Misc observations from messing with corner scales:
- Suspension tweak doesn't make much difference in getting the total left/right and total front/rear weights. Your cross weights will be way off if it's tweaked, of course.
- An un-level setup board doesn't seem to move much weight around. It makes a difference, but not a huge one. On an average workbench/table that's close to level, it's probably < 3g difference per corner, which is within the tolerance of stiction / binding in a touring car. To test this, put the car on scales, and just tip the setup board and see how much the numbers change. Your results might be different from mine.
- Steering angle makes a big difference, at least with setup wheels and 6* caster blocks, when looking at what's going on with the front. Just being a few degrees left / right from center, I was seeing variances of 10-20g on the front end, which is pretty big. I'm pretty sure this is from the weight jacking effect of the caster. So turn on your transmitter / car, and make sure your steering is trimmed straight, before you start messing with preload.
- Scales alone will not tell you which end of the car has suspension tweak. Something I tried recently that seems to work, is to stack my two droop blocks and put those under one end of the chassis to keep the car flat to the setup board, while the other end is on the scales under the wheels. This will let you check tweak at that end of the chassis in isolation.
At the end of the day, I've found ways of checking everything without using the scales, as long as the car is balanced left to right. I only use the scales during initial setup to balance the car left to right, or when I've got a weird tweak going on that I just can't get figured out. I leave them on my workbench at home, and just use the simpler techniques for checking things trackside.
Also, IMO, it's not enough to get the cross weights even. You really need to get the car balanced left to right to make it handle properly. If it's unbalanced, it will do weird things when it pitches on throttle / brakes.
-Mike