Here's the big brake track testing write-up I promised - The Unofficial BMW M5 Messageboard (m5board.com)

DZeckhausen · 24th February 2003, 07:30

Way back in 2002, I challenged StopTech to let me observe some of their track testing because I wanted to understand their methodology and, being the skeptical type, I wanted to see if there was the possibility of any bias in the results. Are we supposed to believe their kit results in shorter stopping distances just because they say it does?

They invited me to California in December to help with the track testing of the new Nissan 350Z and I jumped at the chance. It was a fun trip and I learned just how much I didn't know about brakes. I came away with a much greater respect for their design and testing methodology. In fact, I became a convert and started selling StopTech products. Some of you old timers will find that to be pretty amusing, given my initial interactions with StopTech on this very board.

About a month ago, I promised to post my write-up on the track testing. I've pretty much finished it, so here's the link. Some of you might find it interesting.

If you have any comments to improve readability or if you catch typos or errors, please let me know so I can fix it. I was working on it late, so who knows what sneaked in there!

Testing brakes with StopTech

kAtAnA309 · 24th February 2003, 10:48

Dave,

Great write up! I never heard of the modified J-turn before.. excellent stuff!!

Found the following discrepancies:

Quote:

Stopping distance vs. front/rear brake bias

If the brakes are too front biased, the front brakes tend to lock up prematurely and the stopping distances become longer, both with and without ABS. StopTech engineers the bias of their kits by retaining the stock master cylinder and juggling caliper piston and rotor sizes to recreate the factory brake torque balance.

And this one..

Quote:

The fraternal twins cooling down after the initial brake tests

Now the real work was about to begin. It was time to test the StopTech 322mm and 355mm front brake kits But first the cars needed to cool down a bit.

Regards,

Gerrit

MIB · 24th February 2003, 12:25

Great write up Dave, just two problems.

One all that talk of chicken made me hungry. And 2. Don't keep us in suspense about the 4 Wheels package.

Thats the one I wanted to know about.

Notice that there really isn't some huge difference in stopping distance. The biggest difference really is in Temp. And therefore it is very obvious that the real benifit is Repetition. Which is what is needed on the Track.

I laugh at all the Ricers with huge break upgrades that think they can tailgate people because they have more stopping power.

Little do they realise that their stopping distance has only improved by a few feet.

The Terminology needs to be changed to reflect this. Most layman and non Track persons think that better brakes means they will stop incrediably faster than normal. And this is rarely the case.

You just increase the number of cycles before fade. Or I suppose ultimately have a set up that doesn't fade reguardless of usage.

This is great news for track guys, and racers, but it doesn't half stopping distances. A common misconception.

Let me know how the Four Corner set up goes. Our $ is looking good at present, and the StopTechs look like good value at $5000USD.

I would have preferred the Tests on a Beast. But you can't have everything I suppose.

MAVERICK · 24th February 2003, 14:07

I love the pictures and you explained everything very well.

Comments:
1) In the "summary of test data" table it would be easier to read if you said "Temp 60mph, Temp 80mph, and Temp 100mph" instead of just "Temp 60." It is confusing because I thought the test took the ambient temperature into account as the day progressed.

2) Perhaps you can add, under the section titled "Measuring Rotor Temp. after 100 mph Stop," a suggested explanation as to why a 100+ degree Fahrenheit difference exists between the temperatures of the stock rear rotors when paired with the StopTech 332mm versus the StopTech 355mm front brakes. From what I've learnt from the rest of your article about brake bias, I'd venture to say the 355mm setup has more rear bias. So does this mean the 332mm setup is not as optimally balanced as the 355mm setup or is it the other way around? Also, I just noticed the first figure titled, "Stopping distance vs. front/rear brake bias" tells us that while the 355mm and 332mm StopTech are within the normal zone, the 355mm is slightly front biased while the 332mm is slightly rear biased. Yet the summary test data shows the opposite, doesn't it? At all three speeds, the rear stock rotors show higher temperature in 355mm setup than the 332mm setup.

3) Under the "summary of test data," I suggest you add a small note (to make the data look more scientific) stating the approximate sampling error for length and temperature measurements as well as the approximate error in the data associated with the changing ambient temperature of the test conditions as the day progressed from dawn to dusk.

pride355 · 24th February 2003, 16:44

Dave,

Great write-up

Thank you for that..

