How effective is weight reduction?

In my '90 Camaro 305ci V8 I stripped everything from the interior. Plastics, speakers, radio, spare tire, jack, automatic hatch release, seats (with exception to the driver's seat), seatbelts (with exception of the driver's) and trust me it made a difference in acceleration. I can't remember exactly how much weight I took out but it was over 175lbs. Now comes the downside, it was very loud and hot. The carpet--even though it is thin--added a little insulation from the catalytic converter underneath the passenger side. Great for the winter bad for the summer.
 
i can assure you that the single biggest factor in stopping distances is the tyre compound, weight distribution and transfer are a second order effect and the actual weight behind that.


Uh, like I said, everything else being equal, a lighter car will stop faster than a heavier car. That means if you take a car, and change nothing on it except make it lighter (As you would do removing the interior), it'll brake better. Obviously upgrading tires is going to help more than taking off fifty pounds. Even better would be to remove fifty pounds AND get better tires.
 
Scaff
The 1 millisecond you are talking about is obviously a bit silly, but they certainly are doing this to gain 1/10ths of a second per lap, because if you are racing over 70 laps, then even a 0.05 second gain per lap is worth 3.5 seconds over 70 laps and thats the difference between winning and losing.
Agreed upon completley.

to add to it, this is what makes me laugh when people take a 60lb (40kg) or so A/C unit out, and "feel" the huge gain they got.

a weight loss/gain is typically 1/2 - 1/4 what the average trendy "enthusiast" makes it out to be.
 
a/c can also reduce the power of the car
replace "can" with "absolutely"

but, I was talking about handling. I shouldve clarified.
Live4Speed
Braking upto the point right before your tyre's will lose grip if the quickest way to stop
This is about as far from the truth as it gets.
Let me ask you, which cars stop faster for magazine road tests, cars with ABS, or cars without?
 
This is about as far from the truth as it gets.
Let me ask you, which cars stop faster for magazine road tests, cars with ABS, or cars without?

Now that depends entirely on the car, drive and the conditions.

A well set-up ABS system, on a wet road will stop a car quicker than the vast majority of drivers, however a poorly set-up system that kicks in early (and soem road car systems certainly do) on dry tarmac may well not be able to stop a car quicker than a good driver in a car will good brake feel and modulation.

On some surface conditions, particularly very loose gravel and snow/ice ABS can massively increase stoping distances.

It should always be remembered that the principal design reason behind ABS for road use was not to reduce stopping distances, but to allow drivers to retain steering control of the car while braking.

That however is besides the point, ABS or not a cars stopping distance is dictated by the road/tyre interface, period.

Anything else just allows you to maximise the grip avaliable between the road and the tyres or stop you exceeding it.

Regards

Scaff
 
Scaff: While everything you said there is true, I'm thinking you're forgetting L4S said "without locking up the tires".
Now, think of what you're stopping distances without ABS would be, if you werent allowed to lock your tires up.
Magazines NEVER (in America) lock up the tires on vehicles without ABS, and therefore have horrendous stopping distances.
Example: 2002 Dodge Viper GTS: 60-0: 160FT
With ABS next Year: 2003 Viper SRT-10: 99FT
that doesnt come from 10mm of rubber.
that comes from magazine drivers being able to skid the tires thanks to their retarded policy regarding braking.
 
Uh, locking up your tires under braking is bad. Ideally you do want to apply just enough brakes to not lock anything up. This is exactly what ABS tries to accomplish, and a lot of times it will do better than a human driver.

Isn't the 2003 viper entirely different from the 2002? Everything I've read says the 2002 was pretty poorly developed and put together, and that the 2003 is much, much better.

If you want to compaire ABS and non ABS, you need to take a car out that has ABS, run it, then pull the ABS fuse and run it again.
 
lead sled and scaff

i think you are both right.

if one applies the maximum braking effort, one will get the maximum retardation. thats how you do it when you have ABS. but if one is feathering it to not lock up the brakes, you can see how perhaps they might not be applying maximum braking effort
 
If you want to compaire ABS and non ABS, you need to take a car out that has ABS, run it, then pull the ABS fuse and run it again.

