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BrianG · 12.04.2006, 11:24 PM

I guess I'll start with your first unanswered question:

There is no set max pinion size for any motor. The spur/pinion is just part of the gear ratio. If you ONLY had the spur/pinion as the means to reduce the motor speed, you'd need a really small pinion to gear it down enough. To get the total reduction, you simply multiply the diff ratio by the tranny (or slipperential in this case) ratio by the spur/pinion ratio. So, if the reduction ratio is high enough, you can use a large pinion.

Yes, ballooning will make a large difference in speed! And no, you really don't want ballooning because it's hard on the tires and traction suffers. Sure, it's cool to watch, but not healthy. :dft012:

The highest pinion will be whatever you can find that's a 5mm bore Mod1 pitch. The highest Mike has listed in his store is 20T. The problem is if the pinion is too big, the motor physically won't be able to be bolted to the mount because of the diameters of the spur and pinion together.

If you use a standard maxx diff ratio of 2.84:1, the slipperential, 36T spur, 4s lipo, and 7XL, you'll be right at 47mph with a 20T pinion.

Personally, I still think a direct pinion to differential drive would be easier, especially since you're looking for a speedy truck. I know there's no slipper, so that's a downside. However, you'd have lots more gearing options without having to use such a large pinion. And it would allow you to use a slower motor, which will have more torque resulting in more gearing options. For instance, an 8XL, HB Pro diff (3.31:1 version), 4s lipo, and 46T spur on the center diff would give you right around 49mph using a much more manageable 16T pinion. And it would still leave a little room to go up/down a tooth or two on the pinion for fine-tuning.

I don't know, maybe someone else will chime in with another suggestion. I know a slipper would be ideal, and the slipperential is a very nice product, but it may not be the ideal part for this application.

	(#24)
BrianG RC-Monster Admin Offline Posts: 14,609 Join Date: Nov 2005 Location: Des Moines, IA	12.04.2006, 11:24 PM I guess I'll start with your first unanswered question: There is no set max pinion size for any motor. The spur/pinion is just part of the gear ratio. If you ONLY had the spur/pinion as the means to reduce the motor speed, you'd need a really small pinion to gear it down enough. To get the total reduction, you simply multiply the diff ratio by the tranny (or slipperential in this case) ratio by the spur/pinion ratio. So, if the reduction ratio is high enough, you can use a large pinion. Yes, ballooning will make a large difference in speed! And no, you really don't want ballooning because it's hard on the tires and traction suffers. Sure, it's cool to watch, but not healthy. :dft012: The highest pinion will be whatever you can find that's a 5mm bore Mod1 pitch. The highest Mike has listed in his store is 20T. The problem is if the pinion is too big, the motor physically won't be able to be bolted to the mount because of the diameters of the spur and pinion together. If you use a standard maxx diff ratio of 2.84:1, the slipperential, 36T spur, 4s lipo, and 7XL, you'll be right at 47mph with a 20T pinion. Personally, I still think a direct pinion to differential drive would be easier, especially since you're looking for a speedy truck. I know there's no slipper, so that's a downside. However, you'd have lots more gearing options without having to use such a large pinion. And it would allow you to use a slower motor, which will have more torque resulting in more gearing options. For instance, an 8XL, HB Pro diff (3.31:1 version), 4s lipo, and 46T spur on the center diff would give you right around 49mph using a much more manageable 16T pinion. And it would still leave a little room to go up/down a tooth or two on the pinion for fine-tuning. I don't know, maybe someone else will chime in with another suggestion. I know a slipper would be ideal, and the slipperential is a very nice product, but it may not be the ideal part for this application.