Harsh front forks

[bobnoxious67]

Hey guys...hope this is the right spot to put this.

I'm changing out the fork seals (AGAIN) on my '09 TE450, and while I'm in there I would like to soften the compression valve shim stack a touch...like nearly everybody else on the planet I feel they are too harsh on the sharp hits like rocks and roots, deflecting the front end all over the place, especially when going up gnarly uphills. It's good in faster/hard hitting whoops and such.

Here is my stack. If you were going to remove a shim(s) and/or move some around, which ones? Is the one with the arrow called a "bleed shim"? Rumor that the harshness actually comes from not enough damping, and that removing this one helps...? I run my compression clickers all the way out, it's the only thing that makes them bearable.

 

[Kyle Tarry]

Bob-

It's important to know the thickness of the shims, in addition to the OD. This can be measured with a dial caliper if you're careful, a micrometer is easier (and more accurate). The shims will be in thicknesses of 0.05mm (0.10, 0.15, 0.20, etc).

Yes, that first 12mm shim is a bleed shim; it basically holds the stack open so that some oil can get around the shims without having to deflect them first. We could have a lot of discussion about that shim, but my opinion is that it isn't necessary on those forks. Note that removing the bleed shim will significantly increase the damping, and that change by itself may make the forks feel even more harsh; while I would probably remove it, I'm not sure what other changes I might want to make at the same time.

If you're running the clickers all the way out, and turning them in makes the ride worse, than you probably aren't dealing with insufficient damping.

Are these Shiver 50mm OC forks? Can you measure the ID of the cartridge (or the OD of the base valve piston)? It looks like the same piston as my 610's 45mm shivers, same size shims too. I would assume the cartridge is the same size.

I'd like to see the thickness of the shims, then I can see how they compare to what came in my 610's forks and make some recommendations.

The other bit of information that would be useful is:

-What terrain do you ride?
-Do the forks bottom? Do you use all of the travel regularly?

 

[bobnoxious67]

Yes, 50mm Shivers...I would be surprised if these are not the same fork as late 610, and I am under the impression that they are different than the off road bike's.

I ride it all, but I spend the most amount of time in gnarly 2nd gear single track/lots if direction changes/roots and rocks and small-medium whoops. Where the forks drive me mad is where it constantly deflects/bounces off the line driving it over this stuff...especially when making the front end even lighter by going uphill. The harder I drive it into this stuff/more on the gas tank I am, the better it seems...the easier I go, the worse it is. It's always bouncing back at me, and sometimes I think I should try more rebound...but I just checked those, and I have them pretty much all the way IN! (Guess I should take that one apart and measure those too)

Thinking back, backing out the clickers never really softened it the way I hoped (hence I'm here wanting to mess with the shims)...I just left them out figuring it wasn't going to get better turning them in.

I never really notice bottoming out the front, especially in the tight single track, but I never really get that progressive action feeling that a KTM gives...it just always feels like it's "fighting back", like a bucking bronco.

Here's a shot of the shims measured up better:

 

[bobnoxious67]

Looks like 25mm piston/cartridge size.

Here is the rebound stack:

 

[juicypips]

ive been looking for a penny washer just like that to clamp my exhaust up! loads in my suspension i see.

 

[bobnoxious67]

Note the whiteness marks in the washers from the 23 bending backwards into the 17, and the 17 into the 15, and the 15 into the nut...rebound stack.

 

[Kyle Tarry]

What was on the other side of the rebound piston (compression side)?

If you look here, you can see the setup that I am running in my 610. I have actually added a second 23x0.15 face shim since I wrote that post, and it feels great. Super plush.

DIY tuning the Sachs shock

If your thickness numbers are correct, my base valve stack is quite a bit stiffer than yours. Would be good to see if there is any damping on the compression side of the midvalve.

That rebound stack looks pretty light too.

With a bleed shim that thick, I'm not sure that the clicker is going to do much, because there is so much stack bypass...

Need to see what's on the mid, but it might be worth just pulling that bleed shim and see how it feels.

Might also be worth considering drilling out the BV ports, if they are indeed the small (~3mm) ports like my Shiver 45s.

 

[bobnoxious67]

What was on the other side of the rebound piston (compression side)?

Other side of the Rebound is the same as the compression...spring loaded shim that looks/acts like a one way valve.

If you look here, you can see the setup that I am running in my 610. I have actually added a second 23x0.15 face shim since I wrote that post, and it feels great. Super plush.

