Rear spring rates changing?

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8/8/2017 9:32 PM

I've heard that the old process of using static (unloaded) sag to determine rear spring rate is changing. The new process uses actual spring preload in millimeters to help make the decision and goes like this;

1) Set race sag as usual
2) Measure spring preload
3) If preload is between 2 to 8mm spring is probably good (2mm being more on the stiff side, etc)
4) Less than 2mm spring is too stiff, more than 8 and it's too soft.

Heck, 2 mm is practically nothing. Most springs will almost rattle on the perches at that setting but that's the new trend, even if it means your unloaded sag is huge (45-70mm!). I tried it on my bike and it made a huge difference in my spring selection, from 4.5 to 6.0. Wow! And it worked much better to boot. Obviously, this process favors stiffer rates everything else being equal.

Anyway, just curious what others think about this.

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Retired Mechanical Engineer, published technical writer, mscperformance.com, Bisimotoengineering.com,

8/8/2017 11:10 PM
Edited Date/Time: 8/8/2017 11:13 PM

You've piqued my interest. So basically find the spring rate that allows proper sag while barely being compressed? As opposed to cranking down the spring preload a couple inches like I have to do.

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Life's a garden, dig it.

1996 CR250R
2016 YZ450F
2001 Suzuki Bandit 600

8/8/2017 11:55 PM

This is new? blink blink

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Never try to argue with idiots; they will only bring you down to their level.....and being more experienced, they will beat you at their own game!

2020.5 KTM 450 SXF FE
2006 KX250

8/9/2017 12:59 AM

bvm111 wrote:

This is new? blink blink

That's kinda what I was asking! Maybe NEW is a bad choice of word, perhaps "common knowledge" would be better. However, I've yet to find any reference to the process I described on any of the MX suspension "tuner" websites.

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Retired Mechanical Engineer, published technical writer, mscperformance.com, Bisimotoengineering.com,

8/9/2017 1:06 AM

Tenacious P wrote:

You've piqued my interest. So basically find the spring rate that allows proper sag while barely being compressed? As opposed to cranking down the spring preload a couple inches like I have to do.

Exactly. Proper race sag and the resulting spring preload is all that matters, unloaded sag (bike weight only without rider) isn't even measured.

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Retired Mechanical Engineer, published technical writer, mscperformance.com, Bisimotoengineering.com,

8/9/2017 1:54 AM
Edited Date/Time: 8/9/2017 1:58 AM

bvm111 wrote:

This is new? blink blink

mark911 wrote:

That's kinda what I was asking! Maybe NEW is a bad choice of word, perhaps "common knowledge" would be better. However, I've yet to find any reference to the process I described on any of the MX suspension "tuner" websites.

I generally take up slack in the spring with the collar when reassembling the shock after service and then do five complete turns to compress the spring before installation... appx 5mm.

You should be able to get your race sag within 1-2 turns max in either direction.

To confirm my spring rate is good for my weight I then check static sag is appx 30-40mm ish. This is where I have always tried to be with 100-105mm of race sag and corresponding free sag. I am 215 pounds without gear and I am running a 5.8 rear on both my 2016 KX450 and 2006 KX250, free sag is 32mm on the 450 and 36mm on the 250 which makes sense considering my 450 weighs more than my 250 two stroke...so I could probably use a 6.0 on the 450 but I am currently dropping weight so it was a compromise.

If your free sag is too much you need to go up in spring rate and if it's 20mm to fully extended it is too light.

If it is too stiff you will have to much free sag and it will adversely affect your handling do to your chassis being to low in the rear effectively raking your forks out too far... it will be stable in a straight line but good luck turning!

If you are over compressing a light spring rate to get correct race sag you are storing too much energy within the spring that causes your suspension to not operate properly.

You will probably get about as many opinions on this as what two stroke oil to run along with mine as this has always worked for me. So unless slipdog or Ross from Enzo comes on here and says I'm doing it completely wrong I'm going to keep using this method for me! laughing

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Never try to argue with idiots; they will only bring you down to their level.....and being more experienced, they will beat you at their own game!

2020.5 KTM 450 SXF FE
2006 KX250

8/9/2017 12:50 PM

I wish there was a way to try out 5-10 springs with different rates without spending $75-100/spring... Like I mentioned before, I crank down my spring quite a bit (2" or so) to get both sag's correct.

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Life's a garden, dig it.

1996 CR250R
2016 YZ450F
2001 Suzuki Bandit 600

8/9/2017 1:20 PM

Tenacious P wrote:

I wish there was a way to try out 5-10 springs with different rates without spending $75-100/spring... Like I mentioned before, I crank down my spring quite a bit (2" or so) to get both sag's correct.

Most tuners have lots of used springs. Try asking them about an exchange agreement until you find the right one. However, 2 inches is way too much. I was getting into a similar situation of chasing softer and softer rates to get my free sag number in the ball park. So much so that I started to worry about coil binding with the amount of preload they required. That's when I started asking around and got same answer from two reputable shops. Don't bother with free sag numbers, just use race sag and spring preload.

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Retired Mechanical Engineer, published technical writer, mscperformance.com, Bisimotoengineering.com,

8/9/2017 1:45 PM

If my spring was the right rate, I could preload 6-7mm and 9 out of 10 times my sag would be near perfect.

