2006 YZ250 Shock unfolded

Finally getting around to posting this, russ17 had to light a fire under me to get me motivated... :applause:

We ran the 2006 YZ shock on the dyno and did some back to back testing by graphing the stock shock and then running an '05 16mm shaft with '06 valving in the '06 body.

Really interesting, first off, when compared back to back (with the same valving) the 18mm shaft is about 10% softer on compression and 18.5% softer on rebound than the 16mm shaft with the same piston and valving. This

comes at no real surprise because we have less swept volume with the 18mm shaft vs. the 16mm. What is surprising is the rebound damping on the '06 shock is about 450#, which about 25-30% lighter than prior years. Not only are we dealing with less swept volume ( the amount of fluid flowing past the piston), but a much lighter shim stack as well. The KYB usually runs 5ea. of 36.2 mm face shims before the transition, the '06 shock runs 5ea. 36.15mm shims, the rest of the stack is the same.

The 18mm has about 4% less swept volume than the 16mm shaft. But the 18mm shaft will displace about 21% more fluid through the compression adjuster. With a sizeable increase in volume passing through the compression adjuster, you would think that the valving would be changed from '05 and prior years, not so, the compression adjuster is identical to last years model in piston design, spring, and shim stack.

Here are the valving specs for the '06 YZ250 2 strk shock.

Comp.............................Rebound

40.2x10........................36.15x5

29.1.............................25.1

38.25...........................36.25

36.25...........................34.25

34.25...........................32.25

32.25...........................30.25

30.25...........................28.25

28.25x2........................26.25

26.25...........................24.25

24.25...........................23.25

22.25

20.25

The Ti spring has also proved interesting. After weighing the spring against an OEM spring, the difference in weight is about 8 ounces. When you take into affect the increased in weight of the '06 shock vs. the prior years. There is barely a few ounces of difference. Also, Ti springs have seemed to given the spring industry a challenge in manufacturing versus the steel counterpart. If you take a look at the dynamic graph, you'll see a sizeable amount of progression in the Ti spring (I didn’t have a stock spring to graph, but the steel spring is almost a flat line compared to the Ti). Also the two graphs show the difference between the action of the spring with and without the rubber bumpers. The 2006 YZ 250 2 strk shock starts soft and ends up with a about a 5.2kg/mm rate, much stiffer than years past.

Take Care, John

2006 YZ shock (Medium).GIF

2006 YZ Ti Spring (Medium).GIF

05 YZ 250 shock std USA stack. John I see many differences, 05 vs 06. Good info thanks!

compression

40.2x13

36.1

32.1

40.2

38.2

36.2

32.2

30.2

28.2

26.2

24.25

22.25

rebound

36.2x6

28.1

36.3

34.3

32.3

30.3

28.3

26.25x2

24.25x2

22.25

Finally getting around to posting this, russ17 had to light a fire under me to get me motivated... :applause:

We ran the 2006 YZ shock on the dyno and did some back to back testing by graphing the stock shock and then running an '05 16mm shaft with '06 valving in the '06 body.

Really interesting, first off, when compared back to back (with the same valving) the 18mm shaft is about 10% softer on compression and 18.5% softer on rebound than the 16mm shaft with the same piston and valving. This

comes at no real surprise because we have less swept volume with the 18mm shaft vs. the 16mm. What is surprising is the rebound damping on the '06 shock is about 450#, which about 25-30% lighter than prior years. Not only are we dealing with less swept volume ( the amount of fluid flowing past the piston), but a much lighter shim stack as well. The KYB usually runs 5ea. of 36.2 mm face shims before the transition, the '06 shock runs 5ea. 36.15mm shims, the rest of the stack is the same.

The 18mm has about 4% less swept volume than the 16mm shaft. But the 18mm shaft will displace about 21% more fluid through the compression adjuster. With a sizeable increase in volume passing through the compression adjuster, you would think that the valving would be changed from '05 and prior years, not so, the compression adjuster is identical to last years model in piston design, spring, and shim stack.

Here are the valving specs for the '06 YZ250 2 strk shock.

Comp.............................Rebound

40.2x10........................36.15x5

29.1.............................25.1

38.25...........................36.25

36.25...........................34.25

34.25...........................32.25

32.25...........................30.25

30.25...........................28.25

28.25x2........................26.25

26.25...........................24.25

24.25...........................23.25

22.25

20.25

The Ti spring has also proved interesting. After weighing the spring against an OEM spring, the difference in weight is about 8 ounces. When you take into affect the increased in weight of the '06 shock vs. the prior years. There is barely a few ounces of difference. Also, Ti springs have seemed to given the spring industry a challenge in manufacturing versus the steel counterpart. If you take a look at the dynamic graph, you'll see a sizeable amount of progression in the Ti spring (I didn’t have a stock spring to graph, but the steel spring is almost a flat line compared to the Ti). Also the two graphs show the difference between the action of the spring with and without the rubber bumpers. The 2006 YZ 250 2 strk shock starts soft and ends up with a about a 5.2kg/mm rate, much stiffer than years past.

