GT4 and Brakes

[Scaff]

There would be no problem with having a one and a two tonne car having the same weight distribution and the only difference being that the tires of the heavy car in a 1G deceleration would be holding 1000 kgs more.
This is really silly.

Its far from silly, first have a read of my post above, which covers the subject of weight (yet again).

Secondly, while it is not a problem to have a one and two tonne car with the same weight distribution (I never said its was); it is highly unlikely that they would have the same weight transfer characteristics and centre of gravity.

However this is still getting away from the point that weight is not a factor and weight transfer is a second order effect.

You (and others) can argue against this all you want; the simple truth of the matter is that you can not change the laws of physics.

I have provided a huge amount of links, explenations and data to support what I know to be true.

Please read them (and try to understand them) before claiming that they are incorrect.

 

[Scaff]

First because the tires of the Rover can take a much higher force when braking and second because the brakes of the Rover can provide this force.

I never said a lighter car would always stop quicker than a heavier one, I only wanted to point out that the brake system as well must be able to provide more force the more mass a car has.

Just take your everyday car and load it up with 4 friends and 200 pounds of luggage in the trunk. You'll see you need to apply more force to the brake pedal in order to stop the car as quickly as it would be empty (only the driver in it). This higher force must also be supported by the brake system. If it can not, then the braking distance will increase.
(I think in almost all modern cars the brakes are strong enough to support a fully loaded vehicle as well as an empty one - but this might not always be the case).

Or for another example: Swap the brake systems of the above Lotus and the Rover, which one would stop quicker then?

That is not how your original post read to me, and if you read my posts you will clearly see that I have stated that if a braking system is functioning correctly, then the mass of a vehicle (laden or un-laden) is NOT a factor in stopping distance.

I have tested a wide range of vehicles at proving grounds, under a wide range of conditions, and have never found a production car that when loaded to its maximum kerb weight was not capable of providing sufficent braking force to lock the wheels.

I will say it again, provided the braking system of a car is fully functional (and capable of locking the wheels) then the weight of a car, size of discs, type of pads, etc will not have an effect on the overall stopping distance of the car.

I have provided in-depth physics formula and explinations to support this; this is a subject that I work and train on in the Motor Industry.

The physics involved can not be simplified to the level of the formula you have supplied.

Additionally, with no offence implied, you do not appear to have read (or have not understood) the whole of this thread, because you are covering subjects that have already been discussed and addressed. The results are not going to change.

 

[lazydog]

I will say it again, provided the braking system of a car is fully functional (and capable of locking the wheels) then the weight of a car, size of discs, type of pads, etc will not have an effect on the overall stopping distance of the car.

I fully agree with you, sorry if my first two posts were unclear.

I was just disturbed by the one sentence "Weight is not a factor" - it isn't when looking at the maximum acceleration a tire can take, but it could be if the brakes are too weak (small), which, as you said, is never the case for street and racing cars

 

[Scaff]

I fully agree with you, sorry if my first two posts were unclear.

I was just disturbed by the one sentence "Weight is not a factor" - it isn't when looking at the maximum acceleration a tire can take, but it could be if the brakes are too weak (small), which, as you said, is never the case for street and racing cars

Not a problem, and welcome to GTP.

Hope you enjoyed this particular thread, as its a subject I love.

Tyres are one of the most mis-understood and under used components on a car (both in real life and GT4), just trying to help people get a better understanding of how they work and what the real factor involved in braking are.

 

[neilX]

Hi Scaff, interesting stuff. I just have a couple of questions:

Going back to that 0-100-0 test, what is the main thing causing the motorcycle's relatively long stopping distance?
Is it that is has a much smaller tyre contact patch?


Going back even further, I see that my other question has already been answered:
the higher the braking force the greater the weight transfer to the front, which can lower the maximum grip level of the rear tyres and reduce overall braking efficency

 

[Scaff]

Hi Scaff, interesting stuff. I just have a couple of questions:

Going back to that 0-100-0 test, what is the main thing causing the motorcycle's relatively long stopping distance?
Is it that is has a much smaller tyre contact patch?


Going back even further, I see that my other question has already been answered:
the higher the braking force the greater the weight transfer to the front, which can lower the maximum grip level of the rear tyres and reduce overall braking efficency

Good question and one that is very related to this thread.

Motorbikes in general will have a longer stopping distance that cars; the main cause you have already spotted; the much smaller contact patch is the main cause.

