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Old 03-25-2018, 08:54 PM   #1
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Default TRX4 final axle gear ratio?

I get confused due to the portal gears when trying to figure out the axle gear ratio. I am thinking of putting the Traxxas front Portal axle on the rear of a Axial Yeti so I can have 4WS, Portal axle, 2 speed, and diff lock. Can anyone help me out when it comes to figuring out the final gear ratio to see if is compatible with any of the Axial diff ratios? Axial diff gear ratio's are 38/13 (2.9), 36/14 (2.5), and 43/13 (3.3). Thanks a bunch!
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Old 03-25-2018, 09:06 PM   #2
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Default Re: TRX4 final axle gear ratio?

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Originally Posted by Stan3535 View Post
I get confused due to the portal gears when trying to figure out the axle gear ratio. I am thinking of putting the Traxxas front Portal axle on the rear of a Axial Yeti so I can have 4WS, Portal axle, 2 speed, and diff lock. Can anyone help me out when it comes to figuring out the final gear ratio to see if is compatible with any of the Axial diff ratios? Axial diff gear ratio's are 38/13 (2.9), 36/14 (2.5), and 43/13 (3.3). Thanks a bunch!
Just a little info for you. The portal gear ratio is 2.3:1 so that would reduce the stock ratio by more than 1/2. So your front axle would be dragging the rear portal all over. About the only way you could make it work would be to use a transfer case with gearing that add that 2.3:1 back to the rear drive ratio. I don't think what you want to do would work very well. JMO
Ernie

Here is a chart of numbers I crunched when building my ascender portal axles. The final numbers may not work for you but the formula would.


Last edited by CODYBOY; 03-26-2018 at 10:24 AM.
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Old 03-26-2018, 09:56 AM   #3
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Default Re: TRX4 final axle gear ratio?

Thanks Ernie. I saved that chart
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Old 03-28-2018, 09:23 AM   #4
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Default Re: TRX4 final axle gear ratio?

Great Work

Thanks
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Old 08-11-2018, 12:01 AM   #5
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Default Re: TRX4 final axle gear ratio?

I think your numbers are off, Diff gears are 34/11 or 3.09/1

Gear Options:

Underdrive: TRA8288
Standard: TRA8279R <--------this one
Overdrive: TRA8287

(edit) maybe those aren't the dif gears, TRA8282 are dif gears but look different they are 18/11 or 1.38/1

and the portal gears look like 23/10 or 2.3/1 TRA8258 and TRA8257
I cant count the teeth in the picture might be 23/9 which would make the whole axle 7.9/1

I'm just looking at the parts at a online hobby store and counting teeth. not owning a trx4 to see which gears go where.

I think the total axle reduction (front, don't know if rear is different) is 2.3*3.09=7.11
(numbers are rounded)

my calculations for the transmission are also
1st gear 36/18 or 2:1
2nd gear 24/30 or 0.8:1

to calculate your final gear rato
main * trans * diff * portal
1st gear = (spur/pinion)*(36/18)*(34/11)*(23/9)
ex stock = (45/11) * 2 * 3.09 * 2.56 = 64.72
easiest1 = (45/11)*15.8=64.63 first gear
2nd gear= (spur/pinion)*(24/30)*(34/11)*(23/9)
easiest2 = (45/11)*6.32=25.85 second gear

So if you wanted you could probably get a 9T 48P pinon and 68T 48P spur and have 119.36/1 first gear and 47.75/1 second gear reduction.
I don't know if this spur is available, if it is it probably dosen't say trx4 on the package. But it looks like a fairly basic spur to me.

Last edited by Voodoobrew; 08-29-2018 at 01:40 PM.
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Old 08-26-2018, 06:02 PM   #6
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Default Re: TRX4 final axle gear ratio?

I miss read this, but how did you intend to mount the Traxxas portal axles to a axial Diff? oh, you mean match it to the front diff...
nevermind, Im slow

Last edited by Voodoobrew; 08-26-2018 at 06:04 PM.
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Old 09-30-2018, 09:35 PM   #7
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Default Re: TRX4 final axle gear ratio?

I know this is an older post but how hard would it be to put a set of trx portal axles on a scx10 ii? And would the gearing be so low that it would be useless? Thanks for any help.

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Old 11-18-2018, 07:23 PM   #8
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Default Re: TRX4 final axle gear ratio?

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Originally Posted by 4kids crawlin View Post
I know this is an older post but how hard would it be to put a set of trx portal axles on a scx10 ii? And would the gearing be so low that it would be useless? Thanks for any help.

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I did this but have a gcm scale transmission so my initial transmission output ratio is slightly different thanthe 10.2 kit trans. Top speed on a 1900kv brushless 3s is about walking pace though. Putting the axles underneath required custom length links pretty much all around.

I was thinking of putting a trx axle on the front of a toyzuki v2 with an OD gear set, leaving the AR44 I have on it in the rear. Haven't run the numbers but I'm hopeful the OD gears and transfer case OD will overcome the difference between front to rear. Maybe even still have a little OD upfront, this thread should help a lot.


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Old 11-18-2018, 07:52 PM   #9
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Default Re: TRX4 final axle gear ratio?

After crunching numbers, nope. Gonna have to lose the rear leaf AR44s and put the other trx axle back there on links. Final ratio difference front to rear is 1.67. Unless I run a secondary reduction to the rear axle, which is probably doable, but hard to justify, given the space I would have to work it into.

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