Hmmm. I just checked my w/s manual and it says 650ml, or 145 mm from the top of the tube with the fork fully compressed, spring out.

Are you saying that the heavier springs negate the need for oil to create such an effective air spring, so the lower level is okay?

The Hyperpro springs are made from considerably thicker material, so therefore displace more oil. In order to maintain the correct air gap, the oil volume used should be reduced from 650 to 500ml.

Ok cool, thanks mate.

All this talk about fork performance forced me to do something about the nasty fork action happening with my bike. I found some Ohlins springs, but thought I'd try changing the fork oil first.

Well, the goop that drooled out of those forks was grey and looked like metallic paint. My bike was suffering from lack of both compression and (especially) rebound damping - no surprise there.

I bought some BelRay 15wt oil (equivalent to 10W oil as recommended, ie around 50Cst at 40degC), and set the level 5mm higher than stock.

Bike is duly transformed, and a couple of hundred bucks was saved. Nice.

So what you are saying is that the stock springs work well with heavier oil

No, the stock springs work well enough for me with new oil of the correct weight. 15wt on the bottle doesn't necessarily equate to SAE15W (there's heaps of info on this subject).

In the case of the oil I used, it is equivalent to SAE 10W if you look at its actual viscosity. Fork oil makers can put whatever they like on the bottle apparently; there doesn't appear to be a standard. One manufacturer's 15wt might be another's 10wt, and neither are necessarily one or the other in terms of measured viscosity. It seems they label the bottles to simply differentiate their own products. Who knows?

Of course, there are opinions on the matter that say the SAE method is wrong, too. But as Yamaha say to use 10W (as distinct from a random 10wt) oil, I did that and it works for me, really works. The forks are now pretty fair, which I think is as good as they need to be for my bike, considering their internals.

At least they aren't the trendy but hugely overrated upside down forks, and that alone is a big big bonus for me. I'm not saying usd forks don't work. They do. But they're prone to damage and seal leakage. I have receipts to prove it! Oh wait, I think i binned them in disgust!

Did you consider the Ohlins springs Phil? Why did you go with the Hyperpro in the end?
Is the improvement across the board i.e on and off road as well. Really fancy doing this but nor sure which to go with..

May come down to getting an Ohlins sticker on the forks being the decider :)