However bikes have a second problem and that lies with the generally greater weight transfer and higher centre of gravity. Now while these are second order effects in terms of the physics, they do have a major pyscological effect on the rider. It takes a very high level of confidence to brake hard on a bike from 100mph to 0mph.

 

[mudia]

Wieght distribution and transfer do effect stopping distances, overall weight does not.

More tyre contact does, as you say (and as does my first post) help with braking distances.

Better calipers and disks have no effect on braking distance in any way, read the linked articles.

Pleas forgive me if i have missunderstood what you are trying to say: but one thing that is for sure .. the weight of the car DOES have a significant effect on the stopping distance of a car.

if we take two cars that are basically identical and are that are able the generate the same stopping force.. ie have the same brakes and tyres.. with the only difference being that car a weighs 2 times as much as car b... and we try to stop both cars from 100mph... car b will stop in a shorter distance by a long way .. this is simple physics Force = mass x acceleration. As a matter of fact car b will do everything quicker (accel.. . turn etc) except have a higher top speed (unless of course the extra weight is in the wheels .. where the rotational forces will slow the car down)

In the case of cars... the effect of increased weight is seen when you are trying to stop from higher speeds.


once again maybe i am missing your point

 

[Scaff]

Pleas forgive me if i have missunderstood what you are trying to say: but one thing that is for sure .. the weight of the car DOES have a significant effect on the stopping distance of a car.

if we take two cars that are basically identical and are that are able the generate the same stopping force.. ie have the same brakes and tyres.. with the only difference being that car a weighs 2 times as much as car b... and we try to stop both cars from 100mph... car b will stop in a shorter distance by a long way .. this is simple physics Force = mass x acceleration. As a matter of fact car b will do everything quicker (accel.. . turn etc) except have a higher top speed (unless of course the extra weight is in the wheels .. where the rotational forces will slow the car down)

In the case of cars... the effect of increased weight is seen when you are trying to stop from higher speeds.


once again maybe i am missing your point

You are not missing the point, and sorry to be blunt about this, you are just wrong.

Please take the time to read the whole thread and linked documents, as they quite clearly and in great detail show how weight is not a contributing factor in a cars overall stopping distance (if the braking system is fully functioning).

Simply quoting F = M * A is not going to help, as this is a huge oversimplification of the forces at work here.

The full set of formula involved are provided on this link

http://www.miata.net/sport/Physics/07-Circle.html

Please read this fully and ensure that you understand it before you claim that it is incorrect.

This series of well respected article was writted by a Physics Phd and racing driver, and looks at the advanced physics involved in the process.

 

[neilX]

Thanks Scaff,

bikes have a second problem and that lies with the generally greater weight transfer and higher centre of gravity
You're right there, it certainly does take a lot of confidence and concentration to stop a motorcycle at high speeds. A lot of weight gets transfered forward (because of a high CG?) and keeping traction with the rear wheel can become difficult:
the higher the braking force the greater the weight transfer to the front, which can lower the maximum grip level of the rear tyres and reduce overall braking efficency
So, while stoppies might look cool, overall braking efficiency would be better if all tyres have good grip levels throughout the braking manouver.
I'm definitely in favour of keeping both my wheels on the ground!

And in relation to GT, I've noticed that applying maximum brakes can cause skidding, even in a straight line, with some fishtailing etc.. and that by just backing off from max brakes just a little, means that all tyres can stick and hold their grip giving better overall braking efficency.

And while what I was asking about was in relation to Weight Transfer, I've absolutely no doubts that using better tyres is the (best/simpliest/easiest/most effective) way to go for improved braking performance.

 

[neilX]

I'd read some of that Physics of Racing before. Fascinating stuff and I can't claim to understand it all, but I won't argue with his conclusions
When someone can prove they're right, I wouldn't try to argue unless I could prove that they're wrong, and if I can't understand his mathematics, I haven't got a hope!

 

[Scaff]

Thanks Scaff,

bikes have a second problem and that lies with the generally greater weight transfer and higher centre of gravity
You're right there, it certainly does take a lot of confidence and concentration to stop a motorcycle at high speeds. A lot of weight gets transfered forward (because of a high CG?) and keeping traction with the rear wheel can become difficult:
the higher the braking force the greater the weight transfer to the front, which can lower the maximum grip level of the rear tyres and reduce overall braking efficency
So, while stoppies might look cool, overall braking efficiency would be better if all tyres have good grip levels throughout the braking manouver.
I'm definitely in favour of keeping both my wheels on the ground!