DIY tuning the Sachs shock

Gonna read that now ;-)

If your thickness numbers are correct, my base valve stack is quite a bit stiffer than yours. Would be good to see if there is any damping on the compression side of the midvalve.

Could you explain this more please? "Midvalve"? And how do we see if "there is any damping" on it?

That rebound stack looks pretty light too.

Hence the clickers turned all the way in...I'm sure the crappy compression valving has some contributing factor here

With a bleed shim that thick, I'm not sure that the clicker is going to do much, because there is so much stack bypass...

How does this make my suspension harsh? Can you help me understand the theory that too much bleed makes the front end harsh over the smaller sharp edged stuff at moderate pace?

Need to see what's on the mid, but it might be worth just pulling that bleed shim and see how it feels.

Again, how do I "see what's on the mid"?

Thanks for the comments and help ;-)

 

[Kyle Tarry]

Sorry, let me clarify:

There are two pistons inside a regular fork, and both of them can contribute to compression damping. There is the base valve, which is the main compression stack that you already took apart, which has a check valve on the rebound side. Then there is the mid valve (or rebound piston) which has the main rebound stack on one side, and in some forks will have a "secondary" compression stack on the other side. Some forks (Marz Shiver 45s, for example) only use the base valve for compression; most "modern" forks (MX bikes, newer KTM WP stuff, KYB OC forks in my WR) also have compression damping on the midvalve (on the opposite side of the piston from the rebound stack). Both setups can be made to work well, but I like knowing the whole system before messing around with one of the halves.

In your case, the base valve damping looks pretty soft to me. So, I see two possibilities:

1. The damping is truly very light on that fork
2. There is more compression damping on the midvalve that we aren't aware of yet

Compression damping on the midvalve has a bit of a weird setup, in that you need to measure both the shim stack and the "float." "Float is the amount that the shim stack can move on shaft (it'll make sense when you look at it). On a normal "base valve only" fork, you'll only have one or two shims on the (compression side of the) mid, with a spring and a large amount of float (like 1.5-2 mm). On a "mid and base valve" fork (like a modern MX bike, my WR, etc), there will be a more normal looking tapered stack (sort of like your base valve) and a smaller float value, like 0.1-1.0mm.

Hopefully this helps you understand what I am after.

With regard to the bleed shim, I'm not saying that removing it will fix your problems, I just don't usually use them and think that removing it would be a good test, and possibly a step in the right direction.

If you can fill in the last little blank about the midvalve, we'll have all the info we need to work with.

I agree that the rebound looks light. If that were my fork I would probably add some shims to the taper, and maybe a face shim or two. For example, you currently have:

23.1 (2X)
11.1
17.1
15.15

There should be a thick washer after this, what is its OD?

I might run something more like:

23.1 (2X-3X)
11.1
21.1
19.1
17.1
15.15

I don't like the big jump from 23 to 17, but that might just be me being OCD. The rebound stack on my TE is just 6X 23.1, and it works fine but is on the lighter side. Yours is quite a bit lighter...

 

[bobnoxious67]

Mid (rebound) valve has 22mm x .30 shim with a small diameter spring (so does the comp valve) on the opposite side from the stack.

I don't have another washer on the rebound side...what's in the picture is what came out of it.

Can you help me better understand why increasing the compression damping will help the harshness? I (am willing to) believe it, but I guess I just need it explained.

 

[bobnoxious67]

Bueller...?

 

[Motosportz]

Great discussion and nice info Kyle

 

[Motosportz]

Can you help me better understand why increasing the compression damping will help the harshness? I (am willing to) believe it, but I guess I just need it explained.

More slow speed compression allows your bike to not dive into the travel so much and thus not getting into the progressive part of the travel so much as the air compresses and gets stiff. Sometimes turing your comp clickers on a stock fork stiffer will make it seem almost softer because of this.

Also what do you weigh and what springs are you running? Very important. Spring preload should not be overlooked as well. Do you know what oil height were in the forks?

 

[bobnoxious67]

240lbs, stock springs (6.4 rear vs. stock 5.6...I had a spare 610 rear shock to steal it from), oil height was whatever the manual recommended.

My last ride out, I managed to blow both the seals out...thought it was a bit odd, as they had been fine for 7000-ish miles, then started leaking so I replaced them about 9 months/1000 miles ago. I also changed to 5wt suspension fluid at this time trying to soften them.

