Fork Oil Question

[Janusz]

Being a heavy man (225 lbs) I changed my fork springs long time ago for a stiffer ones (I think 1.05 from Lindemann). Recently at the service time I changed the oil into somewhat heavier (15) to hopefully achieve some more damping.

 

Upon reviewing some topics on oil weight I can see that some forum guys (Dlaing, was it you?) recommend LIGHTER oil then stock instead of heavier.

 

It really puzzles me. I am not trying to argue this advice but would like to understand. Why?

 

Could somebogy please explain?

[Guest ratchethack]

15 wt. sounds about right for your weight to me, Janusz. The only reason to go with lighter weight fork oil would be to get less damping at a given damping setting. In other words, if you're not getting enough damping with 15 wt at a max damping setting (compression or rebound), you'd have to use a heavier weight oil to achieve more damping, and you'd get it at a lower number setting. A lighter weight would give you less damping at a given setting.

 

At 190 lbs., after trying 10 wt and 7.5 wt., I went to a lower weight AND higher grade synthetic CARTRIDGE FORK FLUID, 125/150, because the recommended 10 wt. and (also) 7.5 wt. dino FORK OIL were not allowing me to use ANY compression damping - the lowest setting was too much with my up-rated fork springs (.7-1.1 kg/mm Wilbers progressives). 125/150 CARTRIDGE FORK FLUID allows me to use a broader range of compression damping settings (and finer gradient of adjustability) not achievable with either 10 wt. or 7.5 wt FORK OIL.

 

Dino and synth. fork fluids are considerably different in terms of properties and service life, synthetic being superior in every way measurable, if you buy the wisdom of most Pro's, who tend to recommend CARTRIDGE FORK FLUID for cartridge forks over FORK OIL.

[dlaing]

I thought 125/150 was rated at about the same as 7W, varying by brand.

IMHO an oil or fluid should be as thick or thin as is needed to keep you within the range of the adjuster, but a thinner oil will behave better(unless you are fighting seal leak issues), and I believe one should aim towards an oil wait that results in good results in the upper third of adjustability(where a thicker oil might push to the lower third).

Thinner is better because it is easier to engineer thermal stability qualities.

Unlike Ratchet, I was happiest with the Marzocchi set to the minimum compression setting...probably because of the oil weight I was using.

I think the dealer put in Maxima 10W. So, to me going lighter made more sense.

Every notch I dialed up on compression made the ride harsher.

But I never got around to making the Marz work properly.

It needed heavier springs and everything else set better.

Instead I went with Ohlins forks.

The beauty of the Marzocchi with seperate rebound and compression on each fork allows for using different fluid in each fork.