And in relation to GT, I've noticed that applying maximum brakes can cause skidding, even in a straight line, with some fishtailing etc.. and that by just backing off from max brakes just a little, means that all tyres can stick and hold their grip giving better overall braking efficency.

And while what I was asking about was in relation to Weight Transfer, I've absolutely no doubts that using better tyres is the (best/simpliest/easiest/most effective) way to go for improved braking performance.

Glad this thread has been of help, and a greater understanding of these forces and how and why they work does without a doubt help in GT4. I had the same problem with fishtailing in the Viper at the end of the main straight in New York.

The weight transfer in the car causes the rear tyres to exceed their grip limit and lock, backing of the brakes will help this (100% braking force from speed is not always the way to go), as will slight changes to the set=up. Try fitting a brake controller and lowering the rear setting, with slightly less force they should be less likely to lock under the weight transfer.

Have a read of the StopTech white paper (you will find the link in the first post in this thread), should help you a lot with set-up to maximise brake distribution under load.

Edited to add that the bikes greater weight transfer (when compared to a car) is caused by its higher COG, you can experience the same thing (with a car) in GT4. Even without changes to spring or damper settings you can reduce the weight transfer by reducing a cars weight and lowering the ride height, as both these factors generally reduce the cars COG.

Its why most race cars are dry-sump lubricated (allows the engine to be mounted lower and further back in the car) and almost always built to a lower weight that the class the race in allows. This then allows the race engineers to bring the car upto weight, by the carful and controlled addition of balast.

After all if you can build the car below a certain weight for a series, you can at least control where the weight is.

Another good example in GT4 is the BMW M3 vs. the M3CSL, on paper not a lot splits the two cars, but most who have driven them say the CSL is a far better car, and one of its main advantages is the carbon fibre roof, just think how much that lowers the cars COG.

 

[neilX]

Yes, I'll have to read more about set ups, but I've been concentrating on licenses where there is no adjustment options, so I had to control it absolutely right and I achieved better braking performance by reducing the amount of brakes applied.
In particular, tests like A-15 in an old Alfa that'll skid if you look at it too hard.

 

[Scaff]

I'd read some of that Physics of Racing before. Fascinating stuff and I can't claim to understand it all, but I won't argue with his conclusions
When someone can prove they're right, I wouldn't try to argue unless I could prove that they're wrong, and if I can't understand his mathematics, I haven't got a hope!

I know what you mean, took me a long time (and a very clever friend) to get my head around it all.

It helps not to look at the calculations too much to begin with and just go with the text.

Another good source of information is the book "Speed Secrets - Professional race driving techniques" by Russ Bentley, covers similar subjects, but from a laymans point of view. Its published in the USA (not sure where you are), but I got me copy in the UK quite easily.

 

[lazydog]

Thanks Scaff,

bikes have a second problem and that lies with the generally greater weight transfer and higher centre of gravity
You're right there, it certainly does take a lot of confidence and concentration to stop a motorcycle at high speeds. A lot of weight gets transfered forward (because of a high CG?) and keeping traction with the rear wheel can become difficult:

On top of that, a biker has to control TWO brake systems. One for the front wheel and one for the rear, which only adds to the difficulty of braking really hard with a motor bike, especially considering the fact that its necessary to apply different levels of brake power to the wheels (about 80% front, 20% rear as a _crude_ rule of thumb).

There are a few bikes on the market with a CBS (combined braking system) which allows to operate only one of the brakes, while the CBS automatically aplies the correct amount of power to the second brake. Very valuable driving aid which adds a lot to safety, imho.

 

[mudia]

You are not missing the point, and sorry to be blunt about this, you are just wrong.

I doubt very much that I am wrong .. the link you have shown me only proves that the acceleration (whether forward or backward or latteral ) force a tyre can give you is independent of the weight of the car. This does not mean that braking distance is not affected by wt. Maybe you should read the article again.

The fact is .. wt plays a VERY big part in change of speed... I am quite shocked that youare debating it... this can be seen everywhere... and yes it CAN be simplified to F = M * A.

someone has already mentioned a formula 1 car that is low on fuel ( can brake in a shorter distance despite worn out tyres)

also have a look at racing trucks they have HUGE contact patches but have to be limited to 100mph .. WHY ? because you just cant stop them in short enough distances...so would be unsafe at higher speeds.
perhaps you would like to tell me that an 18 wheel truck can out brake a caterham?

simple fact is if you want a car to change speed faster you have to give it more F or reduce the M .. there is no getting around this... if you want to accelerate faster you have to get more torque out of your engine (as much as your tyres can take)...
and if you want to make the car decelerate faster KNOWING THAT YOU HAVE A FIXED DECELERATING FORCE FROM YOUR TYRE... you have to reduce the weight of a car...!!

