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Gear pitch for drag racing - 64 or 48 - and why?


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#1 Bud Man

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Posted 04 January 2024 - 01:49 PM

Will a 48 pitch be smoother than a 64 pitch gearing? Which is better?

 


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#2 Bill Seitz

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Posted 04 January 2024 - 02:35 PM

Typically the larger the pitch number (number of teeth) , the smoother the gears will be. The larger pitch will also permit finer (smaller increment) gear ratio adjustments. I build some inline cars, and for those I mostly use 48P because the available 64P poly crowns aren't very robust. It's possible to get smooth gears with good quality 48P components, and the lower pitch provides thicker, beefier teeth that could be a benefit, though 64P has handled every kind of motor currently available.



#3 Dave Crevie

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Posted 04 January 2024 - 05:17 PM

Bill explains it pretty simply. I know we discussed this before, but perhaps some visuals will help.

 

Notice how the teeth of the pinion intersect with the teeth of the spur gear in these 48 pitch gears;

geargen.JPG

 

Now notice how the teeth intersect between these 64 pitch gears. Both gear sets are 3 to 1 ratio. ;

geargen1.JPG

 

You can see that there is more contact area between the 64 pitch gears, spreading the load over a larger area. All other things being equal, it will be the difference in gear materials that will effect how well the teeth last. And most often, from what I have seen, it is poorly aligned gears and/or improperly set backlash that causes premature gear failure.

 

 

Here we see the geometry the teeth on a crown gear need to have to fully engage the teeth on the pinion. The orange lines show the angle the teeth need for them to mesh with the bevel of the pinion. The yellow lines show the taper the teeth need to fully engage with the tapered teeth of the pinion. ( the red line is the axis of the rear axle )

crowngeargen1.JPG

 

So for a crown and bevel gear to mesh properly, you need to know all the parameters of the spur and straight pinion, but also those other angles shown in the bottom drawing. 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 


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