The 4th Horseman
New Member
Hey everybody,
The main reason I'm posting this is that I recently found one of my fork seals to be slowly leaking. As everyone knows, problem = upgrade opportunity. I found replacement seals easy enough (https://www.ktechsuspensionusa.com/p-20107-k-tech-suspension-fork-oil-seals-wp-pair.aspx), but fork oil selection (even finding OEM) was a little more involved. I've already done 90% of the research, so hopefully this can help someone else out, but I'm also looking for opinions and verification of my findings from people who may be more knowledgeable.
Right now, I have 2 options: 1) Minimize downtime, by only replacing the leaking seal and using OEM fork oil; or 2) Use this opportunity to upgrade fork oil and remove/disassemble both forks. So I want to answer 2 questions:
Repair Manual:
Owners Manual:
For non-experts asking the same question: Here's where I found some good reading: http://www.peterverdone.com/wiki/index.php?title=Suspension_Fluid
Summary:
-Weight number means nothing - It varies by manufacturer (ie: 7W at one supplier could be lighter than 5W at another) so ignore that.
-Viscosity is what matters - Dig that up and use that instead of weight. If you want stiffer, obviously go with a higher viscosity.
-Different forks are made for different weights/viscosities - So don't vary too much from OEM. Your friend may like 20W in his forks that were designed for 15W, but 20W in your RC will probably feel like solid rods.
-VI is also a good metric - This is how much the viscosity changes with temperature (ie: how consistent it will be throughout your ride). Higher VI = more consistent. Low VI = will soften more as you ride and it heats up. However, this is more important for rear shocks. Front forks apparently don't cover a wide temperature range, so this is less critical.
If I don't get any recommendations, I'm probably going to go with OEM to minimize work. However, down the road, I may experiment with a slightly higher viscosity (bump from Motorex 4W to 5W), but keep it close, as I'm not sure what's "too much" or "too little," and the bike is rideable as is.
Please share your knowledge, if you have any.
The main reason I'm posting this is that I recently found one of my fork seals to be slowly leaking. As everyone knows, problem = upgrade opportunity. I found replacement seals easy enough (https://www.ktechsuspensionusa.com/p-20107-k-tech-suspension-fork-oil-seals-wp-pair.aspx), but fork oil selection (even finding OEM) was a little more involved. I've already done 90% of the research, so hopefully this can help someone else out, but I'm also looking for opinions and verification of my findings from people who may be more knowledgeable.
Right now, I have 2 options: 1) Minimize downtime, by only replacing the leaking seal and using OEM fork oil; or 2) Use this opportunity to upgrade fork oil and remove/disassemble both forks. So I want to answer 2 questions:
1) Can anyone verify what fork oil comes in the stock bike? (Mine is 2018 US version)
My repair manual says SAE 4 oil (PN is obviously Motorex, like all stock fluids seem to be). Seems the '4' is weight, even though there's no 'W' after it. 4W is rare, but found some here (https://www.summitracing.com/parts/mxu-154038). However, the electronic OWNERS manual, lists SAE 5 and SAE 4, without any indication of which is in the bike. My hard copy that came with the bike only lists SAE 4, so that's likely what I'm going with if I do option 1. Just be aware, that this seems to varyRepair Manual:
Owners Manual:
2) Does anyone have an aftermarket fork oil recommendation?
I've seen this asked a couple times here, without real informative answers. Not looking to replace springs or buy an Ohlins cartridge, just swap fluid (if it's noticeably better than the OEM). Right now, it seems like there's a little stiction, although not problematic, and I wouldn't mind it being a hair stiffer. Any recommendations? Since I know someone will ask: I'm about 175 lbs. without gear, commute daily, but also do several track days per year. Please provide reasoning behind your selection too.For non-experts asking the same question: Here's where I found some good reading: http://www.peterverdone.com/wiki/index.php?title=Suspension_Fluid
Summary:
-Weight number means nothing - It varies by manufacturer (ie: 7W at one supplier could be lighter than 5W at another) so ignore that.
-Viscosity is what matters - Dig that up and use that instead of weight. If you want stiffer, obviously go with a higher viscosity.
-Different forks are made for different weights/viscosities - So don't vary too much from OEM. Your friend may like 20W in his forks that were designed for 15W, but 20W in your RC will probably feel like solid rods.
-VI is also a good metric - This is how much the viscosity changes with temperature (ie: how consistent it will be throughout your ride). Higher VI = more consistent. Low VI = will soften more as you ride and it heats up. However, this is more important for rear shocks. Front forks apparently don't cover a wide temperature range, so this is less critical.
If I don't get any recommendations, I'm probably going to go with OEM to minimize work. However, down the road, I may experiment with a slightly higher viscosity (bump from Motorex 4W to 5W), but keep it close, as I'm not sure what's "too much" or "too little," and the bike is rideable as is.
Please share your knowledge, if you have any.