• We are no longer supporting TapaTalk as a mobile app for our sites. The TapaTalk App has many issues with speed on our server as well as security holes that leave us vulnerable to attacks and spammers.

Shock Valving 101 and the 07 Apex RTX vs REV-XP MXZ X

ReX

TY 4 Stroke God
Joined
Mar 7, 2004
Messages
1,987
Location
Ottawa, Ontario
I've had many debates with fellow sledders regarding the performance of the suspension in the 07 Apex RTX vs the competition (primarily the Skidoo REV-XP MXZ X).

Most people who ride a stock Apex RTX complain that it seems to almost magnify all of the little bumps in the trail, provides a very harsh ride, yet on top of that, it still bottoms out relatively easily when you hit a big bump.

A few examples of comments about the poor suspension performance:

http://www.ty4stroke.com/viewtopic.php?p=490230&highlight=#490230
http://www.ty4stroke.com/viewtopic.php?t=40062
http://www.ty4stroke.com/viewtopic.php?t=37907
http://www.ty4stroke.com/viewtopic.php?t=43142

On the other hand, when you get on a REV-XP MXZ X, after riding an Apex RTX, it is simply amazing how plush the ride feels - yet at the same time how it seems virtually impossible to bottom out. But why does the REV-XP MXZ X ride so much better than the Apex RTX??

To be honest, it wasn't until I spent more time on the REV-XP MXZ X at the start of this season, that I realized how badly the 07 RTX really rides. I had my springs cranked up and rearched, anti-bottomers installed, clicker cranked up, etc. It handled the bumps without bottoming too much, but the ride was very rough and it kicked and bucked constantly - and was a real handfull on a rough trail. On top of that each and every change I had made previously I had back to back compared with/without the change (like the anti-bottomers, etc.) and this was already riding better than stock (focussed more on the aggressive riding side of things and trying to ride with a bunch of stock MXZs without bottoming hard constantly).

Most argue that the Apex simply weighs too much to ride well and several have argued with me that the ProActive CK is simply a terrible riding suspension and needs to be replaced.

To make it more interesting, Yamaha and Skidoo actually use the same HPG shocks. The pistons, valves, bodies, etc. are all virtually identical and completely interchangeable. Skidoo did select a larger shaft diameter on the REV-XP vs the Yamaha RTX, but the shafts along with the seal caps are interchangeable.

On top of that, the REV-XP vs the Apex RTX is an excellent pair to compare because they not only use the same shock design, they also use the same shock diameter, same length, same IFP depths, same shock oil, same shock pressure, same total shock travel, and a similar amount of total suspension travel.

You could actually take the pistons and valve stacks from a REV-XP MXZ and install them in the 07/08 Apex RTX skid shocks. This includes both the main and center shock. The different shaft diameter does change the oil flow slightly (more oil flows through the piston on the RTX) and more so for the remote reservoir (with the remote reservoir, more oil flows through it on the REV-XP).

I can tell you first hand now that the main problem is the primitive shock valving used on the Apex RTX and that these sleds can ride almost as well as that REV-XP.

Edit: I just wanted to add for first time readers that the reason you can't get the 07-09 RTX to ride quite as good as the REV-XP is due to main shock velocity. With the RTX the main shock speed slows down as you compress the rear suspension and this makes it impossible to tweak the shock to make optimized use of the full suspension travel. At best you get something like 60% of well optimized suspension travel and the remainder (getting closer to bottoming out) compresses without enough damping. This is still infinitely better than stock and still a decent ride - just not as good as well optimized shocks on the competition. If you can't accept anything less than the absolute best you'll unfortunately need to change the skid on these particular sled. The majority, if not all, of other modern Yamaha sleds with rebuildable shocks don't have this issue.

I'm going to try to share details on why the competition sleds ride so much better and how this can be directly applied to a Yamaha, specifically the Apex RTX.

Here is what the REV-XP X uses for the main skid shock (first number is diameter in mm, second number is thickness in micrometers):

17x203 End of second rebound stage
26x254 .
26x254 .
26x254 .
26x254 .
26x254 .
26x254 Second rebound stage (here up to the top)
16x114 Space before second rebound stage kicks in
26x254 First stage rebound
1 slit piston bypass port
30x203 First stage compression
15x152 Space before second compression stage kicks in
30x203 Second compression stage
30x203 .
30x203 .
26x114 Final second stage component & space before 3rd stage
18x114 Space before 3rd stage
Hard stop Hard stop as the 3rd stage

