IamFodi

iTrader: (1)

Been reading up on the effects of having too much tire grip for a given suspension setup (e.g. too soft, not enough camber, etc.). Anyone ever run into that on their RX-8? If so, what were your tires and suspension mods, and how did the car behave near the limit?

NotAPreppie

I think it's impossible to have too much grip in a sports car. Just ask the crazy guys running 285 Hoosiers on their RX-8's in stock/street class competition.

You can have a suspension that is not well-matched for a given tire but I don't think it works the same in reverse.

Loki

iTrader: (1)

Can you share what you've read?

dannobre

iTrader: (3)

I had too much tire for my oil pickup Does that count?

IamFodi

iTrader: (1)

It's pieced together from a lot of different sources, a lot of it in private message boards among my friends. But here's a summary of what I've gathered -- and please, someone correct me if I'm wrong.

Most of the potential problems stem from too much body roll; the extra grip means there's a lot more body motion before the tires start to slip.

If you end up rolling onto the outer edges of the tire too much, you won't use (or heat) the contact patch evenly. Running lots of negative camber can compensate, but if you have to get it by adjusting static camber then you'll end up sacrificing traction under acceleration/braking. However, if your suspension produces a lot of negative camber gain on compression, you might not need to dial in as much on the static alignment.

Excess body motion can also be a problem anywhere on the track where the car's attitude changes -- corner entry, corner exit, left-right transitions, etc. At best (i.e. if your damping is VERY well sorted), the car will take longer to settle; at worst, it'll be less stable than it should be in those zones.

If there's so much roll that the inside wheels come off the ground, you have to be on your game that much more. Ditto on mid-corner bumps; the more your outside suspension is compressed from lateral Gs, and the faster you're going, the more likely it is that you'll end up on the bump stops. Either scenario has the potential to get VERY hairy.

So, the grippier your tires are, the more you need high suspension frequencies, high roll resistance, lots of negative camber, or some combination thereof.

Again, that's my amateur understanding of how things work in theory. I wanted to hear from people about how the RX-8 is in particular, and where the stock car's limits (especially the R3's) are with respect to tire selection.

Loki

iTrader: (1)

While your understanding of how things work is generally correct, I'm not sure "too much tire" is a problem that needs solving. Whenever you load up one tire and unload another, the overall grip is lower than if you had spread the load around.

So if you take the same turn, in the same car, the unloaded wheel is doing nothing for you in either case, but on slicks, the loaded tire has a lot more grip, so you can corner faster.

It sounds like the concern is you could lose control because you could lean over even more and lose even more grip... sure.. but that implies you're taking the corner faster than before, so... great, do that. Also "lose control" isn't really a thing. You either oversteer or understeer... if you find yourself mowing the lawn, that's not the car, that's you not recognizing what's happening and adjusting.

Maybe it's more like too much tire for the driver? High performance tires communicate a lot less than lower performance ones.

As far as how a stock RX-8 behaves, it's very predictable near the limit. You can lose it and recover reasonably easily. Or .. you know.. not lose it in the first place. I would say the R3 setup is a touch more tailhappy, but within what's manageable with tire pressures. That's a good thing if you feel it enough to use it, bad thing if it surprises you. You certainly won't have wheels coming off the ground, this isn't a Golf.

Some cars, like the early S2000's have quirks that you want to avoid, but not this car.

IamFodi

iTrader: (1)

Well yeah. What I was saying is that with stickier tires, you're more likely to corner hard enough to lift wheels in the first place.


On the rest, thanks for the feedback. Completely agree that excess grip isn't a problem that needs solving. Just wondering if there might be some undesirable side-effects that would need to be compensated for.

NotAPreppie

The more you lean, the less grip you have but body lean is gradual and progressive (unless you are doing it wrong). The grip isn't going to suddenly disappear because you took tires with more grip past a certain limit. The harder you corner, the more you'll roll and the less grip you'll have until the lateral forces match or overcome the frictional forces of the tire.

All else being equal, you will lean less with less grippy tires, sure, but that's a consequence of having less overall grip. Looking at it the other way, replacing a 600TW all season tire with a 200TW summer tire will give you far more grip while still resulting in more body roll.

The likely undesirable effect is overconfidence. That leads to bad driving which will lead to unexpected handling behavior (snap oversteer, terminal understeer, lawn mowing, dirt dropping, overcorrection, etc).

IamFodi

iTrader: (1)

Exactly. Did I suggest otherwise?

Kennetht638

iTrader: (2)

Most of your assertions are correct until you get to the part about lifting tires off the ground. Having softer suspension will not make your car more likely to lift tires off the ground. The suspension stiffness and body roll have nothing to do with the amount of load being transferred from one side of the car to the other. The only way that a soft suspension will make your car rollover-prone is if it's so soft that the body actually has enough momentum in roll to pitch it over.

