uprights v geometry...

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Guest

Guest
On my GTD I have had the standard original uprights plus more latterly the new race ones from Ray (on the front). I am now looking to change over to ali ones alround if I can find something suitable. Tomorrow I am going up to see Andy Burrows of Gardner Douglas to see what he has to offer.

I note on this forum that people are talking about a wide variety of readily available uprights.

As a word of caution I hope people are looking at the effects on geometry that having say a corvette upright will have in comparison to the factory supplied item (not just GTD makes here but all makes). The fixed points in this discussion are the chassis pick up points. It is unliklely that these will be changed in fitting your uprights. The relationship to the upright pick up points will have some effect on geometry and it may be dramatic. Roll centres move about enough as it is! In addition any alterations to the trailing links could encourage rear wheel steering on bump and droop by changing rear wheel toe in.

On the front the issues could be changing the king pin inclination and effects on Ackerman and turn in.

And lets not forget the easy one to check, camber changes. If they get large then you could lose a large chunk of footprint and grip.

I have a DOS based program that allows me to experiment on a very basic level with graphical visualisation of the set up. Anyone looking down at changing their uprights or doing their own thing would be well advised to try and find a suspension software package to help predict the effects of what they are doing.

So the question is....

Does anyone recommend a software package they have?

and

Has anyone got any thoughts about their own experiences on the above?

Malcolm
 
Hi Malcolm

I got a full set of Andy last weekend I paid £480 for all 4. You need to bush the fronts to take a ball joint or rod end.

Chris
 
G

Guest

Guest
To report back from my trip to Gardner Douglas.....

I have bought a complete set of Andy Burrows uprights. He does two options for the rear but the short option is the one I picked.

The fronts are designed so that I can replicate the exact geometry of what I had before with a slight change in king pin angle, but when this angle is compared to a std GTD set up, it is an increase/improvement and not a step backwards. However it is less of an angle than Ray's race uprights which I am replacing. Does this equal compromise?

Both these uprights weigh much less than GTD items but take my bearings and spindles without modification. I doubt they will take the std GTD bearings and spindles from the front uprights. I will have to make my own bushes for ball joints for the front and use rose joints on the rear.

I always intended to remake my suspension arms as I had changed them a lot of times already so am starting fresh there.

So the front, to me, on my car, are a good option.

The rears are not as applicable. They are gorgeous but not as applicable which is a bit of a bummer.

The top link on my car had been repositioned on the GTD upright before. The GD upright actually puts the top link in the same space as I had moved mine to so no issue there. The bottom link is quite a bit higher and the only chance of making that work is to alter the chassis pick up point to match. Andy Burrows helped with a solution to that problem.

The trailing links also are not perfect. The bottom link can stay in the same place. The top link will need to be dropped both at chassis and upright. I beleive it is important to keep these arms parrallel as they currently are and at the same inclination. The lenght of these arms could be an issue.

The damper pick up location at the upright end will need resolution too.

I am not intending to put the rears on the car until a winter rebuild gives time to really look into it and get it right. It may be that it is not possible to get it right enough so they will only be used after lots of thought.

I found Andy Burrows a very pleasant fellow and quite knowledgeable. He had good stock on his shelves and has a very nice set up. A bit like GTD in their hey day.

He had two of his cobra replica customers come in with exhaust issues. One wanted to change his SVA pipes to something more appropriate. After removing the two rear silencers and replacing with straight through pipes it was much better but still a bit quiet compared to our cars. However the other car had had an issue with a wall and had basically taken his silencers completely off! Just with stubbies from the engine (Chevy 350) made this car sound great!

I have been given some links to web sites on software all of which look more fancy than what I have. These links are...
www.auto-ware.com www.rapidline.com/calc/suspension/index.htm www.susprog.com

Anyway, I hope my liitle exporation into suspension helps someone else.

Malcolm
 
Malcolm,

V. Interesting. Before you fit the uprights, would you be prepared to weigh them & let me know? I'll weigh the stock GTD items when I get them off for comparison....
 
G

Guest

Guest
I have now (at last)weighed the uprights. These weights are stripped right down, bare upright weights ie no bearing and ball joints etc.

Front
1.43 kg

Rear
3.58 kg

They are significantly lighter than GTD stock items.

Delay in getting these weights caused by some B***ard breaking into my workshop and stealing all my mig welding gear. I became unhappy camper for a short while! Anyway back in workshop last night for some lathe work.

Malcolm
 
Hi, what KPI, wheel offset and scrub radius are you guys aiming for??

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Guest

Guest
The KPI is 7 degrees. Wheel offset is dependant on whose wheels you use. I don't think there is a standard out there. For these uprights I haven't worked out the optimum. For scrub I assume you mean Ackerman Angle? If so this is adjustable by how you make construction of the steering arm linkage. I am planning on going as near to neutral as I can get.

I am looking into using sperical jopints instead of ball joints but haven't fully decided yet. Opinions welcome.

Malcolm
 
Hi, by scrub radius, I am referring to the distance between the steering axis at the ground, and the centerline of a front tire..
This has a very large effect on steering feel and kickback, and also castor jacking effects

Rob

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