I have tokico adj. and h&r springs, stock rear strut tower brace, freedom design front strut tower brace, everything else is stock.
tires are 235/40F and 275/40R(crappy Khumo ecsta). What should I do to get rid of the understeering, without making the car tail happy???
I have the shocks set at 3(medium).
Any suggestions?

 

Bigger tires in the back seem to cause understeer on an FD (or reduce oversteer, which was my goal). You can try going to 255's in back. Even so, I still have understeer with 255's in back and 235's in front.

Believe it or not, this tuning guide is just about right on.

http://www.tirerack.com/tires/tirete...n/racepres.htm

You just don't want to go too "crazy" high on tire pressure or you will loose grip and you don't want to go too soft on shock/spring or you will bottom out and experience sudden loss of traction.

 

2FAST7s,

Yeah, your setup will dial in understeer.

For best results, use same size tires/wheels all around.

Obviously in your case that's hard to do unless you sell off what you have and start over.

Depending on the wheel widths, you can minimize understeer by going to 245/40-17s up front and 255/40-17s in back.

You could also adjust the rear Tokicos to a slightly higher setting than the fronts...ie, "4" in back and "3" up front.... You could remove your front strut brace, as the front strut brace increases front end stiffness, and thus increases understeer ("stiffest end slides first rule").

If all else fails, tire pressures are a way to deal with adjusting the car's handling characteristics...

 

Yeah, after playing with tire pressures a bit I would try softening the front shocks. Try 1/5 F/R just to see how far that will get you, but you probably don't want to end up running that soft in the front because the front will get sloppy feeling (but should grip better). The next thing you could try is a thicker rear sway bar, or better rear sway bar mounts. If you have a 94, you might consider installing the rear bar from a 93 (it was stiffer). Otherwise try an aftermarket bar. Be careful, though, as the rear bar could make it tail happy if you go too stiff.

-Max

 

Like max said, if 94, go with bigger 93 rear bar. If not enough or a 93, go with mazdaspeed rear bar. Same size as 93 but solid, and 2 ajustment positions.

 

Thanx, I'll play around with all the suggestions.
Should be fun!

 

You could also get a larger, preferably adjustable rear-anti-sway bar. Or better yet, get a bigger front AND rear, and adjust the rear one to be stiffer until you get the desired results. Adjusting tire pressures will only do so much. If your car has a heavy tendency towards understeer, adjusting tire pressures won't help much. It will just cause you to not understeer QUITE as much while making your tires have less of a contact patch on the road due to non-optimum tire pressures. Adjusting tire-pressures should only be done to FINE-tune yours handling characterstics, such as at an auto-x or track event when your don't want to mess with your cars already pretty good suspension setup.

 

All these things are good, but bandaids. The mismatched tire sizes are the real culprit here. Sorry, but if you want to cure this, unless you're prepared to spend a great deal of time trying to tune the suspension to compensate for the extra traction in the rear, you need to even this out.

PaulC

 

FWIW, I agree with Paul C...ideally the wheel/tire sizes should be the same sizes and offsets all the way around to preserve the FD's perfectly neutral handling. To be honest, I really DON'T like the way my car understeers (however slightly) on track with the asymmetric wheel/tire sizes...BUT a good driver can compensate....

For those who don't know, I have 9 x 17 SSR Integral A2s in 45-mm offsets with 255/40-17 Yokohama AVS Intermediates all the way around for my road setup. This has been fantastic, and I'm ecstatic about the way the car handles on the road.

My track-only setup is 8.5 fronts, 9.5 rears x 17 SSR Comps with 245/45-17 fronts and 275/40-17 rears, Hoosier R3S03s. Ideally I'd have 275/40-17 Hoosier all the way around mounted on 10 x 17 Forgelines, but was afraid of front wheel well clearance issues with that setup.

Max Cooper has the better track setup with 285/30-18s with 10 x 18 CCWs all the way around. Note that he has 2.5-inch race springs, while I have the stock style H&R springs.

 

SleeperR1,
I have similar set up on my car(-.5"). Any problem with the fronts rubbing on the fender. The H&R springs lowered my car more than I wanted.
I'll probably go with the 245/40F and 255/40R.
Will 255/40 fit fine in the front??? I dont want any rubbing on the fenders(already had them fixed once)

 

Tuning by adjusting tire pressure should be used as a last resort, because what you are doing is reducing the grip of the tires. You might want to pick up a book called "How to make your car handle" by Fred Puhn It's an old book, but physics don't change. He goes pretty indepth about suspension theory and tuning, but doesn't bury you with equations. It's very well written and is systematic in the description of how a suspension works and how adjusting it alters the performance of a car. It's also pretty cheap! about $20

 

Yep, its a GREAT book, thats were I've learned a TON about suspension from. I think I paid $12.00 for it.

 

I presume you have 8 x 17 front and 9 x 17 rear? If that's the case then go with a 245/40-17 fr and 255/40-17 rear, like you plan to do. That will be a good setup for you. Depending on your wheel offsets, you shouldn't get any rubbing even with the H&R springs in place.

My SSR Comp 8.5 and 9.5 x 17s are 42 mm offsets. I can run the 245/45 and 275/40 seventeens because Hoosiers have a much shorter overall diameter because of the shallower tread depth that race tires come in. The overall diameter for both Hoosier sizes is 25.3 inches. Stock overall tire diameter for the 225/50-16 is 24.9 inches. Pretty close. No I have no rubbing issues with the track-only setup.

 

Your setup will induce understeer but a lot of the understeeris caused by driver error. I used to complain about understeer then a coupla SCCA national drivers/champs told me most of it was my fault. A balanced car should have mild turn-in understeer on corner entry, neutral balance in mid-turn, and mild power-oversteer on corner exit. If one dive bombs into a corner, it's sure to cause massive understeer and scrubs a ton of speed off. Are you understeering in mid-corner and on corner exit also?