How do I find my shock spring rate?

[_Hammy]

Ok. Very basic question I know! Do I have to take the spring off the shock to find the spring rate stamped somewhere?

09 ec300. Sachs

I've been reading through all of the posts on static sag, so I have just set the preload to 10mm (from 7.5) and may look at greasing the linkages as well as I'm not sure of its history. Makes sense to know my spring rate while I'm stuffing around.

 

[Jakobi]

The only way to know for sure is to take it off the shock and measure it. Either take it into a suspension shop with the tools, or by rigging up something to determine its rate yourself.

To measure the rate you have to compress the spring and measure the load and the distance it is compressed. The rate is load divided by that distance. You would do it in several increments like 10, 20, 30, 40mm, etc, and you'd need an accurate way to measure the load and fixture to hold the spring staight.

With a shock spring you might get away with stacking weights on the spring on a bathroom scale since the spring is probably wide enough to stay stable.

 

[_Hammy]

Mmmm, sounds like a bit if a hassle I think! I'll be sending it to Dirtworks for a service/revolve eventually anyway so I might wait until then.

My main aim at the moment to give the suspension setup the best shot myself, so I firstly work out how far off "working well" I think it is, and secondly so I can properly communicate what works and what doesn't.

 

[djroggen]

It should be stamped on the spring but likely under the spring were it would be hidden by the base is the shock.

 

[CACTUSREID]

hammy, if you've never changed the springs from stock, they are almost certainly to soft for your weight. unless you weigh 150 pounds, 68 kilos,not sure of the "stone" conversion. the 1st step in suspension is putting in the correct springs on both ends for your geared up rider weight. stronger springs will allow you to ride farther up in the stroke, get more useable travel, and be plusher,as you will need less preload on the springs to get your sag numbers where they should be. lots of folks try to compensate with clickers to over come the wrong size springs. don't be nervous, if you have to go up 2/3 or 4 rates from where you are now on your springs, your ride will be much improved from a bound up highly preloaded spring that's to weak for your weight.notice that i have not used the term "stiffer" as this scares off people-it's quite the opposite, stronger springs, lightly preloaded, are a wonderful improvement !!

case in point, i'm 230 lb,s 104 kilo dressed up ready to ride.

my 11 ec 300,i went from .42's on the frt to .46's, and from .52 to a .56 spring on the rear.
my ktm 525 exc dualsport/baja bike started life with .42's frt and .68 (non linkage bike) on the rear.
i'm now running.50's up frt ( 25 liter baja tank on it ), and a 10.4 spring on the rear.
both my bikes ride and handle beautifully!
try it you will be pleasently suprised!

 

[webmaster]

If the markings have worn off - you can measure the dimensions of the spring to calculate the spring rate.

A quick google search and I found this webpage with formula - it has calculator at bottom of page.

http://www.therangerstation.com/tech_library/coilspringrate.htm

The torsional modulus of steel is 11,250,000. If you are calculating for a titanium spring (e.g. I have a yamaha yz spring on my husky sachs) - the torsional modulus a different value and the calculator above won't work...

jeff

 

[_Hammy]

Thanks for all the info. I think I'll go ahead and pull off the spring and try and find the markings, and also grease the linkage etc... so there's no chance that that's contributing to any poor handling. . This bike has apparently had the suspension serviced/setup twice so I'm not sure how far from stock the whole setup it is. I'm 95kg naked, but the shock action was pretty firm with only 7.5mm preload. Anyway, lots of unknowns still at this stage

The forks seem to be typical of what I read about the sachs. Firm and harsh on square edged hits. I've backed the compression off half a turn and its made some difference already, but I think I need more rebound damping on both the front and rear.

Anyhow, these are just the thoughts of the inexperienced and I'm trying to do the right thing and setup the rear first.

Hopefully as I move through these settings I'll start get get a good grasp of how the handing changes, and work towards my best setting, before heading to the tuner with some better knowledge

 

[_Hammy]

If the markings have worn off - you can measure the dimensions of the spring to calculate the spring rate.

A quick google search and I found this webpage with formula - it has calculator at bottom of page.

http://www.therangerstation.com/tech_library/coilspringrate.htm

The torsional modulus of steel is 11,250,000. If you are calculating for a titanium spring (e.g. I have a yamaha yz spring on my husky sachs) - the torsional modulus a different value and the calculator above won't work...

jeff

Ok. Shock is off and there are no markings on it. I've tried this calculator and come up with a rate of 0.49 (indicating a soft spring?) which doesn't sound right as this shock only had 7mm of preload and was what I'd call very firm. From the way the calculations are done, I'm thinking that there must be quite a degree of error.

So it was firm, with possibly too little rebound damping (as felt by a novice):

7mm of preload
Rebound damping 18 clicks out,
LSC was 11 clicks out
HSC was 13 clicks out.
Race sag 127mm
Static sag 52mm

Thanks for your instructions Jakobi but I don't really have the tools for that approach, and it'll go to a tuner eventually

Anyhow, I'll service the linkages and mull over the next step. I'm suspecting that I'll put it back together with 10mm preload, measure the sag again and see where that leaves me.

 

[CACTUSREID]

the more preload you crank into the spring the firmer or harsher it will feel right from the get go. if you have a suspension tuner nearby, any good tuner will have a spring tester,that they can tell you what you have now. they can also help you with what you will need for springs for your riding level/style/weight etc.

 

[_Hammy]

With 10mm preload I now have 124mm of rider/race sag and 44mm of static sag. Still not in the recommended range of 110-120mm and 35mm respectively, so I'm guessing that this spring is light (as suggested by others)

Id still like to get it working better before I go to a tuner ( for my education more than anything) , so should I add more preload at this point, or just start working with the clickers now? Rebound first I gather

 

[Jakobi]

You can add more preload to bring the static down to 35mm, and then see where the race sag sits. Ideally, a heavier spring with less preload will still allow it to sag a little less in both departments.