won't take the tires to the threshold?
ABS can INCREASE stopping distance, but it cannot DECREASE it.
All a brake system can do is have the ability to lock the tires up, even during repeated, hard, prolonged use.
this is why most cars built by aftermarket companies do not have shorter stopping distances, simply better resistence to fade.
I believe we agree on this
I take you've completed Skip's driving/racing school?
But those people are familiar with the numbers, and can translate them into everyday, real-world terms. they do this with ease. because they've been trained, and have been dealing with them for a while.
A common man can calculate them?
YOU havent even calculated them.
You are. You post a bunch of fancy numbers, numbers that mean nothing to the average person. You fail to translate them in any kind of useful way. Then, when they don't understand, they either assume everything you say is correct, or get a headache.
Just because somebody knows the exact numbers for differences to calculate different cars abilitys, does NOT mean they know what it translates into real-world action. (an engineer)
And vice versa, just because somebody know what differences in the real world equate to, doesnt mean they know the physics.
But both understand it. (A driver)
Look, if you're going to effectively say "I'm too lazy and not educated enough to go through your numbers, but I say you're wrong" you are not doing anything except shooting your own credibility directly in the foot.
Factual errors like you've made about the Viper's ABS - and hanging your logical hat on them - are just further weakening your position. And doing allthat while adopting a much holier-than-thou attitude is not a wise move.
It is if you use it to make a blanket statement about an entire model year based on a single experience, exactly as you have done here. You seem to have based the statement that ABS was not fitted to the Viper before '03 based on it. A point that has now been shown to be incorrect, a point I recall you decided to laugh at me about.
So yes in this case its proven to be a spectacularly bad source of information.
Its very true, and the Elise certainly does not have horrible brakes. But it does have rather small tyres (then again it is a very small car), large tyres would totally ruin the handling if the car (and yes i have driven numerous examples).
I did not at any time say that a tyre rotating slower than the car was not slipping, you however did seem to want to mock me for saying that this is what slows a car down. A point which again you have been proven wrong on.
What I said was that a tyre rotating slower that a car will develop slip and increase its grip up to the tyres Slip Percentage limit, after which it would lose grip. A point which you also disputed and again were proven wrong on.
Weight and load are not the same thing at all, load and how a car transfers it about during braking is an important secondary factor. Have you actually bothered to read this entire thread or are you once again simple stating opinion as if it were fact?
Please read and try and understand both parts I quoted, I also said (and you quoted) The tyre road interface determines the shortest possible stopping distance, any other factor will either allow this potential to be maximised or increase the distance taken., oh look I have just explained your 'crappy' brakes part.
That does not change the fact that the primary determining factor in potential stopping distance are tyres.
Once again it seems that you have not read what I have posted, instead you find the need to shout almost exactly what I have been saying all along.
Please remember that you were the one claiming that the reason why the '03 Viper could brake so much better than the '02 Viper was ABS, you also claimed repeatedly that ABS stops cars quicker.
You seem to have changed you mind on that one?
Living in the UK I have not had the opportunity to take Skip's school, I have however completed a number of advanced road and circuit driving courses in the UK, I have attended a race school in the UK.
Having worked at various levels in the motor industry for well over a decade I have also taught in the motor industry for the last eight years (including vehicle dynamics and driver training). I am also a member of the Institute of the Motor Industry, hold training and motor industry (management & technical) qualifications.
Now I've laid out my credentials in this area, I would be interested to hear yours.
I'm not a qualified engineer yet I can understand them.
I did not realise I was required to calculate them into working example here, silly me thinking that providing source material to provide detail of my posts was a good idea. Maybe I should just post up conjecture and opinion as if it was fact and then throw my toys out of the pram if questioned.
No, sorry I would rather provide people with a good solid range of source material to back up what I know to be correct, if someone is too damn lazy to read it that's simply not my problem, what it does not do is make it any less correct.
Should anyone have a problem understanding any of the information I have posted or linked to, then I am always ready to answer any questions that may arise. Provided the person in question is actually willing to learn, something I ask of all my course delegates.
By the way a good driver wil know the physics related to this (remember most of my quotes and sources come from race drivers and instructors) and good engineers will know the 'real-world' driving, such as the chassis and suspension engineers that work for Lotus (who almost to a man/woman are excellent drivers). How else do you think a good race driver can communicate with his team of engineers? Unless both have a sound understanding of the other it doesn't happen and teams like that rarely win races.
well, you and duke both think I should be educated enough to calculate them, so why can't you?
if you can't figure out what I'm saying, just let it go, you're probabley on drugs.
