Author Topic: Shock spring rate checker  (Read 660 times)

Offline dxhall

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Shock spring rate checker
« on: November 17, 2022, 08:42:21 PM »
I am making one of my Guzzis into a dirt-road worthy scrambler.  I suspect the stock rear springs are too stiff, but have no way to measure the spring rate. A real spring checker is easily $1000 (search for ďIntercomp spring checkerĒ).  Has anyone ever tried to make a spring checker that would measure a motorcycle shock spring?  I could weld up a frame like the Intercomp easily enough, but I donít have a source for the scale (or whatever the thing which reads the poundage is called). Thanks

Edit:  hereís the Intercomp tester:



« Last Edit: November 17, 2022, 09:23:52 PM by dxhall »

Online Tom H

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Re: Shock spring rate checker
« Reply #1 on: November 17, 2022, 10:35:24 PM »
Just a thought. I have a valve spring scale. It's just an electronic scale like you would buy for weighing things, can't remember the right word for that type of scale. My scale, you put it against one jaw of a vise or press, set spring against it and close the other jaw or work the press. Then you measure the length of the spring and look at the pounds. Check book for the measurements.

I think if you find an electronic scale that will go the the weight you need, and use a press of some sort, it would work. Heck, maybe a electronic bathroom scale would work??

Good luck,
Tom
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Offline aklawok

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Re: Shock spring rate checker
« Reply #2 on: November 18, 2022, 01:08:21 AM »
 Back in my snowmachine racing days I dabbled a little with some custom spring lengths and found that the factors to consider were:
Spring length compressed and uncompressed,
Load in lbs. At 1/4 1/2 (but brand specific for dual rate springs!!)
To compare springs place a metal ruler on a vertical mount and use a scale under the spring, even a cheap bathroom scale, a lever attached to a rig in some fashion to apply down force.
Yes the results may not be as accurate as what the manufacturers require, but by camparing springs you get a very good feel of what spring rates will do better for you.
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Offline Moparnut72

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Re: Shock spring rate checker
« Reply #3 on: November 18, 2022, 07:55:53 AM »
When I worked in the airplane shop one of my duties was to test valve springs to verify they met manufacturers specs. I had a special unit that measured pounds which was mounted in a milling machine vice. Then used the milling machine to compress the spring to the specified compressed height then check the poundage.

If I were you I would use a drill press with enough travel such as a floor mounted one. Then with a bathroom scale measure the poundage. You could look up the travel of your suspension and press the spring through the specified range and read the poundage on the scale. Close enough for government work, but that's another story. At least that is what I would do.
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Re: Shock spring rate checker
« Reply #3 on: November 18, 2022, 07:55:53 AM »

Online Tom H

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Re: Shock spring rate checker
« Reply #4 on: November 18, 2022, 09:44:10 AM »
Whatever you make, you might want to find a way to contain the spring if it slips. Maybe a length of ABS pipe mounted/attached to the bottom of the press. Put spring in it and compress. Obviously you would make it just long enough to allow the compression you need.

Tom
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Offline Huzo

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Re: Shock spring rate checker
« Reply #5 on: November 18, 2022, 10:01:38 AM »
If you just make a T shaped tool welded to a steel base, with the horizontal top piece pivoted and the vertical the same as length as the spring with  a short piece of tube for the coil to locate in.
Thatís so you donít get killed if it slips.
Have the spring 100 mm from the centre pivot and the top horizontal piece 2 metres long.
Now you can install the spring and hang weights at the end of the horizontal top piece, it has @ ratio of 10:1
If you need 10 kg on the end to compress the spring 1Ē, then you have a rate of 100 kg per inch..(for example).

Offline Mike Tashjian

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Re: Shock spring rate checker
« Reply #6 on: November 18, 2022, 04:02:16 PM »
Unless you need to check a bunch of springs why not just add weight to bike and measure until you move it one inch. Then divide by the number of shocks being used(two I assume).  I have used a fixture in my hydraulic press along with a ruler to measure spring rates but really you don't need anything special for a one off. 

Offline Huzo

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Re: Shock spring rate checker
« Reply #7 on: November 18, 2022, 07:05:41 PM »
Unless you need to check a bunch of springs why not just add weight to bike and measure until you move it one inch. Then divide by the number of shocks being used(two I assume).  I have used a fixture in my hydraulic press along with a ruler to measure spring rates but really you don't need anything special for a one off.
Because the shocks are on an angle so the numbers wonít mesh.

Offline moto

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Re: Shock spring rate checker
« Reply #8 on: November 18, 2022, 10:00:43 PM »
Because the shocks are on an angle so the numbers wonít mesh.

A little trigonometry would fix that up.
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Offline Huzo

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Re: Shock spring rate checker
« Reply #9 on: November 19, 2022, 12:31:35 AM »
A little trigonometry would fix that up.
Yes it will, but I did not presume it was in the tool kit.

