Cross weight balancing modyfing springs preload

[Xwang]

Hi to all,
I've heard that it is possible to modify and balance a car acting on suspensions pre-loads? How it is possible?
If the cg is not on the car symmetry plane, how can it be balanced changing the pre-loads?

[Greg Locock]

A car on 4 wheels suffers from the 4 legged table problem, one leg is always in the air. Luckily we fit suspensions to help get around this, but the problem remains.

So, take your car, put it on scales for each wheel. Insert 3mm spacers under a spring, note how the corner weights change. repeat. discuss.

[Jersey Tom]

*Cross* weight is easy. But you won't be able to make anything but subtle changes in front or side percentage.

[Tim.Wright]

This is one advantage of a soft warp interconnected suspension - your corner weights are never wrong!

Fun fact: The inventor of the Kinetic/Tenneco suspension which is fitted to McLarens cars among others, has also invented a 4 legged table with doesn't rock when its placed on uneven ground. I imagine its based on the same Concept as the suspension. I think its called No Rock tables or something.

[Jersey Tom]

This is one advantage of a soft warp interconnected suspension - your corner weights are never wrong!

Even if you want 55-60% cross weight?

[Tim.Wright]

In that case, they are never right!

[DaveW]

I've heard that it is possible to modify and balance a car acting on suspensions pre-loads? How it is possible?
If the cg is not on the car symmetry plane, how can it be balanced changing the pre-loads?

This article might help....

[Xwang]

I've read that document and made some calculation and I've discovered that I've initially misunderstood the cross weight balancing. In fact it is not possible to balance for the side offset of Cg and the rear/front weight ratio, but it is possible to balance the total amount of weight on the left and right side by changing the preload.
So the only way to balance the weight on the same axis is to assure that the cg is on the simmetry plane of the car.

[stolenmojo]

This article might help....[/quote]

I realize that article is meant to be a primer to explain mass distribution and wheel weights to a specific intended audience, but that author missed out on the chance to really shed some light on cross weight. Plenty of road race cars use cross weight for a benefit. The braking zone in the Sao Paulo back straight (INDYCAR - 185 mph top speed and 6th gear to 1st gear downshift) called for a little cross weight to balance the car on hard braking. By the same token, every road course has a predominant direction of corners and some may be more valuable in sector time improvement than others of the opposing direction.

Aside from that - I didn't understand the original question. Crossweight is a subtle balance tool not a gross mass distribution fix.

[DaveW]

So the only way to balance the weight on the same axis is to assure that the cg is on the simmetry plane of the car.

Arranging for the c.g. to act on the centreline of a race vehicle is usually a good idea, unless all corners are one way (e.g. ovals). It is also usual to adjust spring platforms for road course set-ups to null the cross weight at the steered axle with the vehicle mounted on a flat plate.

US engineers do sometimes use cross weight to bias the steering (as stated by stolenmojo), but that "fix" is rarely used in Europe. I could argue the case, but I wouldn't convince anybody one way or the other.