Fork Oil Weights?

[:[TYL3R]:]

Im looking at getting some really thick fork oil for my 2005 dirt jam pro forks.
i have that annoying top out that seems to happen with this model.
and it seems that the way to control this top out is with the air.
i have noticed that when you pump the forks up they do get stiffer but they also rebound also faster. thus causing top out.
under 20psi they feel smooth and dont top out, but are wayy too soft for me.
a firmer spring would make them rebound faster also. so thats out of the picture.

i have also heard of running motor oil but im not sure how good this is for the dampening unit.

i am using them for street park and dirt jumps and only want to be able to use around 30mm max whilst riding on the flat.
i weigh 70kgs, if someone could help me with finding oil that would be the correct weight for me ,that would be much appreciated.


Cheers, Tyler.

 

[cretin...rider]

Well, personally I have not seen anything heavier then 20w (I have been living under a rock when it comes to fork spring/oil etc) but it is interesting you mention motor oil as it can be 40w, i would like to here more about this could be interesting.

What about harder spring and more air? Does cost more but who knows.

Another thing, have you rebuilt them as such, recently? if not do it when you put new oil in and it will make them feel a lot better

 

[:[TYL3R]:]

harder spring makes them top out.
more air makes them top out.
they both make them rebound way faster.

i rebuilt them 2 days ago with 10w oil and they are just too soft.
some guy from marzocchi said that im only meant to use maximum 20 psi air. thats what im doing.

i read somewhere that some random who weighed 87kgs put 65w motor oil in them and they felt great.
the thing about motor oil is that its not teflon based like fork oil. (a mate told me this, dunno if it matters.)

 

[skwiz05]

What rebound adjustments do these forks have?

 

[bethextrem1]

Do a search.
But the basics of oil viscosity has nothing to do with the weight of the oil and everything to do with the centistokes@40deg and centistokes@100deg, a standard for oil viscosity. the higher the number the more viscose the oil. then there is viscosity index which means how much the oil viscosity changes with temperature the higher the number the better, 250vi and up is very good.

 

[:[TYL3R]:]

What rebound adjustments do these forks have?

they have no rebound adjustments, they are pretty crappy but can be set up alright.





does anyone have some suggestions on what oil i should get?


cheers, tyler.

 

[bethextrem1]

Here is some info for you to read

www.peterverdonedesigns.com/bikesuspension.htm

 

[:[TYL3R]:]

Here is some info for you to read

www.peterverdonedesigns.com/bikesuspension.htm

gee, there is alot of techy lingo in there.
i kinda get the idea though.
the wt of forks is kinda like clothes sizes. every brands 30 is different (which is bloody annoying!!).

the fork oil i am currently use is motorex 10w wich they say is very thick.
i think i will get some more of that in 20wt and see if i can mix them up to get the perfect mix.

it seems that you can use synthetic motor oil aswell

i just set up the forks abit better then and i think the 20wt might fix them.
if its still too thin i will get some thicker synthetic motor oil.


thanks for your help bethextrem1 much appreciated!!


cheers Tyler.

 

[drivebytrucker]

dont use motor oil

hi mate, go to any moto shop, prefferably one that does more mx stuff. get the heaviest and second heaviest fork oil they have, make sure you get the same brand.

so a 20weight and a 15 weight, blend them 50/50 in a container and bingo. not 35 weight but mor like 25. add them to the fork and a way you go. they shouldnt separate cos your using the same brand. however if it does its not a problem cos it goes from ligh to heavy so it will act as a kind of ramp up.

this is an old school trick that has been neglected over the years thanks to ttechnology and this sort of planning not normally needed any more.

i run this in my 7inch shivers, and my man bottoms out his 8inch boxxers where i dont and i m heavier.

dont use motor oil as most modern motor oils including synthetic have detergent agents in them wich will eat through the seals a lot quicker.

have fun

 

[macca21]

Hmmm.....

20weight and a 15 weight, blend them 50/50 in a container and bingo. not 35 weight but mor like 25.

Wouldn't it be more like 17-18wt. logic says 17.5 but it's not a linear scale i don't think.

i run this in my 7inch shivers, and my man bottoms out his 8inch boxxers where i dont and i m heavier.

Can totally different fork designs be used for a fair comparison?
But yeah, unless 20wt is too light this should work well.

 

[drivebytrucker]

the difference in the fork leg designs, is pretty much that, design. the internal and external theory of compression and rebound remains the same, so yes it can be compared, providing the forks a re both oil and spring and no air cartridges to consider.

i see where you go with the oil weight mix theory but for some reason, one thats too complex for my physics knowledge it does get heavier, even though it shouldnt. i have been running this for years in my mx forks as do a lot of older riders, cant explain why it does but it does.

 

[Tallman]

so a 20weight and a 15 weight, blend them 50/50 in a container and bingo. not 35 weight but mor like 25

Pretty sure a 50/50 blend of 20 weight and 15 weight stuff would be 17.5 weight. You don't add the two weights together (ie 20 and 15), rather average them with regards to the ratio that you're mixing them in.

 

[cretin...rider]

Pretty sure a 50/50 blend of 20 weight and 15 weight stuff would be 17.5 weight. You don't add the two weights together (ie 20 and 15), rather average them with regards to the ratio that you're mixing them in.

I was going to say something like that, except slightly less technical. if you add a thinner product to a thicker one it does not make it thicker, the opposite, thinner i.e. adding water to paint does not make it slightly thicker but slightly thinner (depending how much you add)...