30 Oct 2008

Things are busy this week and next so it’s a bit slow on updates. It’s one of those deals where by the time I get home, take a shower and eat, it’s late and I don’t feel like doing anything!

However, the parallel trailing arms have been modeled in WinGeo and nothing bad has appeared. I’ve had a couple readers express concern that moving away from A-arms is a bad idea. What’s driving the suspension change is packaging; one reason is that there isn’t enough room behind the drivetrain to have A-arms with a base wider than 10″ which I feel isn’t strong enough. I understand the concern but feel trailing links aren’t much different than A-arms when it comes to toe control. No one bats an eye when they have to dial out bumpsteer at the front yet everyone freaks when it’s the same situation at the back – it’s the same thing.

In the 1960’s, F1 cars commonly attached the rear toe-link to the lateral link, so this was tried first – it was terrible, the wheels toing in 0.440″ over the full travel! The reason is because as the suspension moves into bump the trailing links pull the upright forward. Since the toe link is attached to the inboard pivot point, the upright and lateral link rotate forward as one about the inboard pivot, leading to really bad toe-in. The trick is to have a dedicated toe-link not attached to the lateral link, resulting in the much better control.

I was reminded that I got in trouble using trailing links once before, with Kimini. However, in that case I purposely designed in rear toe-in in bump. Older and wiser, I know better now and will design in a very small amount of toe-out.