M's

I disagree, the later you break the less time the pad is in contact with the rotor. The less heat is built up and you allow more time for cooling of the pad and rotor before the next time the two make contact. If you're not overbraking but braking as late as possible, then you're maximising pad life and your times.

Carl Byck

I think it is a question of finesse, and will differ from track to track, driver to driver, and car to car. As far as the argument that late braking means less time with contact between the two surfaces, I do not see what you mean. Late braking would typically be far harder braking for a shorter period of time, I would argue that that is far harder on all equipment than a combination engine braking, light linear braking, and correct car placement entering a turn. It is really not an argument at all, since each has its purpose, invariable, extremely late braking will often be paired with an upset suspension, poor car placement on the track, and too much time spent gathering the car back up so that you can properly accelerate out of the turn. For this entire conversation I would defer to Carroll Smith in the end. I am a late braking fiend, I am not the fastest, and certainly not the smoothest. Watch a pro when he is not in traffic, or trying to pass, he will use much less brake than when he is battling, this is because it is simply not the fastest way around. Anyway, like I said, there are so many different circumstances, that it is not even a disagreement, just observations about how to treat various competitive situations. Peace OUT. Carl

RX-Heven

iTrader: (1)

The brakes slow a car (actually the tires are what really slows the car) by converting the rotational inertia of a wheel assembly (and the mass of the car) into heat generated by friction between the pad and rotor. Due to this thing called the conservation of energy, it does not matter when you start braking, the same amount of heat energy will be produced, all else being equal. The braking systems ability to dissapate the heat during braking is the only difference in the amount of heat the system retains at the end of a braking cycle.

SPiN Racing

Continuing this thought process....

Realistically.. in a perfect world.. your car should be doing one of two things.

1. Slowing down

2. Accelerating

In the perfect environment you should be accelerating till the last possible moment, to make the best distance from teh speed you are traveling at.

Then decelerating at the LIMIT of tire adhesion... Including the turn in and trail brake through to the apex.

At that point you should transition from braking to acceleration smoothly, with ZERO neutral time between.

Granted... we all have a variety of corners with steady state throttle through them... is that the perfect line?? Very Very Likely not. But it works for 90 percent of the world out there...

The real fun is to ride with a person who is in the 1/2 percent or so that is a top level driver. The pro drivers.... or people who SHOULD be..

Having seen/ridden with a few people who were at the highest level.. I know for CERTAIN that I do not drive to the vehicles limits.. and have a nice goal to work towards. But MAN.. when the person is carrying a TON more speed than everyone else into the corner.. and is cornering and breaking and downshifting, and keeping the car solidly, smoothly, flowing through the corner.. and rolling into the throttle as they are letting off the brakes.. and you dont feel the change... THAT is a fast line.
Granted they are at that top level.. and I dont mean club racing... that is something to see.

There is a manuver my instructor used to do back in college flight school when I was getting my CFI.
He would have you look down and then VERY smoothly manuver the plane around in gentle turns and banks, getting the plane gradually more and more out of shape, until he said "Your Plane" and you would look up to see the plane UPSIDE DOWN, but in a banking dive.
He would very smoothly keep the plane pulling 1G without getting out of shape so you couldnt feel it moving around. In the end it was inverted.

Finesse as Carl said. The question.... (Not to you Carl.. but to all of us) Do you ever find yourself at neutral throttle? When not accelerating or decelerating? How can you change it so you are slowing down to that point you are at.. and or accelerating from there.
I do.. I find myself there at times.. Some times it is neutral or go off track because speed is too high to do anything in the corner but hold on. Different line?
sometimes..

I try to make sure I am doing one or the other. Going or stopping.
Not just waiting to do one or the other.

(Man I need to stop writing books LOL)

jgrewe

iTrader: (1)

Scott, you didn't mention you're a pilot. Me too.

SPiN Racing

Much much info. I REALLY do need to stop by the shop and BS.
Degree in Aviation Technology/Professional Pilot....
Course I am a LAN Admin specializing in Storage Management...3 days a week.. and play with cars 4.

Carl Byck

I disagree, if your average speed is close to optimum, you will be going slower into the turn, but exiting faster. Since you are slower in, you need less brake. Like I said, I have watched the on board telemetry for an LMP900 at Sears, he uses the brakes less than I do. We should both be tuned in a couple weeks, we can settle this at the track

RX-Heven

iTrader: (1)

I don't know what you are disagreeing with me over. I wasn't advocating late or early braking in any way. All I was doing was pointing out some elementary principles in physics applied to braking. You're not disagreeing with the laws of physics are you?

