Local track season is coming up for me - late March. Got every thing prepared except for actually getting the car clean. Local track is a big braking and handling track so to improve upon last years performance (which shouldn't be difficult ), I've got:

*Kumho Ecsta V700's, stock sizes, fronts are backordered until mid-April though, damn Miata spec racers. Hopefully, they'll come a month sooner.
*Carbotech Panther Plus, just received them the other day. Good guys those Carbotech people.
*Dali slotted rotors. Good guy that Dali dude.
*Dali brake ducts
*Motul 600
*Okyuma Strut Brace, from Science of Speed, but haven't rec'd it yet. Should be soon.
*Last but not least, I'll be signed up for a "performance driving class" in April.

Last years tire and brake setup included:

*Dunlop SP5000 tires. Came w/ car when I bought it. Don't laugh, they were a world better than the Nitto's I bought with some spare wheels.
*Dali Street/Race brake pads
*Dali slotted rotors
*Dali brake ducts
*Motul 600
*No track experience

Needless to say, I'm anticipating a world of difference in braking performance. Last year, I had a lot of brake fade until I changed fluid and was a little easier on the street/track pads. Toasted my clutch too, it was slipping when I bought the car, but changed that out to a Dali race clutch (not the Tilton CF one). I'm planning on doing some braking performance measurements, 60-0, etc. I'll post results.

Gettin' excited!

 

Best of luck man!

 

goodLuck man

 

I had no fade problems at Road America on the Dali Street/Track pads. My problem was shudder. I don't know if it was from rotor warpage or from pad material getting deposited on the rotor. I did have Motul 600 in there.

Have you remove the dust shields / splash guards from the front brakes? That supposedly helps cooling a huge amount.

Those Kumho V700s will make the biggest difference, though. Like, HUGE difference. Be careful, though. When you get slideways, they will grab much more sharply than street tires, which can throw you back the other way faster. I just drove on my V700s (old used hard ones) yesterday for the first time since the middle of last summer. Man.... I had forgotten how sticky they are.

-Mike

 

Yeah, I removed them a while ago when I put the Dali air deflectors on. I didn't track without those on. I wish I had a pyrometer to meausure heat on my parts. Maybe before the April event. I thought about getting the RM front spoiler with brake ducting but thought that I took care of the weak part of the brake system. No brake fade since I switched to Motul 600 and stainless brake lines.

If your rotors are warped you should be able to feel shudder braking at highway speeds or "spirited driving." at Carbotech told me to take some sandpaper and "clean" my rotors to make sure the pad material has a clean surface to bond to.

You're right - the Kumhos will make the biggest difference. Have you read that GRM brake article that says basically neither caliper, pads, rotors, fluid, or lines stop your car? The author says it's the tires that do it. So I'm really looking forward to outbraking people and making any passenger's eyes come out. Just have to play with air pressures a little.

 

That's one of those statements that make you say "Yes, but..."

Tires do indeed stop your car. Usually, your brakes can stop your car fast enough to make your tires skid - which means that any greater stopping power (due to calipers, pads, etc) won't make you stop any quicker. However, the reason that brake upgrades are important (particularly for those who track their cars) is due to heat, and fade. If you repeatedly stop your car hard, like when you're doing laps around a racetrack, the brakes build up a lot of heat. Unless it gets dissipated, this heat can cause all kinds of problems - boiling fluid (felt as a squishy brake pedal, as the bubbles in the fluid compress), fade (brake pads that lose their effectiveness when they get too hot), warped rotors (which create shudder at all times you are braking, not just when the brakes get hot), shudder like Mike felt (which, on the NSX, usually shows up only when the brakes get hot and is probably due to "hot spots" on the surface of the rotor, which expand at uneven rates), etc. The brake upgrades are ways to counteract these problems - high-performance fluid that boils at a higher temperature, track pads that are less susceptible to fade, cooling ducts, larger calipers and rotors to dissipate the heat better, etc. They are not designed to make your brakes stop your car any faster than your tires can; they are designed to avoid these heat-related problems.

