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Tracking / Autocross / HPDE / Drifting What these cars were built for!


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Old 09-17-2018, 04:31 PM   #4705
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my caliper pistons are very stiff to retract, even when using the spreader tool, but braking operation feels fine...
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Mine too. I really have to crank down on them with the spreader, even with the reservoir cap open.
The calipers actually depend on seal stiction. Normal brake operation is within the range where the piston seals only flex inside the caliper. As the pads wear past a certain point, the seals slip a little and go back to flexing.
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Old 09-17-2018, 05:14 PM   #4706
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So improving mid range, or shifting the power curve earlier, is no good for tracking?
Unless you're sweeping that improved part of the powerband, it does nothing to help you on track.
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Old 09-17-2018, 05:16 PM   #4707
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my caliper pistons are very stiff to retract, even when using the spreader tool, but braking operation feels fine...
It should be smooth, and you should be able to push the pistons in by hand. Time for a rebuild.

Typically, CP8350 need rebuilds every year. It is a race caliper, and does not have outer dust boots like mixed/double duty calipers and street calipers.
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Old 09-17-2018, 05:17 PM   #4708
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Great question.

Over the weekend I participated in both a track day and an autocross with brand new RE71Rs. Previously, I have been on a set of maxxis rc1s for the past 35+ track events. With the RE71Rs installed, I found myself stiffening the suspension quite a bit more than usual to get the car to behave as I like.

When I got to the point to where the car felt right I noticed I would loose grip (rather violently) mid-corner on flat corners. The only thing I can think to compare the violent loss of grip to would be like trying to slide a piece of tape across a table. It grips for a little bit, then abruptly lets go. But then it grips again, until it lets go.

It was minimal at the track but at autocross it seemed to be more of an issue. I talked to my teams engineer and he suggested that I continue stiffening the rear, run a stiffer spring rate or swap the sway bars. So I figured I would try the sway bars first because they are still stock.
Based on your post, I would disagree with the engineer.

What behavior do you want, and what is it actually doing? What did it do before, and how did it change?

It sounds to me like you may just be adjusting to the extra grip, or the dampers are not quite liking the range of motion the RE71R is subjecting them to. It almost sounds like you have bind or rubbing.
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Old 09-17-2018, 05:28 PM   #4709
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Based on your post, I would disagree with the engineer.

What behavior do you want, and what is it actually doing? What did it do before, and how did it change?

It sounds to me like you may just be adjusting to the extra grip, or the dampers are not quite liking the range of motion the RE71R is subjecting them to. It almost sounds like you have bind or rubbing.
I'd like to know what "stiffening" up the suspension is to him. Just dampers? Too much compression can cause abrupt loss of grip.

Based on the mid-corner stuff it sounds like bumpstop issues to me. Using more of the suspension with a better tire, now mid-corner steady state you get deep into them then the car just breaks loose.
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Old 09-17-2018, 06:33 PM   #4710
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I'd like to know what "stiffening" up the suspension is to him. Just dampers? Too much compression can cause abrupt loss of grip.

Based on the mid-corner stuff it sounds like bumpstop issues to me. Using more of the suspension with a better tire, now mid-corner steady state you get deep into them then the car just breaks loose.
Try using a 1 inch longer spring, and lowering the spring perch collar.
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Old 09-17-2018, 07:13 PM   #4711
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Try using a 1 inch longer spring, and lowering the spring perch collar.
Unless you're changing the ride height I don't see how that changes anything...

If it's coil bind sure, but you'd inspect the spring (the paint will wear off when coil-bind happens) before coming to that conclusion. Certainly possible with some of the no-brand springs that come on even some high end coilovers.

Edit: Easy test, a small zip tie around a coil, the spring will press that thing right off if it's coilbinding. Tape may work as well.
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Old 09-17-2018, 07:27 PM   #4712
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Try using a 1 inch longer spring, and lowering the spring perch collar.
I already did that. I don't have any more room for spring. Maybe I didn't explain the issue properly. I will check for tell-tale signs this week when I check the car over and report back.

The car used to slide smoothly which made it easy to catch. Now it breaks loose violently and the rear kind of linearly hops about. "Hops" is a terrible word to use bc it obviously doesn't jump but that's the best word I can use to describe it.

Also "stiffening" means adding compression and this issue was much worse with less.

For the record, do most people that track their cars stick with the stock sway bars? I appreciate the concern about why I want sway bars. I feel like that is a good sign of someone that genuinely cares about the parts they sell or recommend. I am just curious at this point.
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Old 09-17-2018, 09:11 PM   #4713
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I already did that. I don't have any more room for spring. Maybe I didn't explain the issue properly. I will check for tell-tale signs this week when I check the car over and report back.