Which is exactly what Ross Bentley discusses in his book Speed Secrets.

Ross Bentley
I once spent a couple of days testing a showroom stock Corvette. The first day it was dry, the second it rained. Each day we ran with and without the ABS activated. In the dry I was half a second wuicker quicker with the ABS turned off. The next day, in the rain, I was over a second quicker with the ABS on.


Scaff: While everything you said there is true, I'm thinking you're forgetting L4S said "without locking up the tires".
Now, think of what you're stopping distances without ABS would be, if you werent allowed to lock your tires up.
Magazines NEVER (in America) lock up the tires on vehicles without ABS, and therefore have horrendous stopping distances.
Example: 2002 Dodge Viper GTS: 60-0: 160FT
With ABS next Year: 2003 Viper SRT-10: 99FT
that doesnt come from 10mm of rubber.
that comes from magazine drivers being able to skid the tires thanks to their retarded policy regarding braking.
I'm not forgeting what L4S said at all, ABS does not magically give you more grip from your tyres, it simply allows you to try and maximise what grip they are able to provide. Something most drivers are not able to do, however a lot of professional drivers can maximise the grip levels from tyres without the use of ABS.

The purpose of ABS has never been to shorten braking distances, but it will allow you to maximise the potential grip avaliable. This is a subject I have taught (and demonstrated) as part of my job, ABS system development and its practical uses is a subject I know very, very well.

I would love to read the exact test conditions from the two Viper tests, as ABS alone is certainly not capable of producing a difference of over 60ft in stopping distances. Different track conditions are however, certainly if one was the result of even slight brake lock.

Steve Sutcliffe who carries out the annual 0-100-0 tests for Autocar (and who has held the world record for it a number of times) is capable of stopping a non ABS car far quicker than an ABS equiped car, as can be seen by any of the 0-100-0 test results (links to most years can be found in the GT4 & Braking thread.

In fact in this years test two of the three cars that dropped below 4 seconds in a stop from 100mph were non-ABS cars (Caterham CSR260 and Aeriel Atom 300), the only ABS fitted car that could do it was the Veyron. These stops were certainly done without locking up the tyres (because its discussed time and time again in the articles), as that would have resulted in a massive increase in both distance and time.

In this piece...

LeadSlead#2
Now, think of what you're stopping distances without ABS would be, if you werent allowed to lock your tires up.

...you seem to be implying that a non ABS car will stop quicker if you lock the tyres up.

Could you please clarify that, because if that is what you are saying then it's an absurd statement.

The only other possiability is that you are saying that ABS stops a car quicker that non-ABS, even if you are able to use the maximum grip availiable from the tyres in both scenarios. In which case can you explain how the ABS car manages to do this, because ABS is not able to generate additional grip in a tyre.

Remember that all along I has said that I am talking about the 'best' possiable stopping distance for each, for the average driver an ABS fitted car will stop quicker that one without ABS, but this is not because it improves the cars stopping ability, but because it allows the driver (with no specific control other than an ability to stomp on the brake pedal) to maximise the tyres available grip limits. I also said that in the wet a good ABS system will be able to do this better than any human driver could, this is clearly show in the piece from Ross Bentley I quoted above, in the dry he is better able to use the tyres grip, but in the wet the ABS was better able to do it.

The following is an explanation of exactly how ABS systems work, written by StopTech (who manufacter motorsport brakes systems.

StopTech
ABS Control In Super-Slow-Mo
In order to best explain how the ABS "depends" on the base braking system, let's have a look at a typical ABS event at the micro level - from the processing algorithm's perspective.

Say you are driving down the highway at 75 MPH (the posted speed limit, of course) when all of a sudden the truck in front of you spills its load of natural spring water across all three lanes of traffic. Now, this alone would not be so bad, except the water is still sealed in 55-gallon drums - one of which would certainly make a mess of your car's front fascia. Time to take evasive action.

