Understeer on an 88TII, could it be the bushings? (autox guys help!)
05-19-04, 11:58 AM
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Understeer on an 88TII, could it be the bushings? (autox guys help!)
I've been starting to autox my car more lately, and I've been really fighting with some fairly bad understeer. At times I feel like I'm driving a FWD or something
Anyway, I have eibach springs, tokiko shocks, and a front strut tower brace as far as suspension stuff goes. Tires are Yokohama AVS ES100 225/50/16 all around, fronts I run at 40PSI and rears at 35PSI for autoxing.
My questions:
When I'm turning hard, besides understeering sometimes it feels like the car is trying to "walk", or something. Like the suspension is loading and unloading in the front (I keep thinking I blew a tire or something). Could this be a dead bushing, or something else? Where can I get bushings for an FC?
Next, would adding a rear strut tower bar help? I'm planning on doing this sometime (mostly so I can mount a camera), but if it will help I'll do it sooner.
Any other tips guys? I generally try to brake hard before a turn to load up the front and then accelerate gently through the turn, but it really does feel like at times the front is unloading during the turn and reloading, repeated over and over. I really want to get this ironed out, and see if I can't start getting better times.
Anyway, I have eibach springs, tokiko shocks, and a front strut tower brace as far as suspension stuff goes. Tires are Yokohama AVS ES100 225/50/16 all around, fronts I run at 40PSI and rears at 35PSI for autoxing.
My questions:
When I'm turning hard, besides understeering sometimes it feels like the car is trying to "walk", or something. Like the suspension is loading and unloading in the front (I keep thinking I blew a tire or something). Could this be a dead bushing, or something else? Where can I get bushings for an FC?
Next, would adding a rear strut tower bar help? I'm planning on doing this sometime (mostly so I can mount a camera), but if it will help I'll do it sooner.
Any other tips guys? I generally try to brake hard before a turn to load up the front and then accelerate gently through the turn, but it really does feel like at times the front is unloading during the turn and reloading, repeated over and over. I really want to get this ironed out, and see if I can't start getting better times.
Last edited by MountainTurbo; 05-19-04 at 12:01 PM.
05-19-04, 01:18 PM
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More tire pressure out back versus up front will help dial out some understeer...make sure the car is aligned properly as well.
I would check the AWS bushings in the rear suspension and swap them out for solid pieces...over time these don't work as well as they used to, even if they aren't falling apart. These bushings adjust toe once deflected and they are designed for use with the stock suspension, not a much stiffer aftermarket system with wide/sticky tires. I like the AWS on stock FC's but it really takes away from driving at the limit on a high performance suspension.
A rear strut brace will help the car bite down through a turn - if you still can't dial out understeer with a proper alignment and solid rear steer bushings then try upgrading JUST the rear sway bar to a bigger unit.
I would check the AWS bushings in the rear suspension and swap them out for solid pieces...over time these don't work as well as they used to, even if they aren't falling apart. These bushings adjust toe once deflected and they are designed for use with the stock suspension, not a much stiffer aftermarket system with wide/sticky tires. I like the AWS on stock FC's but it really takes away from driving at the limit on a high performance suspension.
A rear strut brace will help the car bite down through a turn - if you still can't dial out understeer with a proper alignment and solid rear steer bushings then try upgrading JUST the rear sway bar to a bigger unit.
05-19-04, 01:22 PM
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those tires for some reason have been known to do that. I have friends that autocross in Silvia's (conversions) and DSM, and the both complained about similar characteristics. In fact some people describe it as the tire rolling under. play with pressure to see if you can minimize it, but i don't think it'll cure it completely.
05-19-04, 04:06 PM
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Both the TII and NA FCs I have driven had understeer stock. Much of it is caused by the DTSS bushings and resultant factory toe setting, mild rear anti-sway bar stiffness compared to the front, mild front negative camber situation compared to the rear.
Keep in mind that "turn in understeer" exists naturally, in most cases, even on cars that are very neutral or even tail happy when estabilished in a turn. This is because when turning in, the front tires will always have a larger slip angle than the rears before they begin following the turn. Understeer happens when front tire slip angle exceeds rear tire slip angle. In other words, it is necessary to do some *light* trail braking on turn entry with a neutral car. If your car is not nose heavy like an FWD car, this turn in understeer will be more pronounced due to no front wheel weight bias.
There are many types of understeer and I'm not in the mood to go into it here, but if I were you, I would get rid of the DTSS bushings in the rear and set up some toe-in on the rear wheels (about 1/4"), get a stiffer rear anti-sway bar and provide for some negative camber in the front. I did all this to my own FC NA and it was basically neutral before I installed my LSD last week. It's understeering a little now, so I'm going to dial in a tad more rear toe-in. This increases the slip angle of the rear tires in a turn, which decreases understeer / increases oversteer.
One other thing. Common wisdom among experienced autocrossers I've met is that higher pressure in street tires causes increased traction and vice versa. If you're understeering, going down from 40 PSI in the front will make it worse. I have observed many racers let air out of the rear tires when they were understeering on the course.
I'm pretty sure the tire "climbing" feeling is pretty normal for steep turn angles. My car does it and so does an FD I rode in that got a couple tenths away from top time at a semi-large event I was at.
Keep in mind that "turn in understeer" exists naturally, in most cases, even on cars that are very neutral or even tail happy when estabilished in a turn. This is because when turning in, the front tires will always have a larger slip angle than the rears before they begin following the turn. Understeer happens when front tire slip angle exceeds rear tire slip angle. In other words, it is necessary to do some *light* trail braking on turn entry with a neutral car. If your car is not nose heavy like an FWD car, this turn in understeer will be more pronounced due to no front wheel weight bias.
There are many types of understeer and I'm not in the mood to go into it here, but if I were you, I would get rid of the DTSS bushings in the rear and set up some toe-in on the rear wheels (about 1/4"), get a stiffer rear anti-sway bar and provide for some negative camber in the front. I did all this to my own FC NA and it was basically neutral before I installed my LSD last week. It's understeering a little now, so I'm going to dial in a tad more rear toe-in. This increases the slip angle of the rear tires in a turn, which decreases understeer / increases oversteer.
One other thing. Common wisdom among experienced autocrossers I've met is that higher pressure in street tires causes increased traction and vice versa. If you're understeering, going down from 40 PSI in the front will make it worse. I have observed many racers let air out of the rear tires when they were understeering on the course.
I'm pretty sure the tire "climbing" feeling is pretty normal for steep turn angles. My car does it and so does an FD I rode in that got a couple tenths away from top time at a semi-large event I was at.
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