FWD susp help: Grassroots Motorsports forum: Grassroots Motorsports Magazine

Subscribe get a full year for only $23.95 Sample Free Test Drive—no strings attached

Dec. 23, 2011 12:11 p.m. coors75 None

Okay. I have been to 4 autox. I have a 1991 nx2000. This last one i went to gc coilover sleeves on kyb agx 350/250 spring rates from road magnet sprngs on agx 325/250. So basically the same?

My alignment was -1.6 camber i front with 2.4• of caster. 1/32 toe in (insisted on by alignment shop to reduce tire wear) -1.2 camber rear again 1/32 toe in (same reason). Caster was increased using whiteline caster bushings and ground control camber plates. I have an suspension techniques rear swaybar with stock front.

First few autox's the rear rotated nicely things seemed quite balanced. Now it oversteers a lot. I mean you have to really be smooth and cautious. Too much so. (car was driven by very good instructor who agreed).

I think the caster improved turn in and front grip so much the rear cannot keep up.

We both think this is to much oversteer to correct with tire pressure. Any ideas? I know a front bar could help but i prefer to fix this problem at the rear since the front is pretty good. Hankook rs2 front 37psi rear 33 went down to 30.5 in back which helped slightly. Pressures arrived at using chalk on the sidewalls. No pyrometer yet.

Agx used to be set at 8 (stiffist setting). Backed them off to 6. Helped minimally. (only adjust how spring rate is applied of course not the rate itself.

I think i need adjustable sways but can anyone offer opinions/ help to improve my setup andsolve this severe oversteer issue. Sorry no video.

Thanks
Dec. 23, 2011 1:17 p.m. wbjones SuperDork

first off ... find another alignment shop .... I won't take mine to any shop that tries to dictate to me what my settings are going to be

what kind of car ?
Dec. 23, 2011 1:26 p.m. DeadSkunk Dork

Nissan NX2000
Dec. 23, 2011 2:15 p.m. Hal Dork

wbjones wrote:

first off ... find another alignment shop .... I won't take mine to any shop that tries to dictate to me what my settings are going to be

And have them set the rear toe to 0.
Dec. 23, 2011 2:23 p.m. failboat HalfDork

try disconnecting your rear swaybar?
Dec. 23, 2011 3:52 p.m. coors75 New Reader

I think disconnecting the rear sway bar would lessen the oversteer but the car was balanced before the caster change.

I think that would be a step backwards and make the car slower than if I can find a solution that adds enough grip to keep from spinning out but still let the car rotate. If nothing else works I will do that as a la,st resort
Dec. 23, 2011 4:13 p.m. trucke New Reader

The commnet to find another alignment shop is right. If you are autocrossing, you will want the front toe-out slightly to improve turn in response. Toe-in does not reduce tire wear, it only keeps the car on center so it doesn't dart around on you.
You say the rear is already toe-in in the rear and the car is oversteering so do not change that. Going 0º in the rear will make the problem worse. It seems unusual for the FWD car to rotate that quickly with only 250# springs out back. I would be looking for something that is broken or flexing on you. There may be a mechanical issue somewhere that you cannot see except under load. Get the car on a lift and put a wrench on every bolt and try to wiggle everything in that rear suspension. If it is okay, disconnect the rear sway bar. You said it worked well with the bar before the GC change, but now you have a different set-up. Do not be afraid to disconnect to test at an autocross. If it works, remove the rear bar or put the stock rear bar back on.
Dec. 23, 2011 7:16 p.m. wbjones SuperDork

I'm assuming the 2 1/2° of caster you refer to is positive not neg... I really don't understand how that could loosen the car up

Positive caster tends to straighten the wheel when the vehicle is traveling forward, and thus is used to enhance straight-line stability. taken from this article http://www.ozebiz.com.au/racetech/theory/align.html

the way it was explained in class was it helped straighten out the front wheels ... i.e. self-centering ....
Dec. 23, 2011 9:33 p.m. coors75 New Reader

wbjones wrote:

I'm assuming the 2 1/2° of caster you refer to is positive not neg... I really don't understand how that could loosen the car up

Positive caster tends to straighten the wheel when the vehicle is traveling forward, and thus is used to enhance straight-line stability. taken from this article http://www.ozebiz.com.au/racetech/theory/align.html

the way it was explained in class was it helped straighten out the front wheels ... i.e. self-centering ....

Yes you are correct that is positive caster. My understanding is that positive caster on macstrut suspension not only help with straight line stability but help reduce the increase in positive camber that happens as the suspension compresses (ie loss of neg camber). This in turn gives more grip in the corners.

Basically I think this gave significantly improved front grip which the rear can no longer match.

I will do as mentioned and have a serious look around the rear susp and remove and reattach the sway-bar and see if it was causing bind.

Next autox I will then test both with and with out the rear bar. thanks guys.
Dec. 23, 2011 10:46 p.m. Flogger00 New Reader

Any chance that when you did the suspension swap you also rotated tires front to rear, putting slightly more cooked tires in back? Even in just 4 autocrosses, that could potentially have more of an affect than your suspension changes, as I understand them. I'd also look carefully for a binding rear sway bar.

Wait a minute - spring change - coilovers now, used to be "road magnet" springs (whatever that is). Could you have changed ride heights so that you're operating in different regions of the camber change curve and/or affected roll centers?
Dec. 23, 2011 11:37 p.m. coors75 New Reader

Flogger, good point my ride height was increased from the road magnet (brand) springs. about 1/2 an inch. Could this really cause such a dramatic change? After all both the front and rear were altered the same amount.

I think the rear bar may be binding; as above I will remove and re-install and see if that helps. Other than that I am not sure.

It is not every day a FWD is oversteering too Much!
Dec. 24, 2011 12:02 a.m. SkinnyG HalfDork

I initially fought oversteer with my B13 Sentra many years ago. I was also one of the first to run the Whiteline caster bushings.

Chassis Rake was to blame on mine - start by setting the height so the rear control arms are sitting pretty much level. If the back is too high, it will get VERY loose. No more than 1/2" rake!!

My B13 was fairly easy to drive, but would bite you if you did something stupid. I ran Hypercoils, AGX's, rear Suspension Techniques bar, chassis braces, stock front bar (GA16).

Run as much camber as you can, 1/8" toe out up front, zero toe rear. When mine was dialed in, I ran 30psi all around on V70A's (sold the car in '07)

http://www.gwellwood.com/project-cars/the-sinister-sentra/
Dec. 24, 2011 9:25 a.m. steverife New Reader

If you like how the front is working and the car is too loose, add rear camber/lower the rear of the car.
Dec. 24, 2011 4:32 p.m. wbjones SuperDork

I kept screwing with my Integra 'till I had it so loose I had trouble even driving it on the highway .... and basically what I'd done was get it just a tad-bit too low... so that every time I went into a corner and had some weight transfer I was compressing the springs / shocks totally and completely ... so that I effectively had zero suspension in the rear ... and around and around I'd go
Dec. 25, 2011 4:56 p.m. iceracer SuperDork

When I essentialy doubled the caster on my ZX2SR I found I could run less camber. Although you don't have a lot. Wher caster helps on turn in, the outside tire increases in negative camber while the inside wheel goes positive. A general rule: oversteer, soften the rear or stiffen the front