Being the trained high-speed individual that you are, you immediately lift off the gas, push in the clutch (you are driving a manual transmission, right?), and simultaneously nail the brake pedal...but in the heat of the moment you hit it a little too hard.

Meanwhile, the ABS is hanging back watching the world go by, seeing a constant stream of 75 MPH signals from its four wheel speed sensors. Let's call this "observation mode." Upon your application of the brake, however, the ABS snaps to attention, its antenna up, ready for action. You have just hit the brake pedal after all, and who know what's coming next.

After 50 milliseconds (it's actually much faster than that - 7 to 10 milliseconds is typical - but it makes the math easier) the ABS takes another snapshot of the wheel speed information in an attempt to figure out what's going on. This time the wheel speed sensors are all reporting a speed of 74 MPH. Doing a quick calculation, the ABS determines that in order to have slowed 1 MPH in a 50ms period the wheels must be decelerating at a rate of 0.91g's. Because you are driving a sports car, the engineer who calibrated the system 'taught' the ABS that your car is capable of decelerating at this rate, so the ABS continues to hang back and watch the event from the spectator's booth. No problem so far.

The next 50ms, however, are a little more interesting. This time around, the wheels are reporting 72.5 MPH. Now, it may not seem like a big jump, but to slow 1.5 MPH in a 50ms window equates to a deceleration of 1.36g's. Not alarming, but the ABS 'knows' that based on this deceleration level, the wheels are probably beginning to slip a little more than they should - after all, your car is probably not decelerating at quite 1.36g's..and any error between the two indicates slip.

ABS is now in "ready mode." It's probably too soon to jump in, as the wheels might spin back up on their own in the next 50ms loop, but things are definitely looking bad!

As the first barrels of spring water bounce left and right, missing your car by inches, you stay on the brake pedal but push even harder. This time around, the left front wheel speed sensor is registering 68 MPH - a 4.5 MPH drop in the last 50ms, or a deceleration level of 4.1g's. Doing the math faster than you can (after all, you are busy dodging barrels of spring water), the ABS quickly comes to the conclusion that, unlike the left front wheel at this moment, the car cannot possibly be decelerating at 4.1g's. Best case is that the car was decelerating at 1.0g (or thereabouts) over the last 50ms, so the 'real' vehicle speed is still somewhere around 71.5 MPH, even though the left front wheel speed is reading 68 MPH - a 3.5 MPH error.

So, based on a wheel deceleration of 4.1g's, a slip level of 5% (3.5 MPH 71.5 MPH), and a couple other factors not listed here, the ABS jumps in and enters "isolation mode." (Note that the wheels are nowhere even near "wheel lock" - the 100% slip point.) The first thing the ABS does is shut off the hydraulic line from the master cylinder to the left front caliper, isolating the driver from applying more pressure - after all, it was the driver that got us into this mess in the first place.

Next, the ABS starts work in "decrease mode," releasing the excess pressure from the left front caliper in order to allow the left front wheel to reaccelerate back up to the vehicle's actual speed - 71.5 MPH in this case. Since the ABS knows how quickly the wheel is decelerating (4.1g), how fast the car is actually going (71.5 MPH), and the pressure-torque characteristics of the left front caliper/pad/rotor assembly (we'll come back to this one in just a second), it can precisely calculate how long to open its release valve to vent that extra pressure, leaving just enough pressure in the caliper to maintain 1.0g of deceleration (or thereabouts).

Let's say that calculated time turned out to be 10 milliseconds (this again makes the math easier later on). Bang! Valve opens, pressure is released, and 10ms later it closes, leaving just the right amount of pressure in the caliper so that the wheel spins back up to exactly 71.5 MPH, but continues to decelerate at 1.0g. Everything is going as planned.

Time to close the loop and enter "increase mode." Once the ABS sees that the left front wheel has returned to near the 'real' vehicle speed, it slowly reapplies pressure from the master cylinder to make sure that maximum sustainable brake force is being utilized. To this end, the ABS calculates precisely how long to pulse open the isolation valve, slowly building pressure at the left front caliper until once again the left front wheel begins to slip. It performs this calculation based on - you guessed it - how quickly the wheel is re-accelerating, how fast the car is actually going, and the pressure-torque characteristics of the caliper/pad/rotor assembly.

