DIY tuning the Sachs shock

[Picklito]

Any more shim progress?

 

[Kyle Tarry]

Modded: The same as everything else- go to a linear damping curve instead of the stock digressive curve.

Digging this one up because it's a good flippin' post. Sparked, I was hoping you could give me some insight:

On the compression side, I've always held the belief that digressive damping was good. My theory was, a decent amount of low speed damping helps keep the bike from "wallowing" and feeling unresponsive, such as diving under brakes and not feeling "direct" under steering input, turn-in, etc. On the other hand, I figured you wanted less high speed (at least, for rocky/bumping trailing riding, or fast rocky riding), so that you don't get pounded to death by all the sharp impacts every time you hit a rock or other square-edged bump.

On the rebound side, it's not so easy for me to visualize. Somewhere between linear and digressive seems to make sense to me; progressive would certainly seem like it would result in losing traction on the backside of sharp bumps/drops (climbing a steep hill), and that's bad.

Obviously you've ended up with a much more linear setting all around, than the stock digressive stuff. Why's this? Why do you think this is what actually works, instead of what I "think" I like?

Thanks! Great post!

 

[Sparked]

Of course what you want depends on where and how you ride. Based on what I've read: to put it as simply as possible, for Supermoto you want the damping digressive, for MX you want it linear and for enduro you want it progressive.

With the setup that I have right now the bike does wallow a bit if I'm sitting down, but that completely goes away when I stand up. So it would be a bad setup for sumo or flat track type riding.

From the what I've tried myself it seems that the best way to think of the damping is that the total damping is for large bumps and the low speed is for small ones. Chassis stability is in the "small bump" bucket. Trying to think about
it as 'fast' and 'slow' bumps is just confusing.

For the rebound, the low speed controls the traction and the chassis stability. The total damping controls the amount of kick on big bumps and packing on whoops. On another bike I tried to deal with a heavier spring by moving a shim from the high speed to the low speed side of the stack. The bike handled big bumps about the same, but would try to swap ends on washboard. It was really bad. Returning the low speed damping to the original level and increasing the high speed damping with more shims made it work much better.


For compression the low speed controls the harshness over small bumps and chassis stability, the total damping controls the bottoming. By going with a more progressive setup than stock the ride is plusher but bottoms out less. The downside is that the bike pitches more on braking and acceleration.

Here's the basics that the shim program authors describe:
http://www.shimrestackor.com/Code/Sample_Applications/Damping_Profile/damping-profile.htm

 

[Kyle Tarry]

From the what I've tried myself it seems that the best way to think of the damping is that the total damping is for large bumps and the low speed is for small ones. Chassis stability is in the "small bump" bucket. Trying to think about
it as 'fast' and 'slow' bumps is just confusing.

Hm. Interesting; not exactly the way I've thought about it.

For example, landing on the backside of a tabletop is definitely a large bump, and may use near the full stroke of the suspension, but it's definitely all low speed.

On the other hand, riding through a bunch of exposed roots on the trail at speed is only going to use an inch or two of stroke, but it's definitely high speed damping.

It's not the size of the bump that matters, it's the "shape."

This is all for compression damping, but rebound is a similar idea, except the velocities don't get as high, since the most force you can put in is just the spring force. For rebound, the speed of damping is a function

In any case, it seems like linear damping is working for you, and the proof is in the pudding, so...

 

[Picklito]

GREAT thread!

 

[Picklito]

Hey Sparked!
I tore into my 2012 WR 144 shock today. One of the easiest I've ever done. Just wondering... does yours have this bleed hole? It would greatly affect how I set up the low speed damping.

 

[Sparked]

Yes, 2.0 mm diameter.

Here's the valve geometry of the TE:

For the rebound side:
Rport = 10.25mm
Dport = 6.7mm
Wport = 9.5mm
Nport = 4 (number of ports)

For the compression side:
Rport = 10.25mm
Dport = 10.2mm
Wport = 10.62mm
Nport = 4


18mm rod diameter, 50mm piston diameter


I'd guess that these are all the same on the TE and WR, but if we're comparing stacks on different bikes it'd make sense to confirm that.

