I thought I had this figured out, but I recently read in Corvette Fever that changing over to ceramic coated titanium brakes were reducing brake distances by over 30 feet in 60-0's which is huge. Here is what I don't appear to understand.

I have always thought that your limit of accelerating, turning or braking is entirely based upon your tires. Specifically, if you can lock up your brakes, you have the ability to maximize tire traction and that is all there is. One thing I've always thought is that you could change the suspension to change the geometry of the front tires under hard braking to try and use more of the tire's ability to brake, but as long as you can lock them, them actual brakes are doing as much as they can.

I thought the reason for upgrading is to primarily have a brake that will last longer over time (bigger, better thermal transfer, largers swept area reduces fade etc.), however you are still limited by the ability of the tires. Also, perhaps some of the larger brakes give a better feel and help you modulate more effectively, but still limited by the traction of the tires.

So I don't undestand how a set of rotors and pads with no tire, brake hardward or suspension changes could knock an average of 30 feet off of a 60-0 stop. I must be missing something, so please chime in.

Thanks

 

Stopping is really about dissipating kinetic energy by converting it to heat. You are right that the tires are the determining factor but if you lock them up you actually have less stopping power. The tire gets its best traction with a little bit of slip (just like acceleration in a drag race you get better traction if the tires are slipping a little). If on decel you can keep the tire at that point where it is slipping(but not locked up) just a little you will maximize your stopping traction. This is the point where the tire is dissipating the most energy. If the stock brake system isn't using all of the tire's traction at that point then you can get better stopping by going to a set of pads and rotors that can convert the remaining energy into heat quicker than the stock pads/rotors (without causing the tire to lock up) you will slow down quicker. To do that you need a pad that can operate at a higher temp and a rotor that can absorb more heat without overheating. On a car without ABS this may be hard to do since people can't modulate the brake pedal well enough to keep all the tires on the car at that max traction point all of the time.
Bill

 

I agree with your premise that traction is ultimately limited by the traction (or grip) of the tires. That asumes that you have Horse Power and brakes that can overwhelm the tries in acceleration or deceleration. But , if the power of the engine or the brakes are insifficent to spin the tires or lock them up, then the limit of accelerating or braking is not limited by the tires.

Heat is a big enemy of stopping power of the brakes and grip of the tires, depending upon which one gets too hot too soon, either the tires or the brakes could be the limiting element in stopping quickly. I suppose it is possible that in the test you describe, the brakes were not up to the grip of the tires, and by changing the brakes the had more stopping power, the tires could handle it and so the car stopped in a shorter distance.

Most brakes will diminish in their stopping power as they get hot, but the aftermarket large exotic brakes will handle the heat better and provide shorter stopping distances than the stock brakes. A great equalizer is to get lots of cooling air to the brakes so the stopping power stays at a high level. The tires stay relatively cool under stopping and acceleration as long as you don't spin or slide the tires, but the tires heat up quickly during hard cornering.

I think what your seeing here is the tires in the test had greater potential grip than the stock brakes could utilize, while the exotic brakes utilized more of the tire's grip.

Jim

 

I'm with both of you, but still have the same problem. In this test, they specifically mention they let the car sit for 30 minutes between runs, hence heat shouldn't be a factor. I still don't get if the brakes (stock C5 brakes) can lock up the tires (I also know that a locked tire loses about 30% of its braking capacity), how titanium/ceramic or anything else can make the car stop quicker. I'd give my left **t to stop my car in 30 feet less in the 60-0.

In this test, they don't mention whether they could get lock out of the tires with both sets, but I have to assume they do in order to get max performance. The mag suggests 60-0 in 89 ft, vs. 124 with the stock system. Rippie suggest he can get 13 feet with his kit. Curious to me still

 

How often in a race or DE school that your are going 60 to 0?? More like 135-150 to 50 and back up to 120 then slam on the brakes again down to 40, back up to 130 then slam on the brakes down to 50 again. Doing this 3 or 4 time evey 60 to 95 sec for 20 min to an hour. That is brake demand, not 60 to 0 two or three times.

