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Lighter fork oil/fluid for plushness??

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I have a 2017 Beta 390 Race Edition (which I love) and it has the new closed chamber Sachs forks up front. I'm over 210lbs w/o gear and I have had the suspension revalved (several times) and heavier springs installed. It is much better, but still spikey and harsh over rocks and chunder. I'd like to get more "plushness" in the first 4" - 6" of travel. I saw an article from a guy who had the exact same complaint on these forks and he wrote about simply changing the fork oil to a lighter weight oil. His post raved about the plushness of the forks after the simple fluid change. I "pm'd" him but haven't heard back.
So here's my question(s). He stated in his article that suspension fluid and oil were not the same and that 5w fluid was the equivalent to 3w oil. He further stated that he simply used Blue Rock Oil 5w Synthetic Suspension Fluid to achieve all this plushness. I went online to find this stuff and it looks to be mountain bike fork fluid. So:


*Has anyone heard of doing this and achieving these desired results with a simple oil/fluid change to a lighter oil?
*Is the Rock Oil bicycle fluid OK to use? (Oil is oil right?)

*I have read that oil viscosity ratings are inconsistent from one brand to another - so what's a guy to do?
*How much oil should I buy to do both forks?
*Does the new/lighter oil go in both chambers of the closed chamber forks?
*Does this same logic apply to the rear shock of the bike if it's too "kicky" over rocks etc?

Sorry for the all the questions, but I really appreciate the input. Thanks much,

Man on mission to achieve plushness...

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I have used 2.5 Silkolene and Bel Ray fork oil with great result in my CR250 stock forks. I used it at the amt recommended in the manual. That alone worked better than several revalves.  Rocky Mtn has it. 

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On 2017-5-9 at 7:10 AM, cardoc said:

*Has anyone heard of doing this and achieving these desired results with a simple oil/fluid change to a lighter oil?
*Is the Rock Oil bicycle fluid OK to use? (Oil is oil right?)
*I have read that oil viscosity ratings are inconsistent from one brand to another - so what's a guy to do?
*How much oil should I buy to do both forks?
*Does the new/lighter oil go in both chambers of the closed chamber forks?
*Does this same logic apply to the rear shock of the bike if it's too "kicky" over rocks etc?

I've heard of people using lighter fluid and liking it.

I don't like it because I want my fork internals to last longer. Higher viscosity = better film strength.

Compare the CsT figures for various oils.

Oils aint oils. Some are bad in terms of friction, wear, foaming, etc.

Buy 4 or 10L of Dex VI ATF.  It's near the same vis as 5w Motorex. Works great. I cannot feel any difference compared to Motorex. Actually might be a bit more slippery in SSS forks.  Certainly very cheap.

How much oil depends on the fork design. My SSS forks needs about 900ml (minimal wastage), and my 48mm OC forks need about 1100ml if my memory is any good.

Don't use light fluid to fix harsh valving. Just fix the valving.

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On 2017-5-9 at 7:10 AM, cardoc said:

but still spikey and harsh over rocks and chunder. I'd like to get more "plushness" in the first 4" - 6" of travel.

I've never ridden or opened Sachs fork, but I have a thought ... If your CC forks are harsh over rocks and chattery bumps then a common cause is not enough float gap in the mid comp valve. The mid comp valve is hyper sensitive to the amount of float and general bleed. Since that valve moves 1:1 with the wheel. The mid comp impacts the initial damping a lot.

Another common way to create harshness is to have a mid comp valve with far too much damping for very high speed strokes. Good CC forks can easily be setup to blow well open on very fast hits. I suppose some have bad designs and need some creative thinking to fix them. But someotimes very simple things can fix them.

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Lotsa good advice here and yes, lighter weight fork oil should provide less damping which can provide a softer, less harsh feel.  If valving is designed using 5wt fork oil then a 2.5wt fork oil will move more easily thru it however, this would just be a way to feel the difference and not the best way to go about tuning the fork.  Revalving the fork is the proper way although not as quick and easy. 

Not sure if lighter weight fork oil will not provide the same level of wear protection as that of a heavier.  Modern witchcraft has changed the rules on how lubrication works and has eliminated lots of shortcomings of the past.

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I agree generally a lighter oil is not so good for lubrication, but if a owner is too nervous to revalve, can't afford a revalve, a light fluid is a band aid that's worth the compromise

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Some of you guys better go change the oil in your autos, those 0-30, 5-30 oils that the mfgrs are rec and using from the factory are destroying your engines! :lol:  Not sure about your location but in mine its 2017.

Edited by YHGEORGE
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19 hours ago, YHGEORGE said:

Some of you guys better go change the oil in your autos, those 0-30, 5-30 oils that the mfgrs are rec and using from the factory are destroying your engines!

In my opinion that's mostly irrelevant. We all know engines and transmissions have tiny oil paths and critical oil pressure and flow rates. Manufacturer designs and oil specs take all that into account so anyone is a fool to not trust them when choosing the oil for their use/temps.

Have a look inside your forks next time they're apart. See which surfaces show the most signs of wear and think about how those surfaces get lubricated.  More than just bushes and seals wear out. When the oil gets old and thin the wear can be very depressing if you prefer the new feeling.

Film strength matters a lot. When the forks are getting worn out and you want low friction performance then the film thickness comes into play a lot too. Regardless of any modern oil technology, viscosity plays a huge part in film strength and certainly film thickness.

In my opinion, if you subject your forks to high stress and don't want to service them every 15 hrs to get the longest life out of them, then 2.5wt is too light.

Obviously we use what ever we want to believe in.   In my mid-life forks, I'll enjoy using 5wt fork oil.

22 hours ago, MetricMuscle said:

lighter weight fork oil should provide less damping which can provide

I was told by an experienced tuner that oil viscosity mostly impacts low speed damping. Which makes sense to me considering the function of low speed bleed ports versus high speed large piston ports which offer minimal flow resistance. I understand that the fluid has to flow around other parts at high speeds, so low viscosity fluids can feel a bit softer - if friction is kept low enough.

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I understand your point but shocks operate in a much much much harsher environment than forks,,,,with 2.5 wt oil.  Quality is the key. I have total confidence in Silkolene and Bel Ray products.

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Thanks very much for the replies. I'll blender all this up and come up with a course of action. :ride:

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I don't know the Sachs design but when you take your forks apart check if the cartridge is not over filled. If it is you need to fix that 1st because here is your harshness and lighter oil will not fix it.

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Maybe it's time for a new tuner. Perhaps someone that knows that fork better. I've ridden the new Sachs CC set up a fair amount lately and agree that in stock form the fork deflects and feels harsh on rocks and trail trash. I thought the fork was fairly plush but seems to get unsettled easy on terrain where the fork is hitting lots of small stuff fast. I also find that the shock does not feel very planted and is easy to spike.

Have you looked into other things such as your suspension set up, tire, tire pressure? 

Maybe try playing with the fork rebound a bit? 

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