 

[Picklito]

Above and beyond the call of duty there, Mr. Sparked!

So I went ahead and buttoned up the shock before I knew if you had the same bleed hole, as you apparently do. It has been my experience that if the bleed is significant, then we may not need to go too heavily into a two-stage stack, as the bleed essentially handles the lower speed oil flow. Had I known you had the same bleed, I might have made a more aggressive change as you did. Consequently, I made a very modest change to the valving which I'll post here for good measure:

2012 WR 144 Sachs

Stock Compression
44 0.20
44 0.20
44 0.20
44 0.20
44 0.20
44 0.20
44 0.20
44 0.20
36 0.20
42 0.20
40 0.20
38 0.25
34 0.25
30 0.25
28 0.25
26 0.30
24 0.25
large OD spacer

Stock Rebound
38 0.25
38 0.25
36 0.30
34 0.30
32 0.25
30 0.30
28 0.25
26 0.30
24 0.25
22 0.30
24 mm clamp/spacer

Very close but a bit lighter overall than yours. Makes sense, it's a 125/144 smoker. Here's what I did:

Comp Mod 1
44 0.20
44 0.20
44 0.20
44 0.20
44 0.20
44 0.20
36 0.20 (moved up 2)
44 0.20
44 0.20
42 0.20
40 0.20
38 0.25
34 0.25
30 0.25
28 0.25
26 0.30
24 0.25
large OD spacer

Rebound Mod 1
38 0.25
38 0.25
36 0.30
34 0.30
32 0.25
30 0.30
28 0.25
26 0.30 (24 and 22 below this have been removed)
24 mm clamp/spacer

Would be nice to see what Shim Restackor says about my changes, but I haven't yet had the time to get it going. Took a little test ride around the property this afternoon but the changes are subtle enough that they don't really show here. Unfortunately, we're looking at 108 temps this weekend... I think I'll stay away from the trails and a little closer to the fridge!

 

[Kyle Tarry]

Hey Sparked, you got a Dthrt number for the base valve?

 

[Sparked]

Nope, I left it at 0 since the valve throat didn't look very restrictive. It's more like the KTM one than the XR one.

 

[Sparked]

Picklito, if anything I've got too much free bleed and soft low speed damping, so it's probably best that you don't go as far as I went.

 

[Kyle Tarry]

FYI I measured the throat last night and it's on the order of 4mm in diameter (perhaps slightly more, off the top of my head I think I measured around 0.15 inches). So yeah, it shouldn't be a restriction.

On the fork compression side, are either of you guys running the open chamber KYBs? My WR has those on it, and I can't figure out how to get to the midvalves without removing the factory crimped bottoming ring from the damper rod (no thanks!). I did pull my base valves and make some changes:

NOTE/EDIT: ERROR BELOW. SHIMS ARE ~0.11mm THK, NOT 0.15mm (as originally stated)!

Stock '12 WR300 base valves:
24x0.11 (6X) (!)
12x0.11
22x0.11
20x0.11
18x0.11
16x0.11
13x0.11
11x0.25

I has my compression adjusters fully out for rock riding and mostly out (15 out of 20) for NJ enduros, mostly for roots and braking bumps. I started out by pulling 2 of the face shims (24x0.11), hopefully that will reduce damping in the whole range and let me dial the adjusters back in. I have not had a chance to ride it yet, except for around the yard; it's definitely softer. I am a little worried I may have taken out too much low speed, wondering if I should have just pulled 1 of the face shims and then also taken out the 22x0.15 or 20x0.15 from the high speed stack...

I was/am attempting to buy a copy of shim restackor, but so far I can't get it to run so all I have to compare stack stiffness is some crude calculations and simplified FEA...

 

[Kyle Tarry]

Hey Sparked, do you have fork midvalve geometry for the compression side? I'm trying to get a handle on how my total damping (not just the base valve) looks...

 

[MOTORHEAD]

Hm. Interesting; not exactly the way I've thought about it.

For example, landing on the backside of a tabletop is definitely a large bump, and may use near the full stroke of the suspension, but it's definitely all low speed.

On the other hand, riding through a bunch of exposed roots on the trail at speed is only going to use an inch or two of stroke, but it's definitely high speed damping.