 

[mudia]

On top of that, a biker has to control TWO brake systems. One for the front wheel and one for the rear, which only adds to the difficulty of braking really hard with a motor bike, especially considering the fact that its necessary to apply different levels of brake power to the wheels (about 80% front, 20% rear as a _crude_ rule of thumb).

There are a few bikes on the market with a CBS (combined braking system) which allows to operate only one of the brakes, while the CBS automatically aplies the correct amount of power to the second brake. Very valuable driving aid which adds a lot to safety, imho.

layydog actually .. when brake hard on a bike.. the distribution in braking more like 98 % front and 2 % rear!

 

[mudia]

Hi Scaff, interesting stuff. I just have a couple of questions:

Going back to that 0-100-0 test, what is the main thing causing the motorcycle's relatively long stopping distance?
Is it that is has a much smaller tyre contact patch?

hi neilX .. you will find that in that 0-100-0 test ..shows only the times of the vehicles and not the distances covered

things you should note ... bikes actually stop better than cars from higher speeds... cars stop better at lower speeds... the reason for this is that when stopping on a bike you have to reduced braking force at lower speed so as not to flip the bike... and at higher speeds the rider acts as an air brake when he sits up ... this can give you 0.5g at 120mph (ie quite a bit extra) . At low speeds this effect is lost .. and the far superior braking systems of cars has a greater impact.

"how can that be true if the car stops in a shorter time ?" you might ask ... well think about it... if object A decelerates from 100 to 1 mph in a second then takes 9 seconds to go to 0 mph ... and object B decelerates from 100 to 99 mph in a second then takes 8 seconds to go to 0 mph... object B would have travelled a much further distance because it spends more time at a higher speed.

also in the 0-100- 0 ... as has been pointed out cars have a nicer weight transfer when going form hard acceleration to braking ... but once the bike is in full braking .. it is stopping faster from higher speeds .

anyway its by the by .. it was in a car mag .. and they are very biased against bikes ... a week after one of the 0-100-0 test.. a bike mag showed that bikes stop in less distance.. it is imortant to not that the reason why a bike with so much less contact to the road and an inferior braking system can stop so quickly is becasue of its WEIGHT!!!!!

also evo magazine showed the telemetry of a Yamaha R1 (with shagged front wheel) outbraking a caterham into the first corner of the pit straight on the track they were testing. and the writer commented on how impressive it was despite the bike having far less contact with the road.

fyi .. i have an impreza wrx sti-R ... and 2004 yzf-r1 .. and even though i am much braver in the car.. the bike does brake much harder at high speeds. It does take FAR more skill though

also .. when i had my R6.. i had mag which a had data log of an stock(R6) braking 100-0 in 82m and whilst testing brake pads on a fireblade they had it stopping around the 90m mark... my point ? --> not many cars can stop in that distance !!!!

 

[mudia]

here are the things you need to stop faster (in no particular order)

Tyres - the more grip (ie the stickier) the tyres are the more force you will have

Brakes - you need to be able to provide sufficent force to the tyres....... and also obviously having the most modern abs also helps (even on dry surface). Brakes need to be stronger the heavier the car is and the faster the car is going (ie the greater the momentum)

Suspension - as the tyre grips it skips of the road...better suspension keeps contact with the road for longer ..

aerodynamics - the less aerodymic the car the better it will stop.. because the greater the added force (drag) there is to help the tyres

Weight - with all things being equal a lighter car will stop faster. period!

 

[lazydog]

I doubt very much that I am wrong .. the link you have shown me only proves that the acceleration (whether forward or backward or latteral ) force a tyre can give you is independent of the weight of the car.

Take a second look at the article. It shows that the maximum acceleration (or decelaration) a tire can give you is independent of the weight. It does not say anything about the maximum possible force and as long as the brakes can provide this force, braking is not affected by mass (and only then).

It seems, from your quote, that for a moment you confused/mixed force and acceleration, yet they're different things (which you obviously know).

 

[mudia]

Take a second look at the article. It shows that the maximum acceleration (or decelaration) a tire can give you is independent of the weight. It does not say anything about the maximum possible force and as long as the brakes can provide this force, braking is not affected by mass (and only then).

