for those who've adjusted front bumpsteer...

[jmitro]

thanks guys; I posted this on the Rennlist 996 forum also since it gets a lot of traffic.

what I'm trying to do is dial out (what I perceive to be) understeer on corner entry and midcorner. It occurred to me that, after installing springs/shocks along with adjustable tie rod ends, I hadn't set my bump steer.

It's PROBABLY not necessary, as the bump steer is probably minor, if anything, and the understeer is likely driver-induced rather than setup. ( I need more practice )

Additionally, I think my alignment was off (per my home measurement of toe, I had 1/8-3/16" of total front toe out. So I've got some other changes to make as well.

Running a square setup with 255/40/17 RE71R on 8.5" rims all around.

[Gilles]

Jmitro, do you have adjustable bars? These will allow you to adjust the turn in and rotation to your like :-)

[maytag]

Good read here.
Technical Articles

[truegearhead]

Originally Posted by maytag

Good read here.
Technical Articles

That’s a great summary. Still I don’t see any actual grip impact and I’ve never noticed my car “steering itself” I only drive the car on smooth tracks so maybe this is why. I’m curious if 986/996 really need bump steer adjustment.

[steved0x]

Originally Posted by jmitro

what I'm trying to do is dial out (what I perceive to be) understeer on corner entry and midcorner.
...

Running a square setup with 255/40/17 RE71R on 8.5" rims all around.

With a square 255 setup on all 4 corners, you should have tremendous amounts of front grip. The time I drove a spec boxster with a square setup like this the front grip was incredible. The challenge with a square setup is to tame the oversteer at the limit.

Even with my 225 front 255 Boxster I didn't have any understeer trouble on corner entry, especially if I had any amount of trailbraking, even like a big toe worth.

I did have mid-corner understeer on long sweepers like at Roebling.

And then I would have a little understeer on full throttle track out.

What sway bars are you running, and if adjustable, what settings do you have them on?

What brand of springs/shocks and if adjustable, what settings do you have them on? Since you talk about ride height, I am guessing coilovers?

I have seen 2 cars now that had terrible oversteer due to too stiff springs in the rear and also set too low and running out of strut travel. I've never seen one that had that condition in the front but maybe it is possible?

[Racer Boy]

Originally Posted by jmitro

what I'm trying to do is dial out (what I perceive to be) understeer on corner entry and midcorner. It occurred to me that, after installing springs/shocks along with adjustable tie rod ends, I hadn't set my bump steer.

It's PROBABLY not necessary, as the bump steer is probably minor, if anything, and the understeer is likely driver-induced rather than setup. ( I need more practice )

Additionally, I think my alignment was off (per my home measurement of toe, I had 1/8-3/16" of total front toe out. So I've got some other changes to make as well.

You say that the perceived understeer may be driver-induced. What do you mean by that? Are you giving the steering wheel a large input all at once while braking hard, or something else?

How much track driving experience do you have? Sorry for the questions, I just want to understand what is happening.

Straying too far from zero-toe will cause understeer, whether it's too much toe-in or too much toe-out. 3/16" of toe-out is a LOT.

Bump steer refers to toe change as the suspension moves through it's travel, either up or down. All suspensions have bump steer. You will get toe change when the suspension reacts to a bump, but you will get the same amount of change if the suspension reacts to body lean caused by hard cornering (lateral loads).