ride height

[911pcars]

Here's a corner balance worksheet and a couple of links to automate the calcs.

http://members.rennlist.org/911pcars/

Click on "corner balance worksheet".

Since we're talking about an asymetrical street car and not a race car (driver not sitting in the middle, every component weight not equally balanced on center, etc.), the equal diagonal scenario (LF = RR and RF = LR) may not work out even though the chassis is balanced.

Basically, here's the simple math. If you can achieve the same Front to Rear weight proportion on both sides (LF/LR = RF/RR) at the desired ride height settings, then you're doing fine. You are not aiming for exact numbers, but close to the same proportion.

Sherwood

[GreenT]

New poster here - I can add a good picture of this process since I just went through it a month ago. And I can recommend someone good in your area. I changed over my 70T to SC generation suspension and brakes and needed a complete setup after that. Roger Kraus is the Goodyear racing tire distributor in our area and his son Brandon has set up a lot of 911's for street and track and does a good job. They're also experts with the hard-to-mount early style Fuchs. You get your wheels back unscratched, with taped weights, new knurled metal valve stem caps and the the point of your hub crest lined up with the valve stem on each wheel. Can't do better than that. They give you a nice booklet showing everything they've done and a nice primer on suspension terms and setup. I'll attach the before and after for my car to show what's involved.

BTW - I'm also trying some new tires I got at the same time. As you know there aren't a lot of good choices in 205/60x15 to go on six inch wheels. I swapped out Michelin Pilots for a new Goodrich tire, a G-force model that's only been out a few months. It's a directional tire with the latest compound and sidewall improvements, and most of the line are large sizes for new cars, but they also build this one down to 'our' level. Good looking tire too. I love 'em so far.

[scargo70]

This post and the great replies are worth the cost of membership, thanks guys.

[Chuck Miller]

GREAT POST JOHN !!!!!

... And welcome aboard

Cheers,

[scargo70]

How exactly do they add or subtract weight from a particular corner of the car?
And GreenT, have you noticed a difference in your car's handling?
Also it seems to me that you would want to corner balance with the spare tire in place and a full tank of gas.

[ttweed]

How exactly do they add or subtract weight from a particular corner of the car?

By changing the ride height at that corner. It is commonly called "weight-jacking", since when you raise the ride height, the corner weight is increased on that diagonal and decreased on the other. Remember to keep in mind that it is not really adding and subtracting "weight", but rather altering the "load" on the wheel (measured in lbs.) Shifting fixed weight around in the car is another issue- such as moving your battery from side to side.

Also it seems to me that you would want to corner balance with the spare tire in place and a full tank of gas.

Standard practice for race preparation is to put the car in race trim when corner balancing- this usually means no spare tire (if you usually remove it for track events), the driver's weight in the left seat, and anywhere from 1/2 to 3/4 of a tank of gas. For a street car, you may leave the spare and toolkit in and not add the driver weight, if you normally drive the car with a passenger. The corner balance on a street car is not as critical anyway, as you do not drive the car at the limit of grip constantly. I think the factory spec is something like 20 kgs. difference on the diagonals.

[GreenT]

Yes, I noticed a huge difference - but I changed a lot of things and the corner weighting and alignment were the simply the final icing on the cake. I had everything from worn bushings to dead shocks to petrified tires to contend with first. Without everything underneath being up to spec, they can't dial in the suspension settings they want and you won't have the ride you're expecting from your car. I had the same folks do the same work on my car several years ago when the old suspension parts were on it. It helped, but I knew the car still didn't ride or handle anything like when it was new, and never would until it was new again.

In my case, I decided as long as I was having to revamp everything, may as well improve it. So I went to an SC rear suspension with the aluminum banana arms and adjustable ride height on the spring plates. In the front, the SC struts fixed the negative camber problems I had and gave me bigger and better brakes and got me away from the troublesome Koni front shocks I had. The stock SC swaybars allowed me to get rid of the POS Weltmeister setup I had been talked into, and every bearing, bushing and hose was replaced along the way. I didn't want to have to worry about anything under there again. It took a year of sourcing and refurbishing parts before it all went on last month. Only then was I ready to wobble off to the alignment shop for the corner weighting.

Net result? As usual, about the standard three times more expensive than originally planned. Worth it? Unquestionally, the car is transformed. I'm actually having to learn how to drive it again after owning it 15 years. Limits seem at least 15 mph higher on my favorite curves and the seat-of-the-pants feeling is much more balanced and composed, less twitchy. The clunks and squeaks from the old suspension are finally all gone. The car doesn't wander all over the freeway anymore on our grooved concrete. So my advice, learned the hard way, is do it once, and do it right.

As far as the half tank of gas, that's what's normally in it. I've learned not to keep a full tank in it in case I start an afternoon project that ends up taking six weeks. My 'traveling' spare was an old Goodyear NCT with about 6 nails in it, so I was getting that replaced that morning as well. I'm going to hang my never-on-the-gound original on the wall and start carrying a real spare so had them include that up front. I had them go with a driver weight of 200 and no passenger weight because that's how the car is usually driven - just me. Ok, so the 200 was a little light.........still, it handles good!

[66S]

Im corner balancing my track 911 now and it is not a simple procedure. From what Ive learned only compromise settings are possible in an assymetric car.. Most important is the ratio (front divided by rear) of each side is close to equal and the front corners close to equal so one wheel wont lock up under braking. After that diagonal totals and rear side to side balances. My biggest problem is ride height, they dont want to cooperate with the procedure. Definitely not thinking about weight jacking but making one diagonal total lighter makes the car turn in better in one direction, that why roundy round racers do it. F. Mysterioso, with much experience, says side to side front and rear.