It seems, from your quote, that for a moment you confused/mixed force and acceleration, yet they're different things (which you obviously know).

read this
"The maximum acceleration a tire can take is , a constant, independent of the mass of the car! While the maximum force a tire can take depends very much on the current vertical load or weight on the tire. If a tire can take one g before sliding, it can take it on a lightweight car as well as on a heavy car, and it can take it under load as well as when lightly loaded."

then 'The tire will give you so many gees and that's that. "

what this says is that there is a finite accelerative force you can get from a tyre.. and that maximum is not affected by weight" IT DOES NOT AT ANYPOINT SUGGEST THAT BRAKING DISTANCES ARE NOT AFFECTED BY WEIGHT..

why is nobody questioning the fact that acceleration and deceleration are the same thing..????

if i said to you a lighter car accelerates better than a heavier car .. would you question that ??? this is essentially the same thing in the opposite directiong.. The whole principle of making cars lighter is to be able to reach the maxiumum acceleration a tyre can give.. and by acceleration i mean in all directions ... forward back ward and sideways

ok let me ask you this you have a car that is made of titanium and weigh X kg .. it has super strong brakes and it sits on tyres that can give you 3 g's .. you do a 200 - 0 test .. and measure it ... you know magically turn the titanium to lead... and do the same test.. are you saying that you think it will stop in the same distance???? SURELY NOT!

Have you ever been go karting ... why is it that the same go kart with a 60 kg person accelerates brakes and turns faster than one with a 100 kg person .. ???? surely not weight destribution... both driveres sit in the same place dont they ??

that article only serves to complicate issues.. the simple fact is ... you need more power to stop an object with greater momentum.. this is not a disputable fact...

you will see .. cars like S65 AMGs.. despite .. huge tyres.. and the most poweful brakes... beaing outbraked by gold gti hatch backs and the likes.. why ? not becasue the gold has more force from its tyres.. but simply because it is lighter...

,, and OH i just thought of a perfect example... for those of you who want to argue that weight plays no part in acceleration/deceleration .. and it is all down to COG ... why is it that a car that is turned into a convertible and has had its roof removed... and has had more weight added to it (to provide tortinaly rigidity) so has a lower COG .. is slower to accelerate/decelerate/turn??????

why do they limit the weight of race cars for safety .. if it has not effect on the performance of the car?

come on .. this is really not that hard.... all you have to do is look around you and you will see the effect of weight on performance... and not read articles that seem only to have confused people...

 

[Scaff]

here are the things you need to stop faster (in no particular order)

Tyres - the more grip (ie the stickier) the tyres are the more force you will have

Brakes - you need to be able to provide sufficent force to the tyres....... and also obviously having the most modern abs also helps (even on dry surface). Brakes need to be stronger the heavier the car is and the faster the car is going (ie the greater the momentum)

Suspension - as the tyre grips it skips of the road...better suspension keeps contact with the road for longer ..

aerodynamics - the less aerodymic the car the better it will stop.. because the greater the added force (drag) there is to help the tyres

Weight - with all things being equal a lighter car will stop faster. period!

I only disagre with you on two points here.

1. ABS does not stop a car quicker, in was never designed to do this, regardless ofthe age of the system. ABS was designed to stop tyres locking and you losing grip while braking, allowing the driver to steer while under hard braking.

ABS systems are activated when a wheel loses grip under braking, by that you have already exceeded the maximum level of threshold braking and have lost control of the car, the system intervens to give that control back.

This is a subject that I train professionally within the motor industry and have done for over 10 years.

You also forgot another point on tyres, contact patch size, the larger the more grip you have, the quicker it will stop.

Also you stated that Autocar was a biased sorce, now this is pure rubbish (particularly as you then go on to prove this point by quoting another magazine), Autocar have included a bike in the 0-100-0 test almost every time they have run them. In the 8 years they have do this only one road car (the Caterham) have ever beaten it. Please check the acuracy of statement such as this before you make them.

On the subject of trucks, are you aware that the stopping distances for modern truck is far shorter than that on more cars! As weight is not a principal factor (whatever you may claim) the sheer size of a trucks contact patch is huge.

The reason truck racing is limited in speed is for safety, yes that is true, as if one was to leave the circuit and hit spectators then its mass would result in serious loss of life. As they run without ABS, they can (and do) lock wheels regulalrly and at higher speeds the loss of control on a circuit would be dangerous, normal tyre walls and armco is not goingto stop one.

