I’ve carried on using Susprog3D on the suspension and it’s really rather interesting, or alarming depending on your point of view. All I’ve done with the suspension in the past is just calculated the roll centres and used that, along with a nifty spreadsheet, to calculate the roll stiffness distribution. That was fairly successful. However, the current investigation is producing all sorts of odd things.
What follows is a bit pernickety. If you don’t know what any of the terms means then feel free to ask, although I might bottle out of coming up with a succinct answer. Mind you, I’m on pretty thin ice here as I’ve only spent 2 years trying to understand this sort of stuff. If you’ve got a lot of time on your hands then feel free to buy a copy of Milliken and Milliken and read it. I managed to get Anthea to buy me a copy of this for Christmas 2006. I’ve nearly finished it… It would be even better if I understood it all. A cheaper alternative, and recommended by the Susprog chaps, is Herb Adams’ book. The problem with both these books is they use Imperial units which really does my head in.
Front suspension
After much fiddling, I’ve got all the numbers in for the front suspension. Susprog calculates the static roll centre as being at 22mm which is commendably low. Thankfully, Susprog can be set to work in metric units. However, on closer examination there are two problems. First of all the roll centre whizzes sideways as the car rolls which is not the point. Rather worse, or so I’m told, is that the suspension appears to have essentially no camber recovery built into it. If a wheel starts at, say, -2.5° camber and then the car rolls 1° you’d hope that the suspension system would reduce some of that camber change at the wheel. However, the Fury front suspension actually rolls the front wheel by more than 1° which is not really the point.
I’ve done quite a lot of fiddling around with Susprog and I think I’ve come up with a way of changing the pickup points that is both feasible to effect and ameliorates these effects somewhat. Once I’ve got the engine out I shall see if I can work up the courage to do the changes indicated. The problem is, it’d be nice to be able to do them in a manner than meant I could revert the suspension if it turns out that I don’t know what I’m talking about, which is perfectly feasible.
Rear suspension
The rear suspension is rather different. In many ways it seems to be predicated on where the frame is around the diff, as that’s where the pickup points are attached, rather than them being in the place where you want them to be.
The end result is that the static roll centre is at a lofty 180mm. This means that the suspension won’t roll that much but it’ll suffer from jacking which means that lateral loads, such as those which occur in cornering will tend to lift the car up in the air. I’m pretty sure, now, that this is the source of some problems I had at Anglesey when the car had a very odd attitude round one of the corners.
Working out how to change the rear suspension actually seems to be a bit harder, mainly because of that diff carrier mentioned earlier. However, I think I’ve come up with something. What’s more, I’m pretty sure that I can do this in such a manner that I could revert the suspension if needed. The “only” problem is whether the wishbones will bash into the chassis as the suspension articulates. I shall have to do some careful measuring and mocking up before I actually cut or weld anything.
Adjuster ladders
If I do have to change any of the wishbones to effect the changes I’m talking about, then I will incorporate adjuster ladders into them. That would mean that I could adjust things (that is for camber and toe) without continually taking the thing to bits which would be a great relief.
Engine
A final note on the new engine. Andy rang me up today and said that he’d probably be able to get the new engine package together for the final RGB race of the season at Mallory in a couple of weeks. That’d be nice. Mind you, it’ll just sit on the floor of the garage until after the Birkett…