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Old 03-31-2017, 01:45 PM   #1
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Default I pulling my hair out with gearing

I have a HB TCXX with a 2.0 ratio diff. I am using a Hobbywing 21.5 motor for 1/10 on road. I just want to know what is a good gear set for this car on a medium size track and have close to a 4.00 final drive ratio.Dont need any sarcasm just want a hood starting point or one that is proven to work with low motor temps. 48 pitch prefered. I have no timing in the motor.
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Old 03-31-2017, 01:52 PM   #2
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Have you actually raced it yet? You won't be able to figure out a good gear ratio until you see how your car performs against actual competitors.
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Old 03-31-2017, 02:08 PM   #3
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I have a HB TCXX with a 2.0 ratio diff. I am using a Hobbywing 21.5 motor for 1/10 on road. I just want to know what is a good gear set for this car on a medium size track and have close to a 4.00 final drive ratio.Dont need any sarcasm just want a hood starting point or one that is proven to work with low motor temps. 48 pitch prefered. I have no timing in the motor.
4.0fdr with no timing will be quite slow for 21.5, try around 3.4 to start with and the factory timing on the endbell. Also is this indoor or outdoor?
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Old 03-31-2017, 03:14 PM   #4
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Pulling your hair out? Just make sure you don't get any hair into the gear mesh. Sorry, you said no sarcasm!

I run a medium size track with 21.5 and 48 pitch gears. 69t spur and 36t pinion for a 3.833 FDR with 48 degrees of timing on a D4 motor. Works great.
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Old 03-31-2017, 03:25 PM   #5
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Switch to 64p to really hone it in.

I run 82 / 54 for 3.7 fdr on 40 deg timing.

Not sure you are ready for a "hood" starting point though. Got to be a real OG first.
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Old 03-31-2017, 03:54 PM   #6
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I take it that your motor have a fixed timing since you said that you have no timing. If so put the motor on a motorlyser to find out what the timing is and people will be able to point you in the right direction.
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Old 03-31-2017, 03:56 PM   #7
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Pulling your hair out? Just make sure you don't get any hair into the gear mesh. Sorry, you said no sarcasm!

I run a medium size track with 21.5 and 48 pitch gears. 69t spur and 36t pinion for a 3.833 FDR with 48 degrees of timing on a D4 motor. Works great.
Yes but your f/r toe settings might also affect top speed, acceleration, etc...
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Old 03-31-2017, 03:59 PM   #8
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Switch to 64p to really hone it in.

I run 82 / 54 for 3.7 fdr on 40 deg timing.

Not sure you are ready for a "hood" starting point though. Got to be a real OG first.
I like 48 pitch gears, much more forgiving. I've tried 69/37 and that gives me 3.73, but I've found that is a little too tall for my track.
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Old 03-31-2017, 04:14 PM   #9
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I like 48 pitch gears, much more forgiving. I've tried 69/37 and that gives me 3.73, but I've found that is a little too tall for my track.
They are. 70/36 puts you at a nice 3.8

70/35 puts you at a perfect 4.
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Old 03-31-2017, 05:01 PM   #10
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They are. 70/36 puts you at a nice 3.8
It's closer to 3.9 than it is to 3.8
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Old 03-31-2017, 05:05 PM   #11
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Thanks guys for the info that really helps me out a lot. The track is a outdoor track. Ya sorry about the hood starting point I meant good starting point but I figured most of you figured that out lol. Yes the motor does have a fixed endbell so no timing can be added.
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Old 03-31-2017, 05:37 PM   #12
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It's closer to 3.9 than it is to 3.8
True but with 70 spur gives him two gearing options with one spur.


Plus my math skills are only so so in my head.
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Old 03-31-2017, 07:29 PM   #13
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Thanks guys for the info that really helps me out a lot. The track is a outdoor track. Ya sorry about the hood starting point I meant good starting point but I figured most of you figured that out lol. Yes the motor does have a fixed endbell so no timing can be added.

64 tooth 48 pitch spur gear with a 32 tooth 48 pitch pinion gear will yield a 4.0 FDR with room in both direction to explore.
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Old 03-31-2017, 07:43 PM   #14
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64t 48p might be hard to get.... 66t 48p from robinson is available everywhere, and will yield the same 4.0fdr with a 33t pinion....
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Old 03-31-2017, 11:49 PM   #15
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64 tooth 48 pitch spur gear with a 32 tooth 48 pitch pinion gear will yield a 4.0 FDR with room in both direction to explore.
I agree, & with those particular motors(assuming it's the 3650 G2 series, since you said it has no timing advance), you will need to gear it taller than most of us would motors that do have timing advance to get similar speeds, so an FDR of 3.4 might actually be appropriate, considering that many of us go closer to a 3.7-3.8 using motors with timing advance. Additionally, you may need to mount a fan near the motor to keep it from overheating(like this one from Yeah Racing, you can just shoe-goo it down next to the motor to blow air on it, here's a link to it: https://www.tqrcracing.com/shop/prod....asp?p_id=2334 ), even mounted behind the motor they do a GREAT job of keep temps under control(I've noticed a 20-30 degree F difference in my motors temps using them, on both my 2WD buggies & on my 21.5-powered touring car)....
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