Fork oil weight?

My Seca 750 suggest I use 20 weight oil, however that was oil used 30 years ago. Also I am getting Progressive Springs. Is 20 weight oil still be the optimal weight oil to use?

Thanks!

 

Don't think oil has changed much, but 20W seems kinda high. I tried 20W, and I just about rattled my teeth out. I'd go with 15W, but I have a 650 seca, which came with 10W, originally.

 

EDIT: (removed info about motor oil.

Yamaha did recommend 20 wt oil for the Seca 750, in part due to the relatively soft springs used in conjunction with the anti-dive system.
I use 20 Weight fork oil and find it a bit harsh over closely spaced bumps (a common criticisim in contemporary reviews).
15 wt would be a better choice, and I'm switching to that as soon as I make time to. In fact I may get it done before the weekend and report back.

 

FORK oil. The question was about fork oil.

Yamaha's usually-recommended 10W generally proves to be a tad too light in their forks. I've gotten the best results with 15W, even back in the day with the Yamahas I owned then. You may find 20W provides too stiff a fork.

 

I'm switching to 15 weight Fork oil.
Seems like a good comprise especially with the new Progressive Springs.
I called the dealership and they said they generally use 5-10, so 20 sounded crazy to them. They felt I'd be fine with 10!

I have a 750 Seca with the fork dampening and all that too. That must have something to do with the heavy weight recommendation?!

 

I had enough time after dinner to change mine to 15WT. The equivalent of 15WT anyway. I had a bottle of 10 and a bottle of 20 (both Sikolene). They are pretty consistent with their labeling, so I did half and half. I'll go on my usual fun loop tomorrow and report back.

 

I rode for about 45 minutes after lunch today over varying surfaces. I'm calling 15WT about perfect. The front was much more compliant, while still being firm enough for somewhat spirited riding. I normally have the anti-dive set at 1, but think that bumping it up to 2 will be warranted as there is more front end dive with the lighter fork oil.

I didn't notice any wallowing in the two curves that are avaliable around here (a rising right-hand corkscrew, and a decending left-hand corkscrew), but didn't ride as hard as the bike wanted to because of the cattle trucks that had been spraying effluent through both turns.

The highway bypasses here are primarily concrete, but not made from large continious pours. This means that there are joints every 6 feet, which gives a bumpy ride even in a car. With 20WT fork oil the Seca would give quite the jarring ride. While the ride is still bumpy, the change in fork oil reduces the bounce enough that it's no worse than would be in a small car.

 

Alternately, you can use ATF. Works great for me. YMMV.

 

ATF is roughly equivalent to 9.5WT to 10WT fork oil, but that depends on exactly which ATF you use. There are auto trans fluids on the market with lower viscosity.

 

Perfect! Thanks guys!
Get my 15W fork oil tomorrow! (Well I hope at least)

 

k-moe, I can't remember which one I used the last time I changed oil in the forks, but I'm fairly certain is was Dexron-III rated, which is supposed to be a higher viscosity. I'll take your word for the equivalent viscosity. The biggest reason I like it is it's very good at preventing foaming, has excellent compatibility with seals, and it's relatively inexpensive.

myasylum, I'm sure you'll be happy with the 15W. I think you'll find the Progressive springs and fresh oil (of any weight) makes the most difference. The important thing is getting miles anyway!

 

Dextron III is typically equivalent to 10 WT fork oil. Dextron IV is somewhat less vicious. Using ATF is fine, particularly when you don't need the sort of tuneability and repeatability that fork oil (usually) offers. If I hadn't had the 10WT fork oil on hand already, I would have used ATF to blend my 15WT mix.