Beck 550 spyder, AX Candidate? Options

[Joseph Mills]

Looking at some of the specs on this kit made me start thinking how good a candidate it might be for auto crossing.

As far as I know Beck is the only kit that has a hand made tubular frame instead of a VW frame. Maybe that accounts for it's lightweight?

Something around 1200 pounds total! (IMG:http://www.914world.com/bbs2/html/emoticons/ohmy.gif)

We all know that light cars turn corners fast, and with even meager HP it's going to scoot in a straight line.

Suspension... well, maybe that is the bugaboo... Volkswagen. VW's on an autocross course are always scary with their positive camber from the swing axles. Maybe limit the amount of travel? Are there after market handling kits for such? Or additional link systems that bolt up?

Would a kit car be up to handling the torque and twisting forces of AX?

Thoughts? (IMG:http://www.914world.com/bbs2/html/emoticons/idea.gif)

[lapuwali]

On the swing axle problem, Formula Vee cars have used mid-engined swing-axle rear suspensions for decades, and there have been a lot of clever solutions to the "jacking effect" problem. I have to disagree with Jake that just going mid-engined solves the swing axle issue. I've witnessed a couple of cars that didn't have anything to deal with this problem in a mid-engined configuration, and they were pretty much undrivable. The outside wheel would go 15-20 degrees positive camber on the gas.

With swing axles, as the rear of the car rolls, it levers itself on the outside wheel's contact patch. The body leans on the outside spring, which resists the roll. The mass wants to keep moving, so it will shove the top of the outside tire outwards, pivoting on the contact patch, which causes the axle to tilt upwards, which forces the transaxle and everything attached to it to rise, which all causes a dramatic positive camber on both rear wheels.

The easiest "solution" is to run a lot of negative camber statically, but that compromises straight line grip, and only works up to a point.

The next idea is to use a Z-bar, which looks like a sway bar, but is a Z shape in plan, rather than a U shape. This means if both wheels go up or down together, the bar will resist this. If the outside wheel goes up, the inside wheel is also pulled up, so it ends up trying to keep the transaxle mass from rising.

The better, but more complicated, idea is to develop a rear suspension that has zero resistance to roll. The easiest way to to this is to have one coilover mounted above the transaxle horizontally, with pushrods from the hubs "squeezing" the coilover through bellcranks in bump. The coilover is ONLY attached to the bellcranks, so if you lift one wheel, the pushrod moves in, the coilover moves sideways, and the other pushrod moves out, pushing the opposite wheel down. Good suspension, but no resistance to roll. The body and transaxle will simply pivot along the car's center of mass, so the outside wheel can roll inwards, rather than outwards. In practice, it usually ends up staying more or less vertical.

The latter idea is better than the former, because you still need to have some "regular" suspension with the Z-bar, and that suspension will unavoidably provide some roll resistance, so it only reduces the jacking, it doesn't eliminate it.