gszczyrbak New Reader
1/29/21 10:49 a.m.


If I have two linear rate springs, one has a spring rate of 139 lbs/inch and a free height of 14 inches.  And I have another spring with a rate of 218 lbs/inch with a free height of 12.6 inches.  What would be the effect on deflection if each were applied a weight of say 500 lbs.

Here is what I came up with, but I'm not sure it is correct.

Deflection = Load/rate.

Spring 1 would deflect 3.5 inches. (500 / 139) for a  compressed height of 10.5 (14-3.5)

Spring 2 would deflect about 2.3 inches (500/218) for a compressed height of 10.3 (12.6-2.3)

Am I thinking of this correctly?



cyow5 Reader
1/29/21 1:24 p.m.

Yes. Of course the linear assumption is only ever good over some range, depending on the spring. But if you are in that range then you'll be right. 

boxedfox (Forum Supporter)
boxedfox (Forum Supporter) Reader
1/29/21 9:03 p.m.

In reply to gszczyrbak :

In theory, yes. In reality springs aren't the same rate all the way through as cyow5 pointed out. They're also usually a few percent off of the advertised figure even within its usable range. So I think you'll find that while you can get pretty close, the actual compressed height may be off of your estimates by as much as an inch.

frenchyd UltimaDork
1/30/21 10:09 a.m.

In reply to gszczyrbak :

May I suggest you ignore the math and deal with reality?  Stiffer gives the illusion of being in control while the reality is the tires become less compliant and traction is reduced. We all seek that Go Cart feeling  but if your tires are skipping over the bumps your traction is less.  
put a tie wrap tightly on the shock absorber rod and shove it against the shock body.  Then go out and run as hard as you can. If the rod wrap is shoved all the way to the top OK stiffen  the suspension.  But other wise remove the coil over and measure bump steer. Change geometry to minimize bump steer.  
    If you're getting too much body roll and you've already removed as much top weight as possible go to a larger diameter sway bar. Use tubing though. The center doesn't do anything except add weight. 

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