The toe-in is to take care of the aft movement of the front wheels due to rolling resistance and air resistance while driving. You also need a little to compensate for any negative camber.

 

I posted up my alignment calculator and DIY video on the main DIY Alignment Thread.

https://rennlist.com/forums/6390423-post143.html

 

Does anyone know how much toe change is one full turn of a tie rod?

Dan
'91 928GT S/C 475hp/460lb.ft

 

Ok, I will answer my own question now that I've tried it One full turn (360 degrees) of the tie rod is approximately 2.1 degrees of toe. After changing my ride height, my car was 4.47 degrees toed in

Oh, and I was kinda confused as to why sin(x) from Jim's post was being used, then realized that the hypotenuse and adjacent lines are so close to each other that the error would be negligible. Still, to avoid confusion you should really be using tan(x) which will give you a 100% accurate value since you have the adjacent side and want to figure out the opposite using the toe angle (inv tan(x) of course to go the other way). I can't believe I still remembered SO/H-CA/H-TO/A from school

Dan
'91 928GT S/C 475hp/460lb.ft

 

Unfortunately I had already "closed shop" when you asked and had never thought to calculate it. But that's good information to know.

 

Dan, thanks for answering that question, that's good info!

I used sin(x) since the radius (i.e. the tire diameter) was constant in this case. But you are correct that alignment calculations in general should be tangents, and also that for small angles it doesn't matter.

A toe error of 4 degrees? Holy tramline! Which way did you go with ride height?

 

Yeah, but funny there was no tramlining?? I think tramlining is caused by toe-out. Too much toe-in just burns the outside of the tires. I raised my ride height a bunch, then totally phased out on the alignment. 10k miles later the outsides of my fronts were wearing down fast. With that much toe-in, I would have expected this to happen much earlier.

Dan
'91 928GT S/C 475hp/460lb.ft