2. all things being equal a lighter can will not stop quicker, you have mis-understood a funedmental principle here that it is not the brakes that stop a car, the slow the wheels and that stops the car. While the braking systems are affected in the way you describe, the tyres are not. Lazydog explains this well in the post above.

Take a second look at the article. It shows that the maximum acceleration (or decelaration) a tire can give you is independent of the weight. It does not say anything about the maximum possible force and as long as the brakes can provide this force, braking is not affected by mass (and only then).

It seems, from your quote, that for a moment you confused/mixed force and acceleration, yet they're different things (which you obviously know).

Spot on lazy dog, and thank you. It is a concept that does take a while to get your head around, but it is correct.

The force is applied to the braking components and providing they are up to the job (as I have always said) they then brake the wheels, but it is the slowing ofthe wheels that brakes the car and they are not affected by the vehicles mass, only the weight transfer.

 

[Scaff]

I think you guys have all been confused by this article!

read this
"The maximum acceleration a tire can take is , a constant, independent of the mass of the car! While the maximum force a tire can take depends very much on the current vertical load or weight on the tire. If a tire can take one g before sliding, it can take it on a lightweight car as well as on a heavy car, and it can take it under load as well as when lightly loaded."

then 'The tire will give you so many gees and that's that. "

what this says is that there is a finite accelerative force you can get from a tyre.. and that maximum is not affected by weight" IT DOES NOT AT ANYPOINT SUGGEST THAT BRAKING DISTANCES ARE NOT AFFECTED BY WEIGHT..

why is nobody questioning the fact that acceleration and deceleration are the same thing..????

if i said to you a lighter car accelerates better than a heavier car .. would you question that ??? this is essentially the same thing in the opposite directiong.. The whole principle of making cars lighter is to be able to reach the maxiumum acceleration a tyre can give.. and by acceleration i mean in all directions ... forward back ward and sideways

ok let me ask you this you have a car that is made of titanium and weigh X kg .. it has super strong brakes and it sits on tyres that can give you 3 g's .. you do a 200 - 0 test .. and measure it ... you know magically turn the titanium to lead... and do the same test.. are you saying that you think it will stop in the same distance???? SURELY NOT!

Have you ever been go karting ... why is it that the same go kart with a 60 kg person accelerates brakes and turns faster than one with a 100 kg person .. ???? surely not weight destribution... both driveres sit in the same place dont they ??

that article only serves to complicate issues.. the simple fact is ... you need more power to stop an object with greater momentum.. this is not a disputable fact...

you will see .. cars like S65 AMGs.. despite .. huge tyres.. and the most poweful brakes... beaing outbraked by gold gti hatch backs and the likes.. why ? not becasue the gold has more force from its tyres.. but simply because it is lighter...

,, and OH i just thought of a perfect example... for those of you who want to argue that weight plays no part in acceleration/deceleration .. and it is all down to COG ... why is it that a car that is turned into a convertible and has had its roof removed... and has had more weight added to it (to provide tortinaly rigidity) so has a lower COG .. is slower to accelerate/decelerate/turn??????

why do they limit the weight of race cars for safety .. if it has not effect on the performance of the car?

come on .. this is really not that hard.... all you have to do is look around you and you will see the effect of weight on performance... and not read articles that seem only to have confused people...

No sorry, but once again you have missed the point, the reason a lighter can can outbrake a heavy car into a corner is not because it can stop quicker, but because it needs to slow less, its is able to carry more speed through the following corner. This is covered in the piece on transients in The pHysics of racing. The same for your example of an F1 car running with a lighter fuel load.

The convertable example you give is down to teh fact that the convertable with the additional weight is now running with a lower power to weight ratio than its closed example and will almost never match its rigidity, so the weight transfer is increased. Also the additional stregthening in a lot of convertables is around the windscreen, firewall and fllorpan. With the exception of the floorpan (which tends to be the smallest are of increase, these are all locations that will rasie the COG.

In regard to lighter cars Vs heavy cars in acceleration, why do you think that in lower gears you get wheel spin? Lowering a cars weight does not stop this, limiting the amount of power you supply to the raer tyres does.

The maxmum accerative force you can provide to a tyre is limited to its grip level. Weight does not change this (weight distribution and transfer does).

Every motor engineering and racing text I have ever read backs this up, I have supplied information to support it (how you interprate it is up to you), the only counters you have provided is your own theory and some basic physics that would apply to brakes not tyres.

