What weight fork oil for '09 yz450?

Time for new fork seals and the Yamaha manual calls for S1 oil. Is this available on motosport or can I use say Motorex? If so, what weight?


S1 is one of those weird KYB suspension oils that no one really knows the actual weight of. It's really good stuff while it lasts, but it's too expensive for the short usable life it has. Most people use a high quality fork oil from 2.5-5 wt in the inner chamber, and will either use the same oil in the outers, or bump up to the 5-7wt range for that.

I'll go with 5 since it seems like an overlapping weight. Thanks Gray

Bad advice. That's "01", not "S1", in the first place, and it doesn't hold up particularly well, either. 01 is listed in Yamaha owner manuals as the recommended oil for open bath forks, not twin chamber.

motorex racing fork oil is pretty close to s1 yamaha suspension fluid

http://www.peterverd...uspension_Fluid read the viscosity sheet i think Kyb 01m IS yamaha S1 when compared side to side

motorex racing fork oil is pretty close to s1 yamaha suspension fluid

It's not the same stuff.

And there's a good deal more to the picture with suspension fluid than listed or tested viscosity. Since you've stuck your nose into that rather old Peter Verdon post, take a look at the variation between almost any of the listed oils at 40 ℃ and 100 ℃. You'll find the variance is much greater than the difference between a 2.5wt and a 5wt in virtually every case. Now, take a look at all of the oils that have a 40 ℃ viscosity of 15 cSt. You'll see oils listed from 2.5 to 5 wt in that list. Then if you look at the 100 ℃ measured viscosities and start comparing them, you'll see that, for example, Maxima Racing 5wt is lighter than Silkolene Pro 2.5wt. Overall, the numbers on a label don't mean that much.

But going back to the comparison of the high and low temperature viscosities, ask yourself why, if viscosity matters so much, your suspension doesn't act profoundly different in the first minutes of your ride than it does later in the day. The answer is that modern suspension systems are designed specifically to be tolerant of fluid viscosity across a fairly wide range without it affecting their operation.

Viscosity will only have an immediate uncompensated effect on places where oil flows through a fixed orifice, such as the bleed needles you move with the click adjusters. The valves themselves are pressure regulators, and to a large degree, they will respond to the increased pressure of a thicker oil simply by opening farther. If you put 30 weight oil in your forks, you'll feel that, but for the most part, you would notice very little in going from a 3 to a 5 wt under any circumstance.

Far more important is the oil's stability under extreme shear force, it's durability, resistance to cavitation, and other attributes. Two 5wt fork oils are no more necessarily alike than two 10w-40 engine oils are. Viscosity is on the list of things you should consider when choosing one, but it's a long way from being the only consideration.

http://www.thumperta...-yamaha-s1-oil/ grayracer kyb 01 fork oil is s1 yamaha fork oil i use it

I've seen that thread. There's nothing conclusive in it. Use it if you want to, I don't care. Whether it is or is not the same oil makes no difference, anyway, because it's still way too expensive for no better than it works, and especially for no better than it holds up, IMO.

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