I orderded some tall tires for my merv. They are 4.9 inches tall. On 2.2 proline rims. I'm running Nimh batteries in series and parallel either way depending on what I wanna to do at the time. I have the "high speed" drive gear from traxxas the one they say to use when in series. But I leave it on if I'm in series or parallel. Any possible problems? Or things to beware of?