Yargk

My car was corner balanced a while ago and I finally got around to double checking the ride height using the established measuring points.






My front was at 111 mm and the rear was 127 mm. I was wondering whether there was any rake so I measured the height of the lowest part of the metal rocker panels (shown below) just behind the front wheels and just ahead of the rear wheels. I found that the front of the rocker was 8 mm lower than the rear of the rocker. The official spec height is 109/130, which would equate to even more rake (because my front is 2 mm higher than spec and my rear is 3 mm lower than spec). The rake at the rocker should be closer to 13 mm with Porsche specs, which is not insignificant (about 0.5 inches). Is anyone else finding this? Are my measurements off?





(Note: I'm interpreting the front ride height to be measured to the blue highlighted area in the first image of this post. On the car there is a rubber or plastic circular piece in the middle of the blue highlighted area, I didn't measure to this circle which protrudes a couple mm lower than the blue part. Did others do the same?)

okie981

You raise a good question about the front measuring point. Is it the blue colored area shown in the graphic or the round area in the center of the blue colored area? I didn't watch the Porsche tech that measured my car, but I know they had a hard copy sheet showing the exact graphic you have in your post before they went under the rack to measure the car. They also had hard copy of the pages of the WSM that show the ride height spec and tolerances, printed out and gave me a copy. My assumption was they measured the round area in the center of the blue shaded area, but I don't know that for sure. I could call or text the tech that did the measurement and find out for sure if no one on here knows the definitive answer.

Yargk

Cool. Perhaps I'll ask Gunter at Fremont Porsche too. My feeling is that the German interpretation would be that since the arrow doesn't point to the circle, we should use where it points, for what that's worth. The manual that you posted just said "measuring point on crossmember/bulkhead -arrows-" But I admit the circle does seem to be the obvious thing if one was to guess. I didn't measure it, but I think the difference is probably about 2-3 mm between metal and cirlce. So if that circle was the measuring point, the car would still have a slant, with stock specs, as defined by a difference in the F/R rocker heights, but it would be less, 10 mm instead of 13 mm.

If you know your height specs because you had it adjusted, could you measure your ride height at the rockers? (I measured to the bottom of the metal part to be consistent, there is plastic trim too)

okie981

I sold the GT4 to a RL member, ducsfly. He doesn't post much. If I had it still I would gladly measure it. He picked it up on 3 March and drove it back from DFW to North Carolina.

Looking at the graphic and thinking about it some more, I would think the intended measuring point is the blue colored area and the arrow is pointing to this area. But having said that, it is for sure an ambiguous location call-out. I would bet more than one Porsche technician has wondered where to measure, and called Atlanta or Germany to get an answer.

Yargk

Ah, glad the sale went well. That's cool that he road tripped it back.

Mech33

I thought the spec was 106 mm front and 133 mm rear?

I had the same confusion on the front measurement point, but the rubber plug is definitely not a height measurement reference point. I measured to the smooth flat blue area. But to add insult to injury, the part of the blue area most towards the front of the car is a few mm lower than the rear part...

I've been having a hell of a time getting my car heights dialed in. I'm going to let a professional monkey with it.

Yargk

Glad you asked about 106/133, that was just a guess (although a close one) by another RL member based on the Cayman GTS height (and subtracting some number mentioned in the GT4 literature). It's really 109/130 for the GT4, as in the factory manual pages posted by okie here: https://rennlist.com/forums/gt4/9741...t-for-gt4.html

Interesting about the blue area not being level, good luck with the setup.

For anyone who wants to measure their rocker heights, I measured to here:
(yes, I'm about to wash my car)

Mech33

Awesome, thanks!!

MVEED3

Short answer:
Official = No
Corner Balanced = Yes

Here's my data for analysis:



Corner balanced ride heights measured from the fenders to lowest point of wheel lip (no driver weight):

FR=24 12/16"
FL=24 13/16"
RL=25 1/4"
RR=25 5/16"

Yargk

Thanks for the info.

My Fender heights (to the ground) were
FR=27 4/16"
FL=27 5/16"
RL=27 11/16"
RR=27 10/16"

I hesitated to use fender heights to determine rake because sometimes front fenders are taller wrt to the body of the car (early 911s). This is why I thought measurements at the rocker would be better to determine rake. However, my F/R fender height difference is about 6/16 and my rake at the rocker is 8 mm = 5/16 inch, so fenders do seem to be consistent with rockers for rake on the GT4. Your F/R fender height difference is 8/16, but you don't include the tire, so I'd guess your "rocker rake" would be also be about 5/16, but maybe as high as 8/16. I'm just thinking that if the car was completely level, no rake, then perhaps the rocker height F/R would be the same, not off by 5/16 or more.

ExMB

What a difference in height between both cars when accounting for OEM wheel and tire sizing. My guesstimate using a 1/4" weight compression on the tire roundness shows about 5/8" F and about 3/4" R difference if the same location on the fender was used.

stout

To the OP: Yes, it does. (At least, depending on how you define "significant" and so long as it's well short of Big Daddy Don Garlits style.)

A setup I am trying also specifies more or less maxing out the tolerances toward low front and high rear for reasons of roll center and to cancel understeer. You can check it out here:
https://rennlist.com/forums/gt4/9824...r-the-gt4.html

I'm liking it so far, but YMMV!

Yargk

Thanks for the info, your setup looks like a good one too! (And also well short of Big Daddy Don Garlits)