On the other hand, I do like late braking
I've always looked at it this way; If you race to the end of a quarter mile in the same cars but have to be stopped by the finnish line, the one who accelerates the longest and brakes the latest will get there first.
I never understood the slow in fast out argument except for the fact that people tend to overbrake and scrub to much speed going into a corner when they late brake reducing their exit speed. I say fast in and fast out. Certainly easier said than done, but with practice you will be faster. The argument also goes along the line of getting all your braking done in a straight line vs. trail braking. I prefer trail braking except on a few turns here and there.

The LMP900 cars you are referring to is like comparing apples to oranges. Those are race cars, not track driven street cars. They are capable of reducing greater speeds in a shorter distance and can carry much more speed through a turn. Sears Point for example, those cars can go through turn ten around 135mph. When I was racing Star Mazdas, we could go through it a hair over 115. In my vert I can almost get to 100 mph but am on the brakes before the turn. In the Star cars I would just breathe the throttle. See where I'm going with this....

I am already signed up for the August event with NASA for the entire weekend in Group 4. I will also be running the Time Trial event concurrently in TTA. I could certainly use some more competition in that class, however I think your car would bump up to TTU.
btw, leave the 13" slicks at home and bring 700-800 lbs of lead

DamonB

My 2 cents on heat in the brakes...

Some people frequently feel that stomping the brakes very hard and slowing as quickly as possible builds up less heat in the brakes than braking more gently over a long period of time, or they feel just the opposite, or they feel there is no difference between braking hard or braking more softly. The reasons I have heard for this being so are that the pads are in contact with the rotors for a shorter period of time and that the brakes were used over a shorter period of time. Also brakes slow a car by turning rotational energy into heat and the Law of Conservation of Energy says the same amount of heat will be produced in slowing a car a given amount no matter how we choose to brake. That's true.

But...

Braking the car more gently over a longer distance is without a doubt easier on the brakes. The reason is time. The brake system sheds its heat energy into the airstream and if you brake over a longer period of time you give the rotor more time to dissipate its heat energy directly into the air. While the brakes are being applied over a longer time period the rotor temp never gets as high because it has more time to shed heat into the air while the rotor is in use and heating up. As the rotor is heating it gets more opportunity to cool at the same time. If you stomp the brakes as hard as possible the rotor temp will spike up quickly because in the instant you were braking there was not as much air mass moving through the rotor. You put more heat into the rotor in a shorter period of time and because of that fewer air molecules had the chance to flow through it and hold the peak temp down. Now the rotor will still have time to cool before the next corner so you many not ever actually fade the brakes, but without a doubt longer, gentler braking distances always result in lower peak brake temps than short, harsh, braking. Braking over a longer distance will make all brake components last longer since the peak brake temps stay lower. The average temps over a lap however will be much the same.

Carl Byck

Better to try this in person, but essentially, very late braking will invariably mean you are not in the rightclace on the track to apex correctly. Now, if you are coming from a longer straight to a shorter one, and the time gained by late braking is greater than the time gained by completing the turn, and accelerating onto the next straight at the optimum speeds, and turn in points, then maybe. Take turn 7 for instance, if you arevery late on the brakes, the back end of the car will still be light going into that turn, so, you wll have to go through that turn slower, at which point, I will pass you in the turn, and leave your lead filled DOT tired butt behind in the ESSES. BTW, no way I weigh 600 less than you, I still have stock wiring/Dash etc. anyhow, Easier to show you on the track, than in person. Each change in the movement of the car takes both time, and distance. You cannot go fast in, and fast out unless you give up the turn, in which case you will likely be passed...See you on the 8th. I will callyou about Brians Tuning visit today, I booked the flight, and we should be ready to go. Carl

edmcguirk

Ahh, thermodynamics. It's never exactly what you think it is.

Remember heat transfers faster if the surface is hotter. If a truck is coming down a long hill it will overheat the brakes if it rides the brakes but if it stabs the brakes several times it can sometimes survive (forget about engine braking for a minute).

Short intense heat is probably harder on the brakes but the average brake temperature can be lower that way.

Late braking (provided you don't blow the corner) means a few extra seconds of kinetic energy that must be shed, so it's not an apples to apples comparison.

ed

jgrewe

iTrader: (1)

When I got my CDL to drive semis(Used to own a concrete redimix co.) They tell you not to pump the brakes on a long downhill. The rotors can't shed heat as fast as you can put it in no matter what. So, light braking over a longer time is the way to go with a truck. As for racing, unless you're fighting for a corner, brake earlier(only a few milli-seconds)and lighter too. Sometimes you get caught up in a battle with one or two cars with everybody trying to be the last to brake. When that happens the guy not IN the battle, just ahead of it, will pull away. Why? because he is using an earlier braking point and doing everything smoother because of it.

