Martin S.

You must have RS uprights and tie rods, no bump steer for you, right? Well maybe, maybe not. My San Diego alignment guy, Jae Lee at Mirage International, told me that I may want to consider dialing out any potential bump steer in my 993 front suspension..wait a minute, How could I have any residual bump steer? I have the RS uprights and the RS tie rods. At the time I had the RS wheel carriers and tie rods installed, I wanted the RSR style inner tie rods (No rubber), but for years they have been NLA for years so I had to settle for the 993 RS tie rods.

Well it just so happens the inner ends on the RS tie rods have some rubber, rubber equals flexibility, flexibility = potential bump steer. After spending $$$ on the RS uprights and tie rods, I didn't want to admit to bump steer...but going around Turn 8 at Willow Springs, I could feel it, and I don't like the car hopping around at 120 mph +.

I am going to take the leap, and have the RSR style inner tie rods installed and the car realigned and corner balanced at Jae's shop. And "while you are in there", I am going to have the rear alignment done too and any possible bump steer dialed out, will have the KT settings optimized. BTW, the rear suspension is all ERP links.

http://www.tarett.com/items/993-964-...rtr-detail.htm

Here you will read, "These are exact reproductions of the NLA RSR inner tie rods. The solid tie rod design provides improved feedback over the standard or RS rubber links, without any significant increase in noise or ride harshness. Fits 964's converted to RS uprights and all 993's. Kit includes two inner tie rods."

I will document any changes in handling on this Board. I am headed back to Willow Springs May 20, 21, POC's Tribute to Le Mans.

When will I get to the bottom of this "slippery slope": It never seems to end.

OverBoosted28

I'm not sure it can be eliminated, but surely reduced to the point, it doesn't upset the chassis, mid turn. :-)

cgfen

let's connect when you are in SD!

Craig

Martin S.

Craig...I am awaiting confirmation of my appointment with Jae..when that's locked in, I'll let you know. He will have the car for two (2) days. His alignment and
anti-Bump Steer process is very labor intensive.

Send me a PM with your e-mail; I have here somewhere but getting a PM would make it easier. And NO base jumping

Thanks,

Martin

Analog Theory

Martin this is the exact setup Jae upgraded me to also...love it! Fast forward to right now and the reason you have to wait for an appt spot with Jae is because he's been working on installing all new Elephant Sport bushings, new RS rear arms/kinematic and Ohlins coilovers on my rig. Should be done this week.

Bill Verburg

Martin,
2 different issues are being conflated here

issue 1 - bump steer aka roll steer which is caused by the different arcs that the road wheel ball joint and the steering gear travel through. This is what the RS uprights address by moving the outer end of the steering gear back into a more benign alignment w/ the road wheel ball joint. Other means to address thus are w/ o/s tie rod ends. Some guys use both Roll steer can never be eliminated only reduced. To find out how much bump steer you have a bump sweep must be performed, this moves the suspension through it's arc of travel and measures the toe change w/ a dial indicator correlated to the position in the travel arc. Here is a pic of a typical bump steer gauge setup


issue 2 - steering slop , caused by rubber or other flexible components in the steering and suspension. This is the issue that the Tarrett inner tie rod piecs address. There are 3 levels of slop in the inner tie rods, from worst to best; stock, RS, RSR. The Tarretts are clones of the RSR mono-ball inner tierod ends. They don't alter bump steer in any way just eliminate the small amount of give that the RS inners allow.

Martin S.

I appreciate the heads up...and I actually understood the concept before you so clearly bifurcated the two issuers. I am getting the inner tie rod ends replaced, and next going through the dial indicator process you described. This is a very labor intensive process, as one can imagine.

Thanks again Bill for clearing up the issue.

Steve Weiner-Rennsport Systems

Bill nailed it.

Two completely different issues and therefore two different solutions.

Martin S.

Two different issues, and I am addressing both, inner tie rod ends and the dial indicator routine. I can hardly wait to get the car back.

Cupcar

I think the main issue with rubber in the tie rods is toe out under braking leading to some wandering instability and toe changes during cornering loads that mimics bump steer.

While he's in there Marty, have Jae install some stiffer Rothsport rack mounts and a steering rack stiffener (I think you have a rack stiffener?) to keep the steering rack from moving around too.

Both here:

http://www.rothsport.com/Products/Ch...Rack-Brace.htm