Offline Stevex

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Re: Shock spring rate checker
« Reply #10 on: November 19, 2022, 08:55:10 AM »
I checked my LM2 long fork spring rate by compressing it on a set of digital scales, the compressed measurement with the scale reading will give you the rate.

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Offline Stratodisaster

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Re: Shock spring rate checker
« Reply #11 on: November 19, 2022, 04:46:00 PM »
Iíve thinking along the same lines. Maybe Iím dumb but couldnít you just use digital bathroom scales in a fixture similar to the pictured.
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Offline dxhall

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Re: Shock spring rate checker
« Reply #12 on: November 19, 2022, 08:51:42 PM »
Thanks for all the ideas.  I think the digital scale / milling machine quill idea is the easiest and cheapest for me.  Iíll buy a digital scale on eBay and give it a try.

Offline Ed / AF1 Racing

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Re: Shock spring rate checker
« Reply #13 on: November 21, 2022, 01:01:38 PM »
We have that exact intercomp, its a pretty nice load cell under the spring.  Came with two different ones for different rates, and the fork spring adaptors. 

Just about all suspension shops will have one, be easiest to bring your spring by for a measure, its takes all of a few minutes to take some readings at various preloads checking for a progressive wound spring.

If you are close by to us, bring the spring, a 6 pack, and show up at 5:59 and I'll measure it.

Offline Guzzi Gal

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Re: Shock spring rate checker
« Reply #14 on: November 21, 2022, 02:07:49 PM »
We have that exact intercomp, its a pretty nice load cell under the spring.  Came with two different ones for different rates, and the fork spring adaptors. 

Just about all suspension shops will have one, be easiest to bring your spring by for a measure, its takes all of a few minutes to take some readings at various preloads checking for a progressive wound spring.

If you are close by to us, bring the spring, a 6 pack, and show up at 5:59 and I'll measure it.

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Offline Petrus Rocks

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Re: Shock spring rate checker
« Reply #15 on: November 25, 2022, 09:49:09 AM »

Online John Croucher

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Re: Shock spring rate checker
« Reply #16 on: November 25, 2022, 12:33:01 PM »
Yes it will, but I did not presume it was in the tool kit.

There are some charts on the www that make these calculations.  The more leaned from perpendicular, the less travel the shock makes. And affects the spring rate required. 

My bike has a long Magni swingarm.  I moved the top mounting point forward to where older short swing arm frames have the mounting point.  I used a longer shock. 

I made a paper cut out of the shock, swingarm, torque arm, frame to scale.  Moved all the parts to see how the different parts moved together with the Magni swing arm.  It is very complicated.  Especially with the added torque arm pushing on the bottom of the frame.  The torque arm pushes the top of the shock down on acceleration and any road imperfections push the bottom of the shock up.  And then trow in braking that shift the weight forward off the rear shock.  Does it work? Yes.  Magni or Carc is a massive improvement on a shaft drive bike.

Offline Caffeineo

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Re: Shock spring rate checker
« Reply #17 on: November 25, 2022, 06:07:18 PM »
KISS. Most dirt bikes use about 1/3 travel as the sag measurement. Lift the bike up, let it settle and measure the shock length. Then sit on it and measure the length. If you can not get the proper sag by increasing the preload you need a heavier spring. Even easier. Snug a tie wrap around the shock shaft to measure the travel. If you are not bottoming out when riding you are good. Of course this is assuming you are the typical American size.  :grin:
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Offline Wayne Orwig

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Re: Shock spring rate checker
« Reply #18 on: November 27, 2022, 09:01:07 AM »


Scientist have discovered that people will believe anything, if you first say "Scientists have discovered...."

Offline dxhall

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Re: Shock spring rate checker
« Reply #19 on: December 07, 2022, 03:39:17 PM »
Iím continuing to mess with the rear suspension of the frankenguzzi scrambler.  I am wondering if thereís a benefit in making a top shock mount like the one on this Velocette:





Has anyone ridden an old British bike with this kind of adjustable rear shock?  There was a time when shock mounts like these were common.

Offline moto

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Re: Shock spring rate checker
« Reply #20 on: December 08, 2022, 10:59:16 AM »
No personal experience, but the effect of changing the position at the top is to change the effective spring rate. Straight up for maximum stiffness, such as when carrying a passenger. Then the further forward you get reduces effective spring rate to the value that you like best. Without knowing, I expect this arrangement was used mostly to accommodate passengers or luggage.

EDIT: to answer your question, yes, there is an advantage for you here in that you can change spring rates without buying new shocks. The effective damping will also remain as appropriate as it was no matter what setting you use up top.
« Last Edit: December 08, 2022, 11:06:40 AM by moto »
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