WTB: big brake kit
11-13-2013, 05:02 PM
#16
Rennlist Member
Please send me some of your data.
In the meantime, here's another way to think about it:
Most people who feel their brakes aren't big enough are not looking far enough ahead. When you look right in front of the car (e.g. the braking zone while you're in it) the objects rushing past your field of vision are triggering a sense of urgency in your brain. This is just a fact of human nature - we're programmed to become anxious about threats that are close to us, but we can remain calm about threats that are far away. Tigers eat you when they're close; cavemen beat you with a club when they're close.
When you're not calm and analytical about your turn-in, you'll find that a) you've over slowed; and b) aren't maximizing your trail braking.
Why is turn in so critical? This is the point where you start to change the direction the car is pointed, e.g. your lateral g-forces will transition from 0 to some non-zero number. At this point, you know you need to be at something less than 100% braking force. And, from this point forward, your braking force will diminish as your cornering force increases.
What you need to do is, at turn in, have the car slowed down enough that you can modulate the brakes just enough to build lateral force. So, you don't want to be too slow or too fast, and you need to make a smooth transition as the weight transfer happens.
My question to you, Patrick and mr965: How does the car feel to you at this point? Assuming there's room for improvement, what do we have to change to make it better?
Perhaps it is braking one car length earlier (but why would that mean that you have to lift first?) so the duration of the braking zone gets a fraction of a second longer and slows the car down more.
Perhaps it is releasing the brake pressure a wee bit a moment before you initiate turn-in to allow some weight to transfer away from the front wheels.
Looking at your data, especially the driver inputs, will help us figure that out.
Patrick, a "gentle transition" does not mean a "wider/softer" brake trace. Looking at some of my data, the time from 100% throttle to starting brake pressure is 0.225 of a second. The time from 0 brake pressure to almost max pressure is 0.3 of a second, there is a little rounded top between about 85% and 100% - a smooth transition - that lasts 0.15 of a second. Otherwise it is a very steep ramp up. I hold peak pressure for 0.8 of a second - this is a long steady "plateau" at the top of the curve, not spikes or mountain peaks; then I modulate/taper off for another 2.2 seconds. My total braking time is 3.45 seconds and my speed goes from 117 MPH to 70 MPH.
I can also tell you that my steering input starts 0.15 of a second after I've started my release from peak pressure. At my final brake release, the steering wheel is at about 75% of the arc for that corner; and my foot is back to the throttle, and holding it at 25%, 0.08 seconds after I've released the brake. In case you're curious, my braking force for the duration of the peak point is 1 G.
So, let's look at some data and see what you're doing. Let's create the separation between what your brain thinks is happening and what's really happening. Let's also work on keeping vision up so these brake zones and corner entries become non-events. Once it's a non-event, you can devote that brainpower to feeling your traction at each wheel; the weight transfer through the shocks; the surface undulations/bumps of the pavement; how to set up a pass on a competitor; etc.
In the meantime, here's another way to think about it:
Most people who feel their brakes aren't big enough are not looking far enough ahead. When you look right in front of the car (e.g. the braking zone while you're in it) the objects rushing past your field of vision are triggering a sense of urgency in your brain. This is just a fact of human nature - we're programmed to become anxious about threats that are close to us, but we can remain calm about threats that are far away. Tigers eat you when they're close; cavemen beat you with a club when they're close.
When you're not calm and analytical about your turn-in, you'll find that a) you've over slowed; and b) aren't maximizing your trail braking.
Why is turn in so critical? This is the point where you start to change the direction the car is pointed, e.g. your lateral g-forces will transition from 0 to some non-zero number. At this point, you know you need to be at something less than 100% braking force. And, from this point forward, your braking force will diminish as your cornering force increases.
What you need to do is, at turn in, have the car slowed down enough that you can modulate the brakes just enough to build lateral force. So, you don't want to be too slow or too fast, and you need to make a smooth transition as the weight transfer happens.
My question to you, Patrick and mr965: How does the car feel to you at this point? Assuming there's room for improvement, what do we have to change to make it better?
Perhaps it is braking one car length earlier (but why would that mean that you have to lift first?) so the duration of the braking zone gets a fraction of a second longer and slows the car down more.
Perhaps it is releasing the brake pressure a wee bit a moment before you initiate turn-in to allow some weight to transfer away from the front wheels.
