Sketch_hs

Can someone please explain this to me?





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BLUE TII

iTrader: (9)

Sidewall distortion.

Larger diameter wheel = less/stiffer sidewall.

While not exactly a performance car, watch this BMW M5 on a chassis rig. ~1:20 should open your eyes.

Sketch_hs

So less camber to best take advantage of a tire (contact patch) will less sidewall?

BLUE TII

iTrader: (9)

As your tire rolls under the car from lack of sidewall strength you lose even more static camber at the contact patch.

j9fd3s

iTrader: (3)

the amount of camber you need depends on a lot of things; grip, inflation pressures and sidewall height being three big ones.

also tires vary too, the Toyo RA1 wants a different camber setting than the Toyo R888.

basically if you wanted to find the optimum camber setting you'd need to do some testing

BLUE TII

iTrader: (9)

Right.

Street, long track event, short track event, and autocross are just simplifications. Same with wheel diameter.

Tire wear is your indication you are doing something really wrong.

Tire temps correlated to lap times are your indication that you are doing something right.

ZDan

I've run across these "Recommended Alignment Settings" a few times, and I have to say I think the camber #s are way out to lunch.

You will want a lot more camber than that at the track. Whether you're on 16s, 17s, or 18s.

The idea that -0.2 camber for an 18" wheel is equivalent to -0.5 for a 17" and -1.5 for a 16" wheel is ridiculous. Optimal camber will depend a lot more on the specific tire more so than wheel diameter, but in any case -0.2 is ridiculously low for track duty, or IMO even street.

I run -3 front, -2 rear, street and track (235, 245, or 255/40-17 fronts, 275/35-18 or 275/40-17 rears).
Street only, I'd probably run something like -2 front, -1.5 rear. Whether on 16, 17, or 18s.

IMO, throw those alignment recommendations in the round file...

Sketch_hs

This is more along the lines of what I was thinking. It just doesn't seem like enough.

I mostly use the car for very aggressive driving through tight and twisty mountain roads with a lot of surface variety. Some high speed stuff. I don't give a **** about tire wear.

18 wheels with pilot super sports but thinking about going stickier like the dunlop star spec IIs I have and love on my mr2.

j9fd3s

iTrader: (3)

thats the thing. when camber is right tires last longer.

think of it like this, the more grip you have the more the car rolls. the more the car rolls, the more static camber you need so that when its rolled over, the tire is planted.

the more time you spend cornering vs going down the highway dictates how much camber you really need.

ZDan

Tire wear is much more sensitive to toe than camber anyway, as long as you are running minimal toe, you can run a fair amount of camber without tremendously reducing tire life.

On my daily AP1 S2000, I run -1.25 front, -2 rear (both maxed), with 0 front toe and ~0.15 degrees total rear toe-in (about 1/16"). This is a lot less rear toe than spec of 0.32 - 0.64 degrees, but the handling is a LOT more linear/predictable and rear tire life is improved by a factor of 1.5x - 3x vs. the factory spec range. I get upwards of 20k miles on Hankook RS-3s.

"Standard" S2k alignments are generally 0 front toe with some rear toe-in, "standard" FD alignments appear to be a smidge of front toe-in and 0 rear toe.
On the FD I have run 0.1 degree total toe-in all around as well as 0 front toe with 0.1 degrees total rear toe-in without issue.

In my experience, too much toe-in at either end SUCKS BAD for both handling and tire life.

LargeOrangeFont

iTrader: (7)

This. All of this.

1NSIGHT

iTrader: (3)

Shouldnt the amount of castor you have be a factor in the amount of camber you run. If your on a track with a lot of 90 degree turns and you have alot of caster you will be rolling over the tire more.

Sketch_hs

Yeah I haven't seen castor talked about much. What are the ideal setting for the FD for very aggressive mountain road type driving? (mostly under 100mph, tons of elevation and surface variation)

ZDan

Caster + steering angle gives more negative camber on the outside front tire and less on the inside, which is good. This affects very low speed corners with a lot of steering angle much more so than higher-speed corners with little steering angle.

I don't think the difference between 5 and 7 degrees of caster would be so much that you would want to change your static camber setting much if at all.

IMO caster is very much a driver preference thing. Some people think that more is always better, but personally I like the lighter steering you get running minimal caster. I think that the added steering weight you get with more caster can actually mask feel.

I am run ~5 degrees on the FD.

BLUE TII

iTrader: (9)

Caster provides more camber as you turn the wheel and also moves the steering axis to contact patch intersection back (castor trail) as well as very slightly lengthening your wheelbase.

More camber as you turn the steering wheel (from castor) can help correct for body roll in low speed corners with lots of steering angle.

Also, the castor trail (from castor) means the steering wheel wants to correct more strongly back to center which can help during low speed driving maneuvers and helps provide more high speed stability.

------

I prefer lots of Caster as I feel it really helps me pull the steering wheel back to straight in those super fast low speed oversteer corrections or transitions we have in Autocross.

If you ever feel like you are actually flinging the wheel into countersteer with a flick of the wrist or letting go of it, letting it center and catching it once it is at the angle you want- you want caster.

Auto-x, gymkhanna, drifting and constant high speed driving (where you want the chassis relaxed) all can benefit from Castor.

For me personally the added pull to center does not numb the steering. You learn how the steering feels and when there is less pull to center in a turn than normal you know traction is decreasing... without moving the steering wheel.

