Polaris states that their Timbersled 0w-40 is formulated for snowbike use. It is JASO MA/MA2 certified and has a nice additives package. Agreed that they don't make motorcycles (anymore) but it's not hard to have a dirtbike oil formulated and branded. None of the aftermarket oil companies (klotz, mobil 1, royal purple, amsoil) manfacture cars, motorcycles, or motors in general and make good oils. It is up to the user to ensure an adequate weight oil is run. In the case of dirtbikes, that is typically 40 and 50 weights.
Don't know that it is worth the price for the timbersled oil, particularly for those changing oil every or every other ride, when there are many 0w-40 annd 5w-40 oils that perform well. Not that I'm cheap. I will pay for better performance, but failures are few and far enough between that I don't think we have an "inadequate oil epidemic" on our hands. Ha. For example, bearing/crank failures don't seem any more frequent than for summer/wheels-on use and seem more related to performance builds or hours, but maybe snowbike engine failures are simply under reported.
Byeatts,
To answer your Yamaha question, in the owner's manual for a 2020 YZ450F, the recommended viscosity grades are:
10w-40
10w-50
15w-50
20w-40
20w-50
In my opinion, any good quality 0w-40, 5w-40, 10w-40 weight oil, that performs well in load tests, will do the job for snowbiking my bike.
...though that oil temp and temp-reactive polymer discussion is creeping around my brain. But again, doesn't seem like oil-related failures are happening left and right so no evidence that concerns me at this time.