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Determining Spring Rate on rear shock.

matty

matty

Well-known member
Joined
May 19, 2004
Location
Oakland
Moto(s)
Doctor650 and lil buddy
Name
see above
Hi all,

I'm wondering is there a method to determining the spring rate of a given spring for a rear shock? Could a suspension shop do it?

thanks in advance.

and to answer the Why?

i picked up a 900rr shock, modded to fit a hawk, but it has a mystery spring. its neither a hawk spring nor a 900rr spring. and there are no markings on it.
 
Just remove the spring from the shock, hold it up to your chest and compress it between your palms as hard as you possibly can. The number of veins that pop out of your forhead after 10 minutes of doin so is the actuall spring rate :thumbup


But really tho... there are bench testers used by suspension shops that compress the spring and find its rate but I cant tell you where exactly to find one :teeth
 
HOW TO DETERMINE RATE — Rate, which is the change in load per unit
deflection, may be tested by the following procedure:

1. Deflect spring to approximately 20 percent of total available deflection (free
length, minus solid height) and measure load (P1) and spring length (L1).

2. Deflect spring not more than 80 percent of total available deflection and
measure load (P2) and spring length (L2). Be certain that no coils (other
than closed ends) are touching at L2.

3. Calculate rate (R) lb. per in.
R = (P2 - P1)/(L1 - L2)
 
Simple math. But, the shop will need to have a way to compress the spring, hold it there, and at the same time take a pressure reading off the spring. I would think that a suspension shop would have this as a required piece of equipment. But you'd want to ask anyway.
 
ST Guy said:
HOW TO DETERMINE RATE — Rate, which is the change in load per unit
deflection, may be tested by the following procedure:

1. Deflect spring to approximately 20 percent of total available deflection (free
length, minus solid height) and measure load (P1) and spring length (L1).

2. Deflect spring not more than 80 percent of total available deflection and
measure load (P2) and spring length (L2). Be certain that no coils (other
than closed ends) are touching at L2.

3. Calculate rate (R) lb. per in.
R = (P2 - P1)/(L1 - L2)
Click to expand...

Source:

http://www.planetspring.com/pages/22_secrets_calculating_load.html
 
Actually, Lee Spring, but I'm sure the same source is in many places.
 
A competent suspension shop will be able to rate the spring for you. Be great if they would rate them all in advance when they first receive them from their suppliers:thumbup (instant of going with the # stamped on the side).

100061.jpg
 
Thanks to all:thumbup, I'll call around to some shops.
 
I'd be shocked if any suspension place did not have a way to check spring rate. It's key to making informed decisions on suspension setup.
 
Unless the spring is a progressive spring, then it actually has a variable spring rate depending on how far it is compressed.
 
Well, technically you're correct. Sort of.

A spring that has a constant wire diameter, wound diameter and coil spacing is technically a single rate spring. However, when you measure it, it's not perfectly linear. That's why when measuring the spring rate, you take a measurement at 20 percent compression and at 80 percent compression and the spring rate is derived from those two numbers which are at the start and the finish of the universally accepted operational range of conventional compression springs (20 to 80% of available travel). For practical considerations, a conventionally wound compression spring is considered to have a single rate.

However, a progressively wound spring will have a much more non-linear spring rate depending upon how far the spring is compressed. This is because as the spring is compressed, the coils with the finer pitch bottom out and effectively shortens the spring free height which raises the spring rate.

Of course, the further you compress a spring, the higher the forces go. But this is not to be confused with the spring rate.
 
The spring rate is the variable "k" in the universal spring equation:

F (force) = k X d (distance deflected)


Typical linear springs have a "linear" range where K is fairly constant.

A progressive spring can be made any number of ways: changing the physical spacing of the coils in a section of the spring, changing the heat temper of coils in a section, changing the diameter of coils in a section, but the upshot is the same: k is nonlinear by design.
 
Last edited:
Matty needs to know what spring is on his new shock so he can bolt in on and determine whether it works for him. The rate will allow him to order a different spring if it doesn't. The competent shop of his choice won't sell him a progressive spring because they are competent. Unless they are feeling deviant that day. Or its a Monday morning. Or maybe a Friday afternoon :teeth
 
matty said:
Thanks to all:thumbup, I'll call around to some shops.
Click to expand...
Matty how much do you weigh?? I have a 1000# Eibach spring that came on my Fox. Too soft for me... On the spring for our bikes, it's a 6 inch spring... The rate will be real high cuz there's no linkage.Usual the spring will have it stamped on there.

PM me
 
install in bike, ride
too soft= replace w/stiffer spring
too hard= replace w/weaker spring
take it to LE in SJ/they determine rate while changing out spring
if you want bling, get Ti spring= lighter
cheap, easy :)
 
Last edited:
EastBayDave said:
install in bike, ride
too soft= replace w/stiffer spring
too hard= replace w/weaker spring
take it to LE in SJ/they determine rate while changing out spring
if you want bling, get Ti spring= lighter
cheap, easy :)
Click to expand...

All well and good, but many riders can't tell the difference between a soft or stiff spring and light or heavy compression damping.
 
ST Guy said:
All well and good, but many riders can't tell the difference between a soft or stiff spring and light or heavy compression damping.
Click to expand...
maybe, but we'd at least encourage new/young riders to attempt to ride w/enough seat-of-the-pants feeling to find the "sweet spot" for them. It seems to be the way everyone learns; experimentation. Very few get an experienced tutor/teacher to mentor them while learning suspension tuning.

It's the way I learned; playing around w/settings. Noting differences while out riding by meself (riding alone, time/patience to pull over & make a note, then a change, & then ride again, pull over again, & note the difference. Ride again, make a change, note difference.) Seems todays riders expect everything to be close w/o needing a little experimentation.

I met one guy a while back who didn't know what damping meant? :wtf :squid
 
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