What happens to the toe when the rear suspension is under load (ie. passengers/cargo) and when it is unloaded (under hard braking)?

This website says...



and

The diagram shows the suspension toe-out under rebound (braking) and toe-in under compression (load). What is correct?

 

Both.

The toe curve is correct. In suspension rebound, the tire will toe out.

However, the rear suspension also has a dynamic toe component from fore / aft loading of the tire / suspension. Brake, tire pulls back, suspensions shifts from bushing deflection, tire toes in.

"Diagonal arrangement of trailing and leading arms" is referring to the "toe arm" (not sure what the correct term is) and the LCA. Move the trailing arm back, and the toe arm pulls the front of the trailing arm in, and the LCA pushes the rear of the trailing arm out, changing the toe.

You'd need to find a way to measure the toe change while simulating the bushing deflection from the tire pulling rearward under braking, to determine which effect is greater.

A spherical TA bushing will eliminate the toe in under braking condition.

Just thinking through it. I could very well be wrong.

 

^

 

Slight toe out at complete droop - inside rear wheel in hard corner - and toe in under the compression stroke - outside rear wheel in hard corner. What the inside rear wheel does on a front driver is almost not important - I would optimize a set up based on the inside rear wheel unless it were contributing something substantial to the goal. Toe in stabilizes the rear end.

In the end you have to look at camber and toe together.

 

The toe-in under braking described in the Honda link comes from bushing displacement.

Having skimmed over the article, it seems as though that design (and the article) is more optimized for straight-line stability (straight acceleration and braking) and ride comfort than it is about handling through corners. Makes sense as this is a design for normal road-going passenger cars.

 

I'd go further, and claim toe in under braking is good for race cars as well. Trying to trail brake a rear spring biased FWD car (how we generally set them up) at high speed is a rather pucker inducing event as it is, and toe out would only make such a situation worse.

My complaint is that the rear end still toes in under compression without braking, which is when a car on track would probably benefit from toe out (apex to corner exit).

So, I like the passive rear steering from bushing deflection, I just wish the toe curve of the rear suspension was reversed.