I say that not as an insult, rather a possible explanation for the FACT that you havent understood a word of my posts, posts which are pretty simple in point.
P.S. How can tires be more important if they rely on everything else to be up to par?
Tires grip isnt maximized? upgrade brakes.
Now brakes arent maximized.
now tires arent maximized.
do I need to continue?
tires are no more important, they just seem like they are to people who can't grasp the overly simple fact that they are just the FINAL factor, and therefore their differences are more obvious.
look outside the obvious.
I am more than capable of calculating the vast majority of the pieces I have linked to (with the exception of the Physics of racing piece - which I do however fully understand), however I totaly fail to see how that would change any of this?
Are they less correct because I have not carried out these calculations?
Besides most of the pieces I have linked to do not contain any calculations, rather they are well written and clear descriptions of the forces at work. This would seem to indicate that either you have not read them, or you have read them and not understood them.
Lets take your claim about any degree of slip on a tyre causing a lose of grip, you said
.one of the pieces I used to dispute this was as follows.
Now all that you had to do here was read a single sentence and look at a graph, no calculations were required at all. The single line clearly disputes your claim in that it describes grip increasing as slip develops, up to the Slip Percentage that the tyre can take (its threshold) and then reducing. The graph simply helps to visualise this point, the entire piece is clear to read and very simple to understand.
I followed that by an example showing the same happens with slip angles, the only one of the pieces on this area that contained any calculations was the final one from the Physics of Racing. However I even highlighted the relevant section, for which no calculations were needed to understand it, the piece provides proof for those that need it that the laws of physics back up the first two quotes. Please remember it was you that claimed the laws of physics supported your view, dont then sulk if a piece on the physics involved is used to refute this.
I totally fail to see what is over complex or unclear about the first two quotes at all, no calculations are required and only a basic grasp of the forces involved are needed to understand it (the third is more complex, but I have never disputed that). I think that your claims that I am overcomplicating the matter are a smoke screen for one of two possibilities. The first being that you do not yourself understand what I have posted; the second that you understand it perfectly well, but do not like the fact that it proves you wrong.
As far as accusing me of being on drugs not being an insult? Well I fail to see how it could be taken in any other way.
I am more than able to interpret your, at times, rather poorly worded posts (which are at times far from simple or to the point), I simply have disagreed with what you have said, and in disagreeing I have explained exactly why I think you are wrong and provided material from credible sources to back up my points (something you have singularly failed to do).
As far as your point on tyres not being the principal determining factor in potential stopping distance, this is a very naive statement on your part.
Tyres set the shortest possible limit for a cars stopping potential, nothing else that can be done to a car can improve on this limit, only make the most of it or make it worse.
The single factor that governs a cars overall stopping distance are the tyres, every other factor in braking has to work within the limits provided by the tyres. That makes them the single most important factor in braking (and again I have provided source material from well recognised sources to back this up). Quite simply every other factor in braking has to work within the limits set by the tyres, and as such are secondary to the tyres limits.
I am more than capable of understanding these factors, as are the numerous sources I have provided that confirm what I am saying. Sources from the world of motorsport and the motor industry. People you are now saying do not understand this subject.
All in all thats a rather bold claim for someone who has yet to provide any sources to back up his own claims (such as ABS seriously reducing stopping distances or any degree of slip reducing grip) or provided any details of there own credentials in this field.
You bemoan my source material as over-complex and confusing (which I dispute as most is very straightforward, the only exception being the Physics of Racing material), yet you have not been able or willing to provide one single source of information to back any of your disputed claims or sources. Instead you are now resorting to petty insults about drug abuse, not a smart move at all, and not one that is likely to convince anyone that you are actually able to discuss this subject in any meaningful manner. You are unfortunately heading in the same direction as you did with the entire handling discussion, people dont agree with you so the toys come out of the pram.
I would like you to quote me stating that ABS reduces stopping distances.
I did, howvere, say this:
Well, you are right that I should have read your posts. You should also understand that not everybody wants to read a 60foot long post.
