[Z]

I run my TB88 Kit with head and carb and 3 speed manual on the street, and I run a 16/35. My speedo only goes 55mph, and I can hit that mark and have a little left. 10 inch motard tires.



Going larger in the rear will hurt top end. If you want more top end, go bigger in the front, and smaller in the back. Keep in mind there is a fine line, as if you gear to high, your motor won't have enough torque to push the gears, and you'll actually lose top end speed.

 

[Z]

I would say to try running a 16/37 and see how you like that. It should give you a pretty good topend. I run 15/37 and mine will run like right at 52mph and my motor is turning all itll turn, which is about 12,000rpm so with a 16/37 gearing you should be able to go alittle faster but not stress the motor with quite as high of rpm's.

I had a 15/37 on, and at top speed, the motor felt as it was going to tear itself apart. Remember peak power isn't always at peak rpms, and while I have my TB head ported and a ton of other funky work done, the powerband does start to drop off around 10K rpms if you have the clutch on the crank. Pushing a motor to 12000 rpms is not as easy as people think, unless you are running a clutch on the primaries and an inner rotor kit.



If you are going to motard the bike, play with gears until you have the setup you feel comfortable with. It's a trial and error process, and depends on the rider.



As Jetster said, purchase a 15T-16T front sprocket to start with, and go from there.

 

[Z]

If you want to hit 55mph run a 16T front. You should have enough slack in the chain to install it without getting a longer chain. If you don't, get a longer chain. They are cheap.



55 isn't all that easy, but you shouldn't have any problem hitting 50mph with the TB setup.