Thinking about taking the 12mm bleed shim out of the compression stack, and adding it to the small end of the rebound stack...

Thanks for all the replies, and Happy New Year

 

[Xcuvator]

Sorry, let me clarify:

There are two pistons inside a regular fork, and both of them can contribute to compression damping. There is the base valve, which is the main compression stack that you already took apart, which has a check valve on the rebound side. Then there is the mid valve (or rebound piston) which has the main rebound stack on one side, and in some forks will have a "secondary" compression stack on the other side. Some forks (Marz Shiver 45s, for example) only use the base valve for compression; most "modern" forks (MX bikes, newer KTM WP stuff, KYB OC forks in my WR) also have compression damping on the midvalve (on the opposite side of the piston from the rebound stack). Both setups can be made to work well, but I like knowing the whole system before messing around with one of the halves.

In your case, the base valve damping looks pretty soft to me. So, I see two possibilities:

1. The damping is truly very light on that fork
2. There is more compression damping on the midvalve that we aren't aware of yet

Compression damping on the midvalve has a bit of a weird setup, in that you need to measure both the shim stack and the "float." "Float is the amount that the shim stack can move on shaft (it'll make sense when you look at it). On a normal "base valve only" fork, you'll only have one or two shims on the (compression side of the) mid, with a spring and a large amount of float (like 1.5-2 mm). On a "mid and base valve" fork (like a modern MX bike, my WR, etc), there will be a more normal looking tapered stack (sort of like your base valve) and a smaller float value, like 0.1-1.0mm.

Hopefully this helps you understand what I am after.

With regard to the bleed shim, I'm not saying that removing it will fix your problems, I just don't usually use them and think that removing it would be a good test, and possibly a step in the right direction.

If you can fill in the last little blank about the midvalve, we'll have all the info we need to work with.

I agree that the rebound looks light. If that were my fork I would probably add some shims to the taper, and maybe a face shim or two. For example, you currently have:

23.1 (2X)
11.1
17.1
15.15

There should be a thick washer after this, what is its OD?

I might run something more like:

23.1 (2X-3X)
11.1
21.1
19.1
17.1
15.15

I don't like the big jump from 23 to 17, but that might just be me being OCD. The rebound stack on my TE is just 6X 23.1, and it works fine but is on the lighter side. Yours is quite a bit lighter...

Really good stuff Kyle
I'm real sure all the 45 and 50 Zokes TC/OC (installed on Huskys) do all the compression in the base valve and yes the 45s and 50s use the same ones with two slight drilling variations.

 

[Kyle Tarry]

Sorry bob, been traveling. That is a base valve only fork, like I suspected. As such, that valving is super soft. I'd definitely pull that bleed shim. You're going to need to buy some shims to run anything else I'd recommend, is that ok? I can try to make some recommendations later this week if that is ok. IMO that valving is soft to the point of insanity.

You can also consider adding mid valve damping, but I bet we can improve it quite a bit with just base valve changes.

You may also want to consider drilling the base valve ports.

Kelly is right on about how too soft can be harsh.

 

[bobnoxious67]

No worries ;-)

Where can I buy shims? A selection would be best I think...

 

[Kyle Tarry]

Bob, you can get shims from MX-tech. They do not sell assortments, but they do sell singles.

Have you measured the front end sag? You might need springs...

As a starting point on the base valve, try this:

23.1 (6X)
12.1
22.15
20.15
18.15
16.15
14.15
11.2
11.2

So, the changes would be:

+3X 23.1 face shims
Change 20, 18, 16 from 0.10 thick to 0.15 thick.

Honestly, I think this is still on the softer side, but it would be a good place to start. Try it and give us some feedback.

If you want, try out this rebound stack too:

23.1 (3X)
11.1
21.1
19.1
17.1
15.15

Can you measure the size of the washer at the top of the rebound stack?

 

[Kyle Tarry]

Bob, any updates on this?

 

[bobnoxious67]

Yes and no:

I basically worked with what I had for now (needed the shop space, and figured I would experiment/fail a few times to help me figure this stuff out) while I work on getting a shim assortment.

I moved the bleed and crossover shims around to create 2 single stage stacks. Here is a shot of them, with compression on left and rebound on right:

I haven't ridden it yet (snow/frozen ground/cold temps), but the difference just bouncing against the floor before install (had one finished, and one still assembled with old shim stack) is profound. Gonna start with the clickers in the middle and start from there...hopefully I learn something.