Roggaman Posted February 2, 2004 Share Posted February 2, 2004 I have nonadjustably gas dampers up front (on my 280ZX) with 220lb/ft coil-over springs. I'm gone modify a couple of Ohlins adjustably gas damper for my rear (same set-up as original), and I was woundering what springrate I should start with (probebly have to change them to fine-tune the handling, but want to come as close as possibly). My car has close to 50/50 weight distribution and weighs aprox. 2640lbs. I want the rear to be on the firm side. Any suggestions? /Roger Quote Link to comment Share on other sites More sharing options...
ZROSSA Posted February 2, 2004 Share Posted February 2, 2004 Roger, This is going to depend on you applicaton of coarse. I away read that when road racing, cars with semi trailing arm rear suspension needed to be set up stiff to minimise the camber and toe changes that happen with that design. Some even went as far as changing the inner locating points to make it work more like a trailing arm then a semi trailing arm (Look at the rear of a RS500 or first gen M3). What I am getting at is that spring rate is depending on the extent of the modifications done already. If your locating point are standard then you may want it much stiffer then the front. Becuase the weight is neer 50/50 you will want to run aleast 25 lbs up on the front rates any way to stop a spring frequency imbalance. I would have a bit of a search around on bmw m3 sights and see what they run. Hopefully some of the guys here will have more specific info on the ZX. Cheers Douglas Quote Link to comment Share on other sites More sharing options...
Roggaman Posted February 2, 2004 Author Share Posted February 2, 2004 Roger' date=' This is going to depend on you applicaton of coarse. I away read that when road racing, cars with semi trailing arm rear suspension needed to be set up stiff to minimise the camber and toe changes that happen with that design. Some even went as far as changing the inner locating points to make it work more like a trailing arm then a semi trailing arm (Look at the rear of a RS500 or first gen M3). What I am getting at is that spring rate is depending on the extent of the modifications done already. If your locating point are standard then you may want it much stiffer then the front. Becuase the weight is neer 50/50 you will want to run aleast 25 lbs up on the front rates any way to stop a spring frequency imbalance. I would have a bit of a search around on bmw m3 sights and see what they run. Hopefully some of the guys here will have more specific info on the ZX. Cheers Douglas[/quote'] Well, its kind of a semi-race car, so I have everything adjustably, and have modified the hole suspension (the car is lowered ~3,5"). My front suspension works very well, but I never got the rear to hook up the same way. I have also heard, that the way to go (if not completely rebuilding the rear) is to go very stiff on springs and dampers on the rear. Since my dampers can be adjusted in 51 steps, I can turn them ultra-stiff. But I guess (hope) that we are on the right track about the springs, since your figures are what I was thinking about to. /Roger Quote Link to comment Share on other sites More sharing options...
ZROSSA Posted February 3, 2004 Share Posted February 3, 2004 Rodger, Have you changed the locating points where the trailing arm meets the chassis? 3.5 inchs is a big drop for a semi trailing arm. I think you will need to get it set up do that you have very little camber at that ride height and then make it stiff so the camber curve cant change around. I saw a photo of a racing 510 that had the inner rear link made adjustable for up and down movement. May have been in "how to hot rod your datsun". I though about how to acheive the same adjustability youing rose joints for my race car but never came up with anything strong enough. I was trying to put a independant rear in my old corolla race car. I had a early 80's rear end out of a supra but in the end it was much easier and lighter to use a beam axel. I am not sugessting you do that. Your damper double or triple adjustable? Douglas Quote Link to comment Share on other sites More sharing options...
Drax240z Posted February 3, 2004 Share Posted February 3, 2004 1100lbs/in is a fairly stiff setup in the back of a 510... I believe it gives a wheel rate ~275lb/in range with the semi trailing arm setup. Wheel rate is just a ratio of the distance from pivot to spring, and pivot to wheel so it's not too hard to figure out from there... Then you can basically apply the 300 posts here about choosing springs to you car, just use the early Z spring rate and compare it to your wheel rate. (in the early Z, the wheel rate and spring rate are essentially the same, while the 510 and ZX they are vastly different) Once you figure out what wheel rate you want, then use the ratio to calculate your actual spring rate... Quote Link to comment Share on other sites More sharing options...
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