[jhautz]

Get your new batteries first. You will be tons faster with the lipos vs those nicd batteries. get some radar of your speed with the lipos and then go to brians speed calaulator on this site and enter your gear ratios, motor info, battery info and such and see if its pretty accurate. If it is, then just pick the speed you want to go and adjust the pinion size untill you get that speed on the calulator and thats the pinion you order.

If you are going for an insane speed run you will be way overgeared but you will just have to make a run or 2 and then stop and let everything cool down. Then try it again. You cant run consistantly that way, but you can put up some insane numbers that way.