corner balance #'s

[jkcrewsn]

For those who are interested, I just had the torsion bars replaced and the car corner balanced. Here are the numbers...again, for anyone who might be interested.
Total weight: 2947lbs. (Wow! Heavier than I would have thought)
RF: 557
LF: 536
RR: 965
LR: 891
Front Total: 1093 (37%)
Rear Total: 1856 (63%)

Guess it's time to start ripping out the interior.

[ttweed]

Those are very good corner weights, within 7-8 lbs of ideal, but I am curious- did you take them with the driver's weight in the car?

The reason I ask is your L/R weights are 48%/52%, and usually, the driver's weight tends to bias the left side more (unless this is a RHD car). Is there a lot of heavy equipment on the right side of a 930 (maybe A/C stuff)?

TT

[jkcrewsn]

No, but he said he took my being in the seat into account when he balanced the car. I think that may be why it is biased that way. I was hoping someone would say it was good or bad. The guy who did it also has a race only 911, and he holds the track record here in Hawaii. But it is always good to get other opinions as well, and I tend to value what you guys have to say.
It was also measured with a half tank of fuel.
Sway bars are next, the front bushings are so shot on mine that he said it is just along for the ride. I am going to get it aligned this morning, but the steering is already much sharper! I also had poly bushings installed. The ride is firmer, but not obnoxiously so. I just can't wait till they start to squeak, to go along with the brakes.

[Jack Olsen]

I'm surprised you're as tail-heavy as that. It's almost identical to mine, with a too-big engine in the back. I'm 36.6% front, 63.4% rear (total weight 2470 pounds, plus 170 of driver)

[briankeithsmith]

Last Sunday I put my 1983 930 on a set of LongAcre Digital Scales. Here is what I got.

3168 total weight with full tank of gas and driver (me, 180 lbs)

Front Wheel Weight - 1202 / 37.8%
Rear Wheel Weight - 1967 / 62.2 %

Left Side Weight - 1647 / 52%
Right Side Weight - 1521 / 48%

LF - 649 / 20.4%
RF - 553 / 17.4%
LR - 998 / 31.4%
RR - 969 / 30.5%

RF-LR Cross Weight 1551 / 48.95%
LF - RR Cross Weight 1618 / 51.05%

The car contains a DAS roll bar and Kirkey aluminum racing seats.
Other than that, it is pretty much stock (Except wheels/tires).

I haven't attempted to adjust anything yet. I'm going to wait until I can install stiffer torsion bars and sway bars.

Brian Keith Smith

My 930

[jkcrewsn]

Dang Brian, that's a gorgeous car. Are those 17" wheels? I've got my eyes on a used set, but they are kinda beat up. I hope they are still available when I can afford them.

[briankeithsmith]

The wheels are 17x7.5 and 17x9 Mille Miglia's.

Previous owner had installed them. They are a little scratched also. Just have to look closely.

They tend to take a beating on the track.

Brian

[ttweed]

Brian-

That is a nice turbo- "Arrest Me" red, eh?

You are being smart not to do any adjusting until you get the torsion bars done, as that will require re-setting ride heights and alignment anyway.

Your side-to-side weight is more typical for the 911 corner weights I have seen, as it includes the driver's weight. I am a little surprised at the F/R distribution as you said you had a full tank of gas, but I guess the extra weight of the turbos and exhaust may contribute to the tail-heavy distribution. Mine is closer to 40/60% F/R.

Here is what I calculate your ideal corner weights to be given the same conditions. Shoot for this when you get it set up:

LF = 625
RF = 577
LR = 1022
RR = 945

If you can get within 5-10 lbs. of these weights at each corner you will be doing well.

Good luck,
TT

[briankeithsmith]

How did you calculate those numbers? Just curious?

Here are the numbers without me in the car:

2987 total weight with full tank of gas and driver

Front Wheel Weight - 1110 / 37.1%
Rear Wheel Weight - 1876 / 62.9 %

Left Side Weight - 1519 / 50.8%
Right Side Weight - 1467 / 49.2%

LF - 626 / 21.0%
RF - 483 / 16.1%
LR - 892 / 29.8%
RR - 985 / 33.0%

RF-LR Cross Weight 1375 / 46.03%
LF - RR Cross Weight 1611 / 53.97%

[Todd Simpson]

I had my '71T corner balanced, here are the results.

LF-440 RF-437


LR-658 RR-695

Total is 2230 pounds without driver. No sunroof, AC or power options, RS tail and front and rear bumpers and 6 point cage.

Hopefully my weight will offset the right rear weight a little bit.

Todd

[ttweed]

I calculated the ideal corner weights using the Excel spreadsheet that Nick Warinner has made available at http://www.356racing.com/balance.html

The formula is pretty straightforward and is detailed in Fred Puhn's book "How To Make Your Car Handle". Basically, unless you are into roundy-round racing and only turn left, you want the front/rear weight distribution on the left side to equal the front/rear weight distribution on the right side (which will also equal the overall F/R weight distribution of the car).

For instance, in Todd's case, the overall F/R weight distribution is 40/60%, which is typical for 911s. So you want the left and right side weights to also equal 40/60%,when calculated individually.

Many people say you want the diagonals to be equal, but this is not really true. The only time the diagonals will be equal when a car is perfectly corner-weighted is if the F/R or L/R weight distribution is 50/50%. 911s will never have 50/50 F/R distribution, because of the rear engine location, and 50/50 L/R only happens in center-cockpit cars, since the driver's weight is offset to one side, unless great care is taken to relocate fixed weight within the vehicle (battery, fuel/oil loads, ballast, etc.)

If the car is corner balanced without the driver's weight, it will be perfectly balanced only when a passenger of equal weight to the driver is in the right seat. In racing, that doesn't happen. Thus the need to include the driver's weight when on the scales, unless you are only street driving, in which case none of this is necessary, anyway. Equal diagonals would be sufficient for a street car, and Porsche's own spec is for something like "less than 20 Kilogram difference" between diagonals, so you can see that getting it perfect is not vital in most cases. There are so many other variables in your car's setup that perfect corner weights are probably less influential than, say, your tire pressures. If you are 10-20 lbs. off, don't sweat it! Work on the driver first. The "nut behind the wheel" is the most critical piece of equipment in your car...

TT

[katigbr]

Just had mine done last friday for a DE weekend. I was WAAYYYYY off when I updated my torsion bars. I was about 200 pounds LIGHT on my front right. My final corners weights with my 170 pounds was 2545 Total with 3/4 tank of gas.
Front Left : 531 Front Right: 497
Rear Left: 778 Rear Right: 738
It works out to about 40.5/59.5 Front-Rear

I also dropped my ride height 1.5 inches. Rears are at 23.5 inches and fronts are 24.1 inches. What a tremendous difference in breaking and cornering! She corners like she is on rails with the Toyo RA-1s.

Rick

[911pcars]

For those who wish to record and manually calculate the weights, I've got a corner balance worksheet (downloadable PDF) on my personal website.

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