How to Measure Spring Rate

[posplayr]

Necessity is the Mother of invention,

I got a used Ohlins for my GSXR 1100G and was debating whether to paint the spring on it or just buy a new one that matches my weight. Anyway the problem posed is "How to measure the spring rate".

After putting my noggin to this for a few minutes and finally discarding the idea of pulleys and weights came up with the simple method.

Put a rod through a piece of rigid plate with an o-ring (modified tie strap method)

Measure the distance to the tape when the plat is the only weight, now lift yourself overhead with something like a pull up bar (i used my garage door), then let yourself settle slowly down on the spring.

If you do it too fast then you will push further that your static weight.

Measure the difference is distance and divide the distance into your weight.

For me I got
K = (Weight lbs) / 2.205 / (L_loaded - L_static mm)
K = 225 lbs/ 2.205 / (33-20.15 mm)
= 7.95 Kg/mm

You can compare against the Racetech calculations. Apparently the stock springs are 6.01 kg/mm so by this I'm 30% stiffer but still 12% low for street riding. I think I'll give it a try the way it is.

http://www.racetech.com/page.aspx?id=56&menuid=62

 

[BassCliff]

Hi,

Jim, sometimes you make my brain hurt.

Thanks for sharing.


Thank you for your indulgence,

BassCliff

 

[posplayr]

Hi,

Jim, sometimes you make my brain hurt.

Thanks for sharing.


Thank you for your indulgence,

BassCliff

It was Dan that put the idea into my head :-\\\

http://www.thegsresources.com/_forum/showthread.php?t=153233

 

[979roadrunner]

When I try to pull up the racetech site I get a blank page. Drat!

 

[posplayr]

When I try to pull up the racetech site I get a blank page. Drat!

did not work for me either when I switched computers.

just go to racetech and look up your bike under "SEARCH"

 

[979roadrunner]

Figures, I get on and their engine has an error. Have to try again later

 

[Mike Derrett]

Mr Posplayer,

Can I suggest that you may want to try it with two weights and measurements. If the spring is truly linear rate, the second measurement will confirm it or if not then let you calculate the non-linear rate.

Try it a second time, but carrying something convenient, like a backpack with something heavy in it. If you were in Australia I would suggest a carton of beer (we always have them handy)

Best Regards

 

[posplayr]

Mr Posplayer,

Can I suggest that you may want to try it with two weights and measurements. If the spring is truly linear rate, the second measurement will confirm it or if not then let you calculate the non-linear rate.

Try it a second time, but carrying something convenient, like a backpack with something heavy in it. If you were in Australia I would suggest a carton of beer (we always have them handy)

Best Regards

Hi Mike,
Just saw this. If the spring rate is"linear" then you need two measurements. The wider the spread in displacement the more accurate. Going between unloaded and the max weight gives that widest spread.
Doing one of teh measurements which si at a lighte load will yeild the same result albiet more than likely with quite a bit more error.

If there is a non-linear rate, then you need more than two data points to estimate that but the min to max still gives you the average rate.

I was sort of having to do pull ups with just my weight and let myself down easy. Doing that wiith even more weight not be possible in my current state of ill conditioning.