BRZ/86 stopping distance

[Tcoat]

Originally Posted by Stephen W.

Switching from stock to high performance pads will decrease the stopping distance of any vehicle, correct?

Incorrect.
Brakes stop the wheels from turning. Tires stop the car from moving forward. Increasing the efficiency of stopping the wheels from turning does not make the tires more effective at making the car stop moving forward.


Using summer tires a car on the same surface will stop it in a shorter distance at 80 degrees than it will at 32 degrees simply due to the change in firmness of the tires. The rotors and calipers have nothing to do with it as the resistance is transferred to the tires as soon as the brakes are applied.


As stated, the special compounds of performance pads and rotors is solely to combat heat from repeated and extreme braking maneuvers. They are intended to combat fade not stop the car faster.

[venturaII]

A fixed caliper usually has better feel, resulting in better modulation. But if you're relying on ABS to do the modulation, as in a max-effort stop, pedal feel is of no real consequence.

[DarkPira7e]

Another perspective of this that I think most people can relate to - Why would a BIG BRAKE KIT not help you stop any sooner on ice?

It's not that it cannot help you stop sooner, it's just that those circumstances are not the first bottleneck you're encountering. Your tires usually are the first bottleneck.

[churchx]

Tcoat: except cases, where tires are upgraded to point of grip increasing to level of stock or simply previous pads are unable to lock them though. I'm not sure for example, if friction of stock pads/brakes will be enough to overcome torque of race slicks. Heck, me moving up to not race slick like tires, but simply more grippier tires like PSS, made me start considering pads with higher Mu, as hybrid pads like DS2500, while still were able to lock them, but now needed much stronger brake pedal press .. and with such strong press required i found that my leg brake pedal modulation precision suffered. So even if measured braking distance with different pads won't change, in this case with better pads "braking feel" can be more pleasant/easier. People do some "feel" upgrades to steering wheel, shifter, clutch, seats .. braking also is area, where feel can be enhanced.

Funny, how many things in car handling are affected by first and mostly tire choice. Optimal suspension, optimal alignment, optimal aero, optimal brake setup. Everything is changed/depends mostly from those pieces of rubber. All aspects of handling affected, braking, acceleration, cornering, max speed, comfort, pavement type compliance. Load & wear of components, money spent. Even such handling aspect, as fun

[LimitedSlip]

If the theory doesn't fit the reality it's time to change the theory . . .

[Stang70Fastback]

Originally Posted by churchx

Tcoat: except cases, where tires are upgraded to point of grip increasing to level of stock or simply previous pads are unable to lock them though. I'm not sure for example, if friction of stock pads/brakes will be enough to overcome torque of race slicks. Heck, me moving up to not race slick like tires, but simply more grippier tires like PSS, made me start considering pads with higher Mu, as hybrid pads like DS2500, while still were able to lock them, but now needed much stronger brake pedal press .. and with such strong press required i found that my leg brake pedal modulation precision suffered.

This happened to me with my first car; a 1998 Subaru Outback. I didn't lower it or anything, but I did fit some beefy sway bars to it to help it corner better. At the same time, I needed new brake pads, so I put some grippier pads on it. Suddenly I was able to lock up the crappy all-season tires MUCH more easily than I had before. So I figured that was a good excuse to upgrade to some proper summer tires to make use of those sway bars in the corners. That evened things back out and allowed a decent bit more stopping power using most of the pedal travel, rather than locking the tires at 25% brake travel, lol.

[Ultramaroon]

Originally Posted by Stephen W.

So, are you saying that my statement is completely, totally, utterly, entirely, wholly, thoroughly and unreservedly not in accordance with fact? Is that your position?
Please explain what the error is.

A couple errors.
1. The pucks normally rub ever so slightly against the rotor.

2. See below how freely a brake caliper should float in its mount. If it doesn't, it needs attention. The only hysteresis designed in the system is that between the pot seal and cylinder. That's there to prevent kickback.

So, no. A floating caliper does not apply braking force in some weird two-step process.


[ame]https://www.youtube.com/watch?v=4xNZu18bxg4[/ame]

[venturaII]

Originally Posted by Tcoat

Incorrect.
Brakes stop the wheels from turning. Tires stop the car from moving forward. Increasing the efficiency of stopping the wheels from turning does not make the tires more effective at making the car stop moving forward.

It sounds cliche, but tires are literally the foundation of the vehicle. They're the only part of the car actually in contact with the ground. And they're the front line of suspension, since they can accommodate multiple inches of road movement without anything else needing to move. And if they're bad or not up to the task, it doesn't matter what the rest of the car is like - you can't mask it. Tires can probably hide (or expose...) more bad design than any other component in the car. They're not just rim protectors...