Looking at your data, especially the driver inputs, will help us figure that out.
Patrick, a "gentle transition" does not mean a "wider/softer" brake trace. Looking at some of my data, the time from 100% throttle to starting brake pressure is 0.225 of a second. The time from 0 brake pressure to almost max pressure is 0.3 of a second, there is a little rounded top between about 85% and 100% - a smooth transition - that lasts 0.15 of a second. Otherwise it is a very steep ramp up. I hold peak pressure for 0.8 of a second - this is a long steady "plateau" at the top of the curve, not spikes or mountain peaks; then I modulate/taper off for another 2.2 seconds. My total braking time is 3.45 seconds and my speed goes from 117 MPH to 70 MPH.
I can also tell you that my steering input starts 0.15 of a second after I've started my release from peak pressure. At my final brake release, the steering wheel is at about 75% of the arc for that corner; and my foot is back to the throttle, and holding it at 25%, 0.08 seconds after I've released the brake. In case you're curious, my braking force for the duration of the peak point is 1 G.
So, let's look at some data and see what you're doing. Let's create the separation between what your brain thinks is happening and what's really happening. Let's also work on keeping vision up so these brake zones and corner entries become non-events. Once it's a non-event, you can devote that brainpower to feeling your traction at each wheel; the weight transfer through the shocks; the surface undulations/bumps of the pavement; how to set up a pass on a competitor; etc.
11-13-2013, 11:14 PM
#19
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The other part of the equation is the brake pads. Street pads will not work well at the track regardless of how big a caliper you have.
I used stock 86 calipers with stock rotors on a 370hp heavy 951 for years. Used Hawk pads that would last about 4 track days....but they slowed the car just fine.
I used stock 86 calipers with stock rotors on a 370hp heavy 951 for years. Used Hawk pads that would last about 4 track days....but they slowed the car just fine.
11-14-2013, 01:12 AM
#21
Rennlist Member
11-14-2013, 11:28 AM
#22
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I designed the hats with ProSystems who manufacture hats for Brembos rings for the NASCAR teams. It's specifically for the '88 951s & '89 and for 86.5-95 928's. Bolts on, requires 30 minutes a side.
11-14-2013, 02:36 PM
#24
Three Wheelin'
Fluid is a significant part of the issue. When you combine questionable brake pads, standard turbo brakes with Super Blue for example, plan to boil the fluid. On Track you should be using race pads with a superior fluid like Castrol SRF or AP Racing SP600. If you overheat the fluid consider the big blacks.
I currently use Mark's 355mm rotors with Big Blacks Hawk DTC 70's, ducted cooling & AP600 which works very well. I am getting concerned about the number of rebuilds on these calipers (once a season).
I currently use Mark's 355mm rotors with Big Blacks Hawk DTC 70's, ducted cooling & AP600 which works very well. I am getting concerned about the number of rebuilds on these calipers (once a season).
11-14-2013, 02:45 PM
#25
Nordschleife Master
I'm upgrading to the Integra 6R with 330 mm rotors. I'm seeing brake fad on fast tracks were I am braking from 150mph, no problems at Barber, but Road Atlanta and NOLA get interesting after 20 minutes on track. The integra can use pads up to 1.2" thick, which should help to keep the calipers cooler. And yes, I have been running good fluid (Motul 660) and pads (DTC70). Seals for rebuilding are $16.95/caliper instead of $16.95 for each seal 
11-14-2013, 04:15 PM
#26
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Fluid is a significant part of the issue. When you combine questionable brake pads, standard turbo brakes with Super Blue for example, plan to boil the fluid. On Track you should be using race pads with a superior fluid like Castrol SRF or AP Racing SP600. If you overheat the fluid consider the big blacks.
11-27-2013, 03:07 PM
#29
I'm upgrading to the Integra 6R with 330 mm rotors. I'm seeing brake fad on fast tracks were I am braking from 150mph, no problems at Barber, but Road Atlanta and NOLA get interesting after 20 minutes on track. The integra can use pads up to 1.2" thick, which should help to keep the calipers cooler. And yes, I have been running good fluid (Motul 660) and pads (DTC70). Seals for rebuilding are $16.95/caliper instead of $16.95 for each seal
Last edited by zeusrotty; 11-27-2013 at 03:41 PM.
11-27-2013, 04:08 PM
#30
Nordschleife Master