Dax suspension

Willem · 08-26-08, 06:52 AM

Yesterday I came accross the dax tojeiro(cobra) and I saw their front suspension, it looks quite promissing and I wondered if it's usefull on a GT40, altough it's patented, what do you guys think of it?

I hope I am not breaking any rules by asking this and posting this link:
The Camber Compensation and Anti-Roll Suspension System - Page 01

Any info/opinions/experience welcome.

Chris P. · 08-26-08, 11:47 AM

Yeah, I too have lots of sketches of the same idea, as do many many others who went through suspension iterations. The problem I had with it was the linking of one sides' camber to the other. I would be really interested to know what it's like when driven hard.

Here are some inherent issues that DAX did not address:

1) One wheel bump
2) Steering geometry
3) Radial tires require some camber to help traction (camber thrust)
4) Stability from side to side (picture grabbing the top of one tire and rocking left to right)

Just some thoughts....

Jimbean Jimmy · 08-26-08, 01:44 PM

I have also looked at applying this design to a GT40 and have come to the same issues/points as Aero. I'm finding it hard to see what is stopping you being able to grab the wheel and rock them side to side. I havent looked at the maths yet but i am going to create a model in CAD and see exactly what it does.

The only way to address the steering issue is by having the rack mounted as low as the bottom wishbone but this is impractical to package with the current uprights we have available cheaply to us.

It would be good to know what it drives like, i wonder why they had only applied this design to the front suspension?

Willem · 08-26-08, 02:02 PM

When I looked at it closer, the one wheel bump looked like a problem indeed as the other wheel seems to be pushed into positive camber. Thanks for confirming

Jimbean Jimmy · 08-27-08, 01:16 PM

After creating a quick CAD model it seems that if you try and grab the top of the wheel and rock it will make the opposite tyre try and move up and down, so basically the shocks are acting directly against camber change on the opposing side.

The model also shows that a proportion of the cornering forces are used to try and compress the shock on the opposite side whilst cornering allowing you to run softer springs.

The only issues i can see is unwanted camber change over bumps and more unsprung mass. What are the effects of a 'heavy suspension' ?

Jimbean Jimmy · 08-28-08, 03:57 PM

Hey guys, the quick model i came up with utilizes parallel equal length wishbones and gives nil camber change on bump and droop, however in corners or roll the wheels angle the opposite way the body is rolling only by half a degree. So for instance if your car was rolling right (left hand bend) then the right wheel would be in negative camber and the left in positive both by half a degree. Thats from the perspective of the drivers seat.

Can someone tell me what the problems are associated with parallel wishbones in relation to roll centre? Also under roll conditions the upper wishbones actually slope downhil towards the outside.

CRASH33 · 08-28-08, 04:07 PM

If you're talking about a straight front axle, try talking to some sprint car guys that have to run them. I believe most setups run a panhard bar to solve side to side motion.

One pound of unsprung weight is roughly equivalent to 3 pounds of sprung weight. This is a HUGE issue.

Jac Mac · 08-28-08, 04:40 PM

Quote:

Originally Posted by crash33

If you're talking about a straight front axle, try talking to some sprint car guys that have to run them. I believe most setups run a panhard bar to solve side to side motion.

One pound of unsprung weight is roughly equivalent to 3 pounds of sprung weight. This is a HUGE issue.

Crash, Read the link in post #1, your getting way off track with your straight axle references.

CRASH33 · 08-28-08, 05:09 PM

OK. It took me a couple times before that page would load. Interesting, but camber gain is exactly what one wants when the dynamic of weight transfer is added in, and the sprung to unsprung ratio still stands. In the DAX illustrations, the tire is being assumed to be a fixed, solid part of the system, which it is not. Still very interesting as I have been trying to wrap my head around some sort of comparable system that would do the same for weight transfer on a crossweight situation. Haven't figured that one out yet.

MikeP · 08-28-08, 08:11 PM

The Dax system uses rods from one side of the suspension which link to the wishbone pivots on the other side and move the location point of the wishbone. In this way it provides a measure of camber compensation. However the important thing is that the tyre is held at the best angle to the road that maximises grip from the tyre. This is usually a little off vertical to the road to allow for the tyre deflection and keep thetread flat to the road. Whether this is done by good basic suspension geometry or by a camber compensation system does not matter. It may however be easier to maintain the tyre contact patch at the optimum using the Dax system over a wider range of movement. Duncan Cowpers Dax Rush uses this sytem and is well known as a very quick car but whether the system is what makes it quick or other factors is hard to say. A definitive test between a regular setup with antiroll (sway) bars and the camber compensation system would need to be done to find the truth.
Cheers
Mike