boxer-11

I've been looking at this as well. It was suggested to me, just as Matt mentioned above, that the variable ratio might be varied with speed.

If that turns out not be the case though, then there would be a way to figure this out without the need for turn plates or a protractor.

If you go into the "car" pages in the PCM, there's an item in there which shows you the steered wheel angle. When you turn the steering wheel the value displayed moves with it in a ratio that shows small deflection angles, on the order of 5-7 degrees, for a 90 degree turn of the steering wheel.

I haven't done the mapping because I presumed that the ratio varied with speed. But it wouldn't actually take long to do. (BTW: this data is in the PCM in my 991.1 TT and in the GT4 I have so it may be applicable to all PCM 3.X and newer cars). I'm traveling for much of the next two weeks but if someone hasn't tried this by the time I get back I can run the experiment...I have a digital spirit level somewhere about the place at home.

dbbarron

I don't seem to have that capability with PCM 2.x

boxer-11

Hmm, bummer. I've been meaning to do the experiment anyway so when I get a chance I'll do it and try and remember to post findings here. I should be able to measure ratios at start and end of travel from center with the car stationary. That might show if the ratio varies or not with a constant speed (of zero...).

I suppose the other complication for correlating to your car is that I think mine have the electric steering whereas yours has the hydraulic assist.

dbbarron

It would be interesting to see the transfer function of speed v. steering ratio (it is likely a function of wheel position and speed). From my observed data at track speed, the ratio seems the same at different speeds (based on calculated wheel angle v. actual wheel angle at different speeds). I suspect the ratio changes at low speed, but not (so much) at higher, track, speeds; where the transfer function is only dependant on wheel position.

ProCoach

^^THIS^^

Especially for our purposes.

Matt Romanowski

I had copied db on my email, but I'm checking with some friends at PDS Barber. I hope to have an answer soon.