13+ Fork Oil Weight - ZX6R Forum
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post #1 of 16 Old 04-19-2017, 08:15 AM Thread Starter
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13+ Fork Oil Weight

Hey guys,

I've done a fair bit of searching around and can't seem to find the info I'm looking for. I am refreshing my forks since the bike has 7k miles and more than two seasons of track days now...I figured I'm due

I am trying to decide on 5wt or 10wt. The service manual calls out Showa SS-47 which, as far as I can gather, lines up to ~10wt? For the 09-12 guys, the service manual specifically says Showa SS05 or SAE 5W equivalent, so it's different.

I'm pretty happy with my current fork settings so I'm not wanting to deviate too much from the factory oil weight. If it's a toss up between 5wt and 10wt, I figured it would be best to go with 10wt since I am approaching the rebound/compression setting limits of the stock forks.

Thanks in advance!
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post #2 of 16 Old 04-19-2017, 08:45 AM
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I went through this too and decided on Motul 10wt (Data Sheet)due to the price and similar characteristics of the OEM SS47 (very similar to SS08). You can't tell what the true viscosity is through just the label of a certain wt. Just check out this chart. Some 5, 7.5, 10, and 15 weight have similar properties so it's important to take that into account.

http://www.peterverdone.com/archive/...ion%20oils.pdf

Some more info: Suspension Fluid - Pvdwiki
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post #3 of 16 Old 04-19-2017, 09:45 AM Thread Starter
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Thanks JD, I looked at that chart along with a few others online and came to the same conclusion as you. Motul 10wt looks to be pretty close.
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post #4 of 16 Old 04-19-2017, 10:02 AM
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Also make sure you get two bottles. I only ordered one (OEM internals) and I needed a couple extra ounces to get the right fork oil levels.
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post #5 of 16 Old 04-19-2017, 10:42 AM
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It's all about centrastokes, the only true way to measure the viscosity. Consider the viscosity index, the rate at which the oil breaks down and changes viscosity. The higher the viscosity index, the better. Silkolene Pro Rsf is an outstanding suspension fluid with a very high viscosity index. Redline is an awesome fluid as well. But what the fuck do I know, I have just been tuning suspension for over 20 yrs.
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post #6 of 16 Old 04-19-2017, 10:50 AM
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I use Ohlins 5wt (PN 01309-05). It's what is recommended in the manual for the Ohlins cartridges. But I've used that in other bikes with other non-ohlins forks too. Works great but also never tried anything else, so can't give you a good comparison.
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post #7 of 16 Old 04-19-2017, 10:53 AM
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FWIW, fork oil weight is not as much of a factor as it was with damper rod fork assemblies. Once the rebound and compression is controlled by reed valves instead of fixed diameter holes in rods, the thickness of the oil is less critical. You can adjust the rates with the valves, rather than by the thickness of the oil....
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"There's this adage that we have 2 ears and one mouth so we should listen twice as much as we talk. Unfortunately with the Internet people have taken this old adage and turned it around. They have two eyes and 10 fingers so they think they need to post 5 times as much as they read. And since they have 10 fingers and one brain, they only have to think 10% of the time! "
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post #8 of 16 Old 04-19-2017, 11:10 AM Thread Starter
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Quote:
Originally Posted by RJ2112 View Post
FWIW, fork oil weight is not as much of a factor as it was with damper rod fork assemblies. Once the rebound and compression is controlled by reed valves instead of fixed diameter holes in rods, the thickness of the oil is less critical. You can adjust the rates with the valves, rather than by the thickness of the oil....
For sure.

Side note, what is the effect on fork action once the fork oil becomes old and starts breaking down?
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post #9 of 16 Old 04-19-2017, 11:25 AM
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Oil weight almost always becomes thinner than what it started out as..... the guys who pay more attention to this should speak to how it affects action, my expectation is the amount of damping for either rebound or compression would become less due to the change. Eventually, no matter how many clicks you change settings you won't see any change in performance.

"Basic stuff fellas. Use your head for something other than to break your next fall."

"There's this adage that we have 2 ears and one mouth so we should listen twice as much as we talk. Unfortunately with the Internet people have taken this old adage and turned it around. They have two eyes and 10 fingers so they think they need to post 5 times as much as they read. And since they have 10 fingers and one brain, they only have to think 10% of the time! "
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post #10 of 16 Old 04-19-2017, 03:09 PM
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Hence, having a fluid with a high viscosity index helps tremendously because the oil does not break down nearly as fast. Although forks have large surface areas inside of them to contaminate the fluid with aluminum and Teflon (internal sliders) particles. Just sayin, look at centrastokes (thickness) and viscosity index(maintaining ability) when choosing a suitable fluid. Slikolene Pro RSF 2.5 is roughly the same weight( 14 centrastokes) as Maxima 5 wt.( 14.8) but the viscosity index of Silkolene is close to 400 and Maxima is like 150. I will take the Silkolene any day.
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post #11 of 16 Old 04-19-2017, 03:19 PM
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post #12 of 16 Old 04-20-2017, 08:55 AM
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Thanks Teach
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post #13 of 16 Old 04-20-2017, 12:09 PM
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Hence, having a fluid with a high viscosity index helps tremendously because the oil does not break down nearly as fast. Although forks have large surface areas inside of them to contaminate the fluid with aluminum and Teflon (internal sliders) particles. Just sayin, look at centrastokes (thickness) and viscosity index(maintaining ability) when choosing a suitable fluid. Slikolene Pro RSF 2.5 is roughly the same weight( 14 centrastokes) as Maxima 5 wt.( 14.8) but the viscosity index of Silkolene is close to 400 and Maxima is like 150. I will take the Silkolene any day.
Street riders like myself will see the some (possibly the greatest) contamination of the fork oil, due to rain getting swept into the oil. Obviously, the more back and forth sweeping the bushings do on the fork legs, the more surface imperfections are going to be polished out.

I would expect that the greater the motion of the fork (how much of the available sweep) the more opportunity for gunk to end up in the oil.

Does the resulting slurry have the same centrastokes and viscosity index as fresh, pure oil of the highest possible quality? I'd have to say, no. Is there enough of a difference that I should be able to feel it, when replacing sludge for fresh? My gut says the difference would be slight, in my use. There, but not tremendous.

I've ridden street bikes with completely shot forks..... as long as the springs are appropriate, they will allow commuting with moderate risk..... just having the seals bad, and leaking oil on the legs, tires, brakes is enough to park the bike before you have to part it out.

Bad fork oil, like bad coolant is an insidious fault. You don't know it's bad, until it bites you.....

I may be talking myself into getting the forks serviced.

"Basic stuff fellas. Use your head for something other than to break your next fall."

"There's this adage that we have 2 ears and one mouth so we should listen twice as much as we talk. Unfortunately with the Internet people have taken this old adage and turned it around. They have two eyes and 10 fingers so they think they need to post 5 times as much as they read. And since they have 10 fingers and one brain, they only have to think 10% of the time! "
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post #14 of 16 Old 04-20-2017, 01:42 PM
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Fork oil goes bad slowly. So slow you don't realize how bad they work until you service them and say "I should have done this a long time ago ". People neglect fork and shock service. Many street riders don't know shit about their suspension anyway. Unless it really jacked up they just ride unaware of how good the bike could work. They ride around problems.
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post #15 of 16 Old 04-20-2017, 01:46 PM
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While you're at it might as well re-grease the steering stem bearings. I cleaned mine out and put marine grease.

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