linzman

What's a normal brake pressure? Used my AIM brake pressure sensor for the first time at Lime Rock. trying to figure out if I could/should be braking harder. Never hit the ABS, so can't use that as a "mashing it" reference. Car is a 968 with stock master cylinder. Got down to a 1:00.7, but the record is in the low 59s, so there's more time to be had.

Matt Romanowski

It varies depending on MC size, caliper piston size, pedal ratio, etc. I usually see 1000 to 1500 pounds. You can monitor it pushing as hard as you can in the pits to see how high it will go.

ProCoach

Most production cars (small bore), I see as little as 300 to as much as 600.

It's only modern cars that I see a lot more than that. I test a lot to determine mean max pressures without lockup. Then I make sure I SEE that number. Often.

924RACR

Typical current production car, stock chassis, yeah, front axle locking pressure is typically 80-100 bar/1000-1500psi, like Matt said...

Peter, are you talking Prod cars, or stock production cars?? 300-600psi seems absurdly low... maybe with touchy race pads?

linzman

Mine is a stock 968 master cylinder with big black calipers on front, regular M030 calipers on back. I was seeing around 600 psi. Never hit the ABS, but I guess I really need to, to know where that limit is.

Veloce Raptor

My suggestion is gradually keep increasing peak brake pressure to find where it begins to tickle ABS, and then you'll know pretty precisely...

Frank 993 C4S

I don't think there is such a thing as "normal brake" pressure because your brake pressure will depend on tire, track and environmental conditions. At LRP I hit peak pressures of about 850 PSI into Turn 1 on average. The left-hander is barely at 400 and the uphill barely at 290. Rather than peak pressure, I would think about how you want to modulate the pressure in a particular corner to help you set the car for corner entry and exit. For example, does blipping the throttle cause you to release the brake pressure in T1? Can you carry braking all the way into T1 to the theoretical turn in point for T2? How does the brake release help you rotate the car in the Left Hander? Can you brake all the way to where that big rollbar scratch is in the middle of the track? For the same brake point, how soft can you brake through West Bend and still get back on power at the same point?

It is always amazing to me how much better a pro can modulate brake pressure. Their data looks less "spikey", rounder and usually much lower peak pressure.

Of course there is that one time last weekend I had to hit 1351 PSI going into T1.....

Veloce Raptor

This

linzman

Clarification, I didn't mean I wanted to hit the max on every turn, just curious what the approximate number might be. I was hitting 600 into Big Bend, maybe 2-300 at the uphill and west bend. The tracings were pretty rounded, except for big Bend, where I definitely had a spike as I blipped. Need to work on that for sure. I'll try to post the tracing later today.

924RACR

Nominal conditions: straight line, dry hi-mu, no significant downforce, stock/OEM tire, normal working pad temps, etc etc. - in other words, standard ABS stopping distance measurement conditions.

ProCoach

Many of the production based cars I measure read between 450-600 maximum, like linzman's experience. Even my crumby sports racer doesn't ever hit more than about 700.

This idea that you need to hit a particular number WITHOUT calibrating or testing WHERE that number is is absurd and not correct.

That said, in the latest GT3 factory racers, if you aren't at 100 bar or more, you're not pushing hard enough!

linzman

Ok, here's the screenshot from my 1:00.7 lap Max brake pressure only 411 into Big Bend, and I'm still braking too early. Any other comments?

Thanks

ProCoach

Steve,
Double click on the measures numbers to the left of the strip charts. This will auto scale them so we can see the shape of your brake pressure trace.

linzman

fixed it

ProCoach

Yuk.

Attack and decay should not be the same gradual slope up to and down from max pressure.

As you brake harder, the car will stop shorter, making you believe you're braking earlier, which you are now doing, only more so. Move the zone into the entry more...

The trick is to "front load" the max pressure and bleed off (not too quickly, though. Want to leave some up to and past initial steering input) as the cornering loads build.

You should build and show a gSum channel.

Braking (for any car that works correctly) should generate .90 to .95 of the total sustained lateral loading the car is capable of. Then, your job is to vary the duration to tune to the amount of speed you need to lose... And NOT allow the gSum to drop more than 10-15% from peak braking to peak cornering.

Big brakes extending deep into Big Bend. Short, sharp and deep brake into the Left Hander.

This is what the fastest drivers are doing. I'll post something sometime this week.