How do I measure rake without fender reference?

cstreit · cstreit's Garage

Gang,

I see many of the "rake" recommendations reference the fender lips.

What if your fenders are massaged and are not stock?

From my estimatations (and Souks explanations) it would appear that the rear torsion bar center should be about 11cm higher than the front torsion bar center.

Manual says:

Front ride height is (front hub center) - 108mm = Front Torsion bar center
Rear ride height is (rear hub center) + 12mm = Rear Torsion bar center

Substituting my tire radius I get:
FRONT: 325mm - 108mm = 217mm and
REAR: 325mm + 12mm = 337mm

Rake then is 337mm - 217mm = 110mm

Meaning that whatever I set the front ride height at, the rear torsion bar tube center should be 11cm higher.

I'm asking because i have massaged fenders, raised spindles, etc.. so the fender recommendations are meaningless to my car. I know that I want about a 3-5 degree angle on the front a-arms, so I can now set the rear ride height relative to that.

Make sense?

jpachard · 04-05-2004, 06:18 PM

Chris, Check Smart Racing Products website. Somewhere I remember seeing an alternate location for ride height measurements. Maybe in their setup sheets?

Cheers, James

Jim Richards · 04-05-2004, 06:26 PM

Can you measure rake using a level on the door sills, a ruler, and a little trig?

cstreit · cstreit's Garage

Jim,

I don't know what the proper angle is, or if the door sills are level relative to the body... I'm starting at ground zero with a custom suspension, so I needed a baseline first...

I guess with the differential height and the wheelbase I could calculate the angle I'll end up with, question is, what is the desired rake angle

Jim Richards · 04-06-2004, 03:30 AM

Chris, my memory may be faulty, but for a street car I thought it was 1° down in front. I think the door sills may be a good reference.

Other opinions?

Jim Richards · 04-06-2004, 03:45 AM

more on rake...

From a post in October, 2003, CHILI described his alignment settings and his rake was 1.4° down in front.

This is from "Home Alignment of Porsche 911 for Competition or Street":
http://www.dorkiphus.com/porsche/modules.php?set_albumName=album04&id=Porsche_Home_Alignment_3&op=modload&name=gallery&file=index&include=view_photo.php

This thread provides a lot of discussion on rake:
911 rake front/rear

cstreit · cstreit's Garage

Thanks guys.

KTL · 04-06-2004, 07:26 AM

I was going to say doorsills too. Also, the underside of the unibody is pretty flat. Just a bit hard to see.

Pete's SmartCamber gauge has that removable digital inclinometer if you want to borrow it. Mark and I are done with that stuff and i'm sure Pete would like to see others get some use out of it. Also, the SmartStrings are TOP quality. Really nice stuff.

MotoSook · 04-06-2004, 12:01 PM

I like the center of the t-bar method most...it's what the factory recommends and eliminates some of the potential errors..

Anyway....how did it go? Let's see tha new stance......

Bill Verburg · Bill Verburg's Garage

Get a Smart Level

palle7688 · 04-06-2004, 12:57 PM

Chris,

Check this thread
Front tire ground-to-center, how are my calculations?
Front tire ground-to-center, how are my calculations?

Acc. to Kenneth Ball autobook '74-'77 for a non lowered car.
rear: center of torsion bar should be 12+-5 mm above center of wheel.
front: center of torsion bar should be 108+-5 mm for cars up to '74 and 113+-5 mm for cars '74 and on, below center of wheel.

Your car is non standard so I'm not sure if you can use this.

stlrj · 06:05 PM

Why are there no official rake specs in the Porsche Spec Book?

Has anyone ever seen anything from Porsche that refers to the proper amount of rake? Where did 1 degree of rake come from? Why not 1 1/2 or 1 3/4 degree? Or would 3/4 degree be optimum?

What would happen if you ended up with no rake at all? Then you might end up having a car that looked a lot like a 964, 993 or even a 996.

Joe

MotoSook · 04-06-2004, 07:02 PM

You can calculate the rake easy enough using the factory recommended settings for front and rear height... There is a good margin of error, but going much beyond that would change the front to rear weight distribution beyond the norm... I suppose one could experiment to one's heart's content, but that would take time away from all the fun driving...and zero rake and less would make the rear very "biased!"

Too much positive rake (toward the front...is there an established terminology?) would make it look like a muscle car with 1980's rake...we don't want that...no we don't do we?

Pull your trig book out of the basement and have fun...