993 bump steer....
10-08-2002, 10:48 PM
#16
Addict
Rennlist Member
Rennlist Member
Chris:
I have installed the “evo” uprights and tie rods on my ’95 “RS project” street car. I use the car on the street and at DE events. I really can’t feel much of a difference on the street, but I can feel a marked difference on the track. As Greg mentioned, the RS tie rods don’t have any rubber in them and, as such, enhance the immediacy of a direction change. I have purchased all of the suspension parts that are specific to the RS, but have only installed the aforementioned parts with RS shocks, springs, monobals and sways at this point. The car feels more solid in the front than it does in the rear. I am hoping that the new RS parts with their associated harder rubber will bring the “hewn from a solid piece of steel” feel back to the car. I think this is a worthwhile upgrade if you are going to use the car on the track several times per year. The parts are beautifully made and seamlessly integrate with the 993’s suspension. The good news is that ride height doesn’t change, so your old corner balance is still valid. You will have to get a new front-end alignment at a minimum. One more thing, you get more camber out of the front wheels with the new uprights if you want it.
Hank
I have installed the “evo” uprights and tie rods on my ’95 “RS project” street car. I use the car on the street and at DE events. I really can’t feel much of a difference on the street, but I can feel a marked difference on the track. As Greg mentioned, the RS tie rods don’t have any rubber in them and, as such, enhance the immediacy of a direction change. I have purchased all of the suspension parts that are specific to the RS, but have only installed the aforementioned parts with RS shocks, springs, monobals and sways at this point. The car feels more solid in the front than it does in the rear. I am hoping that the new RS parts with their associated harder rubber will bring the “hewn from a solid piece of steel” feel back to the car. I think this is a worthwhile upgrade if you are going to use the car on the track several times per year. The parts are beautifully made and seamlessly integrate with the 993’s suspension. The good news is that ride height doesn’t change, so your old corner balance is still valid. You will have to get a new front-end alignment at a minimum. One more thing, you get more camber out of the front wheels with the new uprights if you want it.
Hank
10-08-2002, 10:51 PM
#17
RL Technical Advisor
Great thread,..... 
As Chris noted, bump steer troubles occur when these cars are lowered close to racecar specs and the tie rods are no longer horizontal at static ride height. Whether a 993 owner suffers from this depends upon where their ride height is set at and this is a big variable for folks with coilover kits.
Unless these cars are lowered beyond Factory RS specs, I have not found this to be an issue although we check this on the alignment rack to be sure.
Since the steering rack cannot be repositioned, ala 911, the only way to correct bump steer is by either using an ERP Bump Steer kit or the EVO uprights. Sometimes we use both to really dial that in.
Since the uprights are cast pieces, its very difficult to change Ackerman on these cars, unlike the 911 which could be changed by re-contouring the steering arms on the struts.
As Chris noted, bump steer troubles occur when these cars are lowered close to racecar specs and the tie rods are no longer horizontal at static ride height. Whether a 993 owner suffers from this depends upon where their ride height is set at and this is a big variable for folks with coilover kits.
Unless these cars are lowered beyond Factory RS specs, I have not found this to be an issue although we check this on the alignment rack to be sure.
Since the steering rack cannot be repositioned, ala 911, the only way to correct bump steer is by either using an ERP Bump Steer kit or the EVO uprights. Sometimes we use both to really dial that in.
Since the uprights are cast pieces, its very difficult to change Ackerman on these cars, unlike the 911 which could be changed by re-contouring the steering arms on the struts.
10-09-2002, 12:10 AM
#19
RL Technical Advisor
[quote]Originally posted by Edward:
<strong>"...change 'Ackerman'"...???
Explain, please!
Edward</strong><hr></blockquote>
My gosh, you do know how to put someone on the spot,....
Ackerman is the name for the difference in steering angles made by the front wheels in a turn. The inside front wheel will make a smaller radius than the outer front wheel, thus aiding the car to turn with less scrubbing.
This stems from the days of horse-drawn wagons,......really!!!!!
Its a suspension setup variable that aids a car in corner entry. With too much Ackerman, the car rotates too much and affects straight line stability. Too little, and you get too much understeer and the car will simply not wish to "point in".
Where feasible, this adjustment is truly left to the pros, as its easy to ruin a car's handling by experimenting around.
You can see some nice diagrams of this (and other principles) in Carroll Smith's Books; Prepare to Win and Tune to Win.
<strong>"...change 'Ackerman'"...???
Explain, please!
Edward</strong><hr></blockquote>
My gosh, you do know how to put someone on the spot,....
Ackerman is the name for the difference in steering angles made by the front wheels in a turn. The inside front wheel will make a smaller radius than the outer front wheel, thus aiding the car to turn with less scrubbing.
This stems from the days of horse-drawn wagons,......really!!!!!
Its a suspension setup variable that aids a car in corner entry. With too much Ackerman, the car rotates too much and affects straight line stability. Too little, and you get too much understeer and the car will simply not wish to "point in".
Where feasible, this adjustment is truly left to the pros, as its easy to ruin a car's handling by experimenting around.
You can see some nice diagrams of this (and other principles) in Carroll Smith's Books; Prepare to Win and Tune to Win.
