Re: Which fork oil? Pointy.
 

But to be fair that sounds a bit too thick for my liking. Stock spings... Silkolene RSF pro 7.5... 37cSt ... VI of 339.

Got the motor oils bum kicked on both counts there.


For my money... buy proper fork oil... if you're going to be a cheap tw*t buy hydraulic oil. Engine oil is not the right stuff for this job.

Re: Which fork oil? Pointy.
 

Everything is standard.

Re: Which fork oil? Pointy.
 

http://www.opieoils.co.uk/p-827-silk...ion-fluid.aspx

HTH

Re: Which fork oil? Pointy.
 

I've got plenty of hydraulic 32 for the digger but I don't think I'm that desperate. By the way, those numbers .... thicker oil has higher VI and lower cSt? And is cSt the key one for suspension?

Thanks, Tony S

Re: Which fork oil? Pointy.
 

Thicker is higher cSt.

VI is more like measure of quality/amount of additive package in there... it is measure of how much oil gets thinner with heat.
In practical terms using thick (high cSt), low VI oil with heavy springs means it feels sh*t on a cold morning.

The "weight"/"w" number is vaguely related based on what manufacturers want to call it. Some other manufactuerers call it light/medium/heavy instead.

Re: Which fork oil? Pointy.
 

VI is an indication of how much the viscosity changes with temperature, which means a low viscosity index is better. If you have the proper initial viscosity in your forks (or shock) when it's at ambient temperature, you want the viscosity to remain, as much as possible, close to that original value. Multi-viscosity motor oil does that extremely well. There are some synthetic multi-viscosity fork oils around lately, they're probably getting to be nearly as good as synthetic motor oil.
Fork oil viscosity is measured differently than motor oil, but, when they put "7.5w" on the fork oil bottle, it's because it's very nearly the same viscosity as 7.5w motor oil. Again, no two fork oils labeled 7.5w are likely to be exactly the same, and they may or may not be exactly the same as 7.5w motor oil, but, they are all pretty close.
Try it. It works. It gives good, consistent fork action and does a fantastic job of preventing wear to fork bushings. Or don't try it, why should I care?
If you want 7.5w oil, you can mix proper ratios of 5w30 and 10w30 to get 7.5w30.

Re: Which fork oil? Pointy.
 

No it isn't like that, you have it backwards.

Re: Which fork oil? Pointy.
 

Also looking up there if that number for mobil 1 5w30 is representative of the general case being 72cSt at 40C then it is WAY WAY different from a 5W fork oil!!!

72 cSt at 40 is more like a fork oil manufacturers would call a 15 or 20!

Re: Which fork oil? Pointy.
 

I guess using anything other than actual fork oil is a matter of suck it and see. I must admit I'm quite tempted to try the hydraulic oil (cst 32 @40 degrees), although I can see that fork oil needs to do some lubricating, which maybe isn't the case in a hydraulic system.

Final resort for would be to put my hand in my pocket for some of that Silkolene RSF.

Re: Which fork oil? Pointy.
 

Yes, you're right of course. There are reasons I shouldn't rely on my memory. Sorry.
All I know is, synthetic motor oil works well and lasts a long time while doing an excellent job of protecting forks from wear. I've used it for 20 years for street riding and roadracing.
I've used it as a straight substitute- if the application called for 5w fork oil, I've substituted 5w30 synthetic motor oil. It has NOT acted like it was 15w fork oil. I have liked the action of all the forks I've used it in. I've put it in other peoples forks, and they've liked it. Some of my friends have tried it, and they liked it.
If I was motocross racing, I might spend the extra money for Silkolene fork oil. Since I'm too old to learn to ride motocross, I'll keep using motor oil in my forks.