MarinS4

Judging by the shorter length steering arm on the RS/EVO uprights I would expect the steering ratio to be faster. Can anyone who has done the conversion comment?

Steve Weiner-Rennsport Systems

The steering ratio is unchanged: thats controlled by the rack.

MarinS4

I understand the rack determines the steering ratio but the steering arm that is on the stock upright is longer. Using the theory of levers a long lever requires less force but must travel a further distance to accomplish the same work as a shorter lever. Based on that theory I would expect the steering to be a little harder and further steering angle per XX distance of steering wheel movement with the RS/EVO uprights over stock.

Stealth 993

They just change the angle of the tie rod to upright for better steering response & less bump steer.

You also get a little more suspension travel for the same ride height.

MarinS4

I know the tie rod attaches at a different angle. To me it still looks like the RS/EVO has a shorter distance to the fulcrum point of the lower ball joint even after taking that into account.

Bill Verburg

The long arm moves the end of the steering arm down too far when the car is lowered, the short arm moves the end back up where it belongs to reduce bump steer.

The RS actually has a slower steering ratio than a normal, but as Steve pointed out, this is from the rack.

cabrio993

It is just an optical illusion due to the angle of the lower arm on the standard upright vs the EVO upright.

As you can see in the picture, the distance between the center of the holes on each one of the uprights is exactly the same. One curves left to right, the other right to left, to accommodate for lower arm while retaining the same distance to the pivot point. This causes the optical illusion that you are probably seeing.

MarinS4

It makes sense now. Thanks Cabrio993

Akerlie

Sorry but i am still not convinced, if you would draw a straight line down from the strut mount ? (the mounts to the right in the picture) the std upright still looks like it has a longer arm.

But i could be wrong . . .

cabrio993

Which of these 3 lines is longer than the others?

sonny1

Why the RS have a slower ratio rack???

jdistefa

nice rack

Bill Verburg

You are right in a sense, look at the following to get a sense of what happens during supension travel

for the purpose of this discussion Vorspur or toe variation related to bump is the curve to look at. Notice that the curve is not linear and goes more horizontal as the suspension is compressed(or the car is lowered). This means that the steering tie rod is pulling more(faster steering is an apt description).

The ideal curve will be linear and vertical(or at least as vertical as possible)

at stock ride height the components are as close to being aligned as is possible, but as the car is lowered the steering arm is pulled further from the tack arm causing steer to increase

look at the following to see why, the steering arm and A arm have different pivots and lengths, so they move in different arcs





once the suspension in extended or compressed the arcs go out of alignment, the further out the more steering action(aka bump steer and roll steer)

Bill Verburg

I forgot to add, the RS wheel carriers restore the geometry to be as good as it can be when the car is lowered to RS or lower height.

Bill Verburg

here are the correct turns lock to lock(this is all documented in factory lit.)
Both 964 and 993 have power assisted steering, however 964RSA and RS manual racks are available(more turns = slower
911 is ~3 turns lock to lock, non assisted
964 is ~2.81 turns lock to lock, assisted
993 & 993GT2EVO is ~2.47 turns lock to lock assisted
993RS 2.73 assisted
964 manual ~2.6

Actual steering ratios, again factory specs, higher# = slower
964 18.48 slowest
993RS 18.25
993 16.48 fastest