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Thread: Gear chart and information

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Old 01-07-2009, 03:17 PM   #1
Join Date: Oct 2008
Posts: 121
Default Gear chart and information

The fixed gear mesh on the HPI system uses a total number of 74 teeth. To change gearing and use the perfect tooth profile, the pinion must be changed with the corresponding spur to total 74 teeth. For example: 17/57, 18/56, 19/55 and so on... For convenience, HPI chose to offer pinions of 16, 17 and 18 while still using the 57 tooth spur gear. The 17 being the proper gear to mate with the 57, meant that they would need to modify or deviate the tooth profile of the 16 and 18 tooth pinion to still create the same diameter and proper mesh. This deviation of 1 tooth either way is still within reasonable tolerances to be functional and convenient. It does however require the tooth profile devaite from the perfect shape and does have some drawbacks.

With the 16 tooth pinions made for the 57 tooth spur gears, the deviation of tooth profile and spacing to compensate for the missing tooth creates more space between the teeth. This spacing creates the situation of only one tooth being engaged at one time. This means all of the force and pressure is being applied to only one tooth. With the 17 tooth and larger pinions, the spacing is such that there are always 2 teeth engaged thereby cutting the forces applied to the teeth in half resulting in a stronger drive connection. This is the preffered set up.

In keeping with perfect tooth profiles for longest wear life, most efficient transfer of power and highest strength, Hostile Racing Products designed thier spur gears to work directly with the perfect matching pinion while still allowing for the use of the deviated HPI 16 and 18 tooth pinion with the 57 tooth spur as well as the Robinson 16 tooth pinion for the 57 tooth spur.

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Old 01-08-2009, 05:56 AM   #2
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Awesome chart!! I was always curious about that!!
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Old 01-08-2009, 06:45 AM   #3
Join Date: Oct 2008
Posts: 121

Originally Posted by sneff View Post
Awesome chart!! I was always curious about that!!
Hi there! Arent you an Upstater like us? I hope to see you at Bajafest this Spring. :) Say hi to Jason.
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Old 01-10-2009, 12:06 AM   #4
Join Date: Nov 2008
Location: New Hampsha
Posts: 216

aw bummer... the new light weight RR Spur only comes in 57 and 55... and the tr clutch system only goes 16-18... i wanted the speed package but looks like im stuck with the stock unless ds has a 56T coming soon, or RR comes out with a 56T...
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