Also, one of the worst things about body roll on a production car is that it has large effects on toe and camber. Production cars are designed to understeer in limit conditions, so they'll tend to toe out in the front and toe in in the rear in most cases. You can limit how much that happens by stiffening the suspension to use less travel. Hence the old Colin Chapman quote "any suspension will work...if you don't let it."

This is not true. Body roll has no effect on weight transfer and pretty much no effect on grip except for how it affects camber. For a normal race car with some negative camber, you'll actually get more grip as the body leans up to a certain point, but that can't be generalized for every car and every tire.

MagnusRacing

iTrader: (2)

It's possible at some point a very wide tire could slow you down on a very high speed track and that it would be advantageous to have a narrower tire. Otherwise, use as wide of a tire as your car can handle! Of course there are things like scrub radius etc that can throw off handling if your offset is changed a lot but this all depends on many factors. As was said above the Autocross guys put in as fat a tire as they can for a reason.


Once stuffed 315mm width tires onto all four corners of a Jaguar XJS Lemon's Race Car. It was awesome.

fossumja

iTrader: (4)

This is one of those things that's all relative. You will gain proportionately more grip by going to a wider / stickier tire on a car with a stiffer suspension than doing the same on a car with a softer suspension, but either way you will increase the grip. In the old BS/CS most cars didn't develop any particular handling vices with sticky R-comps (quite the opposite really), but they used them less efficiently than say an STX car on 200TW street tires, or a DSP car on the same R comps.

Ethanman

How wide of tire can u run on stock?

Steve Dallas

245/40/18

2rotorphil

I run racing beat springs, koni shocks, urethane bushings everywhere, stock sway bars & 245/40-18 RS-3. Alignment is front: 0 toe, -2 camber & rear: 1/16 toe in, -2.55 camber(can't run less). My car rolls as **** and my front inside wheel lifts of the ground under hard cornering thru the last hairpin on the st-eustache road course near montreal. any body have suggestions concerning my setup?

Loki

iTrader: (1)

What does "rolls as ****" mean? :D

That hairpin is on a pretty serious camber/incline, so while you might lift the inside wheel under throttle there, that's not necessarily bad or something you want to fix. Most corners are not on such an camber, so focus on how it behaves elsewhere. Is it neutral? oversteer? understeer?

Are the koni's you have adjustable? Can you reduce the rebound stiffness?

You could try to upgrade the front sway bar, but be aware that this will introduce understeer, so depending on how it's balanced now and how you want to balance it, that may be something you do or don't want.

What kind of lap-time are you getting at Saint-Eu?

2rotorphil

check this if you can see:RX-8 Picture by 2rotorphil | 5695889 | RX8Club.com

(not sure, can you zoom?) the rear outside is compressed, front inside extended

nobody else seems to do that & the ones following me say it's crazy!!!
usually it understeers...


yes, koni sport set to the softest. if i increase rebound, lap times go up. i go thru the dog leg flat out (turn 12)... so i'm balanced ok for that turn but, trying to stabilize for turn 13 gets squirmy & understeers all the way thru 14.

i know, that's why i'm asking. would front & rear bars like RB or maybe progress (adjustable) be an option or should i go for stiffer springs instead?

usually in the 1:03s but i once (with less traffic) managed a 1:01.48

Loki

iTrader: (1)

Sway bars will only help with the left-right sway, not front to rear. So I would say that with sway bars you'll be able to give it even more throttle through the sections where you're currently fully unloading the inside.

Stiffer springs will help with left-right and front-back transfer, so your rear squat/front lift under throttle will be less pronounced. I think you win more with springs, or full coilovers at that point to get the adjustability.

You're working the suspension to its max, which either means you're way too rough on the car, or the car is holding you back from being faster, which is a good position to be in

What club do you run with?

2rotorphil

ASE lapping club, monday evenings i'll be there tomorow.

Loki

iTrader: (1)

14 is sort of the key to that whole complex. Maybe this will help: I go into 13 very early and end up on the outside turtles between 13-14, pointed straight at the outside turtles of 14. You can accelerate as much as there is room, turn in for 14 late almost on the grass, trail brake to help get the turn completed quickly and have a cleaner, straighter shot through 15 and a longer acceleration path, which could mean more wheels on the ground. I don't know if the red/white strips on the wall are still there, but as you apex 14, aim to have the car pointed at the red section far left of the observation tower, rather than the white section immediately left of the observation tower.

I used to turn into 14 early and do 14-15 as some kind of double-apex, but it's messy and you end up spending a lot of time with your steering hard over -- which could be why your inside wheel is lifting.

Give that a shot?

2rotorphil

i'll do

pcs

iTrader: (2)

I've run into too much tire for my skill level, if that makes sense... Got a steal on some new R-comps to take to the track... built some bad habits that the massive grip was able to let me get away with...

then split the time between the r-comps and the street / max perf tires and learned to be smoother and faster... and by then the r-comps were toast. I'm now almost as fast (or slow depending on perspective) on the street tires than I was originally on the r-comps, and without the desire or budget to buy r-comps again unless they're dirt cheap, haha.