OK, Dell - I'll try to keep cool and give you my $.02 on what I use and why - which may be perfectly OK for me and no one else on the planet. Everyone's got to follow their own philosophy with whatever info they've got. Given my latitude/climate, I run 10w40 in all my bikes. It very rarely gets over 100F here, and there are usually a couple months at the start and end of the riding season where the temperatures will be at or around 32F. The 10W40 viscosity works for me and is easier for the starter to turn the engine on those cooler days when I still want to ride.
I use regular dino-juice in all my bikes, partly because some of them had dino juice in them for years ahead of my acquiring them, and SOMETIMES it has been observed that engines may experience leaks when switching to synthetic if the seals haven't been changed. (Similar happenings seemed to occur back in the 70s when folks switched from nondetergent oils to high detergent oils like Quaker State, but let's not fan the flames any more than necessary).. The other reason I stick with dino juice is because I change the oil every 3000 miles or at least once per year, depending on the bike/usage. The major advantage of the synthetic oils is extended mileage/change intervals, and if one isn't taking advantage of that aspect, then one isn't getting one's $$$ value out of the more expensive synth oils, IMHO. I'd rather stick with my more frequent oil changes and use the opportunity to survey the state of the bike/filters, etc. at those times, too.
Lastly, much has been said about ZDDP (Zinc Dialkyl-DithioPhosphate) in motor oils. The US EPA, the same folks who brought us MTBE which polluted our groundwater and now mandate 15% ethanol additive content to our fuel to keep their farm subsidy friends happy are also responsible for requiring the stepped removal of ALL phosphates from motor oil and motor fuels sold in the US. The issue with the phosphate situation is that more modern auto/truck engines, say, since 1990 or so don't use flat lifters/tappets and use rollers, or shim u/bucket designs running off overhead cams. These engines don't require these phosphates to operate well and they don't need the phosphates to guard against wear. The old fashioned, flat lifter engines like our airheads or the old flathead Ford cars NEED the phospohates to help lubricate and protect these flat, solid, high pressure interfaces on the lifters/pushrods. Years ago, before the major reductions in phosphates were enacted on motor oils, the automotive motor oil industry specification was "SG", and it specified a limit of something like 1500 ppm or 1800 ppm of this chemical phosphate content. This seemed to work OK and was adequate to protect our old engine parts. Over the years, regulations have forced motor oil manufacturers to reduce this level, and the latest motor oil industry specification is at revision "SM", I think. This specifies a limit of only a couple hundred ppm of phosphates content, which is too low to be of any good for our engines, in the opinion of many.
Some manufacturers still offer some product lines with higher ZDDP content for the smaller 'niche' market. Some do not. It is becoming harder and harder to find motor oils which still have the "SG" rating or phosophate content commensurate with that revision of the standard. However, there are a number of motor oil ZDDP additives which are being sold which can simply be added to your motor oil of choice which will give you an adequate level of protection, even if you are using modern level oils with virtually no ZDDP left in them from the factory.
I've gotta put my Nomex suit on now - hope that this helped you in some way!
Flame on!
