Suspension Refresh and Bump Steer Question

If I roll into a corner and encounter a bump in the road, as the suspension starts to rebound, the car feels like it wants to lurch away from the inside of the corner. Is that bump steer? I've read a lot about the center or this and the axis of that and have a vague understanding of the concept, but am not able to relate the feeling with what I'm reading about with certainty, so I thought I'd ask wiser and more experienced heads. The car is a 2002 C2 with 51,000 miles with OEM suspension except for new M030 shocks, springs, and roll bars installed in June 24 and a new set of Conti's a month ago. My sister signed me up for a HPDE with the local club for my birthday, so I plan on doing a refresh on the OEM components in the spring prior to that event - so should I install bump steer kits while I'm in there? I'd like to try to get a handle on this handling feature prior to that event since it makes me a little nervous on the highway as it is. Thanks in advance.

Bump steer: When the tie rods & control arm pivots are NOT on the same plane and do not move in unison. Then going over a bump changes steering angle. Bump steer can be felt on a straight road going over a bump/hole and having car pull to one side or another. 996 suspension is very good and does not suffer from bump steer when set up to oem specs. Most good condition oem 996 cars in general step right over bad bumps (with in reason) while cornering in stride, keeping perfect control in an uncanny in control way.... Most German cars are like that, some more than others... Have you had your car aligned after the lowered springs/shocks/struts were installed.? Do you have that alignment sheet/specs. Not sure exactly what "roll into a corner" means..? Are you pushing it to the max or close...? Or is this just an easy 5/10's off ramp corner...? If pushing to the maximum speed thru a corner and a series of bumps upset the front suspension enough, at the corner apex, no doubt car will push/under-steer.

First of all: what direction of car body movement do you call 'rebound': upwards or downwards? The short answer to your closing question: no, don't fit a bump steer kit but certainly get a 4 wheel alignment done. Look up your configuration in the tables below. If the front corner outside spring is compressed, the corner outside wheel will turn ever so slightly towards the outside of the corner. This is intended behaviour, achieved by the design of the front axle kinematics, in order for the car to NOT tighten the cornering line it is running when negating a bump. It would tighten its cornering line, when the steered angle of that wheel would remain the same since the increased (vertical) load on the tyre would result in an increased lateral, I.e. cornering force generated by the tyre, which literally forces the car to run a tighter corner radius and thus increase the risk of the car to become unstable by sudden oversteer.

Adding a lot of camber when lowering can induce a bit more bump, but often some of this stability loss is just the camber which makes a car wander a little more. Don't go silly with the lowering and its likely to be fine.

I have US M030 suspension and have checked its bumpsteer characteristics. I can confirm the following: When the front suspension compresses, the front wheels will toe out. When the suspension extends (rebounds), the front wheels will toe in. Conversely, when the rear suspension compresses, the rear wheels will toe in. And when it rebounds, the rear wheels will toe out. Although I neglected to obtain measurements, I noted an interesting observation regarding aftermarket bumpsteer kits: At US M030 ride height, the best toe curve (meaning that it minimized toe deflection across the entirety of wheel travel) was obtained using no spacers between the toe links and the wheel carriers. The rate of toe deflection increased with each additional spacer. This observation is true for both the front and the rear wheels. So @hardtailer is correct - you don�t need any bumpsteer kits. The most problematic bumpsteer characteristic to worry about, which you touched upon in your opening post, is the rear toe out during rebound. You can address this by adding additional static rear toe-in, but at the expense of rear tire life. I like 0.25 degrees of rear toe-in for the stability that it offers. Although you don�t need a bumpsteer kit, there are benefits to installing rear aftermarket toe links. When combined with a �toe lockout kit�, you�ll eliminate the possibility of the eccentric toe adjuster bolts slipping�. (It�s never happened to me, but other people on Rennlist have posted their experience). Additionally, it�s simply much easier to adjust your rear static toe with the aftermarket links, which I believe is worth the expense. If you decide to lower your car, or you really want to mess around with your suspension, I would advise you to get yourself a bumpsteer gauge. If you start adjusting things without checking, you�re very likely to make the car handle devilishly. Or if you prefer to have a professional (like a Race Shop) work on your suspension, you should see whether they have such tools to help make your car handle more predictably.

Thanks for all the info - it sounds like everything is fine and just a characteristic of the car and nothing to be worried about. I do want to carry on with the suspension refresh but won't worry about the bump steer kit though. And thanks for making me realize that I lost my copy of my alignment specs. The shop did align it for the M030 suspension and I did get a copy which I normally scan right away - but apparently did not for this one. Thanks again.