IF I put smaller wheels on my Genesis, do I have to do anything with the gearing on there? If so, how?

You will want to gear the truck up with the 25 tooth pinion gear. It will be out soon.

Does this mean that I can't run it now? I have the wheel hubs from neweramodels that allow me to use the 40 series tires, don't say I can't use them now.

you can use them now. your truck just won't go as fast.

jigga,

Those wheels are dialed and make the truck more agile. They do bring the top speed down a bit but in the dirt, tearing up hills and over jumps it should be a lot better. The truck will now have more torque (due to the changed rollout ratio and the incredible loss of 4 pounds). Once that 25 tooth pinion comes out you'll have most of your top speed back. Have fun with those new tires. You should have a nimble Genesis on your hands now.

Jeremy
CEN Customer Service

Sounds good. Once I get the parts I need to finish the forward only conversion, I'll take some pics of the new slightly monster truck.