Setup - rake question.
 

Hey everyone,
Just curious if any track guys setup their cars differently than street cars in terms of rake. For street cars I've always generally set them up with 1 degree of rake towards the front. I'm just working on my setup at the moment, and palying with ride heights, and was thinking about changing it a bit. So I thought I'd ask. Any advice is appreciated.

Thanks

rake = camber?

Rake == amount the car "leans" forward; differential ride height front to rear (as measured by the floorpan of the car or the bottom of the rocker panels).

--DD

About 1 for street, 1.5 for race.

yeah... i'm running 0.8 degrees at the moment. I'm trying to decide how badly I want to get it up to 1 degree.

thanks :)

not really sure why you are worried about rake from a setup point of view... that is more asthetic than anything. The correct way to set the car is to scale it, then setup the corner heights for the best f/r distribution and even out the cross weights. So, for a simple case, say you want to shift more % of weight forward, you jack the car up (increase the rake), but setting the car up based on rake is a bit cart before the horse.

Set the weights and the rake will be what it is going to be. Most of us don't have scales, so ask around some of your local performance alignment shops and see if they do this. Here in SoCal, I just took my car to Johnson Alignment in Torrance last Thursday and had the car scaled (I have coil-overs at all corners, so more adjustable than stock) and aligned. All said and done, the cross weights were within 6 lbs and I don't have much rake at all (though I wish I did for looks...)

Careful!

Do not fall into the trap of thinking that changing (raising) the ride height uniformly at the rear of the car (or lowering in the front) will shift weight bias forward. In fact, angle of rake and front-to-rear weight ratio have almost 0 influence upon each other.

RPE:
Could you elaborate a bit more on your statement? It seems intuitive that angle of rake and F-R bias are somewhat related, after all, corner balance is accomplished by raising or lowering corners.
Thanks!
Pat

Rake really has nothing to do with weight distribution. The change is so slight as to be nearly immeasurable.

It's most noticeable effects are aerodynamic, and suspension geometric.

More rake will move the center of pressure forwards, and will reduce caster slightly, and will have a slight effect on caster change, and anti-dive geometries. But like I said, very slight.

Aero is the most affected.

Allow me to preface the following remarks by saying that I could not carry Tyson's bags WRT this subject. But I do find these types of threads very educational.

I have about 1 degree of rake in my SC, measured at the door sills. When we did the corner balance, rake was never a consideration. It is what it is. I would guess rake is simply an effect, with the ride height and corner weighting being the cause. I would guess that most everyone's car will end up in the 1 degree with a plus/minus 1 additional degree.

In theory, if one lowers the car using the adjuster bolts 1/2 inch in front, that only amounts to an additional 0.24 degree rake. Yet, doesn't a 1/2 inch lowering have a relatively large affect on the weighting?

Actually it will have very little measureable effect.

Now, if you only lowered one corner 1/2", now that would have a huge effect.

The center of gravity is so low on a 911, that a 1 degree increase in rake will transfer very little weight forward.


I have to explain this kind of stuff to people all the time. A lot of people think that corner balancing has something to with weight distribution. You really can't change weight distribution with corner balance. For example, can you imagine trying to get a 50/50 left/right weight distribution with-driver just from adjusting the ride height? the left side of the car would have to sit about 2 feet higher than the right side.

Hi, Pat,

Since the subject of the thread is RAKE, let's talk about it first. To reiterate Tyson's knowlegable comments, there are two noticable performance advantages to 1 or 2 degrees of rake on most 911es:
(1) The steering geometry has better track feel, and
(2) Aerodynamic lift is somewhat reduced due to less air entering under the front of the car, AND penetration is enhanced (better wedge shape).

Now to corner weights: In our "Prep Your 911" seminars, for those still puzzling about weight bias and weight wedge, we try to leave them with this axiom:

"Without physically relocating any items in the car itself, the rear will always weigh the same, the front will always weigh the same, the left side will always weigh the same, and (obviously) the right side will always weigh the same."

From the above you can see that if one wants to reduce weight on the RR, one MUST add some weight to the RF AND to the LR. How do we do that? Easy -- magic!

Ed LoPresti

lol, how a simple question can get so complicated.... but yes, exactly... the car has already been cornerwieghted as best as it can... with the current adjustment possible, and weight distribution throughout the car. Without a gutted race car where you pick where to put weight it'll never be perfect.

I was only asking because of the aerodynamic gains. As it stands, I ended up with 0.9 and it seems to feel pretty good, I don't think I'm going to worry about it again anytime soon.

Hmm i just ran across this hate to bring it back up, but tilting the spindles forward will require that the caster is reset or you may find the car akward to drive, (more like darty) if the lower control arms have to much angle the roll center can go crazy under dive causing excessive camber gain. the place ment of the rear roll center will help decide forward bite ie higher roll center loosens the car up on corner entry, running to low of rear roll center can cause the car to be tight in the center of the corner, giving the car a rake will also take angle out of the rear control arms also cause the car to have less bite considering that a 911 squats under axcelleration, Kevin

ps i have no idea why i posted

Rake has an effect on vertical forces at the front of a 911. Here is some exaggerated windtunel data the shows what 5deg of rake does on the top and bottom surfaces of a 911

the x -axis is the longitudinal position(frnt is 0), Cp is aero pressure coefficient, red is the readings across the top of the car black is underneath, you can see the strongly enhanced negative pressure(suction) at the very front when 5 deg of rake are added. No spoilers are installed
http://forums.pelicanparts.com/uploa...1133382557.jpg

i think ill take the right caster and suspension geometry over rake, Kevin

while I don't agree about the suspension geometry... all that can be irrelevant as long as you use the correct suspension and setup, I do agree with finding ways around that much rake... who would ever want to run 5 degrees of rake? That's really excessive. If your choice was 5 degrees of rake or a front spoiler or splitter, I think anyone would go with the spoiler or spiltters.

what do you think the correct geometry means???????????

Kevin,
I just meant that it's possible to do almost anything and maintain suspension geometry, travel, etc... as long as you plan for it, and set up the suspension correctly. I just wouldn't arbitrarily say you can't run a lot of rake because it will mess with the suspension geometry.