godesshunter

So today was my 3rd autox event of the season and lets say I'm not to pleased with how things are going so far.

A little back story: Ive been autoxing only 6 times ever in my life. 3 times at the end of last year and 3 times so far this year. So needless to say I'm still getting my feet wet.
The first mod I did was RB non-res test pipe can cat back before I ever did any racing. I had those on for last year while in the rookie class. Apparently, because of the test pipe I was put into Z-Novice. The first 2 races in ZN I placed 1st without too much trouble at all. The 3rd race I placed 2nd.

So naturally my head got big and I wanted to go faster and class up. So this year I did some more mods and entered in STX. So far its been a slap in the face. I will admit that with only 6 races under my belt (3 before I started the STX build) I am still new to all this and probably dont belong in this class.

But in my defense, let me say that last year the car felt amazing. The power was there. The handling was there. I just wanted more of it. I even remember comparing my times with CS where I would be and they were right on. I thought for sure I was ready to class up.

So here's my dilemma, I'm trying to decide if I ruined the handling of the car with my mods, or what. --The car is all over the track. I feel its damn near impossible for me to handle it. The best way for me to describe it is that It feels like I'm racing on gravel! It slides all over the place. I wouldn't call it understeer. It just starts sliding sideways while cornering. And then bucket loads of over steer while exiting turns. Its very tail happy. Like I'm driving an old muscle car. It's like I'm racing with 4 donut size spare tires on. My times and performance are embarrassing at best.

However on the street, during normal driving it feels amazing and crisp. Much more responsive to steering input than it was when stock.

Here are my mods:
2010 R3
-OEM cat with RB catback
-Powertrix coilovers. 9k front springs 6k rears. No pre-load on the springs. Ride height adjusted with tape measure to be equal front and rear, left and right (forget the measurement) Dampening set to 10 out of 15 equally front and rear.
-17x9+42 wheels
- Falken Atenis RT 615 255-40-17 tires

Alignment:

-Front and rear toe set to factory spec (I forget the #)
-Front caster set to factory spec.
-Front camber -1.5 left and right
-Rear camber -1.9 left and right

Thanks for any advise on how to fix my "slippery" situation.

wrightcomputing

iTrader: (5)

I would change your alignment so you get the max possible on the front and have the rear about 1 less. With coilovers fronts should be 2-3 then the rears 1-2 depending on the fronts. Best to go with 0 toe all round, which helps with tire life and neutral handling.

When I installed my coilovers I have a lot of oversteer and ended up changing the shocks to the middle setting in the rear and 2 off full stiff in the front. Try 7 in the rear and 13 in the front.

Also the most important thing for Autocross is the tires get Hankook RS3, Dunlop StarSpec or similar (below 200 tread wear is a good indication).

You next mod should be a front sway bar which will make the front push a little reducing your oversteer and making the car easier to handle.

The most important thing is learning to drive you car fast which needs seat time. Get as many fast drivers as you can to drive you car and teach you to drive it, as well as giving you advise on setting up your car. STX is actually one of the lowest classes which is why the PAX is 0.822, a lower class then CS 0.833.

godesshunter

Ok...Thanks for the advise. I didn't realize I should be running that much negative camber in front. Maybe I'll try that. As far as rear, unfortunately at my ride height, I cannot get any more positive than -1.9. I was able to get -1.5 in the left rear but the right maxed out at -1.9 so I matched up the right to meet the left.
Im not too concerned with tire wear as long as its not extreme because I have a daily driver that is not the 8.

After today's runs I was beginning to suspect the tires my be giving me some crazy results despite having a 200 wear rating. I wrote up a thread a while back when I first got them and a few people spoke negative about them. The Star Spec gets all the rave. I think for next week I'm going to put the stock Potenza REO50As back on and see how it feels. I had pretty good luck with them last year.

wrightcomputing

iTrader: (5)

Also be aware there are different types of oversteer and different ways to fix them.

Lift off oversteer - If the car starts to rotate as soon as you let off the gas due to the rear end becoming light. A little more rear -ve camber will help but this is mainly a driver mod you need to accelerate to stop this type of oversteer.

Mid corner oversteer - As you are cornering on a long corner or short the rear starts to slide before the front. Add more rear -ve camber or increase front suspension stiffness.

Corner exit oversteer - As soon as you get on the gas the rear breaks loose. Reduce the rear camber so that you have a bigger contact patch and more grip to accelerate.