DamonB

Yep yep. Lighter braking over a longer period of time results in lower peak brake temperatures.

RX-Heven

iTrader: (1)

I think I had summed up your thorough explanation with my last sentence in the similiar post, but that certainly makes it more clear.
Thats what they taught me when I got my Class B license.
Carl, my overweight bitch weighs almost 3300 lbs. without me and a 1/2 tank of gas. If my car was a woman, I wouldn't ***** the fat bitch. In the meantime though, my car has been phucking me. I'm guessing your gutted, fiberglass adorned car with a cage weighs about 2700 lbs.

Carl Byck

Dave, I think you are about right, my goal is to get to a fighting weight of 2450 wet. The Fuel cell is certainly heavier than stock, the bumper is heavier than stock, seats weigh less, and the interior is gone. I will need to pull the dash, and all the glass, not to mention some hole saw action to get the weight down.

edmcguirk

Actually a truck will put more heat into brakes than they can blead off either way. And repeated heavy braking can let the instantaneous heat get too hot for the materials. So maybe that wasn't a good example.

But the concept is still true. I was trying to point out that it's not a simple answer. The higher temperatures can bleed off faster but the stress is higher.

And on the racetrack the guys in a battle drive slower not because they are late braking but because they are not driving on the ideal line. The guy behind can afford to be off line and slower through the corner as long as he gets there first and blocks your faster line (as long as he is not so slow that you can easily drive around him). The guy in front has to brake too late for a fast corner just to stay in front.

ed

Kenku

Just throwing a couple cents in about the braking issue.

I've always heard that braking harder is easier on brakes than going longer and more gradually, at least in some circumstances; the particular article was on NASCAR type setups. Yes, conservation of energy says that the amount of heat generated is going to be the same, but the difference is what happens to the energy. Shorter spikes of temperature mean that there's less time for the heat to transfer through the pad and caliper pistons, since we can assume that the outside of the pad is cooling fairly quickly (parts of it possibly ablating and whatnot) so there's perhaps less heat getting to the fluid. Similarily, on the rotor, it's going to get to a higher peak temperature, but because it's hotter it'll dump heat faster, and the fact that there's more time where heat's not being put into it helps too.

Thing to consider about the LMP900 example is that it actually supports the "lighter braking = more heat" thing; since they all use carbon rotors, in some circumstances there has to be effort put in to keep the discs hot.

... but those're just educated guesses that seem to make sense at the time I write them. Considering that time is at 1:45am after work, YMMV.

Nihilanthic

Sorry to drift off the topic this thread has taken, but while I know the front brakes are great, are the rear ones good enough for track use? I know they wont see nearly as much heat as the fronts, especially the harder you brake (the more leaning forwards), but I havent heard anyone exactlly come out and SAY theyre good. Just.. not much attention paid to them at all, lol.

And weight transfer makes me think of something else... do race suspension setups (with stiff *** springs) control transfer to the front enough you use the rears more than you would with say, stock springs braking hard from 120?

Thanks in advance!

Carl Byck

The rears are also fine, I can go a full season on 1-2 sets of pads. Under heavy breaking they may lock up do to the weight transfer, that can be somewhat remedied by a Bias adjuster, but I find the stock set up to have very good balance, even on the track. You can change bias with varying compounds, but I would stay within a family, ie carbotech XP, PFC, Hawk Blue/black etc. I will be putting my brakes to the test in a couple weeks, when my car is done. Carl

Nihilanthic

Seems ABS is useful for track cars if the rear brakes lock up under hard braking

But, I guess it seems that I might as well just put decent pads on them and leave it at that. Thanks!

Carl Byck

I plan on adding ABS to my car in the future, most high level GT cars utilize it as well. carl

edmcguirk

As much as I have heard from racers that ABS is a "good thing" I have never heard of anyone at a club level adding ABS to their car.

I would very much like to know how to do that.

ed

Carl Byck

ABS was an option on S5 RX7s, and so you simply need all the hardware, including the ABS computer(I think).

edmcguirk

I always asumed that ABS was somehow integrated into the ECU or something.

I thought ABS in the S5 was relatively rare but if it is completely independent in the wiring harness, maybe it's worth a try.

It's probably illegal in my class anyway but I would probably want to stay SCCA legal too. Is that a legitimate update/backdate in ITS?

ed

its66

iTrader: (2)

In SCCA, ABS is not permitted in ITS. Update/Backdate works for using the 89+ rotors, housings, intake, and even installing the aluminum hood. ABS is specifically disallowed-"Cars with antilock brakes must have the system disabled..."

sorry..

jim