Tom

 

Tom it's all relative

 

Jeff I guess your right, and some ppl never experience red line.

 

I agree about the distances vs. you normal track differences. But, extrpolate and say they save 30 feet 60-0, maybe that means 60 feet 120-0?

If you can lock the brakes are you getting all of the traction i.e. stopping power available at that moment in time or am I still missing something?

 

I read the same article, and had the same questions. Frankly, this isn't the first time in recent history that Corvete Fever has published, IMO, questionable numbers.

The only way I can see you being able to get a performance increase in the kind of test they conducted was if you could get a better balance on all four wheels; i.e., instead of having one tire start slipping and engaging ABS, get all four to start slipping at the same time. Other than that, the physics just don't add up to me.

HTH, and have a good one,
Mike

 

i agree w/ all of you about the tires being the limiting factor for braking if the brakes are properly maintained.

I haven't read the article in question, so i'm just guessing here. When my car 1st arrived in europe, i was in bad need of a brake job. The pads had about 1/3 left on them and the rotors looked fine other than being old, but the brake pedal was very soft and the car just wasn't stopping like it should. While i was waiting on my new pads and rotors, i replaced the fluid in the master cylinder and it was a major improvement (i didn't bleed them or anything, just sucked the fluid out and put new in) I would bet that the car used had old brake fluid in it and when the changed the rotors and pads the changed the fluid too, which was the main reason for the improvement.

The only other reason i can think of is the weight reduction from the titanium probably helped some, but not 33ft from 60mph.

 

Well I really dont want to extrapolat that 60 feet less stopping distance when I am flying down the front straight at VIR at 140 MPH heading into that 180 degree right hander. I did that once thank you very much when I boiled one of the most popular brake fuilds ( blue / gold ) and caused vapor lock with my brake system.

I will stick with something that is tried over and over again for now - Iron rotors - NAPA or Rock Auto with PFC 01 pads and Castrol SRF brake fluid with Hoosies for shoes.

. Tom


[Modified by AU N EGL, 3:49 PM 6/29/2004]

 

Here another way to look at it...and Tom (A U EGL) is 100% correct. What he is talking about is the effect of heat and your brakes ability to continue braking after reaching several hundred degrees. Most stock brakes will fade away...that is one of the main differences between a good brake set up and a stock set up.

Here is another point...
You basically ask in so many words, "how can brake upgrades be better if your car is already locking up, reaching their full potential?"

Tires, suspension, and chassis help a car brake sooner, not just brake upgrades, but have you ever hit your brakes HARD at 130mph? They WON'T lock up...trust me. I have a pretty good set up and I have rarely activated the ABS when braking at 100MPH+. What you are takling about is street braking...they will lock up around 65mph give or take on any car. When you take your car to the track, your brakes have to deal with HEAT and HIGH speed. This is where the upgrades show their value.

 

I completely understand that big brakes help over time. No question. At least once a month I spend a day or two braking from 130plus, so I get it. And, I can get into ABS with the stock brakes (for about 20 minutes of hard driving then things get a bit sloppy) . In my first post I specifically say I thought the main reason for changing your stock setup is fade over time or suspension changes to maximize the traction of your tires (i.e. less diving causing contact patch distortion, etc). I get that.

The question that I am really asking is whether tire traction is ultimately the limiting factor in getting a car to stop (or go or turn for that matter). If so, then there is no way changing just pads and rotors (if you take the potential to overheat out of the equation) can actually make you stop faster.

What I am trying to understand (and I think we are getting a concensus that in fact you are limited by tire traction and the Corvette Fever article is likely BS) is other than during a fade condition, how a new set of any kind of rotors and pads could have such a dramatic effect on braking (as I already know you can get the stock brakes when not overheated to get to the point of lock). I'm not knocking big brakes or anything, just trying to see if my underlying thinking is correct or if I'm missing something.

Thanks for all the replies.