 

[mudia]

Scaff ... omg... re: the truck thing .. will come back to that in a sec

with regards to abs... my point with abs is that the best abs systems available today (ie like on the peugeot rally cars) is able to give the maxium braking force as the road surface changes .. since you know that roads are not perfectly smooth.. i have been told by someone in your industry .. and have heard them discuss it on tv.. that the latest systems are able to apply varying amount of brake pressure better than a human foot can... if you say this is wrong the so be it..

with regards to the car mag being biased .. it was a toungue in cheek statement...hence the smiley .... however i am semi serious.. this is because i have read that the bikes used in the car tests are rarely set up properly ( and if you ride bikes you will know the difference that a quick setup will do ).... and secondly there have been occassions such as when EVO and superbike magazine ran the very same test at the same time .. (crescent suzuki vs radical) and if you read the write ups in both mags you will see how biased the car mag is to the cars and how biased the bike mag is to the bikes..

with regards to the trucks.... you cannot honestly tell me .. that you think a truck can stop from a 100 mph ... than letst say a caterham ??? come on please .. lets not take the p!ss
i have been unfortunate to witness a truck unable to stop from a relatively slow speed when i was in the states... trucks cannot stop well.. coz they are too heavy .. simple

 

[Scaff]

Scaff ... omg... re: the truck thing .. will come back to that in a sec

with regards to abs... my point with abs is that the best abs systems available today (ie like on the peugeot rally cars) is able to give the maxium braking force as the road surface changes .. since you know that roads are not perfectly smooth.. i have been told by someone in your industry .. and have heard them discuss it on tv.. that the latest systems are able to apply varying amount of brake pressure better than a human foot can... if you say this is wrong the so be it..

Yes that is true, but by the time the ABS kicks in the tyre has already lost grip, you are already going to have a longer stopping distance than if the ABS had not activated. Threshold braking will always be faxter than ABS braking, its advantages are as you say in variable surface conditions, where it will be faster than a person pumping the brakes. Its why it is invaluable on the road, but a hinderance on the circuit.

with regards to the car mag being biased .. it was a toungue in cheek statement...hence the smiley .... however i am semi serious.. this is because i have read that the bikes used in the car tests are rarely set up properly ( and if you ride bikes you will know the difference that a quick setup will do ).... and secondly there have been occassions such as when EVO and superbike magazine ran the very same test at the same time .. (crescent suzuki vs radical) and if you read the write ups in both mags you will see how biased the car mag is to the cars and how biased the bike mag is to the bikes..

Autocar is by far and away one of the single most respected publications worldwide when it comes to figuring vehicles, a number of their contributors write for both car and bike magazines and the 0-100-0 test generally involve a bike tester.

with regards to the trucks.... you cannot honestly tell me .. that you think a truck can stop from a 100 mph ... than letst say a caterham ??? come on please .. lets not take the p!ss
i have been unfortunate to witness a truck unable to stop from a relatively slow speed when i was in the states... trucks cannot stop well.. coz they are too heavy .. simple

And with the truck in the states were you able to check the heath of the brake system or the condition of the tyres? Did the driver lose control, did the brakes (and therefore tyres) lock. Just because a vehicle can stop quickly does not mean the driver can.

Most truck accidents are a result of a loss of control under hard braking (due to the huge weight transfers), not the braking distance.

And yes I have seen truck stop quicker than cars, at a number of proving grounds in the UK.

 

[lazydog]

ok let me ask you this you have a car that is made of titanium and weigh X kg .. it has super strong brakes and it sits on tyres that can give you 3 g's .. you do a 200 - 0 test .. and measure it ... you know magically turn the titanium to lead... and do the same test.. are you saying that you think it will stop in the same distance????

Yes it does. As the tires give you 3g's (= 29.43 m/s²) in both cases, as you suggested, both cars, the titanium one and the one made of lead, will come to a halt after about 135 meters, the mass of the cars does not matter (assuming the brakes are "strong enough").

And that's the point, the tires can provide a decalaration (there's no difference between accelaration and decelaration except the sign) of 3g (or so and so much), completely _independent_ of vehicle weight!

