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Offline KellyL

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Re: Changing fork oil to higher viscosity only?
« Reply #20 on: April 19, 2019, 02:21:35 AM »
My bike is now exactly 2 years old and done close to 9000km.  The stock damping in the forks had basically become non-existent, and were bouncing up and down even with the rebound tap completely shut off clockwise.  Since I had some Motul Expert Medium 10W lying around, I decided to completely ignore Forks-By-Matt's advice and change out the oil today to the 10W (which is about 36cst@40 deg viscosity).  I only swapped out the left fork oil.

There was about 390mL of oil in the left fork, so I put back 390mL of the Motul Expert 10W.  The stock stuff came out like apple juice.  The whole job took about 2 hours with a Park bicycle stand for holding the fork, and regular hand tools.  (8/10/12mm sockets and spanners, 5/6mm hex, 14/22mm spanner, 14mm hex socket for axle, torque wrench, 500mL measuring cylinder, and plastic funnel).  My subscription to Dave Moss Tuning videos helped with preventing any derpy moments.

Verdict: 10W / 36cst viscosity fork oil seems fine.  Slow speed rebound stabilises at around 3 clicks out, but high speed rebound (i.e. fork overshoot) stops at around 1.5 clicks out.  Low speed compression seems better supported, but still reasonably plush.  It's not perfect, but a hell of a lot better than the stock damping, which started to die around 5000km anyway.  FYI my preload is 14 turns in for a 90kg rider (35mm front loaded sag).

Meanwhile I've got a Nitron NTR R1 rear shock and TVT cartridges on order.  The cheapo oil swap will keep me satisfied in the meantime.

Offline Frontline

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Re: Changing fork oil to higher viscosity only?
« Reply #21 on: April 19, 2019, 03:06:56 AM »
Good job.

Yeah, I recently changed both my front fork oil to Maxima 7wt (cSt 26.7). I didn't want to go thicker, wanted a little more than stock (cSt 15.3). I will say, it was an improvement and 100% worth doing.

I will add, I first changed the right (dead) leg and it actually made a very minor difference. The right leg is much easier to change so why not. However, the right leg took 500ml so be ready.

Old OEM Fork Oil at 12K miles: (it was VERY dark so I had to use a flashlight to show detail)


New Maxima 7wt Fork Oil:
« Last Edit: April 19, 2019, 03:08:33 AM by Frontline »

Offline KellyL

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Re: Changing fork oil to higher viscosity only?
« Reply #22 on: April 19, 2019, 06:23:54 AM »
Frontline I think you're on the right track with the 7W oil.  I've gone for a test ride with the 10W, and the firmer compression damping in the front doesn't quite match the squishier rear shock.  7W / 26cst might be the sweet spot with OEM shock.

Offline Frontline

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Re: Changing fork oil to higher viscosity only?
« Reply #23 on: April 19, 2019, 12:43:17 PM »
*Originally Posted by KellyL [+]
Frontline I think you're on the right track with the 7W oil.  I've gone for a test ride with the 10W, and the firmer compression damping in the front doesn't quite match the squishier rear shock.  7W / 26cst might be the sweet spot with OEM shock.
Yeah, I was too nervous going too heavy...especially with the poor/average oem valving. I think sticking to a cSt weight of 20 through 26 is best option. I'm happy with my results. Klotz and Ohlins make stuff in the 22cSt range...but I suggest one sticking to non-synthetic or semi if they are not going to fully disassemble the fork (and checking for stiction while oil is removed.

This is what I used: (one bottle is enough for both forks)
« Last Edit: April 19, 2019, 12:45:41 PM by Frontline »

Online Forks-by-Matt

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Re: Changing fork oil to higher viscosity only?
« Reply #24 on: April 19, 2019, 04:25:33 PM »
*Originally Posted by KellyL [+]
Since I had some Motul Expert Medium 10W lying around, I decided to completely ignore Forks-By-Matt's advice and change out the oil today to the 10W (which is about 36cst@40 deg viscosity).  I only swapped out the left fork oil.
...
Verdict: 10W / 36cst viscosity fork oil seems fine.  Slow speed rebound stabilises at around 3 clicks out, but high speed rebound (i.e. fork overshoot) stops at around 1.5 clicks out.
The valving on the rebound piston is very light. If you're not going to alter the internals (piston and shims) and if you're happy with 36cSt then good on you. I don't consider a rebound circuit "correct" unless the adjuster is sitting at no less than 1 TURNS (4 clicks) out and better if 6-8 clicks - well actually I'm looking at damping force curves, not 'clicks' as such. Performance also depends on ambient temp when running oils that thick.
Meanwhile I've got a Nitron NTR R1 rear shock and TVT cartridges on order.  The cheapo oil swap will keep me satisfied in the meantime.
You should love the shock. You got the TVT25? nice! The TVT is a 3 piston setup and I would recommend running no thicker than 11cSt@50 in the COMP leg at first. I don't remember offhand what oil they specify on the REB leg but it's probably Ohlins' 19cSt40.
Good suspension doesn't have to be expensive.

Offline KellyL

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Re: Changing fork oil to higher viscosity only?
« Reply #25 on: April 19, 2019, 10:24:56 PM »
*Originally Posted by Frontline [+]
... Klotz and Ohlins make stuff in the 22cSt range...but I suggest one sticking to non-synthetic or semi if they are not going to fully disassemble the fork (and checking for stiction while oil is removed.

Repsol 5W is listed as 22cSt in its spec sheet, and cheaper than other brands in my neighbourhood. I'm going to give it a go for the next oil change.  :152:

Offline KellyL

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Re: Changing fork oil to higher viscosity only?
« Reply #26 on: April 19, 2019, 10:32:52 PM »
*Originally Posted by Forks-by-Matt [+]
The valving on the rebound piston is very light ... Performance also depends on ambient temp when running oils that thick.
Nice warm weather in AU at the moment! Yeah the 10W seems to match the rebound circuit well, but compression needs something lighter. We can't tune the Z900 with different viscosity oils in each fork, like the Z900RS etc.  My guess is that stock valving would work with 15W rebound but 5W compression (which is of course impossible).

I can't wait for the Nitron goodies to arrive.

Welcome back Matt
« Last Edit: April 19, 2019, 10:55:47 PM by KellyL »

Online Forks-by-Matt

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Re: Changing fork oil to higher viscosity only?
« Reply #27 on: April 19, 2019, 11:02:53 PM »
*Originally Posted by KellyL [+]
Nice warm weather in AU at the moment! Yeah the 10W seems to match the rebound circuit well, but compression needs something lighter. ... My guess is that stock valving would work with 15W rebound

The orifices on the comp piston are way too small. you could run 'water' aka less than 5cSt@40 and it would still suck. I wouldn't even contemplate putting a 45+cSt@40 oil in a cartridge system. You'd be certifiable. KYB/Kawasaki really screwed up in this config. You're forced to replace the pistons to have any hope of getting something that starts to work.

We can't tune the Z900 with different viscosity oils in each fork, like the Z900RS etc.

The RS doesn't work like that. It has full valving on both legs.
Thanks, I'm glad to be back.
Good suspension doesn't have to be expensive.

Online zed9

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Re: Changing fork oil to higher viscosity only?
« Reply #28 on: April 20, 2019, 01:26:45 AM »
Hey, Matt's alive.  :047:  :821:

Offline George26

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Re: Changing fork oil to higher viscosity only?
« Reply #29 on: April 22, 2019, 12:46:10 PM »
I just order 105/K21 Andreani Cartridge Misano kit from Italy, its nearly halv price of ohlins kit 610 bucs, someone has a review of Andreani kit ?