TheOtherEric

Hoping you guys can double-check my ride height settings. I set my ride height, using the correct points, at RS +5mm. I measured fender-to-ground to be: 25.4" front, 24.7" rear. Two questions:

1. I have a quite a bit more wheel gap in front than in the rear. Normal?

2. I keep reading here that the nose is typically angled down 1 degree (rake angle). Yet if you look at my fender heights, it looks significantly nose up. Plus, I put a level on the door sill and the car is either flat or slightly nose up. How is "rake" measured??

NoSubEDU

FWIW, I was told by my shop that my car should have positive rake. Sounds funny, but I don't argue. My C2S performs exceptionally well on track.

bart1

If you set the suspension height using the factory points, you do get more fender gap and a higher fender height at the front than at the rear. And I think relative to the US settings, the ROW/RS ones are dropped more on the rear than the front.

Bill Verburg

I suspect you saw this over on Pelican
993 measuring points

and specs


You notice that there is a +/- ?

you want the front lower than the back for aero benefits, you want to keep as much air from going under the car as is possible.

Nose up is bad, nose down is good, high is bad low is good

1) whats normal? Its not good though. Drop the front so that the fender height is about the same or maybe a tad lower than the rear fender

2) You can measure rake on the door sil as yuou have done

TheOtherEric

Are you saying that people intentionally deviate from the target specs (but within the tolerance range) in order to get 1 degree of downward rake? If so, I have to wonder who started that, since Porsche made no such recommendation AFAIK.

p.s. No, I didn't see that on Pelican, but I did see it in my workshop manuals.

bart1

I have mine at ROW Sport -10 (or maybe 12) by the above sheets. They are also in Streather's book. I think the nose is down if set this way, but the fender gap in front is nore. Maybe Bill knows something I don't, though.

Bill Verburg

I don't have a clue as to intentions, but there are all sorts of strange setups.

Go to a track and see what folks that know a thing or two are doing.

1 degree of rake is just a a quideline, you do want some rake and you don't want a huge difference between front and rear heights.

I suspect though don't know that as w/ the 911 a front fender height may be a tad more than a rear fender height and still have some forward rake.

I have mine set up so that the front fender height is a tad lower than the rear, it probably has more than 1* of rake but that's ok too. I set my front up to have just barely enough height to clear the trailer wheel stops w/ the track tires on the car(the street tires are slightly taller than the track tires)

matt777

I never got the impression that rake was a goal or spec when setting ride height. In fact, the rake varies depending on which ride height spec you go with as per the chart below. The alignment shop ends up fiddling with the final ride height anyway when they do the 4 corner balancing.

Bill Verburg

It's not a part of alignment per se, but it is a part of setting the car up correctly. Just like shock settings, bar setttings, tire pressures etc aren't part of an alignment, just something else that is included in car set up

Van1

FWIW, I set my car up for RoW sport height and ended up with 145 front and 130 rear if I remember correctly. Front fender gap is slightly more than the rear. But one thing I learned in doing my suspension is to never rely on fender measurements. Overall, rockers look level with the ground. But more importantly, when I took it in to get it corner balanced I already had it dialed in with in a few pounds per corner. The shop didn't need to do anything.

CWay27

Isn't the rake there (when standing still) just so when the car is under load (acceleration), it becomes even (rake disappear). If the car is set up evenly then the rear would be lower when under load and thus, screwing up the aerodynamics .

Bill Verburg

Under acceleration the car will squat, under deceleration the car will dive, the suspension has anti -dive and anti squat built into it's geometry.

The front needs to be low to keep air from going under the car, the lower the front the less lift and drag and the better Cd.

The rear spoiler works better the higher it is

bart1

I tried to google some info on 993 under car aero, which I didn't find, but this is kinda interesting:

http://autospeed.com/cms/title_Aero-...5/article.html

Anybody have documentation on the aero effects of the 993s fairly smooth underbody? With ot without engine tray? You know, it would be very easy to make a diffuser for the rear of these cars to bolt in where the engine tray is, but I have never seen one.

Bill Verburg

The main docs i go by are the factory race manuals.

The street cars measured the factory way, as speced in post 4 when f/r are at absolute min height have 17mm higher front, that does not mean that the chassis is not raked

The factory Evo manuals for 993 spec the front from 3mm higher to 12mm lower depending on on the tires used.

again the ground clearance specs being higher in front or even the fender height specs being higher in front don't necessarily mean that the car isn't raked. On a 911 a .5" higher front fender certainly is raked.

maybe I'll borrow a guage and start collecting rake vs fender height data.

chris walrod

I think the front fender arch heights are higher than that of the rear for wheel turning clearances, which is a tough way to determine RH and rake for that matter.