How much fork oil?

I have heavy duty springs (for my 16.5 stone weight), but not sure how much oil I should have. The book states 80mm to 150mm from the top, but which should my setting be. Also, what actual difference does it make?


Dunno, but most of these :thumbsup: guys probably dont have any idea how much a stone is. 1stone=14 pounds, so 16.5stone=231 pounds the UK:

Here is what I 'think', not what I know for sure. :devil:

First of all my friend, darn few Yanks, if any, know what values/pounds equate to 'stone weight.' I'v heard of it, but don't know how to convert either.

A book stating 80-150mm from the top, and then not telling you how many mm apply to certain conditions or circumstances is....well, typical of instruction manuals. :thumbsup: Often no help at all. Only serve to agitate one further. Boy, do I know that feeling.

The forks compress and then rebound. To control the bike, ya gotta somewhat control these two motions.

How heavy the springs are, how much oil & how thick the oil is (viscosity), and the type, size, and quanity of assorted 'valves' inside the forks, and how much air remaining inside the forks, all work together to determine your 'fork action' capabilities. Slow & stiff, or, light and free. The trick is to try and find an appropriate middle ground for your weight, riding style, and the terraine your riding on. The Pro Riders hire suspension engineers to figure all this out for them But lets not go there.

As the forks go up and down, the oil is pushed/diffused back and forth "through" the assorted valves, and up and down inside the forks themselves.

The 'more' oil in the forks, the more diffusing is being done, the less air there is, and therefore the action will be slower and "stiffer." Make the oil a thicker-heavier weight, and the diffusing and movement of the oil becomes slower and more difficult yet...making the fork action even stiffer.

Less oil, thinner oil, more air in the forks, lighter springs, all make the fork action freer. Too light, too little resistance, and the forks will slam down and bottom out, or slam up upon rebound and top out. Very bad. :awww:

Gotta tell ya something about the fork springs, then I'll try and draw a conclusion for you personally. :D

Stiffer springs get that way because they are either longer, which leaves 'less room for oil,' or, they're about the same length as the springs you replaced, just wound progressively tighter offering more resistance.

I don't know how kg=pounds, but at 6'8" you gotta weigh at least 180 lbs. or more, and ya put the heavy springs in cause ya needed stronger/stiffer action for your big-self.

I personally would put in a 'medium' weight oil (leaving me the options of later going heavier or lighter) and fill the fork 115mm from the top, the mid-way between the 80/150, again leaving options open for adjustment if the action is not acceptable.

Remember though, if the 80/150 was for the 'stock' springs, and the new springs are 'longer' than the 80/150 is no longer the fill range. Longer springs = less fill mm.

Hey, suspension action, unlike other fixed components, is all about trial and (not error) but...retrial.

You've already made one substantial change...the springs.

Now adjust all other factors to 'medium & in the middle' and feel what the springs did for you. Adjust too many varibles at once, and you definately won't know what single adjustment was responsible for what resulting action. :D

Ride & tweak. Ride & tweak. (tweak=adjust)

When ya feel that one set of adjustments is really too free and soft, and another set of adjustments is really too stiff and your teeth are shaking out, then you've begun to narrow down and focus on the correct working and comfort range.

It's a ton of work for the Pro's.

Hell, I just fiddle with it over the course of time.

If I know I'm going to ride the 'flats' then I adjust for it. If slamming up & down on the tons of rocks in Pennsylvania, then I need some more resistance, but not so much so that the front end can't "absorb" some of the hit.

The end: :lol:

If the above is not adequate, go the the 'Forum Index' and post into the suspension departments. There are a number of very qualified people who have been through the adjustment processes a 100 times. With a little patience, you will get some useful help.

See ya 'Brit' & good luck. :lol:


Don't know if this will help, but here's what I did (and I weigh 195 lb). I started with 120mm from the top. At this level the front end was bottoming coming off of small jumps, so I added 10cc (from a syringe) to both sides. That was enough to stop the unnecessary bottoming.

So I guess you should start at a lower level, and added fluid incrementally until you're happy with it. I would hate to start out too high and have to get fluid back out of the forks.


I am using heavier Racetech fork springs and they recommended 90mm with 5 wt oil and 110mm with 10 wt oil.


Yea, those numbers sound fairly close to my previous guesswork.

How do you like the heavier springs?

Did you feel an improvement right away? Or just so,so?

Asking, because I'm getting ready to put some in my DRZ400.

Thanks for the info.

SSR :thumbsup:


Yep 230 Ibs of lean mean crashing machine (who am I kidding!).

Thanks for the detailed advice. I have 90mm at the moment, with 7.5 oil (I think) and with a heavy duty spring on the back, the front forks don't compress evenly with the rear. To date I have been using most of the front travel, but ideally want a more plush ride for the smoother stuff, so I think I will try a lighter oil to start and then adjust volume as I go. May just stay the same for this weekends enduro though!



Ya know, that was an interesting remark you just made. :lol: About the front & back not compressing evenly, ie.,working together.

The front forks, and the rear shock, are examined and discussed infinately in all sources of media, but come to think of it, I'v never read an article that explained how the relationship between the two should be.

You know, like marriage counceling. :devil:

Doesn't matter how well each component functions independently, for the real ability of the bike to track straight and run low to the ground is contingent on a good balancing act between front & rear.

I had to laugh :lol:when your comrad said we have no clue about stone weights. He's right. I'm glad he told us = 14lbs.

After thinking about you way over in the UK, I went to, and view some very interesting, and totally foreign, info about overseas dirt bike riding.

#1 Had no idea that Japanese bikes were so prevalant there.

#2 The green rolling country side where some of your tracks & practice tracks are located is beautiful.

I'm a tad older than most dirt bikers, and catching "big air" is beyond my scope of regular skills...for now.

Good luck this week end, and stay topside to the end.


SSR :awww:


I was recently told that holding onto the front brake and your pushing weight onto the peg, your bike should compress evenly front and rear - and my front hardly reacts - hence the posting. Can't say I have seen much reference to this in the forum, but I haven't looked that hard.

We do have some lovelly green roads in the UK. Anyone visiting is welcome to contact me and have a ride out some time! But we are also blighted by our NIMBY (not in my back yard) general public who on a small island can't seem to accept the existance of anything with an engine on anything that hasn't got tarmac on it. Hence we are fighting for our rights to keep on green laning (as we call it over here). That's why more of us older folk are moving towards enduros - 4 hours of monkey bum inducing fun.

Re - Jap bikes, have a look at 80% of the field on an enduro over here and you will see Orange - Austrian KTM's seem to rule these days!


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