Fork oil

[RoyC]

With the sidecar and TLS front brake, the front suspension is a bit on the bouncy side.
Will a thicker oil stiffen the fork action up ?

[BSA_54A10]

Yes.
Fork oils are directly blendable so 100ml of 10W + 100ml of of 20W = 200ml of 15W

Corrected for posterity thanks to the sharp eye of the thrasher of tritons

[Triton Thrasher]

25W

That’s not what you meant to say, is it?

[RoyC]

Just had a look and I have Castrol fork oil 15w in there at the moment.
I have got a bottle of Fuchs silcolene SF30 fork oil. I don't know if that means 30w. !!!

[Beeza]

'W' means winter, not weight or such!

[duTch]

 

Fork oils are directly blendable so 100ml of 10W + 100ml of of 20W = 200ml of 25W

 Just at a quick glance I'da thought that'd blend to 15 

[RoyC]

 

Fork oils are directly blendable so 100ml of 10W + 100ml of of 20W = 200ml of 25W

 Just at a quick glance I'da thought that'd blend to 15 

I thought that as well (10 + 20)  ÷ 2 = 15

[BSA_54A10]

25W

That’s not what you meant to say, is it?

Well caught
I will stand in the dunces corner reciting my times tables and perhaps I will learn to add & divide properly

[BSA_54A10]

The point I was trying to get across was to get a bottle of the heaviest fork oil you can find.
Usually that will be 40W from a BMW shop then add a little and a little more till the forks feel comfortable.
Take a note of how much you have added, do the math better than me and that is the oil you should be using.
And a W after a number is the viscosity index.
A single number ie 40W is 40 at Standard temperature & pressure which from memory is 20C and seal level in the Med
A second number  ie 25W 50 is 25 at 20 deg & 50 at 100 deg.

Where it get confusing is the second number is the measured viscosity of that grade of oil at 100 C
SO the oil does not get thicker when it gets hot, it gets thinner, but it thins  to be the same as 50 would be when it is 100 deg.
Because fork oils should never get to be 100 deg C fork oils are generally mono grades

[Black Sheep]

Years ago I settled on 10W-30 tractor universal oil. It's intended for hydraulic systems as well as engines so it's fine for forks. It's also cheap, rather like me.

[hdawson]

Just replaced my fork oil with Belray 30w up from 20.
I had to step into a retailer who specializes in an american v twin motorcycle as it was the only local source.
Got out ASAP but it has improved the front end dive considerably.



 

[RoyC]

Yesterday I put Fuchs Silkolene SF 30 Extra Heavy Motorcycle Fork Oil.
Don't know what SF stands for, but I am hoping this is 30w, I can't find anything heavier.

[bsa-bill]

Don't know what SF stands for,

stiff forks   

[muskrat]

SF would be the grade (composition)  of oil. In the 80's it was SF (higher zinc and others), these days it's up to SM. Trevor will more than likely correct me.
Cheers

[Greybeard]

...these days it's up to SM.

This is the wrong forum for that sort of thing!