It would also seem you are not reading my posts, either. (60 is almost 15% less than 70, thereby being the quoted aproximate, "optimal" slip angle/amount)
Your graph showed me nothing new, either. Quite frankly, it's the exact same with acceleration as well.
Apparantly you completley misunderstood my meaning of "grip". It is common practice in the racing world to call squealing tires, "losing grip". This does'nt mean that you currently have "less tractable force", (though many confuse it) rather, it simply means your tires are slipping. Quite in fact, the tires themselves are "losing grip". So actually, I guess our definitions are the same, but when you say, "losing grip" you are talking about the car, and I am talking about the tire. it is losing grip, that's why it is spinning, or turning slower than the car.
You should have understood this right here.
Maybe you somehow misinterpreted the term "lock", but I used it for lack of a better term. If you can think of a better term for a tire that is only rotating at 85% of the vehicle's speed, let me know, just don't say "slip".
Quite frankly, Until just now, I thought that you thought a tire moving slower than a vehicle, (or faster) was in fact not slipping, or whatever you call it when a tire makes those squeaky noises.
And weight has absolutly zero play?
Let's assume 2 vehicles are identical in every way.
With the same tires, cog, weight dist/trans, wheelbase/track, brakes, etc
Except one of them weighs 3000lbs, and the other weighs 4000lbs. (or 1300kg and 1800kg). which one will stop faster?
This is not to say I think weight has more play than tires, or even equal, I'm just letting you know that whether you meant it or not, what you actually said was dead wrong here.
I would agree if you mean weight has the least value of the 3 main pieces to the stopping puzzle. This is because weight adds friction, which helps counteract momentum, though it is not an equal force, it takes value away from the momentum.
As for the braking system versus tires, however, I cannot say either has more value, as they both can only go as far as the others power allows.
If I put better/bigger/grippier tires on my Grand Am, it would likely not have been able to reach the desired level of lock, let alone full lock-up, certainly not repeatedly, or even from 100. That's because the rear drums suck, and the front discs are'nt anything to get giddy about either.
So how could tires be more important there?
As I said:
You have said…
Now how else am I supposed to take these statements? Every single one of them implies that ABS equipped cars stop quicker than non ABS equipped cars. Its was the central tenant behind your entire ’02 and ’03 Viper comparison until that was completely invalidated. In addition a number of the above quotes suggest that a car with locked tyres will stop quicker than one braking at the threshold, which is incorrect (unless you are using the term 'locked' incorrectly).
I read all of your posts in full, if you don’t want to read my posts or find any part of it unclear then simply say so, don’t dismiss it out of hand. I also go to great pains to ensure that my posts (short or long) are well structured to allow them to be read in ‘chapters’.
In what way am I not reading them when you clearly stated…
You can try and wriggle out of this by claiming I misunderstood how you used grip, that however does not change the fact that you quite clearly say that “they then therefore do not have full traction”.
You have clearly claimed here that any reduction in the tyres rotational speed will result in a loss of traction. Yet now you are claiming that this was not what you intended to say at all; and that its a confusion over definitions.
Well the terms and definitions I am using as the standard ones used within both the motor industry and motorsport (hence the reason why they are used in the same way in my quoted sources).
To try and claim that a tyre losing grip is not losing traction is simply confusing (which you appear to be saying above). Traction is a product of grip, you lose grip and you lose traction. A tyre rotating slower or faster than the vehicle speed is developing a Slip Percentage (this is the correct term) and will gain grip/traction up to the tyres maximum Slip Percentage, after which it will lose grip/traction.
I have always used these terms correctly, so any confusion in regard to use has unfortunately come from you. As for suggesting that I meant to say that the car was losing grip, I meant nothing of the sort, tyres are in contact with the road and tyres losing grip is exactly what I meant.
Why should I not use the term Slip?
It is exactly the right term to use; it is the correct term to use.
When a car accelerates or brakes the tyres rotate at a different speed to the car speed, this difference measured as a percentage is called ‘Slip Percentage’.
When a car turns any difference between the steering angle and the path of travel is measured in degrees and is called ‘Slip Angle’.
No better description can be used because these are the established and correct definitions, and that is why I use them.
I have never said that weight has absolutely no play in this at all. I have said that weight is not a significant factor and that weight is to be considered a secondary effect in this, but I have never totally rejected it as a factor.
