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How to identify spring rate?

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Got a 2009, how do you identify the spring rate? I thought the rear spring had the rate stamped on it, or is that just aftermarket? On my 2009 yz125 it has a silver rear spring, is that the stock color? Doing the fork seals today, will the front springs have a rate on them?

 

Hoping its all stock, cause the stock springs are perfect for my weight. 

 

 

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The stock spring in a 2009 YZ125 is made of Titanium versus more common steel springs.

To confirm it's really Titanium and not simply a steel spring painted silver, a magnet won't stick to the Titanium.

 

The standard spring rate is 4.7kg/mm and about right for a rider in the 140-150lbs range without gear.

As per the service manual it should be identified by 3 red markings on the last coil near one of it's extremities.

 

green : 4.5kg/mm

red :     4.7kg/mm

black :  4.9kg/mm

blue :    5.1kg/mm

 

The only sure way to know the spring rate is to test it in a spring rate tester (suspension shop),

my 4.9's actual rate is 4.925, almost spot-on as rated but springs can have some variance between

nominal and actual rates due to manufacturing tolerances.

It only takes 5% of error in a 4.7 to turn it into a 4.9 or 4.5

Edited by mlatour
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If you have a titanium spring on the rear it is almost certainly stock, as very few folks would pony up for a titanium aftermarket spring.

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If you have a titanium spring on the rear it is almost certainly stock, as very few folks would pony up for a titanium aftermarket spring.

 

Not necessarily. I have swapped springs on a couple of my YZs and I always look for a used titanium in the range I need.

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The only sure way to know the spring rate is to test it in a spring rate tester (suspension shop), my 4.9's actual rate is 4.925, almost spot-on as rated but springs can have some variance between nominal and actual rates due to manufacturing tolerances.

Which 4.9 spring was it?

Was the rate constant? In other words did you measure the rate over a broad range of displacement?

I didn't like the 2007 Ti spring. Felt and behaved too progressive. So I re-installed the stock 2004 KYB steel spring and it's much better. Especially the rear traction.

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Bike is a 2010 YZ125 and I'm about 170lbs. before gear

so I increased the spring rate from the stock 4.7kg/mm to a 4.9kg/mm (constant rate) (stock YZ250 Ti Spring).

 

A local suspension guy doesn't regard the YZ's Ti. springs too highly, he must have about 10 or more

used ones sitting in back of the shelf as he prefers to use steel springs in his customer's setups.

I got it for practicaly nothing (traded him for a used aluminium throttle tube and a few other spare gizmos I had lying around).

 

He tested a few 4.9 Ti  while I was there to find the closest one to the nominal rate, and if I remember correctly

he took readings at both 1" and 2" of compression (perhaps even a third reading as well but can't confirm).

 

From what I understand the Ti spring has it's drawbacks, it reacts quicker than a steel one but can develop 'harmonics' during rapid suspension movements (whoops)

and as you mentionned despite being 'constant rate' aren't as linear as steel springs. (I'm be no means a suspension expert)

If so, I don't think it's any concern for my skill level and recreational MX'ing. I simply prefer the Titanium's lighter weight versus the 5.0kg/mm steel spring I used previously to it.

Edited by mlatour
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To OP,

sorry almost forgot to mention infos about the fork springs,

 

the stock fork springs are .418kg/mm or more commonly referred to as .42kg/mm

 

From the service manual and from what I've seen on mine, the stock .42kg springs are the only ones that do not have any factory markings on them.

All the other optional Yamaha / KYB springs listed in the YZ125 service manual have coded markings at an extremity (spring's flat end)

Edited by mlatour

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