Which fork oil? Pointy.

[jpd72]

Morning Everyone,

I'm a new member to the forum, who passed my Mod2 last friday. Aftet a ride out this week i noticed one of the forks leaking. My question to everyone in the know, is there any prefered spec/manufacturer of oil for the pointy? Any words of wisdom would be greatly appreciated.

Cheers

Jay

[MJC-DEV]

No really - every rider seems to have their own favourite oil type, weight and brand. You will get as many opinions as replies. Same for engine oil, brake pads, chains etc etc. Standard weight is 10W I believe but check the manual.

[jambo]

This is pretty much "Add salt to taste".

For bumpy roads I actually think something like a nominal 10w is about right, if the roads you use are smoother, you may prefer something a little thicker. There's an article here comparing fork oils (http://www.peterverdone.com/wiki/index.php?title=Suspension_Fluid). It's not crucial to match the Suzuki oil exactly, but if you plan to experiment it's important to know that one manufacturer's 10w can be thicker than another's 15w, so if you hop randomly between suppliers you can become convinced that there's no connection between oil weight and feeling.

You'll need about 500ml per leg, be sure to set the air gap on them instead of measuring the oil going in.

Jambo

[wideguy]

I've been using multi-viscosity synthetic motor oil in my forks (and shocks) for 20 years. Very slippery, very durable, resists fade with hard use and cheaper than fork specific oils.

[jpd72]

Thank you all for your Info. The bike was originally setup for track days by previous owner, so I will put it all back to standard, then I can adjust it to suit me.

[aesmith]

I've been using multi-viscosity synthetic motor oil in my forks (and shocks) for 20 years. Very slippery, very durable, resists fade with hard use and cheaper than fork specific oils.
Interesting, that's actual engine oil? Which exact stuff do you use? I have a few litres 5/40 or 5/30 synthetic oil available at the moment.

Tony S

[wideguy]

Interesting, that's actual engine oil? Which exact stuff do you use? I have a few litres 5/40 or 5/30 synthetic oil available at the moment.

Tony S
Yep. Mostly I've used Mobil 1, but they are all good. I currently have Valvoline synthetic in my CB900F forks, because it needs 15w oil with the emulators, and I couldn't find any Mobil 1 in 15w40 (or 15w50) at the time I changed the oil.
There is some viscosity difference between say 10w40 motor oil and what they call 10w fork oil, but, there are also differences between the various manufacturers fork oils- all 10w fork oils aren't the same viscosity either.
I've not found this to be any more of a problem than substituting aftermarket fork oil for OEM fork oil. In other words, no problem at all.
If your specs call for 5w fork oil, sure, use your 5w30 or 5w40 synthetic motor oil.

[yorkie_chris]

5w in stock SV will be squishy as riding a fat bird. See if you can find some cSt@40 degrees numbers for it

[aesmith]

5w in stock SV will be squishy as riding a fat bird. See if you can find some cSt@40 degrees numbers for it
The web site gives Mobil 1 5/30 as ..
Viscosity, cSt (ASTM D445) @ 40ºC 72.8
Viscosity Index 164
What sort of numbers would you be looking for, for a standard SV?

[yorkie_chris]

What springs?

[yorkie_chris]

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.

[aesmith]

What springs?
Everything is standard.

[yorkie_chris]

http://www.opieoils.co.uk/p-827-silkolene-pro-rsf-75-racing-suspension-fluid.aspx

HTH

[aesmith]

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.
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

[yorkie_chris]

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.

[wideguy]

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.

[yorkie_chris]

VI is an indication of how much the viscosity changes with temperature, which means a low viscosity index is better.

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

[yorkie_chris]

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!

[aesmith]

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.

[wideguy]

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

[wideguy]

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.
Hydraulic pumps require lubrication. Hydraulic cylinders aren't any different than forks without the springs and valves, they need lubrication too.

[BanannaMan]

I have stock forks with progressive rate springs and use 20w fork oil with no problems.
Granted I'm no small lad.