Now if we look at you’re example the first thing that needs to be pointed out is that is two cars of differing weights have the same dimension and the same CoG then the load transfer will be different in them, its not possible for it to be the same.
If we however throw that point out of the window for the moment, then the car with the lower weight would theoretically take slightly longer to stop. We are however talking about a few inches at best here and the situation could well be reversed depending on exactly how the car is set-up.
In the real world the difference would be far smaller that the difference the driver’s reaction time would make, much smaller in fact. Which is exactly why I say it is not a significant factor in determining stopping distance.
Load transfer (which is affected by weight but most certainly is not the same) plays a more important role, but still does not have the same importance as tyres.
The starting point for specing any braking system (road or race car) are the tyres, you do not built a tyre to match brakes you build brakes to make the most of the tyres that are to be used.
No part of the braking system can reduce stopping distances over the limit offered by the tyres, they can only increase the distance. Tyres determine the limit you can go to, the braking system then needs to be able to meet those demands. The demand limits (or parameters) are set by the tyre, not by the braking system.
If you had a car with poor brakes you would not fit poor tyres to match, you would upgrade the brakes to make the most of the tyres potential. If you fitted new (and better) tyres you may need to upgrade the brakes to make the most of this new potential. In both cases you move towards the tyres potential, they are the dominate factor.
This is why both the motor and motorsport industries consider the tyre to be the principal factor (and I have provided links to show this, one from a manufacturer of motorsport brake components).
You are acting as if I am saying that the brake system is not important, and I have never said this, but I have, and do, say that the tyres set the limit to work towards and that makes them the single most important factor (note not the only factor).
My comment for this.
Brake or ABS should be recalibrated on each tire change.
2003 version stop better ......
......because smarter ABS:
About ABS vs human, I think whichever smarter, they can reach theoritical optimum braking distance better.
machine can outsmart human, human can outsmart machine.
Superman or Super-ABS, assuming they both control the same braking system, do not make theoritical optimum braking better. But they do make it closer to optimum.
While I would certainly agree with the vast majority of what you have said in regard to ABS being able to make better use the traction available from the tyres (which provide the ultimate limit), and that ABS should be reprogrammed for changes made to the braking.
Most modern ABS systems are capable of self-adjustment to a degree, that will not require a re-programme for most tyre changes. Its only changes to a wildly different tyre compound (say a move to racing slicks) or a change in the braking system itself.
I would however disagree that changes to the ABS alone resulted in the reduction in stopping distance between the '02 and '03 Vipers, particularly as these model years are the change point between the 2nd and 3rd generation Vipers and the car changed in almost every physical dimension.
A more honest statement would, I think, be that the changes in the Viper braking distances between the 3rd generation car and earlier versions is a result of a range of changes to almost every area of the car. Particularly as I think we would all agree that the previous generations of the car were not taking full advantage of the braking potential offered by the tyres.
..But wouldnt there be an whole boat load of contributing factors that would effect the breaking distances anyway IE: tyre size, compound type, tyre pressure, breaking system employed the surface the cars being driven upon and last but not least the jocky?
Or am i whafling on like an OAP at monday night down the local bingo hall
Anyway im still adamant that the viper reguardless of year weather '96 - '03 or '02 - '03
would make a far better cannal boat than it does a sports car and i'd wager it would stop far shorter than 99 feet with or with out ABS or locked up wheels
though i could be wrong, "any one got a viper i can borrow"?
You are quite right that a whole range of factors effect stopping distance, some are major and some minor.
The main point I am making here is that all of these factors are limited by the tyre/road interface, it's that which determines the shortest possible stopping distance. Everything else works to either get you closer or further away from the limit set by the tyre/road combo.
Having now spent more time than I ever thought I would reading up on the 2nd vs 3rd gen Viper braking performance, every road test and review I have now read seems to focus on the major improvements in this area.
Still I'd be more than happy to join you if anyone could provide an example of each gen to test.
Well i've e-mither'd dodge, no replies thus far (no surprises).
So i guess we just have to sit tight and hope a few people will rally to our new found cause.
*ponders*....i bet if i were to e-mither top gear jeremy clarkson might be willing to run the tests for us maybe?!