To get an idea on how a shock works, take a look at the pictures in the following patent (patent #6,640,943):

http://www.google.com/patents?id=uvwMAAAAEBAJ&printsec=drawing&zoom=4#PPA1,M1

To get an idea on how the valve stack and piston works (don't study the piston design too hard, just look at the washers and how they flex), take a look at the pictures in the following patent (patent #3,003,594):

http://www.google.com/patents?id=Sk5SAAAAEBAJ&printsec=drawing&zoom=4#PPA72,M1

To get an idea what is in a shock, take a look at this picture (piston is in the bottom right):

http://snowmobile.off-road.com/snowmobile/data/articlestandard/snowmobile/492005/253208/fox6.jpg

A better image showing the concept of the piston is here:

http://www.mb1suspension.com/sitebuildercontent/sitebuilderpictures/.pond/S4SX.jpg.w300h283.jpg

I'll try to add some pictures of the actual piston from a Yamaha/Skidoo shock (the images above show the concept, but they aren't exactly the same). Unfortunately in my tuning I didn’t take any pictures.

The piston includes holes right through it. The valves are nothing more than tempered spring steel washers of various thickness and diameters. The valves cover up the holes and as oil is forced through the holes, are able to flex "open" to allow the oil to pass through the piston "holes".

To make it a more adjustable, 1/2 of the holes are only sealed by the compression valve stack and 1/2 of the holes are only sealed by the rebound valve stack. In other words, for 1/2 of the holes, the oil can flow around the rebound stack and only push on the compression stack and vici-versa.

The way a shock works is to provide a damping force that is a dependant on the speed at which the shock is being compressed or extended. The faster you try to compress it, the harder it becomes to compress it. If a shock had only a fixed small hole in the piston and no valves to "flex" open, the damping force would increase extremely quickly as the speed increases. For example, if a fixed port shock produced 50 lbs of damping force at 5 inches per second, it might produce a damping force of over 6000 lbs at 25 inches per second.

Basically, the valve stack needs to be selected to open up "just" the right amount in order to keep the damping forces reasonable, provide a comfortable ride on smaller bumps, and not bottom out on big bumps. It also needs enough low/mid speed damping so it doesn’t bottom out going through long, high speed “valleys” (where the suspension is compressed for a relatively long time).

To give you an idea on how this works, I'm going to go over the compression stack for the REV-XP in detail followed by the 07 Apex RTX compression stack:

Stage 1:

The first stage is a single washer that is only 0.203 mm thick. It is very easy for the shock oil to push and flex this thin washer, opening up the compression ports. This provides the ability for the shock to soak up smaller bumps and provide an extremely plush ride on smoother trails.

When the first stage valve opens by 0.152 mm, it now contacts the second stage set of valves.

Stage 2:

The second stage comes into play when the valve is already open by 0.152 mm. At that point, the stiffness of the working valve stack increases to the combination of 4x the 0.203 mm thick washers (first and second stage combined) with the 26 mm x 0.114mm also helping to stiffen the 2nd stage. As the bumps get bigger, this stack of 5 washers flexes, further opening the compression valve.

Functionally with this particular sled/shock, this stage comes into play when the trail bumps get somewhere into the 2-4 inch range and works all the way up to something like 6-7 inch bumps (it is sled speed dependant also, but this is just to give you an idea). This stack is still quite easy to flex so the suspension is able to easily compress, soaking up bumps and again providing a comfortable ride - but with more damping than the first stage.

Stage 3:

Once the valve opens up by a total of 0.152 + 0.114 + 0.114 or 0.380 mm, the stack now contacts a large thick washer that works as a hard stop.

At this point, since the valve cannot open any more and due to the nature of hydraulic oil, the resistance to compressing the shock any faster increases very rapidly.

This 0.380 mm of opening is selected specifically to control bottoming with a certain size of bumps. In this case, it can handle very large bumps; on the order of something like 2 foot moguls at just the wrong speed (jumping and landing on the rise of the next one) before it starts to bottom out.

This hard valve stop also comes into play whenever the bumps get bigger than the second stage threshold. What you'll feel when riding the sled is once the bumps get big enough, the suspension really firms up and you start to experience a rougher ride. At the same time though, you won't be bottoming out and bottoming out is what really hurts the back.


Note that in reality there is a bypass port or "slit" in the piston that is actually the true 1st stage for both compression and rebound. The stages I talked about here are the valve stack stages, but strictly speaking you could add one to the stages if you consider the bypass stage as the first stage (in other words Skidoo actually has a total of 4 compression stages and 3 rebound stages in their main shock).


Now let’s look at what Yamaha uses in the main shock for the 2007 Apex RTX:

12x200 Spacer
26x150 End of first rebound stage
26x150 .
26x150 .
26x150 .
26x150 .
26x150 .
26x150 .
26x150 .
26x150 .
26x150 First stage rebound
2 slit piston bypass ports
30x200 First stage compression
30x200 .
30x200 .
30x200 .
30x200 .
30x200 .
30x200 .
30x200 .
30x200 .
30x200 .
30x200 .
30x200 End of first stage of compression
12x200 Spacers to ensure stack never hits hard stop
12x200 .
12x200 .
12x200 Spacers to ensure stack never hits hard stop


As you can see, the 2007 Apex RTX has an extremely simple, single stage valve stack. For the rebound side this isn't really a big problem because you are only dealing with a relatively linear rebound force created by the suspension springs. On the compression side this creates very undesirable performance compared an ideal multi-stage valve stack.