Incidentally, instead of removing those dust shields, I had a hole cut in them and a flange welded there. I had brake cooling ducts installed that run from the front air dam and are mounted to the flange.



[Modified by nsxtcjr, 6:58 PM 2/11/2002]

 

Great commentary! You know, I thought about doing the same thing with the dust shields (similiar to what Doug H. had done to his S2000) but just put it down on my list of "To-Do's."

Do you have pix you could share? How are you mounting the ducts to the front spoiler?

 

The other thing about people saying it's the tires that stop your car.... It's a lot harder to lock up your brakes at 120mph than it is at 30mph. Just because your calipers, pads, and rotors are fine at 30mph doesn't mean there's not performance to be gained at 120+ mph. Besides, the faster deceleration at triple digits does more to shorten your braking distances anyway. But, that's speculation. I haven't seen any full physics analyses that would explain it. It just seems like it would make sense, since it seems harder to lock your brakes at high speed.

-Mike

 

Not right now, sorry.

There are inlets in the lower part of the front air dam, on both sides. The inlets look like the ones shown on this website. The ducts are two-inch high-temperature ducting; that's the maximum diameter you can use because the ducts have to squeeeeeze alongside the lower corners of the radiator just above the core support, and there's not a lot of room to get them through there.

 

I agree,
The tires may be what touches that road. But the heat that is generated when you slow down is energy taken away from the tires. If you were to lock up your brakes then it would all be up to the tires. So it is a cobination of the two. This is why larger brakes will slow you down faster. Your tires haven't changed, the brakes are larger and able to dissipate more heat (energy).

 

I'm not sure I totally understand this one. I always thought that tires get hotter under braking. From what I hear braking hard is one of the best ways at getting your tires up to temperature. Of course, all components are part of a system that stops a vehicle. I think the article was trying to get across that your tire is the foundation for getting the most out of your braking system. B/c basically the brake pad or caliper doesn't have contact with the road and your tires do.

The energy generated by speed has to go somewhere and is expended in the form of heat. In this case, that heat is stored and dissipated by the rotor, the caliper, the fluid, and the tire. There are methods at cooling these parts. Brake ducting cools the rotor, caliper, and fluid. Cooling the tires means not braking as hard or turning as aggesively. Larger brakes, I think you're meaning larger rotors and calipers by themselves, will not slow you down faster. Over time they will be more effective than a typical stock setup but only because they're more effective at storing heat. By nature they have more mass. And on some tracks larger rotors and calipers may be a hinderance by simply adding to unsprung weight when you don't need that amount of heat dissipating mass. If you can get enough cooling to stay w/i the operating temperatures of your pads, fluid, and tires then you'll be braking as good or better than the next guy running the 4K big brake setup. You'll be braking as effectively only with a lighter vehicle.

This is just what I'm thinking though. I could be wrong - been wrong many times before.

I don't know about locking up brakes at 120+mph, but I'd think that it'd be more difficult b/c of the momentum involved. Taking more time to react against and store the energy built up by speed. Besides we have ABS. . .

Hey, where's Andie Lin when you need him?

 

Ponyboy is right.

Tires heat up, and brakes heat up, for two different reasons. Actually, it's the same reason - friction - but from different causes.

As Ponyboy describes, brakes heat up during deceleration because the kinetic energy of the car's speed is converted to energy in the form of heat. The heat is created by the friction of the brake pad material on the surface of the rotors. This heat is dissipated through the rotors, the brake fluid, the calipers, and the air.

Tires heat up because of friction between the tire and the road. This will occur just driving down the highway; that's why tire pressure is measured cold (when your car has been sitting unused for a while). As soon as you drive for a few miles, the tires get warmer and the air pressure in the tires rises.

The tires heat more, and the friction is greater, when there is a "slip angle" between the tire and the road. This means that the wheel is not moving in a direction exactly parallel to the road surface. This occurs whenever the car is turning. When it's turning at high speed (like on a racetrack) for the same angle, the tires get hotter.

