General Info on Spring Rates

[DMWWEngr]

Can anybody provide general info on spring rates?? Good links on the topic??

I'm curious as to know how they effect the cars handling and how they are considered when designing a suspension.

Just looking to build up my knowledge base on the subject.

TIA!! ---
Andrew

 

[GregLocock]

Spring rate for a production sedan is designed to give a comfortable ride, primarily. As I remember the front bounce frequency is set to around 1.2-1.5 Hz, and the rear a little higher (say 0.4 Hz higher). These do get tuned a lot further down the track, but these are a good starting point. The higher rear rate is to give a more level ride when you go over a step. These frequencies ar ecalculated using the SDOF equation, f=1/(2*pi)*sqrt(k/m)

The other considerations are to ensure that the spring can handle the loads (particulalry as it approaches full compression), and that it doesn't drop out of the suspension on full droop. Both of these can involve a lot of messing about with variable rate ends, bump stops, and other things. There is a surprising degree of black magic in road spring design.

I would have thought that the effect on handling is not all that great, directly. Many sports suspensions use high spring rates to reduce wheel travel because the tyres are oversize, and it keeps the suspension geometry in a more linear part of its motion.

Cheers

Greg Locock

 

[DMWWEngr]

Greg,

Thanks for the response. In your equation you listed above what is "k" and what is "m". I assume "k" is spring rate...if so, what units is it in, lbs??

TIA!! ---
Andrew

 

[GregLocock]

k is the spring stiffness, referred to the contact patch (typically springs move less than the wheel) , and m is the proportion of the cars sprung mass carried by the relevant wheel. That equation works correctly in Si units, for imperial units use lbf/in and sprung mass in lb, divided by 32.2*12, I think.


Cheers

Greg Locock

 

[sasank]

Hallo!

Can any body explain me what is the bushing rate (refering to body mounts). How to decide how much bushing rate required.

Thanks
Sasank

 

[GregLocock]

Could you start this as a new thread? It is complex Cheers

Greg Locock