Stage 1:

When you hit a small bump, the entire stack of 12 0.200 mm thick washers is too stiff to move. What this does is create a very harsh ride out of a virtually smooth trail. The shock simply will not compress (other than using the bypass slits) without a large amount of force being applied to the shock. This means that the entire sled needs to bump up and over even the tiniest 1" or less stutter bumps.

When you hit a medium bump, again, the entire stack is too stiff to move easily. It will open, and the shock will stroke a little, but instead of a plush ride, you will experience a very harsh ride. These "medium bumps" would be your typical stutter bumps.

You might think to yourself "Hey I'm riding on a rough trail extreme sled, so I should expect a harsh ride in order to handle BIG bumps without bottoming out".

Then you'll suddenly come upon a 8" or bigger bump. This time that entire stack of 12 0.200" washers will suddenly flex open, without any limit on how far they can flex and suddenly the suspension collapses and BANG, it bottoms out.

What you have ultimately is a "rough trail" sled that rides like a brick with a track, yet once the bumps get big enough it suddenly starts bottoming out easily. Obviously this is somewhat of an exaggeration, but compared to the REV-XP this is what it feels like.

This sort of single stage valve stack unfortunately leaves everyone dissatisfied with the ride. Anyone looking for any level of comfort hates the harsh ride and anyone looking for rough trail capability finds the suspension regularly bottoming out.

Even light vs heavy riders find this very undesirable, with the light riders being pounded on even harder on smaller bumpers and the heavier riders bottoming out even more on the bigger bumps.


I spent quite a bit of time experimenting with different valve stacks (BTW, it is very easy to remove the main shock without pulling the skid). Everything was a huge improvement over stock, but eventually I was able to dial in an excellent aggressive riding valve stack that soaks up bumps and doesn't bottom out. I did start with a complete set of compression and rebound stacks from Mike Carver, but I found his main shock setup wasn't ideal for me. I am pleased with his center shock valve stack though and haven't changed it.

From what I've been told, absolutely all of Yamaha's sleds, including the Apex ER and the Nytro FX all use single stage valve stacks.

The center shocks setups are very similar between the REV-XP and the 07 Apex RTX. Again, the shocks are virtually identical but the valve stacks are very different. The REV-XP again uses a 3 stage compression stack with a 2 stage rebound stack, while the RTX uses a single stage compression and single stage rebound. One big problem with the 07 RTX is there is nowhere near enough rebound damping on the center shock. This creates a lot of kick back over bumps, especially once anti-bottomers are installed (to try to control bottoming). The lighter REV-XP uses much more rebound damping on the center shock.

I have now removed the anti-bottomers as they are not needed (with a decent valve stack) and only reduce the ride quality.

One thing I did not touch on is "clickers". On the 07/08 Apex RTX, these work by adding a spring, a ball bearing and a "clicker screw" to tighten up the spring. This all sits on the remote reservoir, restricting the oil flow into the reservoir. The reason oil flows to/from the reservoir is due to the shock's shaft displacing the oil in the main shock body as the shock strokes. By further restricting the oil flow to the reservoir, the damping can be increased by tightening the "clicker".

Unfortunately, again this is a simple and primitive "clicker". As you tighten up the clicker it increases the low/mid to mid/high speed damping, further increasing the ride harshness. Unfortunately, once a big bump is hit, the ball bearing pushes hard enough to move back against the spring again opening up the oil restriction. Once again, although this helps to reduce bottoming, it doesn't do a very good job of it and it greatly increases the ride harshness at the same time.

Now that I have my valve stacks optimized, I have my clicker opened up all the way to provide the best ride possible. I did think about trying to build a valve stack for the main shock to deliberately provide not enough medium speed damping - so I could use the clicker to fine tune this. In the end I felt there was better tune-ability with the main valve stack so I opted to leave the clicker open.
 

this is what i have said right along, poor shock valving on the yamaha sleds!
great post
when are you taking orders for rebuilds?
would you do a swap program?
thanks,
dave
 
Good write up! I will be looking to revalve mine next fall!
 
shocks

i,ve been reading your posts for a long time now rex and appreciate you sharing your findings on these suspensions especially the monoshock. i just find it hard to believe with the resources and technology available to yamaha they still cannot come up with a proper setup. if they ever spend some time on rear suspensions (example ride,reliabilty,wheels,etc.) well ! enough said. i,m ready for an upgade (2009) sled and hoping some of these nagging issues are resolved.
 