Take Care, John

Good Stuff JC

Man this mistifies me. With a 21% increase in volume that the adjuster sees I would of thought there being a change. I know that they went with a bigger rezzy in 06. At first glance this makes me think that there is little impact with these adjuster's (well in the LS anyway), But I wonder how much of a difference this volume change effects the HS through the adjuster.

John,

Would you help me with some suspension settings/spring rates to start off with on my 06 YZ250? I weigh 135 Lbs. and ride/race at the novice level. Thank you for all the work you and the team at MX Tech always do for us.

:applause:

I love this stuff.

John - Thanks for the excellent post.

A couple of simple questions for you on the spring graph.

First of all, what are the rubber bumpers that you're talking about? I know of the shaft bumper, but I assumed that would not show up until the end of the stroke. I must be missing something really simple??!!

Secondly, when you run these test is there ever a need to ensure that the spring is not binding? Would it matter?

Lastly, in your experience, do the manufacture's rating correspond with the early, mid or concluding rating as seen in the graph? I guess I would have my answer if I knew what the 06 250 came with.

Again, great post.

At first glance this makes me think that there is little impact with these adjuster's (well in the LS anyway),

Russ,

What'll even throw you more is that during one test, I removed half of the shims( one each of every size) on the adjuster and only showed a few pounds of compression difference. The dyno is moving that shock that shock at 75% of max shaft speed, makes me wonder what lies in the last 25%??!!

First of all, what are the rubber bumpers that you're talking about? I know of the shaft bumper, but I assumed that would not show up until the end of the stroke. I must be missing something really simple??!!

Dave,

The new Ti spring is wound such that the end coils are a good 1/4 from touching the next coil. (I failed to take a pic of this) As far as I can, the bumpers are there to reduce the progression rate by having the end coils flatten against the next coil as a soon as possible. Although this helps, the spring still has a good bit of progression.

Secondly, when you run these test is there ever a need to ensure that the spring is not binding? Would it matter?

Good point, our Rhoerig sping rater is probably one of the better ones in the industry. It provides flat surfaces for the spring to rest on. But alot rides on the quality of the wind of the spring, it's very possible to get aftermarket springs which the ends are not paralell, this would cause issues during the rating process. Not to mention, the issues it would cause running on the shock.

We are going to be running tests to show the impact of the "twisting" of the spring during compression and extention. We are going to mount the spring on bearing surfaces which will let the shock twist with a lot less resistence.

Lastly, in your experience, do the manufacture's rating correspond with the early, mid or concluding rating as seen in the graph? I guess I would have my answer if I knew what the 06 250 came with.

They seem to take an average across the board, this is excluding the PDS springs from WP, which usually spec out way higher than published.

Vetmxrider,

I would recommend a 4.6 for the shock and a pair of .36 in the fork (this plus the 2.0 inner chamber springs will give you an overall rate of about .38)

Take Care, John

Spring Rater.jpg

on the 2006 yz450f, do you guys think that a 183 lb rider without gear on that races 250B, would need to change out the stock rear spring?

on the k factors have you guys found out what the weight classes are on the 2006 450f thanks

John,

Thank you for the spring rate advice! :applause:

Vetmxrider

John - thanks for the info.

I just checked the fiche and realized what the bumpers are. The earlier models that I looked at didn't have these. Thanks for clarifying that. BTW- Yamaha is calling it a "spring seat".

Lastly, can the dyno move the shock at velocities as one would get in the field?

Can someone please tell me what shock fluid came in the 06 yz250 from the factory?

Now what I have noticed is the valving between the 05 and 06 is that the 05 has a much stiffer stack especially in compression, which seems right. You can definetly tell also the rebound stack is much lighter on the 06. I wonder if this is because of the progreesive nature of the spring. The 05 shock was pretty nice.(compared to the forks anyway). I'm wondering if going to 06 valving on a 05 shock would produce good results??? the complaints I have heard often on the 05's where it feel harsh feeling during accelration bumps and kicking on square edge bumps, especially when hitting them at speed. The compression definetly seems ovelry stiff.