 

[mudia]

really .. i am lost as to how you can argue this..

no one was talking about wheel spin ..... yes a lighter car does not eliminate it .. but that is not the point... then tell me why can a 140 bhp bike out accelerate a 500 brake horse power car even when they are on the move and both vehicles can apply full power... simple cos of power to weight (which you even mention yourself re the convertible) ... power to weight is the key here.... no one questions that have better power to weight allows for faster acceleration .. why do they question it with deceleratin .. which is the same thing ..

you are aware arent you .. that acceleration laterally is the same thing as accelerating in a straight line... if a car can go round a bend faster.. then it can stop fasteer as well... the circle of traction in that article goes to support this... i cant believe that you would even suggest that increased laptimes from lighter cars are due ONLY to cornering speeds.. I watch formula 1 everytime it is on .. and i there have a been A LOT of times when martin brundel has said.."he is low on fuel so able to acclerate harder... brake harder.. corner faster" and the same thing has been said when watching bike racing

i ride a bike .. and i know what it is like when i am carrying someone on teh back... even though i can brake harder (ie pull the leaver harder reduced chance of flipping the bike) the bike does not stop anywhere near as quickly !!!

YES >> MY POINT Exactly . the maximum accelerative force .. you can get is due to grip.. this is why .. so there is always going to be a finite stopping power available.. due to the tyres... and THAT is why the stopping distances are affected by chaging the weight of the car...

 

[mudia]

scaff ... i dont know what sort of tests you have been witness to.. but once again i will try and explain what i am saying

you state that weight does not affect acceleration/deceleration ... and that contact area is the key..

now... have you seen the contact patches on a caterham... yes.. good ... you have obviously seen the contact patches on a truck.. now tell me ... based on your theory .. a truck has what 5 - 10 times the contact area....

are you saying that a truck will be able to stop faster than the caterham from 100mph

also you are aware the the effects of weight become more pronounced the higher the speeds ??

 

[mudia]

layzdog ... thank you for agreeing that accel and decel are the same thing...
now that there is no confusion ... and we can now use just one of those words

what you just wrote is totally IMPOSSIBLE.. and i ask any body here to bring a proper physicist to the forum to agree with you.. you wont find one .. i have no done any physics since A-level .. but i know that it breaks the rules..

there is NO WAY that lead car will stop in the same distance... you just said that accel and decel are the same thing .. why do lighter things accelerate faster ??? but dont decelerate faster ???


i have asked several times why there is a difference in performance that we can observe in real life that has to do wth power to weight ration... and you have not answered... ie the go kart.. a bike vs car.. etc...

 

[lazydog]

tell me why can a 140 bhp bike out accelerate a 500 brake horse power car even when they are on the move and both vehicles can apply full power... simple cos of power to weight (which you even mention yourself re the convertible) ... power to weight is the key here.... no one questions that have better power to weight allows for faster acceleration .. why do they question it with deceleratin .. which is the same thing ..

We are not questioning this. We only say that the tires of a vehicle limit the maximum possible acceleration (or decelaration) it can experience, nothing more and nothing less.

I watch formula 1 everytime it is on .. and i there have a been A LOT of times when martin brundel has said.."he is low on fuel so able to acclerate harder... brake harder

Not everything a formula 1 pilot says on TV makes sense...

i ride a bike .. and i know what it is like when i am carrying someone on teh back... even though i can brake harder (ie pull the leaver harder reduced chance of flipping the bike) the bike does not stop anywhere near as quickly !!!

I also ride a bike, sometimes with someone on the back and I can confirm your experience. However, I have never measured the braking distances with and without someone on the back. So, I can only say, that driving a bike with another person on the seat is much more difficult. This does not imply any exact numbers on braking distances, I simply don't know...

Exactly . the maximum accelerative force .. you can get is due to grip.. this is why .. so there is always going to be a finite stopping power available.. due to the tyres... and THAT is why the stopping distances are affected by chaging the weight of the car...

NO, the maximum grip available is NOT affected by total weight. I can only recommend to take a closer look at the article...

 

[mudia]

We are not questioning this. We only say that the tires of a vehicle limit the maximum possible acceleration (or decelaration) it can experience, nothing more and nothing less.

i am sorry .. but it seemed that you were arguing that breaking distances are not affected by weight.. ??? which inded you were

Not everything a formula 1 pilot says on TV makes sense...

ok

I also ride a bike, sometimes with someone on the back and I can confirm your experience. However, I have never measured the braking distances with and without someone on the back. So, I can only say, that driving a bike with another person on the seat is much more difficult. This does not imply any exact numbers on braking distances, I simply don't know...

hey i really dont mean to be rude.. but if you cannot tell.. that having a pillion on the back of your bike increases breaking distance ... you really should not be riding a bike... afterall it is one of the questions they ask you when you take your test!!!!!!!!

NO, the maximum grip available is NOT affected by total weight. I can only recommend to take a closer look at the article...

i never said it was !