The car used to slide smoothly which made it easy to catch. Now it breaks loose violently and the rear kind of linearly hops about. "Hops" is a terrible word to use bc it obviously doesn't jump but that's the best word I can use to describe it.

Also "stiffening" means adding compression and this issue was much worse with less.

For the record, do most people that track their cars stick with the stock sway bars? I appreciate the concern about why I want sway bars. I feel like that is a good sign of someone that genuinely cares about the parts they sell or recommend. I am just curious at this point.
Sways are like supplemental non-independent springs. They can be used to hack a car together to do what you want, but should not be the primary method.

Do you have a datalog from your AIM/Racepak/Motec/Bosch?
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Old 09-17-2018, 09:52 PM   #4714
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Sways are like supplemental non-independent springs. They can be used to hack a car together to do what you want, but should not be the primary method.

Do you have a datalog from your AIM/Racepak/Motec/Bosch?
Nope. It's a brand new track and I haven't set my aim up for it yet. I'm headed back to that same track this weekend tho. I will setup the track and log my data. I am not looking to hack anything together and the teams engineer is rarely wrong. Sorry I couldn't provide more data on the issue. Thanks for the help.

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Old 09-18-2018, 02:28 AM   #4715
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Nope. It's a brand new track and I haven't set my aim up for it yet. I'm headed back to that same track this weekend tho. I will setup the track and log my data. I am not looking to hack anything together and the teams engineer is rarely wrong. Sorry I couldn't provide more data on the issue. Thanks for the help.

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I don't need your data to be set up to the track; I just need raw data. I can extrapolate the track from your data without having a start/finish set.

We need the datalog to attempt to discern what is going on. Data + video is even better.
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Old 09-18-2018, 11:47 AM   #4716
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Originally Posted by Takumi788 View Post

For the record, do most people that track their cars stick with the stock sway bars? I appreciate the concern about why I want sway bars. I feel like that is a good sign of someone that genuinely cares about the parts they sell or recommend. I am just curious at this point.
I tried TRD bars. With 550/550 springs the car was extremely loose. Went with stock rear and it had tons of push. Upped to 650 rear (this is with full aero) and the car still had a bit of push. Went to stock front. Problem solved.

These cars require very minimal mods to get it running fast (in front of the pack).

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Old 09-18-2018, 09:00 PM   #4717
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I tried TRD bars. With 550/550 springs the car was extremely loose. Went with stock rear and it had tons of push. Upped to 650 rear (this is with full aero) and the car still had a bit of push. Went to stock front. Problem solved.

These cars require very minimal mods to get it running fast (in front of the pack).

Lutfy
I'm running RCE Tarmac2's and still running stock sways.

No issues, car is hooked up, well balanced and faster than other 86's including one on Ohlins and upgraded sways.

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Old 09-19-2018, 01:04 PM   #4718
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Originally Posted by Takumi788 View Post
Great question.

Over the weekend I participated in both a track day and an autocross with brand new RE71Rs. Previously, I have been on a set of maxxis rc1s for the past 35+ track events. With the RE71Rs installed, I found myself stiffening the suspension quite a bit more than usual to get the car to behave as I like.

When I got to the point to where the car felt right I noticed I would loose grip (rather violently) mid-corner on flat corners. The only thing I can think to compare the violent loss of grip to would be like trying to slide a piece of tape across a table. It grips for a little bit, then abruptly lets go. But then it grips again, until it lets go.

It was minimal at the track but at autocross it seemed to be more of an issue. I talked to my teams engineer and he suggested that I continue stiffening the rear, run a stiffer spring rate or swap the sway bars. So I figured I would try the sway bars first because they are still stock.
Just how brand new were they? Zero heat cycles, zero street miles, literally put on with the stickers still on the tread?

What I'm saying is that the bridgestones are not their very best on the first heat cycle, or two. Plus you have a nearly non-existent data set to base your decisions off of. That place is gonna be weeping things to the surface for the rest of the year. Add in some mold release that may or not still be there, and I say change nothing except maybe tire pressures, and re-roll. Bet you get significantly different results.

If it's still pendulum-ing into snap slides, then start cranking up rear rebound.

You are also describing sort of the situation that makes me choose to do the pedal dance instead of just the 5-second method. Inside rear up>diff says wtf>brakes unloaded wheel>moves all that to the outside>outside wheel spins and slides >bind up relieved>inside rear back down and snatches hard. either a spine-wrenching wiggle, or a snap spin.
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