Schrader

I'm currently running 205/50R15 Toyo R888's and I am having a bit of trouble with tire roll. Tire pressures were hovering at around 37-38 and I bumped them up a bit to no affect. I did a camber adjustment at the track which seemed to help, but looking for some advice to what settings you guys are running with for autox and track?

I just eyeballed it at the track so I will get more precise this weekend when I do the alignment.

johnjw

Tire pressure seems high. I'd start with mid 20's and work around that area. As for camber 1.75 seems to work for us @ around 5inch ride height depending on grip level and weight.

Xian

What sort of spring rates are you running and what width wheels?

Schrader

550/280 with about 2-3mm preload. 6.5inch wide rims

KoRn_vIRuZ

That's too wide of a tire for a 6.5J wheel. Compared with say, a 195 section tire, you have less steering feel but are probably faster still...

Xian

That's ^^^ a big contributor to the roll over problem. The rates are awfully soft and that's a bunch of tire crammed on a narrow wheel. To keep it from rolling over you'll need to either get kinda wild with either a bunch of camber (3.5-4*) or pressure (42+).

dirty19

iTrader: (1)

I have to give a plus one here on the rates... if 280 in your rear is correct you are way too soft.
Other poster with the mid 20's inflations was more closer to what I have found to work with a R888 24-26,27 ish is the place I started, nothing higher.
The R888 I found to have a firmer sidewall than say RA-1
My off track pressures after a run never exceeded 38 which I found to give me the best grip.
These are things you will have to tinker with to find your best set up.
Start with the spring rates especially in the rear (280) is way way too low

johnjw

yeah spring rates should be in the 400# to 600# range. no higher unless going with a R6 grip level of tire.

we use 300#/250# but use a 200tw tire. same car. in the wet is goes down to 250#200#

Xian

Those rates ^^^ are insanely low and not suitable for an autoX car IMO. Mid-tier r-comps can take a pretty hard "hit" to the tire as can the current crop of 200TW tires. Body roll on my ITR with street tires is "acceptable" right now with 650/550 and I'll likely bump up both the front and rear rates. I ran 850/650 on my EF (also with street tires) with very good results (and manners).

PS
Don't confuse "workable" with "ideal"... Or you'll end up running rates that are about equal to some of the OTS stuff Honda offers. Also, don't neglect to factor in chassis weight, bars, and the shocks into the equation.

KoRn_vIRuZ

Xian, can you please clarify what you mean by "workable" vs "ideal" spring rates?

If you do the maths, the ride frequencies for some of the setups people here use are insanely high. Something like 400/300 lb/in is much closer to the ideal/theoretical values. I always wondered why you use such high rates, seems like you'd be loosing out in terms of grip.

For Auto-X (i.e. low speed, very tight corners) I can understand how you could prefer response and rotation over grip but for road racing I really don't get it. Maybe I'm missing something.

SHG_Mike

ultimate technical/theoretical tire grip figures /= usable real world lap times. You have things like camber gain vs body roll loss which could very easily over heat the outside edge of the tire, and how quickly or slowly you can transfer weigh etc to get you through chicanes and quick transitions. A soft car may in theory have more mechanical grip but could also be slower than a stiffer car.

OP i would get tire temps and that will tell you more information on what needs to happen next.

Xian

Yep ^^^. You can't blindly stick with a dogmatic like faith to the "ideal" ride frequencies. We're talking about FWD'ers with econocar roots.

At 400#, you'll need a massively higher static ride right to keep off the bumpstops. If you're on the bumpstops then you've just cranked your ride frequency thru the roof. At your higher ride height, you've got a higher CG and more roll. So the outside front de-cambers when it's loaded up. So you've got to add static camber. But now it doesn't brake so well on entry and can't put down power as well on corner exit.

If you double your front rates, almost all these problems go away. If you've got high end shocks, you can still have a car that's very compliant over bumps and uneven pavement. As far as rear rates go, I prefer to go somewhat softer than the front but make up for it with rear bar. Given the lighter rear corner weights (vs the front) it makes the car less skittish and therefore easier to drive while still maintaining a decent spread in roll rates front to rear. (This is assuming a street/autox and sometime track car)

For a 100% dedicated road race car, I've always run a rear spring biased setup. I suspect you could get the above setup to work also but I haven't done it yet.

KoRn_vIRuZ

Thanks, that's some good food for thought.

SHG_Mike

for going more in depth and explaining it further.

rice_classic

My ITA CRX had 600/750 with no front bar and skinny OEM rear. (roadrace setup)

I just put on the 450# on the front so I'm at 450/750 with OEM barz front/rear and I'll see how it works next weekend but last weekend was a wake up call that the front wasn't working well enough and the rear worked great. So I decided to make the front work better instead of reducing the function of the rear.

Also, I run 225/45/15 RR on 15x7" wheels and rolling over wasn't my problem. Heat was. It was a cold day and I couldn't get enough heat in the tires to function. I was faster on the 205's because I could generate another 20F in tire temp. IMHO, a 205 R888 on a 6.5" rim is just fine. We see 225 Hoosiers on 7" rims. Pretty common in ITA cars.

I'm hoping this coming race weekend delivers us a sunny day with track temp >80F so my bigger tires get a chance to do their job.

rice_classic

I did this one yesterday:

shane(showtime)

iTrader: (1)

THanks always wanted to do this.

Xian

Wow... Somehow I flubbed up the OP's tire size. It plainly says "205" but in my head he had 225's. FWIW, I ran 225/205 stagger on 15x7.5's and I thought the 225's were a little too pinched but workable (looked like it would have been more at home on a 9" wheel).

Tossing out the common ITA fitment of the 225 R6 on a 7" wheel is a bit of a red herring as it's construction (semi-cantilever and super stuff sidewalls) is quite a bit different than the R888. Also, the camber curve on the EF is wildly different and better than the EG. I'd loooove to have the EF's camber gain on my ITR.

I'm interested in hearing how your new setup works out. The softer rate plus a small front bar isn't what I'd do for that car but I also wouldn't have the stock rear bar on it either so...

Schrader

Great post guys, thanks! The spring rates are what came originally in the K-sport Pro Coil overs, so I might look into putting something a bit stiffer for next season. The body roll isn't that much of a concern at the moment and the corner turn is awesome, even more so now that I increased the camber. Though I had a bit of toe in after doing so which kind of burned up a right front tire, but that's racing Anything to beat corvettes and BMW's! I'll be tying out the new setup this weekend at Castrol Speedway and see how it is.

shane(showtime)

iTrader: (1)

I would suggest getting new coilovers. Don't bother with new springs on those K-sports. Currently using over the shelf Bilsteins that I revalved. Liking them a lot compared to my old Ground Control Advance designs. 800 Front 700 Rear. The profiles I got from Bilstein are pretty good but could be better. Im sure I will invest the $50.00 next year and work on them again.

Good luck at Castrol that's way to far of a drive from Kelowna B.C for me