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Take it to the limit, one more time!

8/9/2017 2:14 PM

Tenacious P wrote:

I wish there was a way to try out 5-10 springs with different rates without spending $75-100/spring... Like I mentioned before, I crank down my spring quite a bit (2" or so) to get both sag's correct.

Funny, people said the same thing about fork springs. The factories listened and out came air forks, which are endlessly adjustable. Now there is a mad dash back to coil springs because people are too dumb to understand their air fork pressures! (im exaggerating, but you get the point).

Personally, i would much rather the factories provide the correct fork and shock spring for your weight from the factory. When buying a bike, you tell them your weight and the bike comes set up for you.

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8/9/2017 4:30 PM

mx317 wrote:

If my spring was the right rate, I could preload 6-7mm and 9 out of 10 times my sag would be near perfect.

In that case either procedure would result in the same spring (or very close). However, I've noticed in cases of a light rider on a heavy bike or a heavy rider on a light bike can result in completely different spring rates depending on what method is used. If faced with this delemia I've been told to use spring preload and not free sag as the guide.

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Retired Mechanical Engineer, published technical writer, mscperformance.com, Bisimotoengineering.com,

8/9/2017 4:35 PM
Edited Date/Time: 8/9/2017 5:56 PM

theycallmeebryan wrote:

Funny, people said the same thing about fork springs. The factories listened and out came air forks, which are endlessly adjustable. Now there is a mad dash back to coil springs because people are too dumb to understand their air fork pressures! (im exaggerating, but you get the point).

Personally, i would much rather the factories provide the correct fork and shock spring for your weight from the factory. When buying a bike, you tell them your weight and the bike comes set up for you.

This. One would expect an $8-10k recreational purchase would include 30 minutes of suspension tuning and some free spring changes. Valving is another beast, but springs are relatively easy to change out. I would love to see one of the big companies implement this type of customization upon purchase. Maybe multiple bar bends as well? Can you say competitive advantage??

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Life's a garden, dig it.

1996 CR250R
2016 YZ450F
2001 Suzuki Bandit 600

8/9/2017 5:15 PM

bvm111 wrote:

This is new? blink blink

mark911 wrote:

That's kinda what I was asking! Maybe NEW is a bad choice of word, perhaps "common knowledge" would be better. However, I've yet to find any reference to the process I described on any of the MX suspension "tuner" websites.

bvm111 wrote:

I generally take up slack in the spring with the collar when reassembling the shock after service and then do five complete turns to compress the spring before installation... appx 5mm.

You should be able to get your race sag within 1-2 turns max in either direction.

To confirm my spring rate is good for my weight I then check static sag is appx 30-40mm ish. This is where I have always tried to be with 100-105mm of race sag and corresponding free sag. I am 215 pounds without gear and I am running a 5.8 rear on both my 2016 KX450 and 2006 KX250, free sag is 32mm on the 450 and 36mm on the 250 which makes sense considering my 450 weighs more than my 250 two stroke...so I could probably use a 6.0 on the 450 but I am currently dropping weight so it was a compromise.

If your free sag is too much you need to go up in spring rate and if it's 20mm to fully extended it is too light.

If it is too stiff you will have to much free sag and it will adversely affect your handling do to your chassis being to low in the rear effectively raking your forks out too far... it will be stable in a straight line but good luck turning!

If you are over compressing a light spring rate to get correct race sag you are storing too much energy within the spring that causes your suspension to not operate properly.

You will probably get about as many opinions on this as what two stroke oil to run along with mine as this has always worked for me. So unless slipdog or Ross from Enzo comes on here and says I'm doing it completely wrong I'm going to keep using this method for me! laughing

bvm, you have the right idea but you are backward on the results of the free sag measurement. If your free sag is too much, you need to go DOWN on the spring rate. It sounds completely backward, but it's true. Here's why:

Spring rate too light: you must crank the preload down considerably to achieve the proper race sag. At this amount of preload, the spring pushes back harder than it should. Thus, the bike has little or no free sag when you are not sitting on it.

Spring rate too heavy: you achieve race sag without much preload on the spring. Thus, it is not pushing against the subframe very hard while you are not on the bike and sags too much.

BTW, I got this info from Enzo. cool

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Braaapin' aint easy.

8/10/2017 3:21 AM

Tenacious P wrote:

I wish there was a way to try out 5-10 springs with different rates without spending $75-100/spring... Like I mentioned before, I crank down my spring quite a bit (2" or so) to get both sag's correct.

theycallmeebryan wrote:

Funny, people said the same thing about fork springs. The factories listened and out came air forks, which are endlessly adjustable. Now there is a mad dash back to coil springs because people are too dumb to understand their air fork pressures! (im exaggerating, but you get the point).

Personally, i would much rather the factories provide the correct fork and shock spring for your weight from the factory. When buying a bike, you tell them your weight and the bike comes set up for you.

Tenacious P wrote:

This. One would expect an $8-10k recreational purchase would include 30 minutes of suspension tuning and some free spring changes. Valving is another beast, but springs are relatively easy to change out. I would love to see one of the big companies implement this type of customization upon purchase. Maybe multiple bar bends as well? Can you say competitive advantage??

Are you two fucking serious? You obviously have no idea how the mass production cost saving thing works.

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