Anir

Is "bump steer" kickback through the wheel when traveling on uneven pavement? I noticed Gert's bump steer conversion package for the 993, that comes with "GT2 EVO uprights" (not sure what these are either).

My car is currently lowered by the previous owner with the 7209 Eibach springs, and I plan to convert to the M030 ROW suspension. I'd like to do this right, so I'm wondering if I need to address bump steer as part of the conversion.

Thank you for indulging my lack of knowledge.

Viken

You got it right! This usually happens when you're going relatively fast. You hit a bump and the car tries to steer left or right depending on the direction. When this happens, you fight the steering wheel for a short time. The kit Gert is selling will allow the steering rack links to be mounted at a lower point thus reducing this bump steer tendency. The lower your car, the more pronounced bump steer will be.

Do you experience this with the present suspension?

Anir

Viken,

I have noticed it before on my car, but I can't say it's a nagging problem in day-to-day driving. However, I've yet to do a track day (I'm hoping to attend Putnam Park on 10/13-10/14). Therefore, I may not have pushed it hard enough yet.

I really want to make the car as good as possible. BTW, what are EVO uprights?

Thanks!

Viken

It is the item shown on Gert's web site. The hub carrier as it is also called.

Anir

Viken, are there any drawbacks to installing the GT2 EVO uprights, new wheel bearings, and Motorsport tie-rods in terms of servicing and driveability on the road? Does the car require more frequent adjustments to maintain proper suspension parameters? The closest good racing alignment shop is 90 miles away.

Unfortunately, Lexington is no automotive or racing mecca. In fact, most of us that live in Kentucky belong to the Ohio Valley Region PCA. They have Mid-Ohio and Putnam Park, although the Kentucky Motor Speedway was recently completed here, so maybe our options will improve.

Thank you again for your help.

Viken

No, there is nothing more to the new parts than otherwise needed with the standard issue items.

The only drawback (at least to me) is the high cost of the new parts.

Joe@Fabspeed

Anir and Viken, my friends, you're both completely incorrect in your assumptions about bumpsteer. Anir you or anyone else on this board doesnt need GT2 front uprights on a stock 993 with M030 suspension. The GT2 993 uprights and tierods are only usefull if your 993/964 is really really lowered to maintain suspension geometry under race conditions. These came stock on 993RS, Supercup 3.8, GT2 and 964RScars. The GT2 kit is not for making your steering OKAY/better if you hit a bump. You'll spend around $1500 to upwards of $2000 for parts and labor. Youll need new wheel bearings for the conversion. Correcting bumpsteer and /or bumpsteering a front or rear suspension is a real pain in the *** and is part of suspension tuning for the very seriuos amateur racer and mandatory for proracing! You are trying to minimize toe in /toe out under suspension travel!!!! Joe Fab Fabspeed Motorsportweb page performance for the next millenium

Viken

Completely incorrect? Well, my car only has the ROW M030 suspension and it suffers from bump steer. Oh yeah, I don't know what I am talking about because you and some others say so.

Previously, I suggested to you that you think before you post. Had you done that, you would have had a bit more credibility on these boards. But, you continue posting like an immature kid and make yourself look like a fool!

George Helser

Anir,

My understanding of bump steer is when ONE of your front tires goes over a bump or in
a pot hole it causes your steering wheel to turn although you are going straight. 914s
have a lot of bump steer.

With your car on the ground, look at the angle of your tie rods with respect to horizontal. When you lower the chassis of your car the angle of the tie rods will change and it will effect the steering wheel response as the front suspension deflects.

When I lowered the front of my 914 (20 years ago) the bump steer went from bad to awful. The solution was to “bump steer” the steering box. i.e. unbolt the steering box
and raise it using longer bolts and spacers. The aluminum spacers were about as high as the car was lowered. (This was not very difficult to do in a 914.) After the 914 was “bump steered” the tie rods returned to about the same angle they were before the car was lowered so the steering wheel jolts returned to about equal to that of an un-lowered car.

Regards,
George
In sunny Arizona
(In the market for a 993 C2 coupe with LSD)

Rocket

Put simply, bump steer is the tendency for the front wheels to splay outwards when the front suspension is loaded up due to weight transfer or under braking.

A Bump Steer modification will counteract this effect and thus improve stability under braking, and generally increases front end grip when cornering.

As stated above it has nothing to do with effects on the steering wheel when going over bumps.

Rocket.

Anir

Thanks to everyone for educating me. The question I'd like to answer is this:

Did Porsche design the tie-rod angle to be most correct with the M030 ROW suspension set-up or the M030 USA set-up. In other words, would the ROW set-up qualify as lowered from an engineering standpoint, or is the USA version simply "raised" from ideal.

If the ROW set-up corresponds to the engineers' original design of the tie-rods, perhaps further tweeking with the GT2 EVO uprights / Motorsport tie-rods is not necessary (unless further lowering will be done with a competition suspension).

Any insight is appreciated.

SundayDriver

First, I am pretty sure the car was designed for ROW height, so you would not be lowering it, from an engineering standpoint.

Second, my car is lowered another inch or so from ROW height. I do a fair amount of track stuff and am an OK driver. I do not feel any ill effects from not having bump steered my car. My suggestion is to spend the $$ on driver training. When you can run laps within 1/10th second of each other and can consistently place the car witin a few inches of the reference points on each lap, then get a pro to drive you car and let them tell you if bump steering would likely help.

If I were racing a 993, I would certainly have it bump steered (new uprights) and might do that if I were doing serious time trials, but I do not see how it is worth the cost and effort for a street 993 even with lots of DE events. I rarely try to drive my car at 10/10ths at DE events, so the little errors from bump steering are not a factor.

Anir

Mark D,

Thank you for the straightforward & helpful response. I suspect you (and Joe and Viken, for that matter) are correct that the money is better spent elsewhere.

Thanks to everyone for putting the bumpsteer issue in its proper perspective.

tom_993

The technical definition of bump steer is that the toe angle changes as the wheel goes up and down. This is often caused by a tie rod not being horizontal, but there are other causes.

Think about it this way. If you have your wheel turned to a certain angle (to negotiate a turn), it should stay at exactly that angle as the wheel goes up and down through suspension movement. If that angle changes as the wheel goes up and down, then you have bump steer. The bump is causing the wheel to steer.

You won’t necessarily feel kickback through the steering wheel when this happens.

Greg Fishman

Best and correct explaination.

Anir,
You don't need these (not yet at least).

In my best Ray Calvo impersonation: The only thing you need to do for your first DE is make sure you have fresh brake fluid, brake pads with at least 50%+ wear left, and a helmet SA 95 or later.



Greg