How to determine correct spring rate for coilovers?
Turbo Mini Forums

Hi guys,

I was reading a post made by 1380Rich over on TMF, and it got me thinking about coilover spring rates.

I've currently got Gaz lowered coilovers all round, and the car handles OK, but the spring rates just don't feel right somehow.

the car is very light at the back, with no battery in the boot (PC680 in car), a custom alloy tank sat in a dropped floor, and a modified rear subby cut down to form a beam and lightened.

the rear arches are tubbed and turretted, to allow it to run fairly low without rubbing.

The springs I've currently got are those that come as standard with the shuddersfield gaz coilover kit, so I'm not sure what rates they are, but the car feels VERY light and skittish, and from what other people have told me, the back end bounces around like crazy on the road and looks pretty unsafe.
I've tried softneing the rear shocks right down, and it's helped matters greatly, but it's still not right by a long way.

my question is: is there any relation between corner weights, and appropriate spring rates? is it just a case of 1 rear wheel carries 125lb, so needs a 125lb spring?
Would it be a wise idea to have my car corner weighted at the ride height I want it at, then get springs corresponding to these corner weights, then have it setup again on the new springs to ensure the corner weights are as they should be?

I'm SURE coilovers can be made to handle better than rubber cones, I reckon it's just a case of fine tuning it all until it's right.

Any advise on choosing appropriate spring rates would be awesome.

Cheers

Nick (writer of exceedingly long posts)

Mr. Prawn, the friendly Crustacean- slowly making steps towards forced induction.

I think with the right springs they would work well. Tbh i was a bit bored and winding someone up lol. The back of mines not bad on coilovers since i softened it up but need to fit me anti roll bar. Rich

2012 Avon class c 2nd place 13.8 @98mph

I'm thinking some slightly softer springs, with a rear ARB could be the answer to getting it to handle right.

are you back on a beam and coilies now Rich>? I thought you went back to rubber cones for Combe?

I want to keep trying with the coilovers, the weight saving is brilliant, and I'm not even sure I could fit a rear subby now due to the size of my dropped boot floor!

Mr. Prawn, the friendly Crustacean- slowly making steps towards forced induction.

i only changed the front to rubber cone over the coilovers .. i have a rear beam so had to keep them on the back, but other than having to have them a bit softer than i would like, i've had no problems on the back.
i thought the front coilovers (gaz with steel brackets) were quite heavy compared to a hi lo, cone and damper. was going to change my spring rates but didn't know how to go about it and combe suddenly came round.

rich

2012 Avon class c 2nd place 13.8 @98mph

interesting idea mate, how did the car feel with coilovers on the rear and cones on the front?

I'm not 100% happy with my front coilovers like you wernt, I've found they have very little droop, and feel very harsh over drain covers and the like. the rear end seems fine in terms of travel and movement, it's just too bumpy!

Mr. Prawn, the friendly Crustacean- slowly making steps towards forced induction.

hi mate
it feels like a mini again now.. , i wasn't sure with leaving coil overs on the back and having rubber cone on the front but it works really well.

cheers rich

2012 Avon class c 2nd place 13.8 @98mph

you're really tempting me Rich!

I still want to find out the ideal spring rate for the rears though....

How are you fitting a rear arb with the beam? will it be a home made jobby?

Mr. Prawn, the friendly Crustacean- slowly making steps towards forced induction.

lol .. do it haha
i've allways wondered what they should be on the rear.. be good to know.

bought a kad arb at combe last year for 80 quid brand new still wrapped.. so going to mount off rollcage (just deciding weather to make a t45 cage for it) if i do it will be encorporated with in it

cheers rich

2012 Avon class c 2nd place 13.8 @98mph

does the KAD rear arb mount inside the boot between the turrets then? I thought it went onto the rear section of the subby like most do....

Mr. Prawn, the friendly Crustacean- slowly making steps towards forced induction.

it does mount at the rear... shall be fun cant remember if it mounts at the front as its the older version

2012 Avon class c 2nd place 13.8 @98mph

Prawn.

OK mines alot heavier anyway to start with (814 kg at the TM RR day a couple of weeks ago) but I too decided to go with cones/hi-lo's on the front and Gaz coliovers on the back.

The first set of Spax coilovers AND the new set of Gaz dampers both came with 1.9 inch ID, 80/175lb progressive springs. This is the norm I think but was shite on the van and I had no end of bottoming out going on.

Through speaking to Protech, I've now ended up with 9 inch 125 lb 1.9 ID Faulkner springs and the rear handling is sorted with these. BUT, as I said, it's a lardy van, even with the rear discs fitted.

I'm about half way through the damping settings with a tyre/arch clearance of 1.5 inches but could go another 10 mm lower if needed. Trouble is, when the rear is full of gear, I end up raising the platforms !

No ARB at the mo but I have incorporated two pads on my beam if ever the need arises. Intention for this would be to keep the bar under the car and pick up with two of the trailing arm bolts on either side. Merlin at Combe do nylon or resin blocks made especially for mounting arb's and the like.

Richard.

Minivanless, but reluctantly happy living with the decision. There'll be another one day.
http://www.youtube.com/profile?user=minimadmotorman#p/u