The tires also heat more, and the friction is greater, when the car is accelerating or decelerating, because forces are being applied to the tire to make it go at a different speed from the road. The harder you brake or accelerate, the warmer the tires get - especially if you get them to lose traction and spin.

 

The question I was trying to raise, though, was:

"Does the same tire have more braking capacity at high speed than it does at low speed?"

With my Kumho Ecsta Supra 712s, it's plainly obvious that a big brake kit wouldn't help me at all at speeds under about 60mph. The tires are totally the limiting factor. But what about dropping the anchor at the end of the straight at 140mph? Is the only reason I don't lock up my tires because I'm just not pushing the brake pedal hard enough? Or is it because the tires have more capacity than the rest of the braking system at those speeds?

(I already know I'd see benefits in the fade dept with a big brake kit, that's well understood. I'm simply trying to understand some underlying science.)

-Mike

 

If you are doing a single stop from 140 mph, then the tires don't lock up because you aren't pressing the pedal hard enough, or because the ABS engages to prevent lockup. With a single stop, the brakes shouldn't get so hot, and fade so much, that they are less effective than the tires.

However, if you are on a racetrack, or if you are repeatedly doing stops from 140 mph somewhere else, then the second answer may be appropriate. If this repeated braking is sufficient to cause the brakes to fade (lose effectiveness due to heat), then it is possible that the limiting factor in braking becomes the brakes, rather than the tires. If you've ever felt your stopping distances lengthen after a bunch of laps, when the brakes get really hot, then you are almost certainly experiencing the pedal fade. The only way you can feel it is when, indeed, your brakes can't slow down the car as effectively as the tires still can.

 

Good question, er, I don't know. If I restate the question to "Does the same tire have more traction at high speed than at low speed?" And I would think that it doesn't and the traction would be a lot less. Simply because the tire is being asked to do so much more at that speed than at a way lower one. The amount of energy the tire is being asked to dissipate, say from 120-0 vs. 60-0, I think, would be exponential. I don't think I'd like the feeling of just absolutely slamming on my brakes from 120mph. I'd have to modulate into braking. But if I were to apply the same about of pedal force at 60mph - I think I could control that.

 

Ok so I was wrong won't be the first.

Here is what I found off of Brembos site
At the speeds that stopping distance is generally measured from (60 to 70mph), the test is primarily testing the tire's grip on the pavement. As delivered from the manufacturer, nearly all vehicles are able to engage the ABS or lock the wheels at these speeds. Therefore, an increase in braking power will do nothing to stop the vehicle in a shorter distance. For this reason, we do not record stopping distances at this time. The Brembo systems will show their greatest advantages when braking from higher speeds, or when tasked with repeated heavy braking. The increased braking torque provides for maximum deceleration at speed, and the ability to absorb and quickly dissipate the intense heat generated during repeated braking insures that the braking system will perform at the same high level each time.

It has some additional useful info Brembo

My guess on why it is harder to lock the brakes up at higher speeds is because that
kinetic energy is = 1/2*M*V^2
1/2*1406*13.41^2=126419 J of heat at 30 mph
1/2*1406*53.64^2=2022706 J of heat at 120mph

At 30 mph you would need 93241 foot pounds of force to lock the brakes
At 120 mph you would need 1491867 foot pounds of force to lock the brakes.

My guess and only a guess is the brakeing system might not be able to deliver 1491867 foot pounds of force. Also the heat generated at that time I'm sure degrades the braking systems efficiency more than it would at 30 mph.

As for why its harder to skid the tires at higher speeds my guess would be that the heat generated at that time I'm sure degrades the braking systems efficiency more than it would at 30 mph. At the same time the tires increase traction as they get warmer.

To give a idea as to how much power that is if you were to stop it instantly it would require
At 30 mph 169HP
At 120mph 2712 HP

Ok so if I'm wrong don't flame me this is just my poke at it I don't know.



[Modified by nsxxtreme, 5:51 AM 2/14/2002]

 

Good info. No flames here. 1491867 is lot of foot pounds!