Anyway jocking, apart to me it seems obvious that a driver that knows his/her way round a car and how to slow one down with out ABS and / or putting there foot / break pedle through the floor pan and thus inducing wheel lock, Would be able to stop a car in less distance than say a car with ABS, as to my knowlage what ABS does is constantly alter the the pressure applyed to the discs / drums to avoid lock up and there for give you a better degree of control over the car till you either A) slow down to the desired speed, B) take your foot off the break (yeah i know its practically the same as A) or 3) drive smack bang into the tree your trying to avoid. In essence its a mechanism that adjusts the pressure appling more breaking force and taking it away also in quick sucession, in turn allowing the wheels to rotate in order to maintain grip, (a blind man on a galloping hourse would beable to tell you the cars going to cover more distance).As for the other option of more or less deliberatly locking up the wheels, ...well there are easier ways to burn good rubber though it does involve fire!
Ok, my mistakes for blaming only ABS. It has many changes indeed:
All that and more, between the 2nd and 3rd gen cars almost every physical dimension on the Viper changed, all of which are factors that will have had a massive change in the cars CoG and how load is transfered under braking.
Thats also without looking at the figures we are almost never going to see, such as how the brake bais is set-up.
okay Scaff here we go:
Now, please tell me how calling it "slip" is so much more drastically correct than "losing grip"
And by the way, when you take those direct quotes, yes, it sounds like I'm saying ABS stops cars faster.
too bad you did'nt read/comprehend the rest of the post(s) that went with it.
It would appear that your knowledge of the english language could be improved, as you seem to think "slip" and "grip" have massively different meanings, and perhaps that's why you don't seem to get what I've been getting at this whole time.
Yes, the tires set the limit. all those factors are limited to the tires.
but if the tires grip outweighs the rest of the factors power, than they are setting the limit.
that is why neither is more important. because they rely on the other, and no matter, either brakes, or tires, will be the vehicles limit, and it could be either or.
Well done you copied and pasted the entire definition list for the word slip, its a shame that you did not bother to search for it within the correct context, which is the motor and motorsport industries (and engineering). Why not put LSD into dictonary.com and see what you get? Well I did just that and what a surprise it does not mention Limited Slip Differential (despite mentioning other acronyms), dictonary.com is very useful for common terms, but is hardly the place to search for industry specific terminology or jargon.
I have already outlined exactly how the terms Slip Percentage and Slip Angle are defined and used within the industry. I have also shown how as slip develops grip/traction increases, up to the limit of the tyre, after which any further increase in slip will reduce grip/traction.
So I am sorry, used correctly, you can't say that slip and losing grip are the same or similar, they describe different things in the context being discussed here.
You see my grasp of the English language is just fine, the problem exists here because we are talking about language specific to the motor and motorsport industries, and its you that appears to be very unfamiliar with the language used within it. Otherwise you would have no problem at all knowing that slip (as in percentage and angle) is not the same as gaining or losing grip (rather its the situation under which grip is gained or lost).
Hence the reason your posts are unclear, you are misusing these terms to a massive degree.
It does not just sound as if you are saying ABS stops cars quicker, in this this quote...
.. I don't see how it could be taken any other way, and please remember I posted these quotes quite simply because you asked me to show if you had ever said exactly that (hence the reason why your later posts are not even relevant to this - please try and remember the question you asked).
No it can't. What is so damn hard to understand here, the final limit is set by the interface between the tyres and the road, brakes can be uprated to this limit but not beyond it.
The vast majority of modern cars are more than capable of locking up tyres in a single braking incident (in this case uprating brakes will principally improve you're ability to repeat the act) and a serious number of older cars are perfectly capable of doing the same. Locking tyres is hardly a 'new' concept.
Its extremely uncommon (and please do remember I have over a decade of experience in the motor industry) to come across a car incapable of exceeding a tyres limit under braking, unless the brake system is poorly maintained, faulty or very badly set-up.
Its is accepted within both the motor and motorsport industries that the tyre is the principally factor in braking, I have provided source material to back this up (which you have so far failed to do on any count) and could certainly provide more if required.
I have to say that you now seem to be responding simply for the sake of it, I have provided source material (both in print, on the web and in some cases visual) to back up every single point I have made. Yet you still seem to want to dispute them, without providing a single verifiable source for anything.
You have chosen to mock me and at least one other member, yet on all the points you picked to do this with you have been proven wrong. Do you not remember this.....
......and just how wrong you were?