Tire pressure for 17x9 36F-34R, 18x8 40F-38R is a good starting point and drop 1 psi to reduce understeer or oversteer at the respective wheel.

To be honest there is a lot more to the suspension then what I mentioned and more then I know but this should get you started. It sounds like you do the work yourself (like me) if so play around with the settings see how the car feels and test and adjust.

dmitrik4

iTrader: (5)

If you're having balance problems, changing tires isn't going to solve that, especially if you're going from one "max performance" tire to another. No one is going to be winning any national championships on the Falkens, but they are perfectly fine for what you're doing.

don't think anyone can give you setup advice without knowing more about what you're feeling...as mentioed above, what sort of oversteer/understeer are you getting?

Are you sure you're not overdriving the car (e.g., too fast into corners, too quick with steering inputs, too much gas on exit)? A lot of "handling problems" are driver-induced...try getting an experienced competitor to take a few runs to give you some feedback on what they're feeling.

godesshunter

Ok. Some good input guys, Thanks. Apparently according to wright, Im running way too much air pressure. I currently have them set at 40. I was under the impression from all the car prep things I've seen that you want to be running higher pressure than street. I guess I took it too far. And yes I do my own alignment. Doesn't mean its not a hassle though. The approach angle on my rack is too steep for most lowered cars. I have to build up the ramps with blocks to get on.

I'm pretty sure I'm not over driving the car. I certainly know what that feels like. On fun runs Ive given it some over the top maneuvers and gotten the results I expected.

Corner exit oversteer seems to be the biggest concern. It seems that I cannot give it even the slightest bit of throttle without it getting tail happy. Even at that last bit of the corner when I am transitioning from a corner to a straight away If I give any more than a quarter throttle it will begin to slide. I can only accelerate when the car is pointed straight a head.

I considered asking another driver to take my car out on a fun run to get a feel for what its doing. But after my 4th run I was so frustrated I just packed up and left. Luckily I had already completed my work assignment.

Thanks for the input.

JCrane82

iTrader: (3)

If you provide full alignment specs (toe included) it would help. Currently you are running half a degree more negative rear camber, yet still getting oversteer. A rear toe out setting will possibly get you this result. Specifying "in spec" isn't good enough as Mazda provides a very wide factory range.

The more negative camber you run, the less tire pressure needed. Have you been taking any tire data (pressure deltas before/after runs, tread surface temperatures)?

Also, are you on stock anti-sway bars?

godesshunter

Yes "in spec" is a broad term. Toe was in the center of what was acceptable from toe in and toe out. I will have a better idea in a day or so. I'll put it back on the rack and have some real #s to show for.

No tire data to speak of. I just kinda took the "set it and forget it" method at 40 psi. I do have a hand held laser thermometer I can take with me to get surface temps with. What exactly should I be looking for? The pavement is still pretty cold this time of year and the runs are only about 40 secs. Is that enough work to even be looking at tire temperature?

I have the oem sway bars that came form the factory. I started looking at sway bar options but really wanted to get a solid feel for the car as it sits first. I was afraid putting stiffer sways would make the car fell even more rigid and turn my "driving on gravel" feel into "driving on ice"

Either tomorrow or Thursday Ill get some readings on the alignment specs and report back. That way you will know where I'm at and can throw some numbers at me to set the car up on Saturday for race on Sunday.

Thanks.

Ps. What is "pressure delta"? Is that the crayon mark on the sidewall?

JCrane82

iTrader: (3)

The IR thermometers will at least get you some skin temps, but it won't accurately measure carcass temps. You want to take the temps as soon as your are done with your runs, and after every run. Take three temps accross the surface of the tire. This will help provide some data so you can better understand what setup changes you should make. Also record pressures.


Delta is just a fancy way of saying difference. Mathmatics/Engineer speak.

olddragger

iTrader: (3)

have you ever corner weighted the car?

BRODA

iTrader: (7)

I used to set my RT615's at 28 psi cold. YMMV.

blazenblue63

I've only been autocrossing a little while but alignment and tire psi is everything I've learned. My tire psi is lower in the front than rear and I have toe out in the front. -1.7 and -1.5 camber F/R and 6.8 caster.

