MX5 Donor, Using as a Donor/problems/solutions/advice Info

[PorkChop]

Originally Posted by skov

Those shock lengths are fine, but I wouldn't take the spring rates as gospel.

Nathen had started supplying 400lb springs for the front as he thought it rolled too much, which is what I ended up with.
From my experience that's a recipe for massive understeer. It also gives a horrible jolty ride on bumpy roads as the rear can't react fast enough to catch up with the front.
I'm not convinced Saturn's original values would be much better either.

Having done some calculations (albeit full of assumptions/guestimates/errors) I came to the conclusion that the rear needs to be around 100lbs harder than the front, and that 300 front / 400 rear would be a good starting point.

As a quick test I swapped mine over and put my 250lb springs on the front and my 400lb springs on the rear and went out for a drive.
Have to say it's transformed the car!
The ride is far more composed on bumpy roads, and I've got shed loads of front grip.
It's possibly gone a little too far the other way, as it's ever so slightly tail happy now. It is however nicely controllable and much more fun that way
I'll get some 300lb springs for the front and report back at somepoint.

Ah, didn't know that Nathan had changed the specs John - I copied them off the website when Nathan announced he was going to shut up shop, because they weren't in the build guide.

I don't know the spring rates used, but Spud's car seemed fine to me WRT suspension set up when I've been out in it. I'm guessing Spud used his car as a starting point for speccing the MX5 build.

I need to buy rear dampers and springs for my build (I already have Protech front dampers, which funnily enough are Sierra spec rear dampers and 250lb springs). I've been impressed by the reviews Procomp have got so I was planning to source the rear dampers through them and hopefully get their opinion on spring rates etc to start with.

[skov]

Originally Posted by PorkChop

I don't know the spring rates used, but Spud's car seemed fine to me WRT suspension set up when I've been out in it. I'm guessing Spud used his car as a starting point for speccing the MX5 build.

That was my guess too. The thing is, Spud's car was Sierra based which has a very different rear geometry.

Talking to procomp sounds like a good idea, let us know what they recommend!

[jason 82]

I don't mean to be thick, but if the coilovers we require is 13inch + a 1 inch extention, why don't they specify 14 inch coilovers ? Or am I missing something ?

[Stot]

Originally Posted by jason 82

I don't mean to be thick, but if the coilovers we require is 13inch + a 1 inch extention, why don't they specify 14 inch coilovers ? Or am I missing something ?

I would say they said 13" + 1" as they thought people who had already built and or purchased shocks could add an inch extension to their build and carry on but theres no reason not to go straight for 14" if you are buyng new.

I'm using standard GAZ 14" at the front no problem.

Cheers
Stot

[jason 82]

Cheers for that stot.

[CTWV50]

Originally Posted by skov

Those shock lengths are fine, but I wouldn't take the spring rates as gospel.

Nathen had started supplying 400lb springs for the front as he thought it rolled too much, which is what I ended up with.
From my experience that's a recipe for massive understeer. It also gives a horrible jolty ride on bumpy roads as the rear can't react fast enough to catch up with the front.
I'm not convinced Saturn's original values would be much better either.

Having done some calculations (albeit full of assumptions/guestimates/errors) I came to the conclusion that the rear needs to be around 100lbs harder than the front, and that 300 front / 400 rear would be a good starting point.

As a quick test I swapped mine over and put my 250lb springs on the front and my 400lb springs on the rear and went out for a drive.
Have to say it's transformed the car!
The ride is far more composed on bumpy roads, and I've got shed loads of front grip.
It's possibly gone a little too far the other way, as it's ever so slightly tail happy now. It is however nicely controllable and much more fun that way
I'll get some 300lb springs for the front and report back at somepoint.

Cool I'll swap my 250lb and 400lb around during the final build.

[Davidbolam]

Originally Posted by CTWV50

Cool I'll swap my 250lb and 400lb around during the final build.

I've gone for the rear springs at 250lb and the front 375.

Will give it a go and maybe swap them around see what the difference is.

Hopefully I will get to test it on an airfield before the road and iva anyway as a shakedown

David

[CTWV50]

Originally Posted by Davidbolam

Hopefully I will get to test it on an airfield before the road and iva anyway as a shakedown

David

That's Handy!

[Stot]

I bought a Haynes Manual for the wiring diagrams on Friday only to find the diagrams didn't really match my car too well.

A bit of hunting turned up this page with LOADS of MX5 service manuals.

http://www.mellens.net/mazda/

Really useful to an MX5 builder.

Cheers
Stot

[CTWV50]

Some more info on mx5 donor front suspension and experimentation....

http://www.haynes.co.uk/forums/showt...t=6206&page=31