Steering rack and other questions from a Newbie

[JohnK]

Been busy (late nights) on Autocad trying to get my 'copy' of a Caterham SV chassis sorted. ...Consequently the castor bit is confusing this old guy.

The fact that there is a choice, more than anything I suppose :-)

Design with the typical proven 5 ? or play with the Europa setup of 3 degrees??

 

Re drawing suspension with a CAD package and trying to figure out how the suspension works:

I used a highly-regarded purpose-built suspension geometry product by Wm. C Mitchell called WinGeo3 to attempt to understand my suspension (http://www.mitchellsoftware.com). It allows me not only to see my suspension in multiple perspectives, but how it responds to bump and droop and roll and braking. I can change the length of a link and see the result on Caster, Camber, scrub, ... at a range of roll + ride-height change, ... And an add-on spreadsheet done by a mathematician allows me to determine the spring and roll-bar movements similarly (at 0.5G right turn and 0.2G braking, for example) so I could arrive at the right spring rates given the geometry of the car.

However, ... I ALSO learned that really really tiny changes can make big changes in the results that you see, depending on what you're looking at. In the main, it gave me a much much better picture of what my car's doing, but, when it comes to something like getting rid of bump-steer, or minimizing scrub at the expense of camber - well, now I understand why serious race car teams spend millions of dollars on equipment and setups to align their cars to 0.001" values. It was pretty disheartening when I saw how little that three days of work crawling around under the car and measuring x-y-z for over a dozen points to a 1/16" or better bought me. And to add salt to the wound, I remember that I read a long time ago in Allan Staniforth's Competition Car Suspension that scrub, caster and camber all work against one another. There is no 'solution' to the problem of how to dial in the suspension. For even more gloom read what Caterham paid a consultant to do to improve their latest car (http://www.usa7s.com/vb/showthread.php?p=29481#post29481)

 

The only thing anyone can do is measure the car real, real accurately, understand, and if possible measure, how the car is working, then propose a hypothesis as to what should happen when you change something in a particular direction, and then repeat the process. Or you can just buy a Caterham, ensure that it's aligned as the factory said it's supposed to be, hope that nothing's been bent since it left the factory, and the go out and enjoy the damn thing!

[danilo]

Thank you...

Yesss a 'can 'o worms ' indeed. I've looked at similar programs (likely not even near as comprehensive as yours) and the complexity can be boggling.. Also IMO, serious overkill, unless an F1 designer.

Best avoided.. I think :-)

I've seen basement built Dune Buggies consistently outperform distributor sponsored/prepped Porsches in Solo events.

In fairness using the ancient Spitfire uprights with their trunnions masquerading as lower ball joints, instantly eliminates half of the potential design possibilites. IE: Caterham went to that spherical bottom joint on their later cars to drop the front lower A Arm pivot to the end of the chassis tube as an Anti dive 'improvement'. IMO there wasn't much of a problem there to solve. But product "must" be improved. Marketer's mantra.

 

I'm starting to suspect that the Europa setup is likely due to either a Lotus Printing error :-)

Or that the Europa, with little weight on the front wheels simply required less castor.

 

I'm now wondering Where/How? can I get a few basic SV measurements:

1) Length of lower A arm .

2) Distance between Front Upper A Arm pivots (chassis width at top)

3) Distance between Front Lower A Arm pivots (chassis width at bottom)

 

I'm trying to establish the base dims for the front suspenders..

To check and see if I'm drawing something even similar

Edited January 26, 2011 by danilo