Cloud9...68

I was poking around under my car the other day, and noticed something that had escaped me before. My 968 is lowered a pretty typical amount for a track car - in the 24.5 - 25" range from the bottoms of the wheel arches to the ground. This has caused my axles to be inclined to a noticeable degree. I didn't measure the angle, but it has to be at least 10 degrees. We all understand the implications of tilted front control arms on things like roll center height and a host of other issues, but I've never seen anybody talk about the effects of inclination of the axles as a result of lowering a car below factory ride height. It isn't like there's anything that could be done about it, short of getting tires with a significantly smaller overall diameter, which is pretty much impossible. Does the inclination of the axles put excessive stress on the CV joints? If so, is there a recommended replacement interval on a lowered track car? I think mine have about 60,000 miles on them. Thanks.

V2Rocket

offroad VW guys say 944 CVs allow 22 degrees of articulation range (11 up or down)

trig'd out that would give you ~9-10" of wheel travel on a 944.

Droops83

I'm sure I have asked you this before, but have you ever measured your ride height using the factory method (the distance of the center of the torsion bar center below the wheel center)? This makes for an accurate apples-to-apples comparison of actual ride heights between different 944/968 cars with different wheels, different body kits, etc. The fender-top method is good for measuring before-and-after changes on the same car, though.

Anyway, as far as axle articulation goes----I don't have an actual spec for you. My short answer would be to not worry about it because short of engineering a 935-style upside-down transaxle, there is not much you can do about it anyway. I cannot recall my 951's exact rear ride height, but the axles are noticeably inclined upward between the trans and wheel hubs (I can measure both next time I get a chance). I will say that in 10+ years of track use (lots in the first 5 years, not so much during the last 3, however), I have gone through 2-3 right inner CV joints (clicking during acceleration/deceleration due to wear). This is likely due to a combination of the axle articulation and the right rear CV joint's proximity to the exhaust piping. I have somewhat mitigated this by periodically removing the axles and re-packing the CV joints (using Swepco 101 moly grease) and flipping them around to even out the wear.

From what I remember, I replaced the individual CV joints a couple of times, and the last time I simply swapped in an entire new GKN axle shaft.

951and944S

You can raise the transmission.

Ultimately, you would never want to raise weight on a road race car but we are not talking about much to get back into a safer cv angle zone.

We only had one fail, in 8 years of racing, outer race cracked and left stranded with no fwd drive but it was actually coupled with rear 1/4 panel damage and a spin (hit in LR on start) so this could have contributed to the failure.

That said, this is 2.5 8V car with 140 rwhp.

On an estimated 400 rwhp car I built once, I modified the crossmember and raised the transmission 1 inch.
I had to heat the plastic fuel tank with a heat gun and use a piece of metal, shaped such to mimic my clearance interference portion of the transmission/linkage and press into the softened tank to make a depression.

T

Cloud9...68

Chris,

Yes, I've measured my car's ride height using the workshop method, but I have the measurements written down in a notebook at home. I'll post them tonight, and would be curious as to the ride heights, using this measurement method, other people are running. My car is definitely significantly lower than stock, but I can't remember exactly how much. I'm due for re-packing the CV joints, and flipping them arouind sounds like a good idea.

T,

Yes, raising the transaxle would certainly mitigate the axle tilt, but I agree that this is not something I would want to do on a track car. It sounds like a few degrees of axle inclination is nothing to worry about, and the benefit from lowering of the center of gravity outweighs any potential negative impact of the tilted axles. It was just not something I had paid attention to before, so I was curious as to peoples' thoughts on the subject. It certainly isn't unique to our cars, and there isn't much that can be done about it anyway.

Cloud9...68

The distance from my torsion bar center to my wheel center averages 78 mm, or just a shade over 3 inches. For reference, at the front, the distance between the bottom of the castor block bolt heads and the wheel center averages 189 mm, or about 7.4 inches. How does this compare to your car?

Droops83

I can't remember the exact values for my car (and it's at the body shop right now so I don't have easy access at the moment), but I remember it being just under 2" lower than 968CS ride height front and rear (which is -147MM in the front, -37MM in the rear). So, mine is in the same ballpark as yours.

I can't give you a definitive spec for axle articulation, but with stiffer, track-oriented spring rates and relatively smooth race tracks, I doubt your car would experience the amount of suspension travel (in compression) it would take to cause a CV joint to come apart. Sure, the inner CV joints will probably wear faster, but so does everything else with track use!

rlm328

I am with T, I do not remember what my ride height is but it is pretty low. I have only seen a couple more that are as low. I had trouble with CV bolts backing out which led to the cages breaking. I went to stage 8 bolts and have not had a problem since. You will get varying opinions on the stage 8 fix, but it worked for me.

Cloud9...68

Thanks, Chris. Actually, there's quite a bit about our cars that's similar, right down to the color!