mattipuh

Looking for motion ratios for front and rear suspension in stock 911 3.2 Carrera. Any hints welcome. Setting up friends 911 and I've mostly fiddled with 944s and 968's, 911 is a mystery territory..

Amber Gramps

It all depends on how firm you want to go. Are we talking a 915 or a G50 tub?

My target for my G50 car was 21/28. The 21 in front was easy. The rear proved to be a nightmare. My vendor wanted $800 for the bars and said it would be several months until the next run.

I chose to add coilovers from Rebel (and leave in my stock Tbars) because 150# Eibach springs was supposedly equivalent to the 28mm I was after.... It wasn't even close. Rock hard. Cost something like $300 for the kit and springs.

Searched around and found D Faulkner (in my sig) springs. They make a variety of springs that are rated in the range I needed, unlike Eibach who's lightest spring was 150#.

I called Faulkner and had a great conversation. We agreed that adding a 60# spring and a 4# helper spring was exactly what i was looking for. A few days later the springs came in and I could not be more pleased. to my recolection this was about $220.

Car is now crisp, and if anything, under steers. Much firmer than stock, but not bone jaring

I did take an old set of Bilstein Sports to Bilstein Poway for coilover grooves, new rods, seals, valves, bushings, stickers, and serial numbers. Don't recall the exact numbers we went with. Head of tech is named Juan. Again, only about $300 for everything.

In the end I still spent $800 and it took a couple months, but I got so much adjustability both in rates and in ride height, that there is no question that I made the right choice for me on my car.

mattipuh

Hunting for motion ratios to calculate wheel rates with stock setup. I assume in this spring ratios are not main criteria, but of course theyre needed when we want to know how much mm in corner height effects to kg's at the tires.

mattipuh

I presume tub is 915 with coilovers. Actually dunno yet.

Amber Gramps

915 would have started with torsion bars. Torsion bars for a 915 tub are easy to get and are a dime a dozen. The 911 switched from a 915 tranny to the G50 in 1987.

And ya, all that motion stuff goes right over my head.

mattipuh

Motion rate squared times spring rate = wheel rate = defines spring weight at tires, useful to know when setting up corner balance and when defining spring rates for the car, depenging on if you want more oversteer / understeer in comparison for example to stock setup.

Wheel et and such affects the motion ratio as the geometry where tire contacts the ground may change in comparison to stock setup.

theiceman

i just change stuff till it works better..

Amber Gramps

Word!

kjchristopher

I've never actually seen it on a forum. I'd recommend searching for the lever arm length and then do the math on the torsion bar twist. You may even see spring rates online for various torsion bars. Unless you're seeing pounds/degree, that rate is likely the wheel rate.

Petevb

You're looking for numbers at the shock to calculate either shock valving or coilover springs rates, I assume?

Best numbers I have are .91 front, 1.01 rear, though sources vary somewhat.

If you're trying to use this to calculate a setup based on rules of thumb that work on 944s (ie Milleken wheel frequency targets, etc) I'd caution you that the 911 is different enough that many of those rules of thumb don't seem to work well.

If you're sticking with torsion bars and are not attempting to tune shocks you may be asking the wrong question.

mattipuh

Thanks for comments. didnt need to start adjusting as it was almost perfect without adjustments!
Ive also got torsion bars in 944 race car and didnt figure that it changes this stuff. Duh.