OP another thing I've learned is mods mask your mistakes/lack of experience. Adding sway bars to correct over/understeer could just be cured by rolling on the throttle instead of mashing it. Maybe the back steps out because your steering input is too violent. Do you know how grip circles work? First adjustment you should always make after a run is psi. If the back is too loose, drop a few lbs. Keep doing that till it acts how you want it to. But remember, what setup works for you, might be terrible for someone else.

blazenblue63

Also I just read that your suspension is set the same front/rear. I have mine set full stiff front and 25% stiff rear. Reason for that being, if the surface is bumpy where you race, combined with a 40/45 psi tire (pressure increases as tire heats up) the tires will hit a bump and bounce of off them instead of absorb them. So if it was me, I'd soften the rears to about 4 or 5 and do 3 or 4 runs till the tires are good and hot. Then adjust psi accordingly.

godesshunter

I appears that the rear camber settled a bit more than expected from my initial alignment. And toe got kicked out a bit in front too. I'm leaving it as is for right now just to hear some feed back over the next 3 days. Ill take the suggestions into account and re-adjust on Saturday.

The car has not been corner balanced. I had the opportunity to buy a set of corner weight scales from a pawn shop about a month ago. But they had already been sold by the time I went back with $ a week later. Cant really afford a new set at the moment.

I know the car needs it done but I'm extremely prejudice when it comes to other people wrenching on my car. Especially given the nature of rear height adjustment. I would only be comfortable doing it myself. I hadn't looked into renting scales. Not even sure if its a possibility. Or where to even look.

JCrane82

iTrader: (3)

Nothing really odd to suggest an oversteer situation. Your front toe isn't really all that aggressive (I am running over double that), and you have lots of rear toe in. Your camber settings will also create understeer. My guess is that your tire pressures were too high and you were getting more temperature growth in the rear, causing pressures to increase more compared to the front; and therefore giving you oversteer. This is just a wild guess, and without any data to prove, it will only be a guess. Lower pressures to 28-32 cold and try again. Remember, the more camber you run the lower your tire pressures should be.

godesshunter

Unfortunately we are not allowed consecutive runs just for that reason. But I do plan on dropping some pounds.

olddragger

iTrader: (3)

check the local road race courses--many tracks have corner weighting scales built into their tech sheds. Some dont.
I doubt that unbalanced corner weights is causing your oversteer--but when the time comes to make your different alignment the weight knowledge needs to be addressed also.
In comparasion to road racing --thats a lot of chamber in the rear for a street driven car.
if you rear suspension is stiff, tire pressures go up and less rubber on the pavement from the chamber setting--yep that could do it.

dmitrik4

iTrader: (5)

I'm sure someone in your region has scales; ask if you can borrow them. But corner weights are probably not the driod you're looking for.

d walker

scales alone is not the answer, there is an entire procedure to corner balancing and aligning a car precisely.

Your suspension might (probably) have been simply too stiff for the conditions. Surface temps are an oft-ignored part of your setup. I think your too stiff on your springs for cool weather, but they might work fine in warmer temps. For some strange reason a lot of tooners think that stiffer is better, but fail to realize that when a car is too stiff it skates across the surface. Since a large portion of autocross time is spent in transition between throttle and brake, you need to be able to go to throttle as soon as you possibly can, and that means a suspension that works.

Also agree on tire pressures, too high will make the car skate across the surface as well.

The RX-8 typically does not need to run as much camber when running radials as other cars do. This is because we have an actual suspension and not some compromised strut solution. You CANNOT take suspension advise from Honda/VW/etc drivers! What works for them will not work on an RX8. Oddly, the Corvette suspension has the most in common with an RX-8. What this means is there is less camber change throughout the suspension travel and a more predictable camber arc. Running too much camber will also lead to handling issues.

Good luck.

JeffH

Your setup seems pretty fubared. Based on my calcs, you have over a 1/4" toe in the rear? I remember looking up that .08 minutes was approximately 1/16". Decrease it to anywhere from an 1/8 and 1/16 total in. As everyone also noted you have less camber in the front than the rear...not good. Set front camber anywhere from 2.5 to 3+ negative depending on front roll stiffness, the tires you use and how hard you drive. As for the rear, you're at a good starting point.

The springs you have will also work fine. You're just going to have to increase your front roll stiffness to settle the car. Relatively, you have too much in the rear. A easy way to do it is with a stiffer front sway bar. You can either test with drilling an additional hole in the stock bar, further in. Or go with an aftermarket bar. The Hotchkis MX-5 bar is a good starting point and not very expensive. You can also experiment with disconnecting the rear sway bar.