Adjusting Ride Height Without Messing Up Corner Balance

[CalebChristy]

Hello,

I recently changed my wheels and tires out to a wider front wheel and tire. I am getting some rubbing now. My fenders are already shot, so I am going to pull them slightly and see if I can get it to stop. My main concern is damaging a tire if it catches on the inside of the fender wrong on a hard corner.

That said, I'm thinking about trying to raise the front a few mm. Loren was nice enough to teach us how to do a garage alignment and when the tools I have, I'm confident I can make any small adjustments after raising the ride height to get it back where it was (mostly camber). What I am most worried about is messing up my corner balance. The math in my head tells me that as long as I raise the front evenly, the weight transfer to the rear will be nominal and proportionate and should keep the corner balance somewhat similar. It wasn't exact to begin with, so I think I can keep it in range.

I've never done anything like this myself and want to learn, BUT I don't want to completely mess with the work that Speed Syndicate did. I would take it back to them but the time commitment to do that is not something I have the freedom to do right now.

Thoughts? Am I way off in my thinking? Just don't want to make it worse.

[CaptainSquirts]

I'm just posting this text that I got from the Evo forums about changing ride height/rake and weight transfer. This is more about an Evo but it should be pretty much the same across the board.



(Pasted Text)
If you run the numbers, changing the rake of the car has effectively zero effect on weight distribution. I was trying to point this out in the other thread that links to here. Here's how the math works:

The Evo IX has a wheelbase of 103.3 inches. Using this, and assuming 1" of rake (i.e. 1" lower at the front suspension than at the rear) we can calculate how much it rotates the car forward:

arctan (1/103.3) = 0.554 degrees

Now assume that the roof is a 100 lb point mass on the centerline of the car at a height of 57 inches. By rotating the car forward 0.554 degrees, we move this point mass forward by:

57 * tan 0.554 = 0.551 inches

We'll simplify this to 1/2". This move changes the weight distribution by:

103.3/2 = 51.65 <--- distance from center to front wheels
.5/51.65 = .00968 <--- fraction of that distance that is 1/2"

Since if the weight were directly over the front wheels (i.e. 100% distance) the front would see a change of +50 lbs and the rear would see a change of -50 lbs, you can calculate the change in weight by multiplying your % change in distance by your weight:

0.00968 * 100 lbs = 0.96 lbs

So by raking your car 1" you've managed to transfer 1 lb of weight from the rear wheels to the front wheels.

So if it doesn't transfer weight front to rear (or the other way), how does it have an effect on the car's handling?

It works by changing the suspension geometry and weight transfer in a turn. With the car raked, the front tires are deeper into their camber curve (what little we have in a McStrut car) and they will add camber more quickly than the rears under compression. It also changes the roll centers and the CG of the front vs. the rear. The higher CG in the rear should result in more roll force. This will increase the amount of weight transfer on the rear tires when the car starts turning. More weight transfer = less grip.

[CaptainSquirts]

As for messing up your corner balance. I had my car corner balanced from Joe and it was pretty much set perfectly. I raised, lowered the fronts and rears so much since then (due to geometry reasons) and car handles better and my times have gotten a lot better. My corner balance is most likely so shot up and way off but I can't really tell a difference.

[CalebChristy]

Great points. Thanks!

[twistedwankel]

I recently changed my wheels and tires out to a wider front wheel and tire. I am getting some rubbing now. My fenders are already shot, so I am going to pull them slightly and see if I can get it to stop. My main concern is damaging a tire if it catches on the inside of the fender wrong on a hard corner.

I put a wider rear wheel/tire with different offset on a RWD car front once when I had a flat on one side the morning of an event. Drove to event. Then I raced on it. Then drove home on it 100 miles. The turn in was awesome even with only one side offset out. The ONLY thing that happened is the screws on the fender acted as a lathe and cut off about 1/8" of rubber off the outside corner edge perfectly (where it's thickest). When I got home I used a jack handle to bend up the inside lip of the fender 1/8" on both sides so I could run the wider rear wheels/tires for the rest of the season:) Once the tires wear down they will never rub again unless they rub on the inside of the wheel house plastic when in grid? Who cares? You said your fenders are crap all ready. Bendy bendy. Or get your tires shaved next time?

[CalebChristy]

Once the tires wear down they will never rub again unless they rub on the inside of the wheel house plastic when in grid? Who cares? You said your fenders are crap all ready. Bendy bendy. Or get your tires shaved next time?

That is pretty much what happened