probably been asked...

[dadsafrantic]

if you rejet and add some after market exhaust how bad does you mpg get??  i need to keep this thing for another year or two and would maybe like some more zip in my commute.  i don't want the mpg to suffer too much though.

[ben2go]

Depends on you.You may see a slight drop in mpg.If you ride it like you stole it,it may get a little more dramatic.

[cd]

i had a gs i put through the ringer. pretty much redline everywhere, im not nice to bikes, and it was my commuter in place of sportbikes. even when i flogged it as hard as possible it would give me 40s and 50s mpg

worst you would get would be somewhere in the 40s i would estimate, but i dont know urvrythang

[yamahonkawazuki]

i think my worst ever, like he said, mine was around 35-40 ish

[Y2K6GS500F]

My bike is jetted with an aftermarket exhaust and I consistently get around 60mpg on the highway, and about 45-50mpg in stop and go traffic.

[dadsafrantic]

My bike is jetted with an aftermarket exhaust and I consistently get around 60mpg on the highway, and about 45-50mpg in stop and go traffic.

that is very cool to hear.  what jets and what exhaust?

[Y2K6GS500F]

[

that is very cool to hear.  what jets and what exhaust?

The work was done by the previous owner, so I can't tell you what jets he used. But, It has a K&N Drop-In air filter, and a Full Jardine exhaust. If I had to guess, Id say it was a fairly conservative rejet. Maybe somewhere around 20/62.5/142.5. 

My most recent mileage check was on my trip back from Daytona for Bike Week -about 200 miles @ ~75mph.  I'm also pretty good about keeping my Chain Lubed, Tires at F34/R37 psi, and I use a full synthetic oil. While I doubt they make a huge difference with mileage,  every little bit helps.