Leaf Spring and Axle position.

[scrimshaw]

On a leaf spring/live axle suspension why is the distance shorter at the front of the spring - from axle to eye, than the rear? I understand it has something to do with axle wrap but what exactly does the shorter distance at the front do? Also what problems would/might occur if I reversed the spring?

Thanks for your help.

 

[GregLocock]

The short front distance also helps to give some antiroll stiffness.

I'm not sure what you mean by reversing the spring - if you put the shackles at the front that could be quite interesting. If you effectively mean moving the axle rearwards along the spring then you'll just lose some antiroll and gain some pitch/castor change under traction and braking.

I suspect I have not really answered your question.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[evelrod]

All of what Greg said, plus any solid rear axle located on longitudinally mounted leaf springs, even low hp cars, is subject to violent "wind up" of the axle on acceleration and/or braking. Making the front part stiffer (shorter) has a remedial effect on the problem.

I'm not sure I have seen a front mounted axle mounted the same way, at least I cannot visualize one at the moment. I'm also sure that I'm probably mistaken and someone here will correct me.

Rod

 

[patprimmer]

I see it as Rod does, but I'm not a suspension guy.

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[GregLocock]

I have communed with the spirit of the Last Leaf Spring Designer, and his apprentice.

Basically, you do it for traction control. You get less windup, less danger of buckling, less lateral compliance steer, better ride, and a bit of antiroll action.

There is no rule for the front rear split - 40/60 up to 50/50 is used quite often.





Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[scrimshaw]

Thank you for all your replies.

Greg, your second reply was the answer I was looking for. (Sorry my question was not well asked). Before yesterday I thought all springs had a forward bias and I wondered if there was an ideal ratio, but after looking at some more closely I did find some that were equal spacing. I was also wondering how the spring rate would change, I know that car companies would never waste material and in making one side shorter I thought the spring rate would be reduced to the rate of the short side but the longer rear side probably increases the rate somewhat. Another thought I had was maybe the shorter side changed the arc that the wheel made.

I was toying with the idea of reversing a spring (not the shackles) and using it on a different car but I have given up on that as it had quite a large difference in spacing (32" - 27") and would probably suffer too much from axle wrap.