Without knowing more it is hard to answer.
- What is your total ratio from the motor to the wheels?
- How big are the wheels? What type of wheels are they (kit, grippy, smooth, plaction, etc.)?
- What motors are you using to drive?
- What is the width and centerline distance between the wheels?
- and so on.
Changing ratio is a big decision. I would generally find another area to save weight than have my drive system compromised.
When I need to save weight (basically every time I build a robot), I look for big things I can live with out. Toss something overboard so you have the weight to bring something else you like more onboard.
By the way, you have to check your ego at the door. The last thing you want is to have a system on board eating up your weight budget just because you were too proud of it to allow a more important system get ahead of it in line.
Think about priorities and start cleaning house.
Joe J.
P.S. Did I use enough mixed metaphors for you? Because I can use more... ...no really, I can... JJ