[Pwhoever]

I'm a little skeptical of rear shock pressure having any impact on mpg's. But, speed definitely does affect it. The sweet spot is around 60mph but also keeping an eye on your tach and keeping it under 3000rpm. If you do those, your mpg will be the highest. Get up around 70mph and higher and tach over 3000rpm and you will see your mpg suffer...

Oh yeah, welcome to Goldwingfacts. You will find lots of useful info for your GL1500 here.