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so im building a frame for my fj40, leaf with sliders and 4 link rear. right now i have my datum line so it would be essentially level, it is just tacked in so i can change it. so i nee advice from leaf spring experts. should i go for more of a higher in the front than rear setup, or vise versa.

ive searched, there is not alot out there. thanks!
 

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I have a old chassis design book from the early 70's and it said that it is best for handling if it is level as you have it. I look forward to hearing some more info.
 

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IIRC, Higher in the front, lower in the rear should induce roll understeer which is generally regarded as more stable than roll-oversteer.

It also allows the axle to move rearward upon deflection which should absorb bumps better.

The opposite would be true for the rear, lower in the front, higher in the rear produces roll-understeer.

Will you notice the difference? I don't know. Since it is tacked up flat, i would stick with that.
 

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Wilson has some good leaf spring tech here. With a little bit of digging you should be able to find it. I even have some of it copied in my "notebook" thread.
 

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I think having a slightly negative roll axis front and rear is what you want.

I designed my flat fender chassis that way. It is just a regular SUA design without a shackle reversal. You can't find too much about leaf spring geometry, but the idea seemed to work out pretty well for me. In general, having the roll slope slightly negative should make the steering wheel less responsive to input, specifically to things like road crowning. Tracking down the road should improve also. It should also allow the front axle to move rearward slightly on compression depending on spring arch.
 
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