Christer

Not in preference to cornerbalancing, no. But that is just IMHO.

johnfm

What about lambswool mitts?? Are they are good investment in the dynamics and poise of the car?

N105DVV

And, not to forget to mention the Genuine "Porsche" fold away BBQ, just for those hot summer BE events John.....

BR/Phil...

Christer

I don't really understand your point if there was one.

N105DVV

This is has been posted B4. Not the best on corner balancing but it is simple.

Simple corner balance

BR/Phil...

springer3

914und993 says:

"The only way you could be sure you have a proper corner balance by equalizing weight between the two front tires only, would be if by some chance act of God your chassis was perfectly square, the car's center of gravity exactly midline, and you had your weight sitting in the driver's seat. These conditions are rarely met in the real world."

914und993 is correct that balancing the front weight balances the rear only if the weight is distributed evenly about the centerline. Thanks for pointing this out, as I was making a poor assumption.

914und993 is wrong on two points:

1) Balancing the front will compensate for warped frames (see below for discussion).

2) You can't balance the weight of a solo driver with suspension settings - the car will be heavy on the driver's side regardless of how you set up the suspension. I did leave the settings with the driver's side a little higher, just so that the hight is equal with a solo driver, but I doubt you could detect a difference in real driving.

Assume for discussion purposes that a solo driver is located mid way between the front and rear tires, and approximately half way between the edge and the the centerline. Regardless of suspension settings, the driver side will be heavier than the passenger side. With given assumptions, 3/4 of the driver's weight is supported on driver's side, and 1/4 on the opposite side. If the driver weighs 80 kg (175 lbs), 30 kg goes to each driver side wheel, and 10 kg to each passenger side wheel. Each wheel on the driver side carries about 20 kg more than its partner on the passenger side. Interestingly, 20 kg is the factory tolerance for side-to-side balance with the car empty.

Regarding compensation for warped frames or spring differences

Let's assume a perfect car (square, and with correct set height, and the vehicle mass centered about the centerline). Then the frame is warped 1/4" low on the front right. For the sake of discussion, let's further assume that the spring rate is 600 lb/in. The front right and rear left will share the 200 lbs off-balance caused by the frame warp. If you are looking only at the front balance, you will need to lower the front right by 1/4" to get both front corners balanced. The weight transferred to the opposite front tire will come from the heavy rear corner, and the car will be balanced. You will not have equal ride height, but the corner balance will be correct.

The only question not answered is how consistent the sidewall stiffness is on two different tires. I let the air pressure down until both fronts were about half way to the rim. With the sidewalls bowed out, I assumed that there was very little contribution to supporting the weight from the tire stiffness, and what stiffness existed was equal on both sides. I think that is a good assumption, but did not verify it. If the assumption is correct, the balance will be easily within the 20 kg allowance published by the factory.

I will need t check the rear balance to be sure I have the corners balanced. I will check the rear tonight and report back. I have already paid for the alignment, so hopefully I will not find a large discrepancy.

Stephen Grellet

The best way of understanding cornerweights is to liken it to a chair with one short leg. The chair will obviously rock. If the short leg is corrected, then the chair will be stable. This is the same to a degree with the suspension. A car that has diagonally even corner weights ie LF & RR = LR & RF will feel tighter and will corner better left to right. However the major problem is that unless the car has been built with a lot of offset weight to counteract the weight of the driver, then as soon as the driver hops in the diagonal weights will alter significantly. I think corner weights would have to be out a fair amount to feel it on the road, but certainly worthwhile for a circuit. Once the corner weights are almost correct, then by adjusting one corner will alter the four corners. If weight is increased on the RHF then weight will increase also on the LHR and decrease on the LHF and RHR and vice versa. It can then come down to chassis stiffness etc. Perhaps one way of testing the interconnecting tyre method would be to put the car on cornerweight scales after it has been set up to verify the readings. If it works then it is certainly a cheap method.

914und993

The idea behind corner balancing is to make sure that the weight on each side of the car is distributed between the front and the rear tires in equal proportion. This gives balanced handling.

Left side weight (LF + LR) will be different from right side weight (RF+RR), but the left front tire should carry the same percentage of the left side weight, as the right front tire carries of the right side weight.

This is what is meant by corner balancing. Springer3's method is not a true corner balance, but that doesn't mean it isn't good enough for the street - it probably is. I'm not saying the method does not have some merit to it - as you point out, it is very likely to get it withing Porsche's street specs - it just isn't what is known to racing types as a true "corner balance".

Chip

johnfm

Phil

you've been following the BE thread too? A true classic. Some guys on that board actually have senses of humour, its amazing.

Phil Raby

BE?

art

A better approach using this thinking would be to take the weight off all tires, get them all to the same pressure and then lower the car. Check pressure of each tire, and the ones with higher pressure will have more weight on them. You need to be in the range of pressures where sidewall stiffness does not mess up the readings, but if the car has 50/50 balance they will all be the same. You can the corner balance the car just by looking at the tire pressures. I have no idea what the pressure increase might be, it could be difficult to measure the differences.

I bought a cheap bottle jack and installed a pressure guage. I can take each wheel just off the ground and read the load on the jack. I welded a pipe to the jack that fits the center hole of the fuchs. Not as good as scales because I am upsetting the car to raise the wheel, but it is repeatable. I had my 914 on scales once and the reading corresponded.

Art

johnfm

Phil

check out the OPEN LETTER thread on the racing forum, which leads to BE days (BBQ Education)...it gets pretty funny!