Coilover Spring Lengths

[stu8v 68 1 Cars]

Got some Gaz coilovers, well a box of bits...!

 

What spring lengths do people use? I need a reasonable ride height as its a track car.

 

What I don't want is springs rattling around on the strut body so do I need to run helper springs?

 

Also whats the consensus on rates? I have 23mm torsion bars and 25mm antiroll bar (the car is purely for the circuit)

 

 

Cheers for any advice.

 

[Mad Scientist 106]

I don't know about the gaz dampers, but my billies have 8 inch springs with helpers.

 

What engine do you have, because the front spring rate depends on the front axle load to a certain extent.

[stu8v 68 1 Cars]

gti6/vts motor.

 

I was reckoning on maybe 225/250lb as a starting point?

[Mad Scientist 106]

With 23mm bars I am running 275lb, but I also have the weight of a dry sump tank with 8 litres of oil, and a sump guard.

 

It's a bit subjective I'm afraid, but a pair of front springs are £50, so not too expensive to experiment.

 

Others will add their experience, but I'd start at 250lb.

[stu8v 68 1 Cars]

Ok, cheers

[chipstick 382 1 Cars]

I've 8" springs with helpers and it wasn't until it was adjusted down to the lowest possible it luckily came to where I wanted it. 9" springs I wouldn't have been happy with. 7" would give me the ability to go down more, but fortunately I don't want to. Had I known I may have gone for 7" to give me a bit more flexibility either way. I can just remove the helper springs though if required.

 

 

[welshpug 1,646]

probably wont be far off with 250 or 275, the PTS tar spec was 225 lb 8" IIRC and 21mm bars, that's for a sump guarded standard 8 valver.

 

tyres being used will have a bearing on what spring rate you can run too.

[stu8v 68 1 Cars]

Tyres will be slicks or ® track tyres 190/58/15 or 195/50/15

[EdCherry 34 1 Cars]

Decide on your rate, figure out preload, figure out your compression travel from ride height, find the block heights of the spring lengths your interested in. Good to go.

[stu8v 68 1 Cars]

Sounds great, any pointers on how to go about this?

[EdCherry 34 1 Cars]

Heres the short version, excluding how to decide on what spring rate you would like.

 

Once you have your spring rate you need to know the corner weights of the vehicle @ desired ride height. If you can't get this measurement at ride height then a guesstimation will have to do. You now know two things, the rate you want and how far the vehicle will compress when you put the weight of the vehicle on the spring.

 

E.g. You choose a 100lbs/in spring, your corner weight for the front left corner is 200lbs/in so your spring will compress 2 inches to support the vehicle weight.

 

Now you need to know the travel your damper has from the desired ride height. Once you have that figured you should find a spring that has a minimum of the same travel after the vehicles weight has been put on it. The spring manufacturer should be able to give you the block height details, if they can't walk away as they do not know what they are doing.

 

E.g. As per the previous example your spring will compress 2 inches to support the vehicles weight and the damper has 4 inches of travel in compression from ride height. So now you minus your block height from the open height of the spring to give you your travel, which needs to be 6 inches in this example.

 

So far you have determined your required spring travel and have eliminated the springs that are too short. Put your ride height adjuster to the middle of your usable range on the damper. With the car @ ride height this will give you an idea of fitted spring length to narrow your search down even more. Remember to add the back in the travel lost from vehicle weight and you've got yourself somewhere pretty handy to the correct spring length.

 

If the spring is loose in full droop I would use helper springs. Buy the best quality springs you can, just like dampers you buy s*ite you buy twice. Bad springs make a crap dampers job even harder.

[stu8v 68 1 Cars]

Thanks. Ill give it a go. :-)

[Cameron 16]

I found 350lb/in springs too soft for A048's.. so I would recommend at least that if you're running decent tyres purely on circuits. If you go too soft up front then your transient response (i.e. turn-in) is going to suffer.

 

The slight problem with Ed's method above is that you won't be able to accurately measure what your wheel travel will be, as you won't know the block height of your Jounce Bumper (bump stop). If it were me I'd play it safe and measure the gap from the top of the strut body to the underside of the top mount at full rebound (i.e. the amount of piston rod showing, including that hidden by the JB) as this will give you the spring's full travel. If you do this with your current springs then you will be positive that you have enough travel on any stiffer springs you fit.

 

Then go into the Eibach spring catalogue (you can find it on the interwebs) and find a spring that has the rate you want with a travel of at least what you've measured, and that will also tell you the spring's free height. The necessity for helper springs will be down to whether or not your dampers top out with your chosen spring and ride height, but with Gaz coilovers I'd expect there to be enough damper travel past your rebound point (point at which the weight on that corner is zero) to warrant fitting them.

 

Edit: That is if you want to be all mathematical and precise about it! You could always just fit 7" springs of a decent rate (300lb/in+) or 8" in a softer rate and be done with it.

Edited August 21, 2013 by Cameron

[Henry 1.9GTi 36]

I use 350lb fronts with 25mm TBs and 25mm ARB.

 

Its a bit pushy mid corner. BUT, is extrememly dependant on track temp, tyre condition, and the type of corner; angle of road etc.. I also think the shell is too floppy and going 300 or 400 probably wouldn't make much different.

 

They are 7" and dislocate at full drop by about an inch. Cant fit helpers as they increase ride height too much (spring pans as low as the can go without touching the tyre)

 

As a quick note this amount of roll stiffness is not enough to control the camber either.

[petert 578]

I'd start with 350lbs too.

[welshpug 1,646]

Guess rallying is quite different then, ao48's work fine on 225! Were using dunlop moulded slicks on the saxo with similar!

[engine killer 6]

i made a worksheet before for my spring selection. hope this will give you some idea and i am currently running one 120mm 50N/mm and one 120mm 80N/mm for mainly street use.

spring.pdf