Dave Sims

Anybody have a rough rule of thumb for adjusting the weight on the front with M030?

e.g. you turn by this much for so many lbs in weight

RPG951S

Never seen a +/- mm/verticle = +/- lbs/corner type conversion, but I have noticed a very simplistic view (that's been reflected by my P-car mechanic). If you prepare the car correctly for a race setup(with proper air pressure, driver's weight, half fuel, full fluids). Simply making sure that the left/right have an identical ride height almost invariably puts your car within the specification.
This is of assuming that the chassis itself is straight and not damaged. If the left to right weights are off, adjusting the preload on the springs by either adjusting the torsion bar, or by turning the spring perch collar can jack the weight around the chassis until a satisfactory setting can be reached.

Danno

Welll.... since we're talking about cross-diagonals, it's actually possible to have two cars with identical ride-heights, but vastly different corner-weights. For example these two cars would have the same ride-height:

CAR #1
__L__|__R__
F 800 | 800
R 800 | 800

CAR #2
__L__|__R__
F 850 | 750
R 750 | 850

The only way to adjust corner-weights is to use scales under each wheel of the car. Disconnect the sway-bars and adjust only ONE wheel to see how the weight changes. Typically, you will raise the corner that has the least amount of weight. You're aiming for 50/50 cross-diagonal sums, that is LF+RR = RF+LR

But due to the driver being on one side of the car, you'll ALWAYS have more weight on the left, no matter what you do. Here's a sample of corner-weights on 951:

CAR #3
__L__|__R__
F 869 | 809
R 814 | 763

Notice that you have 50/50 cross-diagonal distribution LF+RR=1632lbs and RF+LR=1623lbs; just about perfect. But the L/R balance is L=1683 R=1572 (51.7/48.3) which you can't ever do anything about. Same thing with F/R distribution at 51.6/48.4%.

If I was balancing this car, I probably would've lowered the LF a little to take some weight off it and raised the RR to add more. The other two wheels on the other diagonal (RF+LR) would pretty much remain the same.

Dave Sims

The reason I asked is because the car was on a set of scales and both fronts were a little light. Unfortunately ran out of time to adjust

Danno

light front-end on a 951, really? Well, there's not much you can do about that really since you can only transfer weight diagonally. There's nothing you can do to shift weight forwards and back or laterally. You can jack up both front wheels or both left wheels, but you have to raise them 14-20 inches before any significant weight shift is noticeable (SINE function of angle of tilt).

As long as your cross-diagonal sums are equal, you'll get the maximum grip possible from your tires.

Dave Sims

Sorry, must put brain into gear
Light rear end:

__L__|__R__
F 741 | 778
R 716 | 731

UK 1991 RHD car

Danno

Well that looks pretty darn good as it is! You've got a 51.2/48.8% F/R and and 49.1/50.9 L/R weight distributions. Your cross-corner balance is LF+RR=1472 and RF+LR=1494 for 49.6/50.4 balance, less than 1% difference, which is the usual target.

If you really want to even out the cross-corner balance, you can lower the RF a little and the resulting weight would be something like:

__L__|__R__
F 754 | 758
R 710 | 744

Then you can raise the LR a little, but not as much as you lowered the RF and the final weight should be close to:

__L__|__R__
F 750 | 754
R 722 | 740

Notice that F/R balance is now 50.7/49.3% while L/R has remained the same at 49.6/50.4% (due to driver).

And more importantly, your cross-diagonal balance is even better at 50.2/49.8%.