how much longer?

Well, on cars, dino oil lasts 3k miles.  With synthetic, you can stretch out intervals to 5-7.5k miles.  So, I'd say on a motorcycle, you could try to get 50-100% more mileage out of an oil change, as long as you check your oil often and change when it gets grubby.

I was scratching my head when I changed my oil, wondering how Mobil 1 got so grubby in about 1500 miles.  The previous owner changed the oil at the beginning of last riding season, so I figured I should be good.  But... he forgot to check the air filter, and it looked like a mouse was living in there!   The air filter was all decomposed and not filtering.  So hopefully I'll get better results this oil change.  I put in Mobil 1 15W-50 and things are working pretty good

And what I learned during the oil change and other wrenching that day.  If you need to strip paint from metal and don't have any paint stripper, gasket cleaner works in a pinch      I intended to replace my LHS engine cover, and now I have to repaint the replacement cover  :x  Gasket cleaner is nasty!

I have used two different synthetics in my bikes.  I prefer Motul and have used it in almost all of my bikes.  The only time that I didn't were two bikes that had previously only had Mobil 1.  I figured I would just keep using Mobil one since it worked so far.

The Sport Rider article showed improved horsepower on the dyno when using synthetic oils. The oils that show the most improvements are not for street use.  I change the oil after every race weekend but the 0-5wt oils have usable times in minutes.  They are intended for drag racers making quick runs and who change their oil after each run.

Quote from: gsJack

Quote from: Frosthttp://www.yft.org/tex_vfr/tech/oil.htm

That's my favorite write up on motorcycle oils.  I used the 15W-50 Mobil 1 in my 97 for about 70k miles and then switched to 15W-40 Delvac 1300 after reading this article and others like it.  My 97 GS runs cooler on the Delvac than it did on the Mobil 1 and will run on a lower grade of gasoline w/o pinging under load in hot weather.  Using the Delvac in both bikes now.  About $6-7 a GALLON at any Walmart.

Digging up this old thread.  Got one of those "too tight" fitting filters in the GS right now so it's gonna get an early change and I'm deciding what oil to use (have generic Exxon 10W-40 currently).  

Jack, in that writeup the guy favorably mentions Mobil Delvac 1, which is a "heavy duty" gas & diesel rated synthetic.  He says it's typically only available at truck stops or in commercial quantities.

Not sure when that was written, but Mobil has just recently re-labelled Delvac 1 as Mobil 1 "Truck and SUV" 5W-40, which you can get at any old Walmart.  Sounds like that would be a good choice for the GS?  I ask because I'm using this stuff in my Saab, the fewer different oils I have to keep in stock the better!

jeff