On most of the cars, fronts always have bigger rotor size than rears. However on E46 M3, fronts have 326mm rotors and rears have 328mm. M3 has 50/50 weight balance; so why have bigger rear rotors?
Do you know or can guess the reason??

DZeckhausen · 24th February 2003, 17:08

Quote:

Originally posted by MIB
One all that talk of chicken made me hungry. And 2. Don't keep us in suspense about the 4 Wheels package.

My description didn't do the chicken justice. Perhaps it was because I was jet lagged and starving, but those drumsticks were amazing. They were from a grocery store's prepared food section and were very big and very spicy. M

!

The 4-wheel beast (E39) kit has been delayed while StopTech goes through an iterative process of test fitting rear hardware. Two factors have pushed the date back to the end of March. One is that the bracket, for some reason, requires a manual iterative process, and two is that a crunch on a large number of Viper kits is taking up lots of CNC time and getting in the way of doing these brackets.

The issue is that the rear rotor is a 355mm x 32mm and the caliper is the same size as the front (but smaller pistons). It's a very tight fit and initial indications were that a wheel spacer would be required. I told them no way to the spacer because there's very little room between the outside edge of the tire and fender lip, especially if you're running M5 wheels on a 540i.

I'll keep you posted as progress is made. I'm sorry to have pre-announced by so long and raised hopes. I feel like Microsoft, announcing Windows 2000 in 1998 and releasing it in 2002.

Quote:

Notice that there really isn't some huge difference in stopping distance. The biggest difference really is in Temp. And therefore it is very obvious that the real benefit is Repetition. Which is what is needed on the Track.

I laugh at all the Ricers with huge break upgrades that think they can tailgate people because they have more stopping power.

Little do they realize that their stopping distance has only improved by a few feet.

Actually, there is a benefit on the street that the track testing does not illustrate. That's the improvement of reaction time. With any of these brakes (StopTech, Brembo, Mov'it) you can START braking sooner because, when you hit the brake pedal, you don't have to move a huge, 17 pound iron caliper. Instead, the caliper is fixed and the featherweight pistons are the only moving parts. Combine that with ultra stiff calipers and steel-braided Teflon lines and you can shave a significant amount of time off the onset of braking. In a panic stop from 80mph, if you can BEGIN braking 0.2 seconds sooner, you've shaved 24 feet off your stopping distance when compared to the stock brakes. That amount dwarfs the 3-5 foot difference due to bias. Again, this reaction time is important on the street when the stop is unexpected, but it is irrelevant at the track where the driver takes the reaction time into account when determining the start of the braking zone. The tests were designed by racers and for racers. There needs to be another test that can accurately characterize the improvement in reaction time and I've discussed this with StopTech. It's not going to be an easy test to do and, as a result, it may not happen any time soon.

Anyone out there who already has any of the big brake kits on their car knows exactly what I'm talking about. It's the fact that there is so little pedal travel and that when you hit the brake pedal, it's immediately in the linear zone where a given driver input results in a given brake reaction. The stock brakes have three distinct zones. The first is the "nothing zone" where your pedal just sinks a few inches with no braking resulting. Then there's the "non-linear zone" where the floating caliper is just starting to squeeze the rotor but the frame is flexing, the brake lines are flexing, and the pad is flexing (due to the single piston pushing it in the middle). Finally, after most of the flex is squeezed out, you enter the "linear zone." With the aftermarket brakes, there's a tiny "nothing zone" followed almost immediately by the linear zone. Modulation of these brakes on the street is much easier.

I hate to say this, but those ricers in Hondas are right. They know they can react faster than most other cars to an unexpected event. They have increased confidence in their brakes, not because they are stupid, but because they've noticed the change and have learned to trust them more.

Quote:

The Terminology needs to be changed to reflect this. Most layman and non Track persons think that better brakes means they will stop incredibly faster than normal. And this is rarely the case.

I agree that there are many claims out there about huge reductions in stopping distance and it's simply dishonesty by vendors. They aren't talking about improvements in reaction time. They simply don't understand and they make stuff up. It really riles me to see these claims. I may do a search later and post links to the most outrageous claims I find. That could provide some entertainment for the day.

