Does the actual diameter of the rotor make the unit run better? What is better a small rotor, or a larger one. Does one have more torque, one more RPM. Bought a 17.5 and the guy sent me extra rotors, all different in size. Found original size for motor just wondering why this is done.

What brand motor? (I Know ORION has a ROTOR Kit they sell for theirs)

I believe the theory is

SMALL ROTOR = More RPM/Less TORQUE
LARGER ROTOR = More TORQUE/Less RPM

So in a HIGH RPM motor (Low turn) a LARGER ROTOR may cut the RPM a little, but provide more TORQUE...

The STOCK ROTOR in a NOVAK is the smaller rotor (12.3mm) I believe, where their tuning rotor is the larger (14.0mm)

If this is incorrect....someone will correct me I'm sure!~

Thanks for the info. It is a Novak 17.5, Just started this brushless thing this year, have lots to learn.

You may want to check your tracks rule on rotor size , many tracks don't allow the "tuning" rotors during racing.

Butters is correct, many places that only allow the NOVAK MOTORS don't allow the "Tuning" or 14mm rotors, just the STOCK rotor. With that being said, the 17.5 is a very low rpm motor with massive torque from the factory...I'd be hard pressed that the larger rotor would give ANY benefit... (These are mentioned would be better suited for the lower wind motors to help tame the RPM a bit)

The Novak "tuning rotor" is 13MM. At least that's what they call it.

Thanks guys for the info. I do not know the rules at our track but do not plan on bending them anyways, just wondering and trying to learn. I appreciate all the help I can get.

Keep things going in the same line of questioning. Years ago with brushed motors we used to play with what we called air gap, the gap between the armature and the magnets to change performance. With more gap, we got a few(very few) more rpm's. Does this hold true with the brushless motors?

Just a thought from someone new to the brushless thing.

Yes, like the above stated. The bigger rotor will provide more torque. just like tightening the air gap in brushed type motors. In there BRL races you are to use the 12 mm rotor in all classes, but mod classes are allowed to use ether one. + I don't think a 13mm rotor would be the way to go in the 17.5 4 cell class. since you are try to get more RPM's in that class of racing.

It makes a difference on 13.5 with more torque and lower heat. We run them in our 2cell lipo sprinters with 10.5 and it makes a HUGE difference on pull off of the corner and much lower heat. I think too many tracks blow this totor diameter out of the water when they regulate this but yet run open speedos with timing boost.