Do 911's like rake?

[euro911sc]

For a 80% track car:

Scruggs says 3/4" rake as measured from front rocker to rear rocker. My friend says more is better, but could not quantify it

So higher rake will move weight forward I think, but I really doubt it would have any noticeable change... but, what about under braking? More or less is desired? will more rake increase or decrease dive? Increase or decrease stability?

Change in squat under accel? Not that my stock SC engine can make the car squat, but for the sake of education discuss, please.

Whats more important to pay attention to: dive or squat?

Thanks!!

-Michael

[Flieger]

I think the aerodynamic effects will swamp any fore/aft mass center movement.

[euro911sc]

Originally Posted by Flieger

I think the aerodynamic effects will swamp any fore/aft mass center movement.

Agreed. But, why have any rake at all?

-m

[Flieger]

Nose high makes for more lift, more drag, and less grip, especially in front. It would be even more like shooting an arrow backwards.

Zero would be theoretically fine, but it is too sensitive to pitch changes with suspension movement- it would cause handling balance to change between over and understeer, I reckon.

Nose down adds downforce everywhere and the drag penalty is less because it is being used for downforce. It keeps air from getting under the car (until the hot air coming out from the engine) so there is less chance of flipping over GT-1 or Mercedes CLK style.

[J Richard]

Yup, they like a nose down attitude, it really helps in high speed sweepers as well as straight line stability...

[euro911sc]

Great! Sounds good! But how much? Stated 3/4" over the rocker distance?

[RaceProEngineer]

Michael,

While attention to detail means a lot in making the car go quickly. these things are no where near as sensitive to ride height as, say, a formula car or sports racer. Be aware, though, the lower the car in general, the more critical the degree of rake becomes.

We used different reference points than you for ride height, but in thinking about the rocker panels, I believe anything between your three-quarters of an inch, up to one-and-one-half inches, will work fine.

Ed LoPresti

[Flieger]

Rake will also add a small amount of low speed tendancy toward oversteer. Lowering the front lowers the roll center, raising the rear raises its roll center. This is a geometric effect, not just based on height. Raising the rear also raises the center of mass a bit but it being rearward combined with the roll center effects means there will be a tiny bit more weight transfer and that the rear will be taking a larger percentage of that.

[ERN911]

Michael, don't know if you ever noticed my car is raked I never measured it front to back but everybody that has driven it, comments on how neutral it feels with a slight feel for over steer, what I like the best about is on acceleration you don't really get the squatting in the rear. and to me the car feels much more level, as others said the front end is not getting much air under the vehicle either, attached pic at AX probably doing 55-60mph the car is pretty level.

[jpachard]

Mike, as Ed said, .75-1.5 is good. Judging by your weight post though, it looks like you need to increase your rear spring rate, then again, I like a car that's a little loose so your preferences might be different.

James