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i figure this has been discussed, but i'm buggered if i can find the conversation that really answers my question...

i wanna change my fork oil, and the manual says to use 5wt, but the fella in the local supply shop convinced me to go with 10wt...he told me that it would make the extra wt would stiffen the rebound? is that right?

i'm 70kg without gear, which is about 155lb i think, and i believe my forks are stock if that helps...most of my riding is gonna be clay based trails...

what weight oil do you use?
is this even an issue?

Which bike do you have / which forks??

Most forks are designed to work with 5 wt oil. If your forks don't adjust enough to fall into the range you need, you can use different weight oils to compensate. Just remember that the heavier oil will increase resistance for both compression and rebound. Going from 5 weight to 10 weight is a fairly large jump...a cheaper and effective alternative is ATF which is about 7.5 wt.

What type of atf fluid?

Mercon, dexron, atf+4....any of them will work. Don't forget that fork oil height will affect travel - the more oil the less travel - if the forks are getting the right amount of travel now, then replace with the same amount, too much travel: add 10 cc's at a time until it's right - too little travel (bottoms too soon) try reducing the amount of oil by 20 mm from where the oil height was to begin with (it's easier to add than to remove). More oil will also firm up the stroke before reaching bottom too. The right oil height and weight can't correct a wrong spring rate, but can definitely help make things work better otherwise. Many manufacturers give a range for oil height for their forks as fork oil tuning is a variable. For open chamber USD forks I run the oil 120 mm from the top (fully compressed) for woods work.

ok dumb question im reading the svc manual and it says oil level 140 +- 2mm and oil capacity 618+- 2mm. now the capacity is what the whole fork tube can hold right and the oil level is what it should be set at?

Yep.

dnovack wrote:... and oil capacity 618+- 2mm.

Shouldn't that read: "618 +- 2cc"??

Well, I only bought a iitre so I gonna need more, so I think I'll mix it with a 5wt and try and get somewhere around 7.5....I'd heard that atf can get a bit foamy or something in the shock?s

atf will come out looking just as it did when you first put it in

fork oil will come out as a nasty goo in no time at all

FWIW - I have rebuilt and worked on a lot of forks and shocks. A few years ago, I tried some Pro-Honda SS-7, which, oddly, is 5 wt. Now, I swear by it. It just seems to make the suspension components work much more smoothly that any others I have tried. Even the ultra-expensive Race-Tech oil ($30/Liter!) does not feel as nice as the Pro-Honda stuff.

it wasnt too long ago that i was having trouble with my clutch and so now am using type f auto trans fluid in my gearbox, and now i'm thinking about putting it in my shocks too?...surely theres some advertising twerp thats missing an opportunity here!...(no offence to any advertising personel out there, i'm sure you're not all twerps in the advertising world)

dnovack wrote:ok dumb question im reading the svc manual and it says oil level 140 +- 2mm and oil capacity 618+- 2mm. now the capacity is what the whole fork tube can hold right and the oil level is what it should be set at?

I would interpret this to mean - If you add 618 cc (or ml?) of fork oil to one leg, the level should end up right around 140mm (from the top of the tube with the fork collapsed, and the spring removed).
If 1 quart is around 950 ml, then a 16 oz bottle of Pro-Honda SS-7 is around 475ml, I am about 143 ml short right now...

Yep. What i did was made a depth gauge so i could measure how far down i was from the top of the fork when i was adding my oil. Then i used a syringe to get it equal on both sides.

Wait im sorry its too early. Ur ok u wanna be 140mm from the top of the fork tube compresed. So ur ok. I really put in 450ml in each leg. The 600 ml is what the whole fork leg would hold. I wasnt thinking when i wrote the other post.

dnovack wrote:Wait im sorry its too early. Ur ok u wanna be 140mm from the top of the fork tube compresed. So ur ok. I really put in 450ml in each leg. The 600 ml is what the whole fork leg would hold. I wasnt thinking when i wrote the other post.

Ok, so let me get this straight. You put 450 ml of oil in each leg, and your oil level was in between the correct limits (140mm +-)?

Yes. I was alittle confused at first but talked to my brother and he explained it to me.

That all sounds right. The last time I did a fork oil change I used two bottles of the ProHonda SS-5 and had some left over. The bottles are 500 ml each, I used 375 ml per leg on a KTM

well in that case, i will have enough since i've got 1 litre of 10wt oil, so i think i'll just try that then...glad i"ve been a little slack and not got around to buying more now then...cheers for clearing your own mishaps there for me...