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05-23-2019, 12:18 PM | #1 |
Rock Stacker Join Date: Apr 2019 Location: Reno, NV
Posts: 86
| TRX4 Overdrive vs Underdrive Gearing Options
After having installed both the overdrive (12/33) and underdrive (10/35) gearing in the axles of my TRX4 Sport, I decided that both provided too much difference in the front to rear rotations of the wheels...especially when sidehilling. So...which end should be replaced with the stock gearing (11/34)? Initially thought that it shouldn't make any difference...But, I was wrong as follows: - Underdrive with a 10T pinion and 35T spur has a ratio of 3.50. - Standard with an 11T pinion and 34T spur has a ratio of 3.09. - Overdrive with a 12T pinion and 33T spur has a ratio of 2.75. So, the difference between Underdrive and Standard is 0.41 compared to Overdrive and Standard being 0.34. So, some minor tuning is possible when picking between these two options because Underdrive gearing is a 20% greater gearing increase than Overdrive. Thinking I will be keeping the Underdrive at this point. Comments? Last edited by Still Bill; 05-23-2019 at 12:21 PM. |
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05-23-2019, 12:25 PM | #2 |
Gold Star Baby! Join Date: Dec 2017 Location: Las Vegas
Posts: 2,554
| Re: TRX4 Overdrive vs Underdrive Gearing Options
You’ll want the front spinning faster than the rear, so put the stock up front and under in the rear.
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05-23-2019, 12:30 PM | #3 |
Go Buckeyes! Join Date: Jun 2017 Location: Mid-Ohio
Posts: 4,134
| Re: TRX4 Overdrive vs Underdrive Gearing Options |
05-23-2019, 05:06 PM | #4 |
Quarry Creeper Join Date: Mar 2019 Location: Low CG
Posts: 266
| Re: TRX4 Overdrive vs Underdrive Gearing Options
I went from overdriving the front to underdriving the rear. I like it much better.
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05-23-2019, 07:01 PM | #5 |
Rock Crawler Join Date: Jun 2015 Location: In the Sticks in the Ozarks
Posts: 940
| Re: TRX4 Overdrive vs Underdrive Gearing Options
The other advantage to UD's is lower overall gear ratio. I ran with UD and stock for a while and liked it. I just recently put in the OD's too and I like it even better, but i guess it all depends where and how you drive. jim |
05-24-2019, 11:32 AM | #6 |
I wanna be Dave Join Date: May 2007 Location: Taylors Falls just hanging with the MNRCRC crew.
Posts: 7,843
| Re: TRX4 Overdrive vs Underdrive Gearing Options
I like it with both over and under for the tighter steering radius. I've seen no adverse effects on performance.
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05-24-2019, 03:28 PM | #7 |
Gold Star Baby! Join Date: Dec 2017 Location: Las Vegas
Posts: 2,554
| Re: TRX4 Overdrive vs Underdrive Gearing Options Same, I have both in one trx4 and just the OD in another (UD was sold out) and they drive similar enough. I’m never really going fast enough for the gearing distance to matter.
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08-23-2019, 02:10 PM | #8 | |
RCC Addict Join Date: Sep 2014 Location: Ft. Lauderdale, Florida
Posts: 1,229
| Re: TRX4 Overdrive vs Underdrive Gearing Options Quote:
So it's better to go with the former set up with the 20%? Sent from my LM-G710VM using Tapatalk | |
08-23-2019, 02:35 PM | #9 | |
Quarry Creeper Join Date: Nov 2018 Location: Oakley
Posts: 479
| Re: TRX4 Overdrive vs Underdrive Gearing Options Quote:
But really you should be trying to understand the change vs the slower axle. So you underdrive the rear and leave the front stock and you end up with (3.50/3.09)-1 = 13.2% wheel speed difference. If you overdrive the front and leave the rear stock you end up with (3.09/2.75)-1 = 12.4% wheel speed difference, so basically the same. Its not 20% different. Over/under driving results in (3.50/2.75)-1= 27.2% difference in wheel speed. I would imagine the advantage to underdriving the rear only would be that your overall gear ratios are lower than overdriving the front. Last edited by mass-hole; 08-23-2019 at 02:45 PM. | |
08-23-2019, 02:54 PM | #10 | |
RCC Addict Join Date: Sep 2014 Location: Ft. Lauderdale, Florida
Posts: 1,229
| Re: TRX4 Overdrive vs Underdrive Gearing Options Quote:
Sent from my LM-G710VM using Tapatalk | |
09-15-2019, 12:47 PM | #11 |
I wanna be Dave Join Date: Oct 2012 Location: Medina
Posts: 2,263
| Re: TRX4 Overdrive vs Underdrive Gearing Options
If you’re only going to do one, under-drive the rear. I typically don’t do both OD and UD on any of my rigs. I’ve tried it on my Wraith, and if I was just straight rock crawling, I could see sticking with it. But, most of my rigs get trailed and crawled, so UD rear seems to be the sweet spot for me. A bigger % difference in ratio from front to rear can make the rig fickle when side hilling.
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09-15-2019, 10:05 PM | #12 |
Quarry Creeper Join Date: May 2019 Location: North Highlands
Posts: 483
| Re: TRX4 Overdrive vs Underdrive Gearing Options
I use both. Love it. |
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