Erik

Hey John,

Do you think that the Ti spring adds to much progression and makes the last half of the stroke to harsh? I don't think I want a progressive spring, kinda makes me want a steel spring. Do all Ti springs you've tested do this?

About the dyno graph, do you have any real world shaft speeds to compare? What are the general speeds one sees in acceleration chop, a kicker or jump landing? Reb. would probably be more constant, whats an average on that at fully compressed or 1/2 and so on?

Thanks for the great post, Chris.

Do you think that the Ti spring adds to much progression and makes the last half of the stroke to harsh? I don't think I want a progressive spring, kinda makes me want a steel spring. Do all Ti springs you've tested do this?

Chris,

The verdict is still out on the Ti spring, at this point there are still alot of other factors to consider before arriving at a conclusion. Pete Payne from Heavy Duty Racing has some numbers on the 06 YZ linkage ratio which need to be considered.

About the dyno graph, do you have any real world shaft speeds to compare? What are the general speeds one sees in acceleration chop, a kicker or jump landing? Reb. would probably be more constant, whats an average on that at fully compressed or 1/2 and so on?

Chris,

We have heard a variety of numbers across the board referring to shaft speed. We are going to be acquiring some data aquisition equipment this years to get a good handle on shaft speeds. This is one piece of the puzzle that should prove very interesting.

Take Care, John

Just by the seat of my pants the ratio seems to be to slow in the initial travel and get to progressive? Couple that with a Ti spring with a progressive nature and it can get a little harsh in the middle.

I might try a steel spring that I have of the same rate and try taking out those spring seats on the Ti and reporting back. You don't think those are there to protect the spring from making contact with it self and causing damage? Just a thought when knowing how brittle ti is.

Chris.

I think I might have figured out why Yamaha added them spring seats/spring bumper or whatever you want to call them (part number 19 in the rear suspension section of the Parts Fiche).

Mine have gone bad because the spring has eroded right through the rubber spring seats. My bike is 7 months old and its already done this.

As soon as the rubber seat wasnt holding the springs ends from touching the coils my bikes rear suspension developed a squeak that kinda sounded like a dry lower shock bearing or something. I guess Ti is more prone to squeaking if it makes contact with Ti so they added them rubber seats to keep the squeaking from happining.

A quick, cheap, and easy fix for Yamaha that will cost me $10 for two of them every 6 months for as long as I own this bike with a Ti spring :thumbsup:

kayaba k2c

Can someone please tell me what shock fluid came in the 06 yz250 from the factory?

kayaba k2c oil

I’m also wondering about the ti spring and its progressive nature. Looking forward to that info John once available! Having a heck of a time figuring out if it’s me or that ti spring giving me fits with tuning? Also for a 180# rider without gear, what rate steel spring would i need if i were to replace the ti spring? Would the front spring need to be change aso?

Assuming the 2006-08 shocks are much the same, this old thread seems like the best match for my questions ...

I bought a 2004 YZ250, and the original 16mm shaft shock on it felt worn out. So rather than getting it rebuilt, I bought a used but healthy 2008 YZ250 shock with the 18mm shaft and Ti spring. This 2008 2-stroke shock shows no signs of fade, and it looks near new (incl spring and ti spring end bumpers). But I'm not liking its performance. Way too erratic, unsettled and hard work compared to what I'm used to.

I thought this "SSS" shock was supposed to be good. Seems like a marketing gimmick to me. I'm guessing riders who like it mostly ride groomed tracks and the only hits are jumps. I want it to perform well on real rough tracks.

Everything I feel when riding it seems to be explainable if the Ti spring has too much progression. On small chop I feel like I need faster rebound to hook up the rear tire, so I do that and on little bumps the rear is very smooth and hooked up. But then on big hits, the rear rebounds way too hard. So I then slow down the rebound just two clicks and no more big kicks, but then I loose so much traction exiting bumpy corners. To try absorb some impact energy, I've tried dialing in firmer LSC and/or HSC damping, but that's a compromise solution at best because I don't want to be hammered on the comp stroke, and often I just need the rear susp travel.

I'm running 100mm of rider sag which gives me 31mm static sag. I'm using some 2010 YZ250F forks which feel like they have some great potential, if only I can get the rear settled correctly.

I've got a good quality fixed 4.8 rate steel spring which I think will fit, so I'm going give that a go on the 2008 shock. I'm assuming the 2004 linkage rising rate is a good one. I weigh 165lbs without gear.

Problem is I cannot go riding again for 2 weeks. So in the mean time, can anyone give me some insight into the pros and cons of this 18mm shaft shock in the small piston body with the Ti spring??

Edited by numroe

The shock is a good one with more rebound damping and get rid of the ti spring

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