IRS alignment setting for wide rear tires

[RonRyon]

Bruce, if the TA pivot axis is higher than the center of the rear wheels, the force transferred from the wheels to the TA tends to cause the TA to rotate about the pivot axis in a clockwise direction on the driver’s side and counter-clockwise on the passenger side. The result is a lifting force at the pivot points, which works to reduce squat. If the pivot axis is lower than the center of the wheel, the opposite is true and the car will have more of a tendency to squat excessively under acceleration. Have you noticed at the drag races how the entire car is “lifted” under acceleration? This is caused by the lift bars. If you crawled under one of those cars you would see that the rear of the lift bars are lower that the front. Therefore, under acceleration, the wheels are causing the lift bars to rotate such that the entire chassis is lifted upward. The Bug’s TA can act like a lift bar.

With the stock Bug chassis, the rear of the TA is lower than the front as it should be -- no problem. However, if you lower the rear of the car much, the rear of the TA will be higher than the front, and handling will suffer. I have seen some people argue that squat isn’t all bad since it helps with weight transfer. I think they are getting confused, thinking that squat some how aids weight transfer. The amount of weight transfer is dependent on the height of the cars center of gravity, the higher the better. When a chassis squats, the center of gravity is lowered. Anyway I hope this all makes sense to you, if not please let me know.

[Bruce2]

I see what you are saying Ron. But you are making a fundamental error. The reactive torque is not absorbed by the TA, but by the engine/transmission unit. This is why the nose of the trans wants to rise on acceleration. There is no rotational torque applied to the TAs. They just support the bearings.

The phenomenon you describe occurs in solid axle rear ends like 60s and 70s American cars have. When they install ladder bars (which look like the spring plate substitute on that red chassis car 2 pages back), the ladder bars are fixed to the axle housing, which is fixed to the diff housing. When they launch, the front of the rear end wants to rotate up. By installing ladder bars, the counter rotational force causes the whole rear end to be forced down, creating more traction. In a VW swing axle, some guys do install links that look exactly like the ladder bars on an American car's rear end. But they don't have any function except as a trailing arm. This is because the VW's axle tube is not rigidly connected to the rear end housing (trans case).

[RonRyon]

I’m not talking about torque causing the lifting action but rather the force transmitted to the TA from the wheels which push the car forward. Physics would say that the force exerted by the wheels to the chassis through the TA has two components, a horizontal force and a vertical force. The horizontal force pushes the car forward and the vertical force pushes the car either up or down depending on the angle of the TA. The amount of the vertical force is dependent on the angle of the TA relative to the horizontal.

Or, a another way of explaining it --- looking at the passenger side for example, if the TA angles down to the rear, the force exerted by the wheel will try to cause the TA to move in a counter clockwise rotation. In order to do so it must lift the car.

It would be easier to explain this with a drawing but I don’t know how to do it on my PC.

Not that it matters, but don’t ladder bars lift the car? I don’t believe I have ever seen a ladder bar design that could push the rear of the car down. Maybe if excessively long, push the front end up and thereby helping weight transfer to cause the rear of the car to squat from the additional load. Also, it seems to me that the counter rotational torque is absorbed by the ring gear in either case (fixed axle or IRS). But then I have been wrong before.

The bottom line is, I think that among other handling problems created when lowering a Bug, anti-squat should also be given serious consideration.

[Bruce2]

Oh yes, of course! There will be a force pushing the TA down due to the forward force on the TA. And the higher the front pivot, the greater the force. When you break it down to the horiz and vertical components its clear.

Ladder bars on American cars do lift the rear of the car. They do it by planting the rear end down harder. Have you ever noticed how some of them don't squat at the line?

[RonRyon]

Bruce, that is what I was trying to say when I said the thing about drag cars being lifted as they come off the line. So, I guess you agree that the angle of the TA can have an anti-squat effect? I have personally observed this on the previous cars that I have built. The benefits were very noticeable and very positive not only for straight-line acceleration but also for overall handling.

[Bruce2]

The only problem I see is that when you raise the inner pivot, you will get positive camber. Raising both will require you to raise the whole torsion housing (a big job). Then it also raises the engine/transmission.

[RonRyon]

The plan would be to raise both the same amount. I'm not using the torsion bars so it will be less complicated. I'll let ytou know how it goes, but don't hold your breath, I move pretty slow these days.