Mark, this is the first time I've ever heard of motion ratio mentioned when discussing our suspension setups. I'll have to do some research on that as this stuff fascinates me to no end.

So is it most beneficial to have a setup with wheel rates equal front and rear? I'm sure driving style and track layouts would dictate to some extent what rate balance F/R is best. But to have a generally well set up car would the average person start with equal wheel rates then fine tune from there? I guess I'm having a difficult time figuring out where to start. It seems to me that my suspension "as is" is nowhere near the middle of the road, and I think Larry hit it that my rear is significantly undersprung to start with.

 

A starting wheel rate would be proportional to corner weight. So if you had 40/60 F/R weight, that would be a good starting point on the ratio of wheel rates. I think that a wheel rate equal to corner weight would be VERY stiff for a production car. Formula cars/Sports racers used to run at around 2-2.5 times corner weight. With moderate downforce (like my car) it is more like 5 times corner weight but that is not the best mechanical grip, rather it is to control ride height - maximize aero at the expense of mechanical grip. High downforce cars may go to 10 (this is somewhat dependent on driver preference too).

If you want to measure motion ratio, it is fairly easy. Remove the spring and measure wheel travel and shock travel. Use a dial indicator and take the wheel through 1 inch and see how far the shock travels. Do this at normal ride height as it changes during the travel of the suspension.

 

I thought that would be a good way to do it.

 

Yes.
525R is about 300lbs in (rough guess) and with 500+ in the front the car will go to understeer. You can see this also in you sway bar settings Full still rear sway is band aid to too soft a rear spring rate. Ideally you sways closer to the middle both front and rear. If you have one full soft and the other full stiff you have mis matched springs and you are using the sways try to correct. Better to fix the spring rates first.

 

Exactly my point, as I have run out of adjustability and the push condition persists. Again, good information guys, thank you.

 

Not only that... sway bars need to be use to fine tune the balance. Using the sways to compensate for springs is LESS effective than proper spring rates.

Example.

my 944 NA (open diff car)

350lbs fronts & 28 mm (254 lbs effective) rear. Car had understeer so I cranked the rear sway bar full stiff. Yipee I got great balance. However this also came horrible wheel spin. So I took out a bunch of negative camber in the rear and that helped some. Still had wheel spin. So I bit the bullet and swapped my 28 mm bars for 30 mm bars. Now I was 335lbs-in rear. I dailed back in negative camber and reduced the sway bar setting.

Results were fanstatic. The car had great if not better balance and much much less wheelspin. I had been using a really stiff sway bar to compenstate for poor spring rates and the down side was poor rear traction. With the right spring rates the car got better overall.

IMHO camber should be set to get even tire wear or better still even tire temps. That should drive camber not understeer/oversteer balance. Gross issues of understeer/oversteer need to be handled by spring rate ratio from front to rear. Fine tuning of balance can be achieved with toe settings, ride heights (front to rear balance) and sway bars. Shocks are used mostly to futher fine tune the balance during transtions like corner entry, corner exit or bumps.

One really nice thing about adjustable sways is that they can be a nice band aid to achieve decient balance with mis matched springs. If you are developing the car and have the wrong springs most of the time you compenstate for some of this by sways. The nice thing is sways are easily adjusted and you can tweak them each track seesion to find the balance rather the replacing springs between run groups.

 

I agree 100%

About bumping the rear spring rate, what Joe found was that his car was "sitting down" on the rear suspension, and even though he could balance the car with the sway bars, it wasn't right. Keeping the car suspended properly under acceleration and braking is the function of the springs.

 

Hmmm...

This discussion shows you just how variable the perception and performance of suspensions can be, as Mark stated. I run 500F/450RR full coil, sways set nearly full soft, damping in the upper third on the Ledas, alignment at -2.7F/-2.3RR/0 toe all around, and I am not just toodling along (2:24-ish laps at the Glen). The Fliegende '44 is exceptionally well balanced.