Fork Fluid Question

I have seen numerous post on using Mobil 1 ATF as Fork oil. What have been the results from you all that use this? Also for those that use Yam 01, Belray or Silkolene. What about 5w vs. 7w? Is airtemp the factor here?

Any advice is appreciated. Thanks

you should talk to these people:

Jeremy Wilkey at MX-Tech

Rob Mann at GP-Racing

Jeff Howe at TrakControl Dynamics

all 3 are very well known for their suspension work. all 3 of them use Mobil 1 ATF in some if not all of thier suspensions setups.

SunRuh, how does the ATF stand up? How often does it need to be changed?

i have no complaints.

i will run a full season of harescramble racing on it before i change it. same goes for the shock.

the one thing about Mobil 1 ATF is that it is thicker (10wt i think) and each turn of the clicker gives you MORE change than a lighter fluid does.

you have to realize up front that ATF is designed for 25,000 miles in an automatic transmission. it is MADE for long term use and extreme heat. your forks and shock will not come close to that kind of environment and therefore it really, really lasts.

Is the Mobil 1 ATF a Dextron III rating? Just curious.

How are you changing the oil in the shock? Are you having it done at a suspension shop?

I still think it may be worthy to investigate why these suspension shops are finding better results, other than profit, with the use of ATF.

There would seem to be a lot of design considerations into forks and shocks based on fluid dynamics, that of O1 fluid. Modify the oil, and it would seem that you would have to modify the component to match.

In addition to this, there has to be a reason why Showa, KYB and Ohlins use the 01 fluid, as do most factory teams.

I'm not saying not to use ATF, I would just like to see a more technical argument made, especially when considering the variables in settings for trail vs. SuperCross configurations.



DaveJ I agree with you. As an engineer I tend to question everything which doesn't match exactly with what is recommended by the designers. After all, they should know best.

Just one more thing to add to your list. I have no proof, but I would suspect that suspension oil would be more consistent viscosity wise than something like ATF which doesn't need to be as precise. Could the average person tell the difference bottle to bottle? I have no idea, but I'll let someone else test it and give me the results. :)

Sir Thump,

Thanks for the addition.

This may sound a little sick, but just to be safe I usually blend multiple bottles of the same fork oil before I refill a set of forks. This assures a perfect visc. match between the legs.



typical 01 fluid has a VI of around 400. M1 ATF is around 198. jeff is currently working on some new blend of semi-sythetic that would flow well, but not cost as much as 01.

i have M1 ATF in my bike and like the way it rides. i race harescambles and plushness is a must.


Have your forks been revalved? I tried Mobil 1 in my stock 00 forks and found them too harsh for a rough MX track. Went back to 01 and was much happier.

Dave S

dave s,

yes, it was re-valved for woods racing before i even took possession of the bike.

So, what is the consensus for ATF in a motocross/supercross set of forks? I am in the process of completely rebuilding my YZF forks this week. I am revalving, checking mid-valve, replacing seals etc... I have .47's already. Last weekend at local Moto - I suffered complete fork failure...With 3 clicks out on the compression -- forks bottomed so harsh that you heard clank on every landing -- braking & acceleration bumps were brutal. They got worse as the day went on. Pictures on WR discussion tell the deal as the forks bottomed so hard my brains rattled. I am attempting fixes with my Tuner. If I am not satisfied, it's off to Enzo or MXTech.

My personal opinion is that you can not go wrong with the fluid which was designed for the forks.

If SUnruh is correct, then the Viscosity Index would be adequate for forks, if it provides the desired viscosity. If I had a Honda, I would definitely use it in the outer chamber. I wouldn't use it in shocks due to the low VI.

Steve, I wouldn't run any fork oil for a whole season. It is better to change it regularly due to how dirty it gets from fork wear. If left in, the aluminum particles in the oil act as an abrasive slurry, further accelerating wear. Since the ATF is relatively cheap, it would be worthwhile to flush the forks with new oil every 5-10 hours riding.

DaveJ, on the oil mixing, I wouldn't call it "sick", just meticulous. :)

Ga, you may indeed have a blown midvalve. While you have Tuner replace it, you might consider bottoming cones.

Scott F you commented on the WR side about the jump & my landing on the Step up. Do you or anyone else think bottoming cones are the ticket or worth the $???????