Quote:

Let me know how the Four Corner set up goes. Our $ is looking good at present, and the StopTechs look like good value at $5000USD.

They are a good value if you compare them to other 4-wheel kits. But if you compare them to other modifications in bang-for-the-buck, they don't hold up too well, unless you include aesthetics in the equation. Most of the improvement in pedal feel and thermal capacity has already been achieved by the time you've installed the front kit. Adding a rear kit is a bit over the top and the development of this kit was not driven by pressure from racers who needed something extra to be competitive. It was driven by the marketplace who has been screaming for big red calipers at all four corners. (Not that there's anything wrong with that!) I just want you to understand that the first $2595 you spend makes a huge difference and that the 2nd $2495 makes much less of a difference in performance.

If you want these for looks and for the slight improvement in pedal feel, the convenience of having the same brake pads at all four corners, and ease of rear pad changes, then go for it! But don't think you need these for extra safety or an extra edge at the track. Your money would be better spent on a Stage III suspension. [/b][/quote]

DZeckhausen · 24th February 2003, 17:17

Quote:

Originally posted by MAVERICK
Perhaps you can add, under the section titled "Measuring Rotor Temp. after 100 mph Stop," a suggested explanation as to why a 100+ degree Fahrenheit difference exists between the temperatures of the stock rear rotors when paired with the StopTech 332mm versus the StopTech 355mm front brakes. From what I've learnt from the rest of your article about brake bias, I'd venture to say the 355mm setup has more rear bias. So does this mean the 332mm setup is not as optimally balanced as the 355mm setup or is it the other way around?

I considered leaving off the temperature data because there was a tremendous amount of fluctuation that was a result of the testing methodology and the accuracy of the measuring instrument. Because the temperature changed with every stop and because only one measurement was taken at each stop, it's hard to produce error bars. You should look at the temperature as something useful for understanding trends but keep in mind that the actual values may be off by more than 20 degrees.

Quote:

Also, I just noticed the first figure titled, "Stopping distance vs. front/rear brake bias" tells us that while the 355mm and 332mm StopTech are within the normal zone, the 355mm is slightly front biased while the 332mm is slightly rear biased. Yet the summary test data shows the opposite, doesn't it? At all three speeds, the rear stock rotors show higher temperature in 355mm setup than the 332mm setup.

You're very observent, but not quite observant enough.

If you read the description under the first diagram, you'll see that data from the Audi S4 kits was used to generate the graph. Your interpretation of the graph was accurate but it doesn't apply to the Nissan 350Z kit. I used the S4 graph because data was available for the platform for the other brake kits, whereas such data was not available yet for the Nissan 350Z.

I'll go back and figure out a way to make this more obvious. If it confused you, I'm sure it will confuse others.

atomic80 · 24th February 2003, 17:46

One thing that I feel compelled to point out is that I constantly found myself having to backtrack up and down through the article to compare the data between setup A, B, C, etc. Perhaps you could make things easier by putting a table comparing the three data between sections? Say at the end of one section, you'd put data from setup A and then the next section you could include the data from A in addition to the new data from setup B, etc. That would make things considerably easier for folks trying to compare the different sets.

KRM · 24th February 2003, 18:00

Excellent write-up, Dave. Does Stoptech currently offer a 4-wheel kit for the Cooper S?

DZeckhausen · 24th February 2003, 18:26

Quote:

Originally posted by atomic80
One thing that I feel compelled to point out is that I constantly found myself having to backtrack up and down through the article to compare the data between setup A, B, C, etc. Perhaps you could make things easier by putting a table comparing the three data between sections? Say at the end of one section, you'd put data from setup A and then the next section you could include the data from A in addition to the new data from setup B, etc. That would make things considerably easier for folks trying to compare the different sets.

Hi Jason! thanks for the comments.

You didn't make it all the way to the end, did you?

At the very bottom, I have a table that summarizes all the data. So you don't need to jump back and forth.

However, you have a very valid point. I do plan to have a linkable index at the very top that allows you to jump down to the various sections. the brake distance testing is only the first of several sections. I also plan to add photos and details of the caliper bench testing and the brake line testing.