spitfun New Reader
12/16/12 2:40 p.m.

Ok guys,I have a question. I am trying to up the spring rate on the rear of my autocross car. I am not sure on the stock spring value as I keep finding conflicting information on the web. If I move the lower free spring INTO the pivot box-in essence disabling the swing operation I believe I will stiffen the whole assembly up. My spring values are .330" leaf thickness (5 leaves all the same),1.75" wide,40.5" eye to eye. The spring is 4.25" off the ground so if I put a 1" lowering block in there I shouldn't have any tuck in problems. The calculator I found online (link below) says the spring rate should be about 394 lbs. at that point. What do you guys think?? Thanks Rich LINK: http://www.therangerstation.com/tech_library/leafspringrate.htm

erohslc HalfDork
12/16/12 7:36 p.m.

All you will do is change roll stiffness (and probably NOT to your advantage).
Same number of leaves, same distance between eyes = same spring rate.

You seem to be fixated on the rear spring rate. But the critical issue on a Spitfire is getting the rear camber (and thus the rear ride height) dialled in.

Anyway, are you SURE that you need to make the rear spring stiffer?

Maybe you should get the rear camber (and thus ride height) set correctly, and then drive the car to see what you actually have. That will tell you what direction to take.


Ian F
Ian F PowerDork
12/16/12 9:05 p.m.

The thing about a Spitfire is by the time you're putting down enough power and have enough traction that the spring rate is a concern, you have much more important things to worry about, like the differential, u-joints and axles.

spitfun New Reader
12/16/12 10:54 p.m.

I already have a Quaife Diff,race axles and stronger u-joints. The car (RotoSpit) will make about 190 HP at the crank. I have another GP Spitfire (the one in my avatar) that does have a stiffer spring in the rear and a camber compensator as it is an older setup. I know that Triumph softened up the spring on the swing axle car and feel the car should be a little more balanced with 480 lb. front springs and a stiffer spring rate in the rear. Rich

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