Whats the difference between 5w and 15 w fork oil???

15 replies to this topic
  • DoctorRzed

Posted May 21, 2005 - 03:18 AM


What does running hevier weight fork oil do??? I see they have 20 w fork oil. What will be the diff of me running 20w versus 5w???

  • jamieyz426f01

Posted May 21, 2005 - 03:22 AM


urm i think more dampening :) i went up to 10w from stock in my 426. alot less bottoming out now!

  • DoctorRzed

Posted May 21, 2005 - 03:29 AM


I run race tech .48 fronts and I weigh 210lbs. I still bottom a bit but rather than just adding more oil I was going to try 10w of 15w oil. I currently run 5w. I was told you cant tell a diff between 5w and 7w. Will I be able to feel a diff with 10w 15w or even 20w???

  • jamieyz426f01

Posted May 21, 2005 - 03:31 AM


u should be able to notice from 5w to 10w or 15w i weigh about the same but have the 46mm forks i filled them with oil to the manuals specifications and much prefer heavier w oil.

  • yz007f

Posted May 21, 2005 - 12:33 PM


If you forks are set up right you will notice the difference between 5w and 15w oil. 15w oil will fade a lot faster and you will notice the loss in proformance in you suspension. 15w will stiffen the fork on the compression and slow the rebound enough to notice it, compared to 5w oil. You will have to change your oil more often running heavier wt oil.


  • DoctorRzed

Posted May 21, 2005 - 03:07 PM


I put 15w in and I notice a diff already. I change my fork oil about each other month.

  • grayracer513

Posted May 21, 2005 - 04:31 PM


Try Mobil 1 Dexron III ATF once. I think you'll like it.

  • BC61

Posted May 21, 2005 - 05:30 PM


I've heard a few people say use atf, what's the deal with it?

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  • grayracer513

Posted May 22, 2005 - 09:42 AM


It's a good stable fluid that happens to work well in the forks on a Yamaha. It happens to be 7 wt. Note that I recommended Mobil 1 Syn specifically. I haven't used other "flavors".

  • Thrash1

Posted August 15, 2005 - 05:45 PM


I was going to try a new oil when I change the seals but isn't M1 SYN ATF a 10w20?

  • grayracer513

Posted August 15, 2005 - 09:32 PM


No, in order to comply with the Dexron III spec, it has to be 7 wt. The viscosity is critical to the calibration of the hydraulic control valves in automatic transmissions, and it's not something you can just fiddle with without consequence.

  • MisterMan

Posted August 15, 2005 - 09:36 PM


What does running hevier weight fork oil do??? I see they have 20 w fork oil. What will be the diff of me running 20w versus 5w???

heres the awnser, ones thicker, the 15w is way thicker...thicker is harder to pass through small holes (internals of ur forks) thus making it slower to pass down, then retract back up. it may also change the entire way ur bike handles. BE CAREFUL!!! take it slow, dont just go to WOT /wo/ testing it first.

hope this helps, PM me for more info, its rare that I check suspention fourms.

  • sirthumpalot

Posted August 16, 2005 - 03:31 AM


Thicker fork oil will slow the forks down a bit, make them more harsh in smaller bumps (assuming the valving is left alone). If you're having a bottoming problem then add some oil (raise the level). You'll be surprised how much this helps.

  • Thrash1

Posted August 16, 2005 - 06:43 PM


I'm not sure about the oil Viscosity that's in the forks right now. The fork/shocks have been reworked by JN Innovations. There's just a lot I have to consider when I tear them down to replace the seals, I need to check Shim stack(Spring Preload) and the spring weight to see if there stock or modified.

The oil is another part of the equation I need find a solution for when I put everything back together.

  • Ray450

Posted August 17, 2005 - 08:51 AM


I wouldn't go crazy with the oil. Suspension fluids have been getting thinner over the years to keep them from fading. The thicker oils lose their viscosity at a much higher rate than the thinner oils. If you start going as thick as 15w, I would suspect you will start seeing drastic changes from the start of a race, to the end, when the oil reaches much higher temps. If you need more dampning, I'd revalve or try higher levels rather than go that heavy on the oil. I wouldn't use anything in the double digits.

  • MisterMan

Posted August 17, 2005 - 09:17 AM


How does it get so hot??? after a hard ride (on a cool day) my forks are warm....friction????

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