Well, it sounds like you just answered your own question. Change the gearing. Of course the tires have something to do with gearing as well. If you change one of your sprockets and soon change your rear tires, then it may very well mean you will have to change your gearing again.
Nicholson 500x (Project)
Nicholson 185s
Nicholson 110 (That takes an atc70 tank)
Ascott 500 head/350x (Project)
Homebuilt Racer Chromoly Suspension 110 (Ragin Runt)
PK Racing Suspension 70
A+ Inc Suspension 70
AWS Aluminum 90 frame
Hi Performance ATC Suspension frame rd350
Hi Performance ATC Suspension frame 90