coilbox

Going to change the worn out konis on my 951.

Gaz recommend 450lb front and 275 rear(leaving the torsion bar), for a daily driven car, with a few trackdays a year.

That looks like double the stock springs. Is it overkill for the road???

JohnKoaWood

Spring rates are a very personal choice. Much the same as color. That setup WILL work, but WILL be stiff. All depends on what you want, and how you like your car to ride.

Luckily for you springs are relatively cheap and easy to swap. Color on the other hand...

aben8057

I ended up with 100's in the rear after starting with 375 and decrementing my way down until I found something that worked.

coilbox

What did you have at the front?

Supposing I take weight off thr car; seats, A/C, carpets....will it make sense to change the springs?

aben8057

400's up front and if you take weight off its only going to magnify it. The issue I encountered was the rear bounced from the stiff rear springs. Going into a sharp corner, the rear would bounce under braking.

coilbox

Ok.

The set-up on the rear, from what I figure out is to lower the A-arm first, and then fit the coilover with that length. So the helper spring only comes to action under load, but in a straight line the torsion bar does the job.

Or did you have to play with the coilover length to preload the rear?

Oddjob

Stock spring rate is 125 lb/in, so 450s are over 3 and half times stiffer than stock. That will be fairly stiff on the street. I personally would be around 300 max for a street car, but that is my preference.

Is the car a stock turbo or turbo s spec (23.5 or 25.5 rear bars)? W/ 23.5 bars, the 450/275 setup is pretty middle of the pack, so a pretty normal rate balance. You will see some guys recommend more spring in back and some like Alex recommend less. A lot depends on driving style, preference, and other setup factors (swaybars, alignment, wheel/tires, track layout, etc).

Indexing can be done either way. I have setup my cars so when static, the car is sitting on the coil spring and the torsion bar is basically neutral. And another car that I recently bought, the t-bars are reindexed so both the coil and the bars are compressed/twisted with the static load of the car. I dont think there is significant benefit or difference between methods. The factory setup/spec on the cup cars when running the rear coil spring was what they called "9 deg pre-stress". My estimate is that means the bar twists/rotates approx 9 degs when the suspension is compressed under the car's weight, so around 2-3" compression at the hub.

You do have to play with the coil spring length depending on how much height adjustment is available on the shock body and how the bars are indexed. Between 6 and 8" spring length is common for the rear coilovers.

coilbox

Its a turbo from 1986, with the 23.5 bars.

Thanks for the info on the rear, suppose the only way out is to try.

Ill keep the thread updated when they are on an see the results.

Makis

I would say more like 300lb front and 275lb rear + standard torsion bar will be the correct balance. 450lb is way too much.

Makis

Also GAZ would more likely recommend 450lb rear and 275 front with torsion bar deleted, that sounds more balanced to me. I would check with GAZ again.

Oddjob

Your comment is based on running or testing similar setups on which road courses?

coilbox

Nope, they clearly stated to leave the torsion bars on, the coilover acts as a helper spring.

Plus, 275 of the coilover + 135 of the stock torsion bar(got the figure on rennforum) adds to 410lb. So seems not too far off the 450lb fronts for a 50/50 weight car.

333pg333

Wow, 100lbs sounds very soft?? Of course it's whatever works for you syndrome, but I think it is very dependent on the shocks too.
I have a friend with older konis and something like 400lbs on the front (can't remember rear but it's balanced) and the car is pretty tough to ride in around the city. By comparison I have 630/710lbs (and am going stiffer) with more modern suspension and it's a softer ride for sure. So it's not always just numbers on paper.

333pg333

Yes but that's not the effective rate at the wheels. Not saying that what they recommend is wrong, but it's not merely a case of adding them up to get your finished rates. Gaz has worked with our type of cars for sometime so they would have figured out what works best for their product.

Makis

Approximate calculation I am using of spring rate at the wheel is as follows.
Front is = spring rate of spring.
Rear is = 0.6 * spring rate of spring.