I've cut you a lot of slack as far as attitude goes in this thread (simply because I do not want to pull the mod thing), but you now have the appearance of someone who simply does not want to admit they may have been wrong. From now on I would like to actually see some source material for you claims, not simply rude and ill considered posts, you may also want to take a little more time checking the spelling and grammar of your own posts before making any further statements about other peoples grasp of the English language.
Well Scaff, it seems you cannot remember the fact that you said calling it, "losing grip" was incorrect, but calling it "slipping" was correct.
I am telling you that these carry the exact same weight in the english language, whether you like it or not.
The fact that you prefer a different term, does not mean it is an "automotive industry" term, as I live in America, and here, when a tire slips, even a little, we refer to it as it having "lost grip".
if that is too much for you to understand, and you feel a need to follow me around threads, even in forums that arent generally "patrolled" by you, just to give me warnings, when no moderators of those specific threads say anything, well then, I guess you'll be looking for everything and anything you can find, and you'll probabley ban me yourself, in other moderators forums.
I remember that quite clearly and don't see how what I have said in this regard has changed at all.
It is not a case that I prefer a different term or that because I use a term I consider it to be an automotive term.
Slip Percentage and Slip Angle as I have described them are industry terms (the SAE (Society of Automotive Engineering) use these terms and the slight variation on Slip Percentage which is Slip Ratio), I have provided details of sources (both European and American) to illustrate this.
The link below will allow anyone to download a (PowerPoint) presentation I found on Tyre Dynamics written by Dr. Richard Hathaway, P.E. (Professor of Mechanical and Aeronautical Engineering, Western Michigan University). It quite clearly uses the terms Slip Percentage, Slip Percent, Slip Ratio and Slip Angle; they are used constantly and consistently in the same manner that I do.
Tyre Dynamics Presentation
I think this quite clearly shows that these are not terms that I have simply made up or chosen to use for some abstract reason, but the correct terms to use when discussing vehicle (and specifically) tyre dynamics. However a quick Google search on any of these terms would have shown exactly the same.
In addition the graph on slide 8 of the presentation also shows the range at which sliding occurs (the dotted lines) and how it is occurring after the peak Slip Percentage of (in this example) 15%, following slides also show that the SAE definition of a locked (braking) or spinning (acceleration) tyre occurs at a Slip Ratio of 1.0/Slip Percentage of 100%.
It is you that have chosen to use a different term and confusion has, in my opinion, resulted from that. Combined with the quite simply fact that you have been wrong on a number of point and seem unwilling to admit that, rather hiding behind a suggested confusion of terms. You quite clearly stated that as soon as a tyres rotation speed changed (in relation to a cars speed) that it would loose traction, and this is simply not true.
My staff role here is Super Moderator, I don't have an assigned forum and the last time I checked I was free to look around, post and moderate any thread I see fit.
I have no desire to follow you at all, and if you are referring to the "World's Best Car" thread then I don't recall you posting in any of the earlier (related) threads or the final thread prior to the post in question. I however have been actively involved in it since the start, so I don't understand how I could have followed you, not to mention that I have a lot better things to do.
This issue however appears to be a bug-bear for you so I will raise the accusation of 'vendetta' with the rest of the staff.
I have a simple question Scaff, and I'm not sure how to word it, so it may sound insulting. I don't want it to be. If better brakes don't change stopping distances in panic stops (barring fade resistance), then why do automobile magazines quote better stopping times with better brakes? Is it the better ability to modulate the brakes, or something else?
Better pedal modulation and control could be part of the answer, however I would ask if you could posts a specific example.
The only reason I ask is that in almost every article I have ever read regarding a change in brake components they have discussed the changes to the feel, fade, modulation, etc and never specific braking distances. Its also worth keeping in mind that these tests are almost never carried out back to back and changes in tyre temp, track temp, moisture levels, driver can all have a massive effect on stopping distances.
Its interesting to take a look around various brake manufacturers (not retailers but the people who actually make brakes), you will struggle to find any reference to stopping distances or brakes improving them.
A good example is this one
Link - http://www.stoptech.com/tech_info/wp_brakebiasandperformance.shtml
Now that piece is taken directly from StopTech who manufacture brake components for motorsport, so if even the people who make these very components are eager to state this so clearly I do wonder when people dispute it.
BTW - No offence is ever taken to a question, as you can clearly see from my replies in this entire thread.