[Stonehorsw]

Originally Posted by Tcoat

Incorrect.
Brakes stop the wheels from turning. Tires stop the car from moving forward. Increasing the efficiency of stopping the wheels from turning does not make the tires more effective at making the car stop moving forward.


Using summer tires a car on the same surface will stop it in a shorter distance at 80 degrees than it will at 32 degrees simply due to the change in firmness of the tires. The rotors and calipers have nothing to do with it as the resistance is transferred to the tires as soon as the brakes are applied.


As stated, the special compounds of performance pads and rotors is solely to combat heat from repeated and extreme braking maneuvers. They are intended to combat fade not stop the car faster.

(Necro mode on)
Porsche did prove that this is not correct. They did change the stopping distance adjusting the brake bias. Anyways, my mind when talking about system, I try to identify bottle neck and go from there.

Brake bias, tire to road friction, suspension setup, brake foundation response time, brake actuation response time, brake modulation response time, unsprung mass, rotating inertia, mass transfer plays a factor on that, and will be different from platform to platform.

BBK may help on bias, unsprung mass and response time.

[Stonehorsw]

Originally Posted by Grady

Exactly. Drum brakes will stop you just as good as disk brakes.... the first time!

Not always true. When designing a system with drum brakes, due to non-linear nature of this type of brakes, it is advised to be more conservative to avoid unstable braking.
Good case is some old toyotas with dual cylinders, which had a tendency to go off the track.

Also, on semis, it is very evident the difference.

[Stonehorsw]

Originally Posted by Ultramaroon

A couple errors.
1. The pucks normally rub ever so slightly against the rotor.

2. See below how freely a brake caliper should float in its mount. If it doesn't, it needs attention. The only hysteresis designed in the system is that between the pot seal and cylinder. That's there to prevent kickback.

So, no. A floating caliper does not apply braking force in some weird two-step process.


[ame]https://www.youtube.com/watch?v=4xNZu18bxg4[/ame]

It does apply in two stage. First the piston moves the inner pads and then when the force is greater than the caliper sliding force, the caliper housing will move towards the rotor and apply the outer. Opposite process will happen when you release. This is one of the reason that on passenger vehicles, the mechanical wear indicator is installed on inner pad (for floating axles, config may vary)


And to your point, always check if your calipers are sliding before a track day, getting a stuck caliper will be bad and, if you live in northen area, check regularly, as this changes quickly, and this will not always gives you warning signs (in stuck calipers, the outer pad can wear faster than inner, and mechanical wear indicator may not be activated)

[ls1ac]

We used to referrer to the best possible braking as threshold braking. This was the point just before the tires locked up. ABS tries to keep you at that point under panic stops. Once the tires start to skid the stopping distance increases and of course steering is lost.
We used to practice stopping at the limit both for feel but also to adjust brake bias. Our old cars (drum brakes) were able to brake (tire dependent) just as well as the new but not repeatedly. Only in a strait line with good surface. ABS is a great improvement as it takes account of tire friction at all four corners. The first ABS unit had timing pulses that were so slow that many thought the could do better but not true today.

[Stonehorsw]

Originally Posted by ls1ac

We used to referrer to the best possible braking as threshold braking. This was the point just before the tires locked up. ABS tries to keep you at that point under panic stops. Once the tires start to skid the stopping distance increases and of course steering is lost.
We used to practice stopping at the limit both for feel but also to adjust brake bias. Our old cars (drum brakes) were able to brake (tire dependent) just as well as the new but not repeatedly. Only in a strait line with good surface. ABS is a great improvement as it takes account of tire friction at all four corners. The first ABS unit had timing pulses that were so slow that many thought the could do better but not true today.

This may be true in some older platforms, when abs reached to a point that was good enough (early 2000’s), there was an increased sizing on rear disk brakes, having that closer to the limit. This helped shortening the brake distance on this configuration.
For deum brakes, it was not done as the brake factor is not linear, and also very prone for changes due to drum expansion (reduced factor) or change on point of contact (heel and toe contact, that could spike the brake factor)

PS: re-read your post. If you had a brake bar and adjusted the brake bias, then I would agree with your point.

[Tcoat]

Originally Posted by Stonehorsw

(Necro mode on)
Porsche did prove that this is not correct. They did change the stopping distance adjusting the brake bias. Anyways, my mind when talking about system, I try to identify bottle neck and go from there.

Brake bias, tire to road friction, suspension setup, brake foundation response time, brake actuation response time, brake modulation response time, unsprung mass, rotating inertia, mass transfer plays a factor on that, and will be different from platform to platform.

BBK may help on bias, unsprung mass and response time.

All that you said just leads back to the brakes being better at letting the tire stop the car.
The point of the matter remains that just swapping out some bigger pads and rotors doesn’t mean you will stop quicker.