REX -

Thank you! I was thinking of replacing the entire skid -- But I think a re-valve seems like a good idea.

I think I will be able to speak to Bruce at Pioneer with just a little more inteligence.
 
I've heard that the 08 RTX has much better shock calibrations.
 
I lack comparison to any earlier RTX --

However, compared to a ‘03 F5 it is a harsh ride. Compared to a ’56 Triumph hard-tale motorcycle, it is – well it is better than that.

I have not really been on a snowmobile for 25 years – so my expectations are based on the suspensions from other things (trial bikes, ATVs, etc).

It is bad enough that if the re-valve does not correct the catapulting rebound, I will replace the skid.
 
smacho said:
REX -

Thank you! I was thinking of replacing the entire skid -- But I think a re-valve seems like a good idea.

I think I will be able to speak to Bruce at Pioneer with just a little more inteligence.

Let me know when you talk to him. I would like to know as well what his shock package consists of. Thanks
 
welterracer had this in another post what do you make of it ?

I got the following from yamaha blog....

brian says:

you never got back to me on the yamaha shock valving..

do the shocks in the sled have more then one high speed valve for controlling compression and rebound like the other manufactures?

Ive been told that yamaha used a single stack valve and all the other manufactures use 3-5 sets of valves that are more progressive as the bumps get larger.. whichl allow a comfortable ride at for small and larger bumps.. ??????

Sorry Brian, have had a lot on my plate the last couple of weeks. I don’t know the answer to your question but I know the guys who do… which ones are you looking at Ohlins / KYB / Soqi? They are all different. I did hear soemthing similar to what you are saying back int the SXr days… I’ll see what I can find out. cheers cr

heres what I’m told by a very respected suspension guy inside Yamaha…

Most Yamaha shocks are now using pyramid stacks in the past this was seldom used.
Ohlins, Soqi and Fox pyramid stacks have been common, KYB in the past few years have offered pyramid valve stacks.
The 2 adjustment used to adjust calibration is (1) piston - number of bleeds and diameter of bleed holes (2) valve stack or shims - 2 types of stacks are commonly used the straight stack were 2 different shim sizes are used and increasing or decreasing the number of shims to increase or decrease force, or the pyramid stack shims start from the largest diameter to smallest in diameter more progressive type of damping force.
Some shocks offer external compression and rebound adjusters but the adjuster influence both high and low speed damping force
We don’t have shocks with external slow and high speed compression adjusters, but I don’t believe any competitors are using these systems
I’m guessing as to what Brians question is and only answering by the difference between Yamaha and our competitors was in the past.
 
I just got off the phone with Bruce from Pioneer -- He spoke in generallities - said better at low speed, better rebound, seemed to be able to predict my complaints. So, I asked him to fix it. ;)!

With luck & timing (& snow) I will have it back on the trail this weekend. I will post my opinion of the results. Without luck and /or snow I will post later --
 
One guy who definitely understands how to do a great job on multi-stage valving is Mike Carver over at Carver Performance. As far as I am concerned, he is one of the pioneers at perfecting the multi-stage valve stack - over 10 years ago.

The one and only reason I was resisting telling absolutely everyone to go there is the fact that he is so busy with Yamaha's race program that quite honestly I have not been able to get in touch with him since the season started - and I have tried many times.

With my Polaris sleds, his valve stacks were simply incredible - and this was something like 10 years ago (before Skidoo, etc. had perfected the multi-stage on production sleds).

Even with my RTX, his valve stack was quite good and he did tune it to the specifications that I gave him. I'm not certain, but I don't think he has as much trail setup experience with the ProActive CK and Yamaha shocks as he does with more traditional suspensions (Skidoo, Polaris, etc.) and Fox shocks. The main shock velocity with this skid WRT to suspension position is not the same as most of the skids out there and the main shock needed some additional tuning to really dial it in for me. I have sent them both feedback and my final stack details so they should be in a position to offer better turn key shock revalves for this skid now.

I think what I'll do is publish my personal main shock valve stack. Since I'm running Mike Carver's center valve stack I don't feel I can share it publicly, but you can always purchase it (or a fine tuned custom one) from him along with the valves for the main shock. They also offer complete revalve/rebuild service. Although Mike is hard to get ahold of himself, there are others at his shop that I've been told also do a good job at revalving. It sounds like Mike has at least one guy he has brought up to speed with his valving knowledge on staff.

BTW, the pyramid stacks that Chris Reid talks about are what Polaris was using about 15 years ago. They can be slightly better than multiple common diameters, but can't compete at all with a multi-stage stack. The pyramid stack is still a basic single stage stack.
 


Back
Top