Rear steer revisted

M

msogren

New member
About 10 or 12 months ago, I brought up the concept of using soft rear bushings to allow the rear to toe out with side load. I did this to my Son's solo car. The car responded very well. This transformed this car into the most neutral VW , that is not running a welded diff , that I have ever driven, I tried to measure the side to side travel on the alignment board , but could not get a very accurate duplication of the dynamic load.
The axle bushings were installed backwards, with very little preload. The tire rubs on the fenders more often and required more clearance. This , itself shows a lot more rear steer. The car is very smooth and does not have a sharp edge to spin, as a very high spring rate does. This is now about the fastest car in a pure slolom and still carves 3rd gear sweepers killer. We have about 200 runs now on this car and I am very happy withthe results. The bushings are a PIA t to do, but I will do the same to the old ITB car.
Now I have to trade the Quaife for a locker and install the tall 2nd gear, raise the rev limit, use the 13 intires, etc.
FWIW,
Mike Ogren
 
Back when I was soloing A2 cars in the early 90's, I heard stories of people who set their rear wheel bearing tightness insanely loose to accomplish the same thing. It was tough on the hardware, but the parts were cheap for the given performance advantage.
 
I'm guessing that this is a front wheel drive thing, right? My 2nd gen RX-7 comes from the factory with a rear steer mechanism. My understanding is that the conventional wisdom is to disable it to make the car more predictable and less tail-happy.
 
We use to run atleast 1/2 " total toe out on the rear of the Mk III ITA and sometimes more on the SSB VR6, it had plenty of rear steer when that inside rear tire lifted up :D
 
This car acts like it has 1in of toe out. We used 1 out in until we changed the bushings. Now i am running about 2mm out total, with 1* camber. The car rolls cleaner and the tires last better. Now we get about 50 runs , if the brake bias is set right, and we stop in the straight....
MM
 
<snip>
using soft rear bushings to allow the rear to toe out with side load.
<snip>
The car is very smooth and does not have a sharp edge to spin, as a very high spring rate does. This is now about the fastest car in a pure slolom and still carves 3rd gear sweepers killer. We have about 200 runs now on this car and I am very happy withthe results. The bushings are a PIA t to do, but I will do the same to the old ITB car.
Now I have to trade the Quaife for a locker and install the tall 2nd gear, raise the rev limit, use the 13 intires, etc.
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Interesting, and it sounds like you accomplished what you set out to do. Keep in mind that a Solo course has a much higher percentage of transitions, while a road course generally has some important steady-state sweepers. The only known way to be fast through those sweepers is to make the rear end share as much of the load as possible. An approach that does not use a relatively high outer rear spring rate, whether with stiff springs and/or swaybars, can never reach that state IMHO.
 
Valid point Eric. We "solo" with a Corvette Club that likes to go fast. We are well up in third gear for most of the run, 65-85mph, while the few slaloms are on the chip in 2nd. This aint no Miata course at 45mph.
The best VW steady state seems to be with the rear tire out about 6in past the front tire. This adds load to the inside front and reduces the outer tire load. A as you said, any way that this occurs is pretty fast, whether it is straight springs balance, sway bars or rear steer, the fastest car will have the least dynamic outer front weight. The softest spring rate/ wheel rate, at which this happens, returns the easiest to drive car, with the softest breakaway, and probably better in the wet. I love racing in the rain.
I will redo the IT car next week or two . it was a rental car and has a safe push. The bushings are instock now tho.
The added benafit is that I can align it with very little scrub, and about .5 rear camber, with e 2mm toe out.
Mike Ogren
 
any way that this occurs is pretty fast, whether it is straight springs balance, sway bars or rear steer, the fastest car will have the least dynamic outer front weight. The softest spring rate/ wheel rate, at which this happens, returns the easiest to drive car
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So you're saying that the rear steer works out because it actually causes more load transfer to the rear. Excellent point, and apparently one that I hadn't fully considered. :023: How did you come up with the 6" figure? I guess the next question is whether that rear steer (such as enough to offset the rear by 6") can maintain as much load transfer as a higher spring rate. Don't know the correct formula, but I would guess that the 6" only affects the load transfer by the extra amount of spring compression caused by the static roll arc from the CG. In the extreme, consider a car at 90 degrees to the direction of travel -- odd, but maybe it could be fast (neglecting air resistance) since it effectively widens the track of the car (swapping track with wheelbase for that extreme example). I look forward to hearing your on-track results. Good luck :)
 
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