It's not the size of the bump that matters, it's the "shape."

This is all for compression damping, but rebound is a similar idea, except the velocities don't get as high, since the most force you can put in is just the spring force. For rebound, the speed of damping is a function

In any case, it seems like linear damping is working for you, and the proof is in the pudding, so...

Kyle, I used think like you 10 years ago, but I've gone to more what Sparked is trying to tell you over the years.

 

[Sparked]

Hey Sparked, do you have fork midvalve geometry for the compression side? I'm trying to get a handle on how my total damping (not just the base valve) looks...

KYB, open chamber, midvalve compression.


DamperGeom D.rod D.valve w.seat Vspec
[mm] 12.5 28 1 Mvc
Valve Geom r.port d.port w.port N.port
[mm] 5.5 6.2 10.8 3
d.bleed d.leak d.thrt N.thrt
[mm] 0 0 0 0
Settings n.click SAEwt T.oil [F] MAX.clks
12 5 70 30
F.max u.wheel
[nt] [cm/sec]
User Manual 100 500




Stack ID Float
[mm] [mm]
8 1.74
Shim Diam Thickness
[#] [mm] [mm]
1 24 0.12
2 24 0.12
3 24 0.12
4 22 0.12
5 20 0.12
6 18 0.12
7 16 0.12
8 14 0.15
9 12 0.15
10 10 0.3
11 10 0.3
12 22 0.4
13 17 2


I think the float number may be off, but I do remember that there is a huge amount of float.

 

[Sparked]

....I can't figure out how to get to the midvalves without removing the factory crimped bottoming ring from the damper rod ....

I unscrewed the top of the cartridge from the body. It was loc-tited on really hard. It was necessary to make tools to hold both parts.

 

[Kyle Tarry]

Kyle, I used think like you 10 years ago, but I've gone to more what Sparked is trying to tell you over the years.

Motorhead and I talked about this a little bit today, but I figure I would post it here in case it helps someone else.

I was/have been stuck in the mindset of thinking that "trail obstacles" (like rocks, roots, etc) were all high speed compression damping, and whoops, landings, etc were all low speed. In hindsight, I am not sure where I got this idea from, maybe from the world of pavement motorcycling where imperfections in the surface are high speed and all the transition stuff is low speed.

Anyway, motorhead pointed out that, for enduro-type riding at least, I probably had it backwards. Crap in the trail at lower speeds (like 20 mph) is mid-low on the damper shaft speed scale, and whoops and jump landings are probably more on the high-speed side. I did some real rough calcs and I think that "trail trash" is generally in the 50-100 in/sec range, while landings and stuff might be more like 150-200. Real harsh stuff, like hitting a drainage at desert race speed, it probably even faster than that.

This has really changed my thinking with regard to valving...

 

[huskyfrk]

for what it's worth, a race tech gold valve works in the sachs shock...

 

[Kyle Tarry]

KYB, open chamber, midvalve compression.
Stack ID Float
[mm] [mm]
8 1.74

I think the float number may be off, but I do remember that there is a huge amount of float.

Hey Sparked, can you comment on that float number? That seems HUGE.

This guy says the stock float on a TE310 (same forks?) is 0.55mm: http://www.thumpertalk.com/topic/954814-husqvarna-te310-kyb-fork-revalve-ask-for-tip/

Not that I trust some random guy on the internet, but 0.6mm seems like a more "standard" number of float; 1.7mm is really big.

Sadly, I can't find any other references, and I was too scared to disassemble the cartridges on mine when I had them apart.

(Should we move the fork talk to another thread or should we just keep it all here? I have a bunch of other commentary on it but there is a ton of great info here from Sparked...)

 

[Sparked]

It was a while ago, but I do remember re-measuring the float a few times so very likely got it wrong. I just copy/pasted from the shim restackor spreadsheat and the 1.74 was what was there. What I am sure of is that with that much float the midvalve is useless. 0.55mm sounds like a much more reasonable number. I went all the way down to 0.3mm of float and my forks aren't harsh at all.


I think this has pretty much turned into a general re-valve thread, and that's a good thing. It's not like it's so active things are getting buried Anything you want to add would be great.