coils versus torsion bars

[kiwi ka]

Can anyone give me some clues (simple) on how to work out torsion bar rates to replace coil spring set ups. Different car but similar front suspension set up / geometry, also any simple ideas on how to achieve the bottom pivots for same.
Cheers
Russell

 

[Cliff Beer]

Russel, sorry, don't have technical data for you regarding torsion bar rates, however, if I was you I'd look at the torsion bar setup on an early 911 - something in the '67 to '73 period. It's a pretty basic and functional setup - lower wishbones with the torsion bars connected to the inboard end of the wishbones with an upright for the hub and brakes that is connected to a vertical damper. The top of the damper can be moved fore/aft or outboard/inboard to adjust caster and camber. Ride height is adjusted by rotating the torsion bar - there is a different number of splines on one end of the bar v. the other end so when you rotate the bar you get relatively small degrees of change in the position of the wishbone relative to the chassis. For large adjustment you can, of course, simply rotate one end one whole spline but that's pretty dramatic.

I would guess that the stock torsion bar is about right for your Mclaren given that you're probably going to want a little stiffer setup than a stock 911 front end.

 

[Jac Mac]

Race Car Engineering & Mechanics by Paul Van Valkenburgh [HP Books]. Page 39. Formulae given for comparision purposes, Can Scan & Email page to you but really suggest you buy a copy--lots of ideas for your? new toy

 

[EGLITOM]

Russel,

bar rate calculation should be the same as on a sway bar. the final wheel rate depends on the levers and angles of your suspension and connection to your bar.
Onby a excel file for calculating sway bar rates, should work also for your setup. Instead of putting in the spring rate just put in the bar rate which you have calculated and your lever dimensions. (just change the values in the yellow fields)

TOM

 

[kiwi ka]

Many thanks for the help, looks like I will have to engage my brain.
Cliff do you have any photos showing general set up by any chance.
Cheers