I have an 01 R6 and I want to start doing all my wheelies in third gear. What size gearing do I need to balance out the wheelies around 50mph in third?

 

You can do it on stock gearing
Just make sure you know how to use the brake b/c if you rock third back to far there's no engine braking like second has. Friend just looped not to long ago on his r6. Plus in using second you can slow it down a lot more before the engine gets out of its powerband. Third may be less stress on the motor but 2nd is better for wheelies IMO.