 

I would be skeptical if these are the same set up as I saw up at Gingerman. Take a look at:
http://forums.corvetteforum.com/zerothread?id=847597

 

Actually you can get this scenario in a good Corvette (not SCCA) Club low speed autocross. Top Speeds will be in the range of 60 to 80 mph with corners in the 15 to 20 range. Total time on the circuit 45 to 120 seconds and there will be at least two corners where you will be max braking from those speeds. Full ABS maximizes the tire traction but may not maximize the brake systems ability to dissipate heat since the stock brakes may not have the capacity to absorb/dissipate heat as well as an aftermarket setup. This means you can go deeper into the corner before lifting and hammering on the ABS. It is more about absorbing/dissipating heat surges vs max heat.
Bill


Bill

 

Actually Corvette Fever had a set of titanium/ceremic coated Red Devil rotors with Red Devil pads. They said they tested them on an '01 vert. They said they waited 30 minutes in between runs and did six stops with the stock setup and 6 stops with the new rotors/pads, so heat no factor in this test. The car went from an average of 124 feet to an average of 91 feet.

 

I believe your original idea is correct - brakes can't stop the car any faster than the tires can supply grip in
this kind of test.


FWIW, the only real use I've found for published 60-0 stopping distances is to check the relative grip of the tires
used in the test. (They are not absolute numbers, just a rule of thumb for comparing things with the limited
information provided.)

If you look at stopping distances with simple math, a car that stops 60-0 mph in ~ 120 ft is stopping at an average
rate of 1 G. (That is true for any type of car or any weight - if you want the math it is in the reference below*.)


If the car stops @ 1 G , that means the tires were capable of a coefficient of friction of ~ 1.0. In general terms,
that friction (grip) level is something like what i would expect from, say, premium street tires in good condition.

Manufacturers don't publish tire friction coefficients, but as a rule of thumb sticky ultra-performance street tires
might be in the 1.1 - 1.2 friction coefficient range (my guesstimate). That would correspond to stopping in ~ 105 ft.

The case you cited had the car going from 120 ft down to 90 ft for a stopping distance? I didn't see the article.

90 ft = 1.35 G average stopping rate; and tires with a 1.35 coefficient of friction. Those seem like VERY sticky
tires indeed. Maybe some mucho warmed-up racing slicks, or some drag tires with traction compound can show
numbers like that. (Grip numbers that high are beyond my experience - perhaps someone else knows where they
come from.)


When you see comparison tests in a mag with radical differences like that, there is usually a micro-tiny footnote
around somewhere that indicates a tire-swap. In this case, one humongous tire-swap IMHO. Or something else is
hokey - at first blush, it doesn't sound like they made a real apples-to-apples comparison. But that's just my HO,
YMMV.


*If you want to brush up on things like weight transfer, grip, acceleration and the like, there is a very readable
primer here that discusses the basic forces and math involved (plus the author was a Corvette driver):

http://www.miata.net/sport/Physics/

HTH

 

Thanks Doctor J!

 

I read that series, and I learned that I really need to brush up on my physics. I understood the part about a tire requiring a certain level or force to make it start sliding, but then the article said adding more weight would still require the same ratio of force to get it to start sliding. That makes me think more weight transfer is good, at least up until the point to where the thermal capacity of the tire has been exceeded, but the article still says it's better to have less weight transfer to have the rear wheels do some work....now that made sense to me before I read this series, but now I'm really confused. To make it even worse, I used to think wider tires would produce more grip, but this series seems to defy that line of thinking. Anyway, I'm headed down to the bookstore in search of a good suspension design book to make sense of this.

 

Physics never lie - Physicists', however, have been known too....

Braking is really the "system" - tires, fluids, lines, calipers, master cylinder, pedal system, ABS (if applicable), rotors, pads, and the nut behind the wheel. Environment is what has a lot impact also....

Articles are meant to sell products all to often....and to get you to think "what if"...

I must admit I enjoy the debate and thoughts!

Now then lets take it where we can play!

I will try anything that will make me faster than Tom!