In our hypothetical little world, the ABS calculated that four pulses of 5ms each were necessary to build the wheel pressure back up to the point that the wheel began to slip again, returning to "isolation mode."

The cycle is repeated on all four wheels simultaneously until either the driver gets out of the brake pedal, or until the car has come to a stop. Hopefully, this did not include punting a spring water barrel or two along the way as the ABS kept all four wheels slips in the 5%-10% range, allowing you to turn and swerve to your heart's content as the drums bounced out of your path. Happy car, happy driver.

Its worth noting that through out the entire piece the ABS system is maximing the tyres slip percentages and angles, far quicker in this situation that any human driver could, but what it is not doing is providing any aditional grip for the tyres (which is what provides stopping potential), but making the absolute most of what is available.


Regards

Scaff
 
Magazines NEVER (in America) lock up the tires on vehicles without ABS, and therefore have horrendous stopping distances.

Locking the tires up rather then threshold braking increases stopping distances.

My car is mid engined and has very front biased brakes, making them incredibly easy to lock, I learned the hard way that if your fronts lock up it's not easy to get them unlocked, and you just plow foward into whatever's ahead of you without any steering. After that little experience I found an empty road and practiced threshold braking.
 
ok, before we proceed, anybody got the numbers on a 60-0 or better, a 100-0 run in a car at full lock-up?

I used the Viper because it remained fairly similar in principal, with almost identical weight, brakes, tires, and weight distribution.
and it's a car with tests for abs - non-abs runs.
however, I've never seen a test at full lock-up.

I DO know that ABS's original purpose was to keep controllability in panic situations, not to decrease stopping distance.
aka - rotating tires turn cars, locked ones do not.
 
ok, before we proceed, anybody got the numbers on a 60-0 or better, a 100-0 run in a car at full lock-up?

I used the Viper because it remained fairly similar in principal, with almost identical weight, brakes, tires, and weight distribution.
and it's a car with tests for abs - non-abs runs.
however, I've never seen a test at full lock-up.

I DO know that ABS's original purpose was to keep controllability in panic situations, not to decrease stopping distance.
aka - rotating tires turn cars, locked ones do not.

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 stoping 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 anywere near as well).

I will however post up the Skip Barber info tomorrow.

This should be of interest in the mean time

http://www.michelinman.ca/care/driving2.html

Michelin Braking Tips from Skip Barber
Rule 4. Locking up the wheels increases stopping distance by about twenty-five percent, makes steering impossible, ruins the tires and scares everybody in the area.


Regards

Scaff
 
Scaff
Because rotating tyres also stop cars (as long as the are rotating slower than the car is travelling),
I'll let you sit and think about that for a moment.

I am quite curious as to how much cars stopping distance increases when locked up.
Also, I'd love to know why these magazine editors can't put a car on the threshold good enough to stop a car within 50FT of ABS from 60.
160ft to 99ft is a hell of a distance, and quite frankly, if that 160ft run is the best they can do, a 25% increase over ABS would be about 35ft better than these supposed "skilled" drivers.
that would indicate:
no abs = no lock = 160ft
no abs = full lock = 125ft
abs = 99ft
(give or take no more than 10ft)
 
I'll let you sit and think about that for a moment.

I am quite curious as to how much cars stopping distance increases when locked up.
Also, I'd love to know why these magazine editors can't put a car on the threshold good enough to stop a car within 50FT of ABS from 60.
160ft to 99ft is a hell of a distance, and quite frankly, if that 160ft run is the best they can do, a 25% increase over ABS would be about 35ft better than these supposed "skilled" drivers.
that would indicate:
no abs = no lock = 160ft
no abs = full lock = 125ft
abs = 99ft
(give or take no more than 10ft)


Reply given in this thread

https://www.gtplanet.net/forum/showthread.php?p=2408724#post2408724

As its more in line with the subject being discussed (braking), please continue in that thread.

Regards

Scaff
 
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