Rear springs for BMW based Sportster
 

I would be interested to know what other builders have done about the rear springs. Marlin recommend using the standard BMW springs lowered by about 1 1/2" bt colapsing one of the coils (by heating).

Cheers

Martinclan

Marlin Sportster springs
 

Forget about the modified standard springs it's completely impractical unless you have a heavy engineering workshop. I've bought some 60 mm shortened G Max ones from Demon Tweeks. Unfortunately these are a bit bigger diameter than standard so the anti-roll bar needs modifying slightly but this is easier than shortening springs.

Rear Springs
 

I found a company that would make the springs to order - Alpha Springs in Buntingford. They copied the original BMW springs but made them about 40mm shorter - cost £80 for the pair - pretty good I though for a 1 (2) off.

MartinClan

How much adjustment do you have with those from Alpha Springs? The AVO ones I bought seem to be too long still and even with the spring seats all the way up I still have positive camber. Not all the weight is in the car yet but there's not that much more to go over the back - I tried dropping the engine in on Saturday so see how it sits.

Do you have a reference number I can give Alpha Spring so they can run off an extra set for the Sportster?

Rear Springs
 

Hi Patrick

The bad news (for both of us) is although the springs are 40mm shorter than standard (as suggested by Marlin) in my opinion, now I have the engine in, they are still far too long and stiff. The suspension still sits at the far end of its travel and is like rocks! I am going to have to get some others made I think (£80 down the drain :cry: )

I am going to wait now until the build is more or less complete before I do anything about it - don't want to get it wrong again. My guess is they need to be about the same length but about 30% softer - I am hoping that someone else will hae this sorted before I need to make a final decision.

Regards

Robin

Thats a bit of a shame! The hardness of the AVO springs seems ok to me, but its the length thats not correct. They were supposed to 55mm lowering for the standard car. I think I will get some made similar to the AVO ones only shorter. I am, same as you, going to leave it for a bit now.

I managed to source a pair of E30 M3 rear springs from FAB but I can't remember the length and no longer have the car to check. These worked fine, however I also gained as much "upwards" adjustment as possible on the upper spring seats as follows - Cut off half the thickness from the big nut on top of the spring seat, fit without a lock-nut and screw all the way up. Also need to cut a length off the large threaded stud that the upper spring seat locates on to allow the rubber seat to fit properly (it pokes too far through otherwise)

Following on from this...
I recently started a Sportster build - and would like to overcome the rear springs problem. Can anyone tell me the actual spring rate and free length that they used. Mine is an M3 donor and I'm guessing the original ones from the donor are going to be too stiff: what is TOO stiff.
I have spoken to Dave at Dampertech - he can get any length and rate made - has this source been tried by anyone.
Thanks in advance,
Martin

Springs
 

I too would also like to know the rate and length. The ones I have had made are clearly to stiff. They were made from the same section coil as BMW use but about 40mm shorter. With the engine in now and the car almost up to weight they just don't move! My guess is the length was about right but they need to be less stiff - perhaps the same rate as the front. Anyway - I am not gonna waste another £80.... So I am waiting for someone else to try first!

Robin

Re: Springs
 

That will be my £80 I suspect :confused: I think the stiffness of the AVO ones are ok - the car moves down as you put your weight into it and it bounces quite nicely. Its just the length is wrong!

I have done a bit more research on this, had a good chat with Dave Cooper at Track Developments. He will be able to work out the exact rate and length for us all. What's needed is the respective weights and desired ride heights of the cars - mine's a bit bare at the moment! The un-sprung weights will be easy for me, and I guess the fronts are all going to be the same. So if anyone can chip in with their car weight, front to rear will be ideal, I can start to collate it all and get Dave started on some calculations.
Q. does anyone else have 300lb front springs ?
BTW he can also sort out most other handling faults and settings on finished cars. The web addess is www.trackdevelpoments.co.uk
Cheers,
Martin

That some good news. Hopefully once were closer to finishing the car we can get the specs he needs to make us some spings. :biggrin:

EDIT: on a different thread, I've been looking into rear coil overs: http://www.madabout-kitcars.com/phpd...opic.php?t=580