Another quest: Scott F or anyone else. If the midvalve is blown, is it better to replace it with Yamaha or does anyone else have a better solution?????


i had mine put in by jeff at

like i said, any of the 3 can do it and are very knowledgeable.

price is like 160. jeff might even fix the mid-valve cheap if he's doing the cones.

in my FC setup the mid-valve was taken out. in the TrakControl setup it was left in and jeff knows how to set it up right. even for offroad (about all i ride). the TrakControl forks whip the pants off the FC ones. period.

[This message has been edited by SUnruh (edited August 30, 2001).]

For bottoming cones check out anti-bottoming systems at the following web site.

And I saw an ad in one of the moto mags showing a picture of the same cones sold by Factory Connection. I'm not really sure who is the OEM on this, but I think it's C-Cycle.

And ScottF and the rest of us are referring to the mid-valve as the stack of shims residing on the opposing side of the rebound piston. This is the piston that is attached to the end of the cartride rod, inside the cartride, moving up and down with each stroke, (the compression piston just sits at the bottom, which is why perhaps some people just call it a valve).

So, unlike the compression piston (er...valve), the mid valve shim stack has a lot more movement or flexing of the shims. I once spoke with Scotts and White Brothers about this and both mentioned the use of a backing plate against the stack to avoid excessive flexing.

This worked, but the harsh ride continued.

When I spoke with KYB about this, they said to just remove the stack, but that they were not offering replacement pistons in this size to re-regulate the flow of oil on the compression stroke as they did with other fork design. Who knew?!

Keep in mind that the compression stack and valve on the bottom of the fork only flow a small amount of oil during the exchange or stroke of the fork.

So I pulled the mid-valve stack and installed a check plate. Then used a restrictor plate that I acquired from Race-Tech from either an earlier experiment with this fork, or something I have built in the past.

The problem is, the Race-Tech restrictor plate, which resides underneath the seal head (the cap of the cartridge tube) does not work with the after market bottoming cones.

Mainly it doesn't allow enough oil to bleed through, which traps air in the cartride tube.

So a bleed spacer needs to be made to go between the two of them, (bottom cone and restrictor plate). A bit of garage engineering. Thickness is critical so that the bottoming cone will mate with the top of the cartridge tube.

As for the longevity of oil, I was beating my bike heavily for about 10 to 15 hours of operation before I noticed serious degradation in performance. With each exchange, I tried a different brand of oil until I found that the KYB 01 distributed by Enzo Racing worked best.

One last note. The factory seal heads also have a shim stack in them. They can only be accessed by grinding off the bottom of the seal head. It’s a useless effort, but it’s worth noting that this assembly can get packed with the residue that ScottF is mentioning, causing it’s own set of issues. These sealheads also offer some hydraulic bottoming resistance, but no more than ¾ of an inch or so.

The aftermarket seal heads (bottoming cones) don’t use a shim stack, and offer about 2 inches of bottoming resistance. Just right.



Unless you're using your bike just to fetch firewood, I would highly recommend bottoming cones. Consider them as a health related issue. ScottF can chime in on some further details as he seems to be a man of big air.

As for mid-valves, the only way to replace it via Yamaha is a complete compression tube. About $275 per tube if...umm....memory serves me correctly.

It's best to pull it and run a restrictor plate, or just rebuild it. Some of the suspension shops have their own way of dealing with this thing. See previous posts for further details.

As for its usage, I'm slowing learning why Yamaha put it in.

For those that have yet to learn this lesson, a soft suspension is not a fast on. This is the concept behind the "plush-but-firm" approach that many top tuners speak of.

Soft causes the mass of the bike to sink and ride deeply into every hole in encounters (with you included).

Firm causes the bike to skip or ride high over the bumps and holes. A rather fast approach getting from point A to B, not to mention it doesn’t beat the rider up as much.

The trick is to make sure you have enough suspension to stick, without skipping.

So back to the mid-valve.

SuperCross tracks are very unique in that they don't have little bumps. They have big jumps and whoops, and the filler is relatively smooth. In this case, at extreme speeds, I can see the application of the mid-valve, but not without some tuning to the track in which you're riding.

Sometime ago I had posted some stuff on fork nirvana. Still true, but with some additional testing at some more aggressive tracks, I have once again learned the importance of application specific.

Clearly the level of plush-ness that works best on the trails does not apply to the big tracks.


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