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Old 11-23-2010, 02:15 PM   #1
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Default FDR change thru clutch bell spur ratio vs differential ratio

I was thinking about this today. What advantage/disadvantage are there for altering the FDR thru changing the spur/clutchbell ratio, vs changing the differential ratio? If there are no inherit disadvantages, I could fine tune the FDR even more by mixing S/CB changes with crown and pinion gear changes. It might even suit a particular engine’s power band better, even though the total load have not changed.

To give an example. I can use 48/14 ratio (S/CB) x 43/13(Pinion/Crown) for a 11.34FDR or alternatively I can use 48/18 (S/CB) x 43/10 (Pinion/Crown) for a 11.46FDR (which is very close)

As far as I can think of, the final output of both front and differential to the wheels are not changed either way. The driveline itself, including the two pinion gears, would turn significantly faster with the lower S/CB ratio. So I might have to compensate with different weight in the center differential. The only possible problems I see are

A) Higher wear on bearings/driveline components when reducing S/CB ratio. Differential mesh are even more critical.
B) Chassis might not physically accommodate certain S/CB combinations.
C) I am not really sure if there will be an significant effect there on the clutch engagement + engine powerband. Even though in theory there is no change on total load, the gear reduction at each connection point have changed.

Any thoughts/experiences with this? Thanks.
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Old 11-23-2010, 02:40 PM   #2
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Well the closer matched you can get two gears, the lesser the wear and the better the efficiency you get. If you remember the Jammin x1 truggy, it had buggy gearing in the diffs and needed a extremely large center spur gear to get the right FDR for truggy tires. Not the best solution since the center diff needs to be very high of the chassis. And as a result racers were putting Kyosho gears(I think) in the diffs to get a lower ratio.
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Old 11-23-2010, 08:50 PM   #3
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A few company's have had different view's on this subject, For Example....The Xray 808 uses the "truggy" gearing's and uses a large clutch bell to make up the final gearing.....Losi on the other hand tested this with their buggy and felt the stock gearing was more then enough and tunable enough to not bother with changing thing's.....Ive personally tried the truggy gearing in my losi buggy and didn't notice a major change in anything really, So As much as the theory makes sense, I dont know how practical it is to put much thought into.
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