This one more thing I like about the RX-8 chassis more then the FD chassis. About 2 degrees more castor potential stock.

I have not gone past what is available with stock alignment parts (~8 degrees castor on the RX-8) though, so I have never felt when it gets to "too much".

ZDan

Yup.

I wasn't lacking for high-speed stability at 160mph at Mosport with 5 degrees caster :p Rock solid.

I prefer minimal effort and resistance to movement of the wheel and don't want any "help" turning the wheel. Again, it's going to primarily be a driver preference thing...

Wait, what? "Letting go of it, letting it center and catching it once it is at the angle you want"?! That must be an autoX thing

I ran old tires day one at Palmer Motorsports Park last weekend, and went sideways around every corner lap after lap:


Totally tossable and controllable with a light touch at the helm (never felt any particular need or compulsion to let go of the wheel!). Sweeet...

For auto-X, I can see that there are benefits, I think the main one would be more loading up the inside front on very tight corners which would help turn-in.

For me, I feel like I don't want the effort added. I think I have a pretty good feel for front end grip and am maintaining right at the top of the grip curve through most corners without any sawing at the wheel finding/losing ultimate grip. Particularly important at Palmer because the turns go on *forever* (where in the HELL is that apex!).

Caster is going to be a lot more important to get right for lower-speed stuff with a lot of steering angle. In my experience at very high speeds with minimal caster, I haven't felt the car lacked stability, quite the contrary.

In the end, for most it is going to be down to driver preference. That said, a good friend of mine transformed the handling of a team of ITS BMWs when he took over suspension setup, including dialing OUT the ton of ton of caster they were running, and the cars went from "undriveable" to ARRC champs.

Anecdotal and 2nd-hand, but the point is that maybe you *can* go too far...

IMO, 5-7 degrees for these cars should work fine. For road course work, if running more caster causes you to lose camber, I don't think it would be worth it even if the driver prefers more caster. For AutoX, probably the opposite is true.

My thoughts, fwiw...

eage8

iTrader: (9)

Depending on how your camber is dialed in (at the hub vs, SAI), you'll actually loose camber as you turn the wheel. Caster makes up for that camber loss on one side of the car and further decreases it even more on the other side (which is good because it flattens the inside tire instead of it having lots of useless negative camber)

general rule of thumb is you want twice as much caster as camber. so if you have -2.5* of camber, you want 5* of caster.

http://www.motoiq.com/MagazineArticl...and-scrub.aspx

only when you've completely messed up a corner lol

BLUE TII

iTrader: (9)

^^ entering a corner leading with the *** end- whether on purpose or mistake.

The auto RX-8 is so underpowered and poorly geared it is often best to enter the corner keeping it floored by initiating drift to keep the rear wheels spinning with the engine high in the rpms while letting your slip angle scrub the speed. All so you can power out of the corner best.

People can't believe the car dynos 108rwhp. How do you drift around on 295 DOT-Rs? When you are at the limit of traction from cornering it doesn't take much to bump you over the edge to oversteer.

Nephew- I can't believe how fast you move your hands.

I had a terrible run on slicks in the rain. Constant fast corrections to keep the car going where I wanted it with the car transitioning from understeer to oversteer to 4 wheel drifting- just terrible. Looked at my time and I was 2nd just behind our usual fastest nationals driver in his Miata on skinny street tires.

Yes, fast hands is rally, gymkhanna, Auto-x thing. Everything happens in SLOW MOTION out on the track where smooth is king.

LargeOrangeFont

iTrader: (7)

With a manual rack I try to get as much caster as I can to help high speed steering. I have 5 degrees in the FC, but I'd like another 1-1.5 degrees. I'll have to make new or change the camber plates for that.

I run 1/16 toe out front and now run 1/4 toe in rear.

At -2.9 degrees camber front and -1.5 degrees camber rear I am actually wearing all 4 tires more on the inside.. which is baffling me a bit.

The car is so much better with the added toe in for the rear. I used to run 1/16" toe in, and the car was much more inconsistent, and harder to drive. I would not recommend this much toe in on lower powered cars. Initially the added toe killed corner entry, but with some other adjustment scorner entry is fine, and I can get back to the gas much sooner on exit.

j9fd3s

iTrader: (3)

i wouldn't worry about it, if it wants less camber, give it less camber

in theory it just means the car isn't leaning over much. either its more spring/bar or less traction.

BLUE TII

iTrader: (9)

Braking eats tires.

If you have static camber braking eats the inside of tires.

LargeOrangeFont

iTrader: (7)

This is a new thing with the maxxis tires. Nt01s wore perfectly. Plus the front and rear are doing it in similar amounts.

Car handles better than ever though.

j9fd3s

iTrader: (3)

different tires are different, if it wants less camber, give it less camber...

LargeOrangeFont

iTrader: (7)

Thank you Confucius for your wisdom.

BLUE TII

iTrader: (9)

Yeah, to me the Maxxis RC-1 VS NT01 in same 255/40-17 size the Maxxis felt like it had a much stiffer sidewall so probably would require less camber.

RC-1 surprised me with its stiff responsive sidewall, but still put the power down really well. How they do that? I wondered if it had to do with the rest of the carcass construction (the belting I guess).

-edit- oooh, yeah. Could be because the RC-1 has the 20 degrees F lower operating temperature and now I am getting deja vu, so we must of covered this territory before...