Suspension mod primer thread?
 

Apologies if I missed an obvious one, and it seems like there has got to be something, but I'm starting to think about suspension modification on my '86. I know what I want the end result to be (good for long distance but really good for twisty roads), but I need more info on what I need to do to get there. Stock is too roly poly and it seems like it could be tighter in general.

Where's the thread I need? Or is this now that thread?:D

I had the same question for my 85.5. A lot of good recommendations here!

http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/734969-best-suspension-800-a.html

There's a lot of choices out there.. if you're not looking to spend a lot but want to refresh your worn and tired struts and shocks Bilstein is a good choice for performance that's not the price of Koni's. In fact I have a set of rear Bilstein for a 944 (If you want PM me). There's also of course Koni, just OEM Sach/Boge, coilover setups. I personally have a 26.8 hollow front sway bar, 16 mm rear, a castor block brace, strut tower brace, and am putting on Koni Ground Control Coilovers ($$)

Also, not sure of your car's condition but with just all new rubber OEM bushings and new OEM dampers you'd probably notice a much nicer ride. Lowering springs combined with Bilstein struts and shocks would be good bang for your buck.

Cool, a few good links in that thread. Particularly this one: Suspension Information and Upgrades. Shoulda thought to look there first!

It's looking like the best option for the rear suspension is going to be coil-overs, either as a helper for the torsion bars or to replace them. On thing is I don't want to get too stiff, because I do drive the car on long road trips. I don't really know what spring rates should be going where...

Also, I want to do the bushings, just replace them with OEM rubber. It's a bit confusing trying to figure out what I need for the suspension and sway bar bushings. Is there a kit or a guide or something?

Look through the Pelican Catalog, and I am running 250# front spring rate 150# rear with 23.5mm torsion bar.. you'll need helper springs in the rear though (and a coupler on each side).

Pelican catalog is why I'm confused!

So if I have a 126 lb torsion bar, and I want a 150 lb total spring rate, do I then find a helper spring that's 24 lbs?

Helper springs don't add spring rate, they keep tension on the spring so it doesn't fall loose off the perch. Only needed if you keep a torsion bar

Eh, then what am I talking about? When you do add a spring (i.e. a full coil-over) to the rear and keep the torsion bars. I know it's a thing...

And isn't a 250 lb/150 lb spring setup really understeery? The impression I have from the Clark's Garage info is you want equal-ish rates F to R on these cars...

150+126= 276 actual spring rate rear

For spring rates, I'm thinking as near to 200-210 lbs as they sell all around, and for anti-roll bars, 30 mm front and 19 mm rear. Still not sure on shocks, or how I want to do the rear suspension (new torsion bars, replace torsion bars with coil-overs, or add coil-overs to the torsion bar setup). Also having second thoughts about the bushings-- seems like a pain in the ass.

Paragon sells kits for $2k that have Koni Yellows (or at least yellow Konis) with torsion bars and anti-roll bars, but the spring rates seem maybe a little high. It's not a race car, ya know?

Thoughts on any of that?

If you think replacing bushings are too much, torsion bar will murder you....

Dude brand new rubber bushings will make a big difference, you really should, it's not expensive either. Makes no sense AT ALL to put thousands into coilovers or dampers etc and have crappy cracked ruined rubber bushings that are all slop.

I still have those Bilstein shocks for cheap

The standard suspension in good condition is good enough for twisty European roads, so for US highways it should be more than adequate. Just change all the bushes, check and replace as necessary all steering joints to start with, and brace the front swaybar inner mountings.

Heh, I'm a lazy bastard; can't be denied! That's why the torsion + coil setup appeals to me. I'm not sure the condition of my bushings, so I think that's my first step. My guess is that they're in good shape for being 26 years old.

I know I can do the work without issue right up until the torsion bar stuff. Pretty sure I would murder a kitten in a fit of rage doing that...

I'm still a few months away from doing this, but I might hit you up for those shocks if you still have them then.

Well now, if I agreed with that, I wouldn't have made a thread!

Yes, I do.. still shiny looking. I like how they say Nordschleife tested on the side :)

How much? And which shocks?

Are you talking with or without a T-bar? Due to the motion ratio on these cars (not the spring rate), you need to have higher rated springs on the rear than the front. So leaving T-bars out of the equation for the moment. You would want at least 10% more in the rear but really you can run up to 20% pretty easily. A friend of mine took his modified turbo to a suspension guru who has him on something like 850lb front and 1200lb rear on Moton Clubsports. I've got 900/1100 on the same Motons. Of course this is more extreme rates than most would run but the ratio should be the same.

Here is an email I had from Karl Poeltl or the owner of Racers Edge. This was from some years ago when I was trying to figure out what I had on some KW suspension. (Very good if you can afford it.) This will help understand what motion ratio is.

"The info on Paragons site is stuff they got from me a few years ago. In any
case, the 47% is a number that I have calculated By taking measurements. I
am now pulling out one of Porsches own Motorsport sheets that shows all the
rates of their Turbo and "Cup" cars back when they ran competitively.
Porsche lists the 25.5 mm bar as 31 N/mm which is 177 lbs/in. They also then
give the variable rate coilover helper spring rates at 34-65 N/mm which is
194 lb/in - 371 lb/in. They then give the total Rate at the wheel(T-bar plus
coilover) as 45.4 - 58.5. Back out the rate at the wheel due to torsion bar
which they list as 31 and you have 14.4 - 27.5 at the wheel due to the coil
over. So take your pick, 14.4 / 34 is approx 42% or 27.5/65 is 42%.

Bob is right about them being inboard but his numbers are off. Actually they
are correct I think in that the motion ratio is about 65%. But when
calculating wheel rates from spring rates it is the motion ratio squared
that is uses. So 0.65 ^2 is , guess what,... 42.25% which is the number that
Porsches own sheet claims as I outlined above. So your torsion bar is 177 at
the wheel, and your helper spring rate is a 285 which is 119.7 lb/in at the
wheel. So working backwards 177 plus 119.7 is 296.7 pounds per inch at the
wheel. Divide this by .42 and that is you equivalent coilover, or 706 lb/in
coilover (initially I had 661 lb/in which is attributable to my measurement
error - I had 47% and Porsche lists it at 42%).

So it may be a bit stiffer in the rear than I might run but with the ability
to tune sway bars etc... you should be Fine. Your setup is actually much
stiffer in the front than the Porsche cup setup which ran progressive front
springs (200 - 371 lb/in) with the rear setup I described above which is not
that far from what you have( yours is 296 at the wheel and theirs was 259 -
334 lbs/in at the wheel).

Hope this make sense, but believe me, what is above is 100% correct. I can
fax you the Porsche motorsport sheet if you think it will help."

I'd love if you'd e-mail me that, ha

I'm not tracking my car, so I frankly don't care what the cup cars from back in the day were doing.

Ugh, Porsche snobbery. ;)



Explain why higher rates in the rear won't make the car understeery, and try to make the numbers you use meaningful to those of us who aren't already experts.
edit: I meant oversteery, derp.