Testing suspesion setups - before and after on a road car

[John_S4x4]

What's the best way to measure the effectiveness of change in suspension setup on a road car ?
I suspect somebody might suggest going round and round a roundabout and looking at the speedo/stopwatch/G-meter. Is there a proper way to do this ?

[Sam_68]

If you're just after increasing ultimate steady-state cornering grip, then yes, you do exactly that... mark out a circle on a nice, smooth bit of tarmac and drive around it at a steadily increasing speeds until the car won't hold the line any longer. Knowing the diameter of the circle and the speed at which you fell off it, it's pretty easy to work out the ultimate cornering G (or, these days, as you say, you can be lazy and just use a G-meter). It also gives you a pretty good idea of steady-state understeer/oversteer characteristics.

It's only part of the story, though - you will also be interested in transitional handling, which is really too complex and subjective to measure. And I'd rather have a car that is responsive and predictable at the limit (like a Lotus Elan, for example) than one that sticks like st to a blanket up to a high cornering G, but then lets go unrecoverably and with little warning (like the Lancia Stratos and classic 911).

[spitfire4v8]

If you get access to a large area where you can play with the radius of the circle then it gives you opportunity to also take tyre temp readings at varying steering angles .. helps give you a good understanding of how the caster of your car is changing the camber and how the tyre addresses the road surface in tight, medium and very open corners. Helped us with fast-tracking the development of our old race car massively. We did our testing at Elvington on their large open square area.