chris walrod

Has anyone converted to the "evo" front uprights (hubs)? I have had a few people tell me the 993 has some bump steer and the evo update makes a huge difference?

I have not checked the bump steer on my car yet to find out myself what the 993 has.

Anyone have experience with the evo hubs?

Chris

Greg Fishman

How much have you lowered your car? If it is near RS specs you might benefit from them. I have them on my race car but I never drove it without them so I can't comment on the difference.

Viken

If you don't feel bump steer and it doesn't annoy you, you don't need the Evo upright kit. Usually, bump steer on the 993 gets pretty bad if your lower the car more than 1" using relatively firm suspension components.

Mark Buka

Viken:

Good timing on this thread. Just installed the HR
coilover kit. Lowered car 1.25 inches and now it's a tad skittish due to, what I believe, to be bump steer issues.

Would you please offer your description of bump steer on a 993. What are the symptoms and should I have invested in Gert's kit?

Thanks in advance, Mark

Viken

[quote]Originally posted by Mark Bukachevsky:
<strong>Would you please offer your description of bump steer on a 993. What are the symptoms...?</strong><hr></blockquote>

Bump steer is when one or both front tires hit a bump on the road and the car goes a bit off course. I have this on my car but it is very manageable. Sometimes, and with a much stiffer suspension, the car could easily change lanes in a fast sweeper.

Mark Buka

Those are the symptoms I'm experiencing. How do the GT2 EVO uprights cure the bump steer?

Greg Fishman

The EVO kit relocates the tie rods to a different location on the upright so the tie rods are closer to horizontal. The tie rods are also stiffer as they don't have any rubber in them.

Greg Fishman

[quote]Originally posted by Silver Bullet:
<strong>What I've found is that issues with bump steer has been mostly from owners of 4WD cars, in particluar the C4S.

</strong><hr></blockquote>


Interesting. Why just the C4S and not the Turbo?

Mark Buka

Interesting indeed. Since I have a C4S, I'd like to know that answer as well.

David '96 993

The only time that I notice bump steer with my PSS-9's is when I have it set on full hard. It is only noticable on public roads, not much on a track as it tends to be much smoother.

It is particularly noticable on freeway overpasses...it is downright scary. Solution: set it on the softer side for street driving (very managable) and set it harder for track events.

Also, don't have it set to hard on the street while trying to hold a cup of hot coffee...ask me how I learned about bump steer. Good thing I already have enough kids

Greg Fishman

That was I thought. My guess is they that are both equally effected. I don't believe that there is any difference in the front suspension from the C4S to the Turbo.
I would have to look in the shop manual but I believe all 993's (US Spec) us the same tie rods.

I think the term "turbo tie rods" is used when up grading older 911's

Mark Buka

It's looking like the GT2 EVO uprights and tie rod ends are in my future. The last thing I want is irregular road surfaces to upset handling karma.

Anyone install this kit and have an opinion to offer?

Viken

[quote]Originally posted by Greg Fishman:
<strong>I think the term "turbo tie rods" is used when up grading older 911's</strong><hr></blockquote>

That's correct. The US 993 uses the same tie rods from the Carrera to the Turbo. Bump steer should be the same in all cars.

For the ROW, the Carrera RS received a different tie rod and the rest were identical as in the US cars.

PramTT

[quote] The only time that I notice bump steer with my PSS-9's is when I have it set on full hard. It is only noticable on public roads, not much on a track as it tends to be much smoother. <hr></blockquote>

David:

I believe what you are describing is not bump steer but more as a result of the stiffer (especially rebound) set-up from the full hard position. As you increase rebound damping, you will also reduce the ability of the tire to mantain contact to the bumpy/uneven surface hence the twitchiness of the car from the centrifugal force (during cornering) when the tires lost contact to the road surface.

chris walrod

bump steer is a result of undesirable suspension steering geometry. its basically toe change (in or out) as the suspension assy is moved through its travel up (bump) or in some cases (rebound)where a lot of down travel is used. Neither positive or negative bump steer is desirable.

Since most of us lower our ride heights, we must be experiencing negative bump steer where we get toe in the bump direction of suspension travel. I would guess that the evo hubs lower the tie rod mounting point--or you can raise the steering rack, but I dont think thats an easy thing to do with our cars.

This has got me wondering how much we have (bump steer). Someday when I get to it, I will have to measure it.

Dont get me started on ackerman.

Chris