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Why not more camber?

Old 09-20-2018, 01:33 PM
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Default Why not more camber?

At the moment I'm running -3.5° front and -2.5° rear. Finding I still get a lot of outer shoulder wear on my RE-71Rs, especially up front. I've also done a few measurements with a pyrometer and find that my temperatures are relatively flat, but they are slightly hotter on the outside—usually about a 5 degree difference outside to inside, with middle being somewhere between the two, depending on pressure. (I normally run 30F, 28R, hot.) Those heat measurements are after a few hot laps. Need to try measuring after an autocross run as well.

So, all these signs appear to point to needing more negative camber. And from what I've read I should be able to get as much as -4.5° front with my SPC joints. Not sure what the stock rear adjusters can do. I'm aware that going too far on the rear might affect the grip while accelerating, so it might make sense to not go farther there—but is there any reason not to go higher in the front, given that temperature and tire wear are both suggesting it would help? And if no, then how come I haven't read of anyone else going past -3.5? (In fact, I'm not sure I've read of anyone even going that high!) Does autocross tend to like more or less camber than TT?

Last edited by Nate Tempest; 09-20-2018 at 03:21 PM.
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Old 09-20-2018, 02:37 PM
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Think of tire temps as a 'short term fuel trim' to adjust camber. However, tire wear (long term fuel trim) is a much better indicator, especially if you only really drive on those tires on track and don't mind adjusting your camber over a longer period of examination. So yes, if you're getting outside shoulder wear, you need more camber. Go up to 4.0. Then maybe 4.5

But always use lap times as a final reality check. If your braking performance gets diminished to the point of negatively affecting your lap times you'll have to dial some out. Though, in my experience, adding camber to the point of getting even tire wear always out performs any reduction in max theoretical braking performance.

Theory is good, empirical data is better.
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Old 09-20-2018, 03:23 PM
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Originally Posted by shind3 View Post
Think of tire temps as a 'short term fuel trim' to adjust camber. However, tire wear (long term fuel trim) is a much better indicator, especially if you only really drive on those tires on track and don't mind adjusting your camber over a longer period of examination. So yes, if you're getting outside shoulder wear, you need more camber. Go up to 4.0. Then maybe 4.5

But always use lap times as a final reality check. If your braking performance gets diminished to the point of negatively affecting your lap times you'll have to dial some out. Though, in my experience, adding camber to the point of getting even tire wear always out performs any reduction in max theoretical braking performance.

Theory is good, empirical data is better.
Right, thanks. And thanks for reminding me that obviously reduced braking performance is the theoretical downside of front camber, as is reduced acceleration for rear camber.

I'll try adding some more. I am curious why everyone with dedicated track or STR cars aren't going higher though; I don't think my car is unique in some way, so why does everyone seem to run ~-2.8 to -3.3 or so up front?
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Old 09-21-2018, 05:32 AM
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Static camber is only one input to the tire wear story. Another is spring rate. A softer spring allows more camber recovery from the front suspension and the S2000 geometry provides a lot. I run 3.2 deg and when I went from stock MY00 springs to 10k, I found that the outer edge began to wear a little more - just as you're seeing - which is not what I had expected. I attribute this to less compression under cornering load and hence less camber recovery.

That said, that doesn't really answer your question why others don't run more camber. But as a remote point of reference, look how much camber Formula 1 cars run, and they have purpose built suspensions. So I don't think there's anything wrong with running more static camber as long as the side effects of reduced longitudinal traction are acceptable.

Lastly, don't forget about caster which adds some additional camber in the corners. If your caster was not maximized, that could also contribute, although it seems unlikely that it would be off enough to make that much difference.
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Old 09-21-2018, 11:58 AM
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Originally Posted by DanielB View Post
Static camber is only one input to the tire wear story. Another is spring rate. A softer spring allows more camber recovery from the front suspension and the S2000 geometry provides a lot. I run 3.2 deg and when I went from stock MY00 springs to 10k, I found that the outer edge began to wear a little more - just as you're seeing - which is not what I had expected. I attribute this to less compression under cornering load and hence less camber recovery.

That said, that doesn't really answer your question why others don't run more camber. But as a remote point of reference, look how much camber Formula 1 cars run, and they have purpose built suspensions. So I don't think there's anything wrong with running more static camber as long as the side effects of reduced longitudinal traction are acceptable.

Lastly, don't forget about caster which adds some additional camber in the corners. If your caster was not maximized, that could also contribute, although it seems unlikely that it would be off enough to make that much difference.
Mm, interesting. My front springs are 750lb/in, so about 13.4k. I guess that is stiffer than most, so that would play a bit of a role. I guess I'll give it a try! Will go up to 4° in the front and maybe 3° rear (or whatever the adjusters will give me) and see how that works. Caster is 6.1 currently, which I think is pretty close to maxed. Might as well see if I can get any more though.
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Old 09-21-2018, 01:36 PM
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I haven't driven the RE-71R specifically, but for any other streetable tire I've ever come across, those pressures are really low. Not surprised the tire is is falling over on the shoulder if you are dipping below 30 psi hot. Try 38-39 psi hot and see if that changes things.
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Old 09-21-2018, 01:55 PM
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Originally Posted by thomsbrain View Post
I haven't driven the RE-71R specifically, but for any other streetable tire I've ever come across, those pressures are really low. Not surprised the tire is is falling over on the shoulder if you are dipping below 30 psi hot. Try 38-39 psi hot and see if that changes things.
I've tried higher pressures, and recorded temperatures while doing so, and at higher levels than this I find that the middle temperature is higher than both inside and outside shoulders (suggesting over-inflation). 30F/28R is when I get a smooth gradient with middle temp being between inside and outside, and also when I have the highest subjective grip. For what it's worth, it's also the pressures that were recommended to me by Brian Karwan (of Karcepts, and a top STR driver). Started there, experimented with higher (and slightly lower), and ended up back here.

As the tires heat I set them back to 30/28 before runs, so I shouldn't be dipping _below_ that level, since obviously they'll be a bit higher mid-run.

Edit: Of course, it's possible that I could compensate somewhat for insufficient camber by setting higher pressures, but I think I'd sacrifice grip.

Last edited by Nate Tempest; 09-21-2018 at 04:14 PM.
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Old 09-21-2018, 02:38 PM
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Originally Posted by thomsbrain View Post
I haven't driven the RE-71R specifically, but for any other streetable tire I've ever come across, those pressures are really low. Not surprised the tire is is falling over on the shoulder if you are dipping below 30 psi hot. Try 38-39 psi hot and see if that changes things.
30f 28r is a very common pressure for RE71Rs on STR prepped cars. I actually run 28f and 28r and get no shoulder wear with about -3.5 or so in the front. On my ES Miata, I was also running similarly low pressures on the Bridgestones. The sidewall on these tires is incredibly stiff. I tend to forget to add pressure after autocross events so I'm frequently ~22psi on the street and you'd never know.
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Old 09-21-2018, 02:41 PM
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Perhaps post toe settings, none are mentioned above.
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Old 09-21-2018, 04:14 PM
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Originally Posted by noodels View Post
Perhaps post toe settings, none are mentioned above.
My full setup is here: https://www.s2ki.com/forums/s2000-ra.../#post24401860

Total toe is 0 front, 3/16" in rear. Toe settings shouldn't affect outer shoulder heating or wear though. Excess toe causes the inner shoulder to scrub, resulting in more heat and wear there.
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