inboard ratios help

[jayz395]

hi im building new race car and gonna try and put in board suspension on the front. my question is why use ratios like 2:1 and not just 1:1. secondly if i normally use a 250 spring and using a 2:1 ratio do i divide the spring by 2 which would make it a 125 spring?

 

[hemipanter]

You may use 1:1 ratio, or any suitable ratio for a good istallation. A 1:1 ratio makes the coilover travel a longer distance than if you use an Mr of 0,5 as the coilover travel only 1/2 the distance which put higer demand for the shock to control the wheel movement regarding play etc. But it allowes for a tighter installation.

However, the spring required is Mr^2, and the reason is that it concern the change in N per mm, and not the lever ratio only.

Regards
Goran Malmberg

 

[jayz395]

ok if i choose a 2:1 ratio, the wheel comes up an 1 inch while the shock goes down 2 inch?? how do i work out wot spring i would need? sorry but im new to this.i normally use a 250 spring but thats on outboard suspension. ive ordered chassis Design - Principles and Analysis by Milliken and Milliken is this book anygood?

 

[Yawing]

To maintain the same rate at the wheel "wheel rate", if you go from a MR of 1 to a MR of 2 you will need to divide the original spring rate by 4 to get the same wheel rate.
ie the wheel rate is the spring rate/MR^2

So a 250lb spring @1:1 means you need a 62.5lb spring @2:1

 

[Yawing]

EDIT*
Sorry,

just had the formula around the wrong way for the convention you used for motion ratio. In that case wheel rate=spring rate x MR^2.

Spring rate still needs to be 1/4 of original.

 

[jayz395]

tell me if im being think but under stand to divide by 4, but say i used 1:6 or that i dont really understand the calcuation.

wheel rate=spring rate x MR^2.
250*2.1 ?????????

 

[patprimmer]

I think an old Greek guy called Archimedes might argue strongly for 1:2 mechanical advantage = 2:1 change in load and 1:2 change in distance. It is a simple lever for crying out loud.

Regards

Regards

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[NormPeterson]

Probably off-topic, but possibly relevant - about a year ago Hot Rod Magazine had a paragraph in one of their issues about this site.


Norm