It doesn’t matter. If the belt skips, it’s going to happen during braking. And I hope you don’t do any breaking! Wear a helmet just in case 
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Lol 10 char
I have not used the double pulley on the reverse motor mounts yet. I have a single pulley on the regular TB motor mounts and it works great.
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Using a pulley on both sides will allow super loose belts so you have great free wheel.
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For sure! I nearly stripped the m4 motor holes on one of the motors, so I just use one.
I get some pms from time to time about links for parts. Figured it’s easiest to leave it here, not sure if I have already
M4-0.7*24mm or whatever size bolt that you can Dremel off the end so that it doesn’t sink to deep and short the phase wires. Socket head is necessary so you don’t need a speed ring as the head is the size of the inner race of the bearings https://www.amazon.com/dp/B01DIVTWYW/ref=cm_sw_r_cp_apa_7ZLqAb1SDVD0X
M4*8mm 6.5mmOD steel threaded spacer. This is necessary for the other side to sandwich 3 bearings, this is also the size of the inner race of the bearings so that speed rings aren’t needed https://www.amazon.com/dp/B00PKLKUX6/ref=cm_sw_r_cp_apa_2YLqAb08V3XP0
4135mm bearings - high speed bearings with a double buna seal to keep dirt out. Don’t use metal shielded. https://www.amazon.com/dp/B071L5FKBL/ref=cm_sw_r_cp_apa_AQLqAbHJZYY0M
Make sure to wash the bearings when you get them, and replace the grease with a high speed oil like Bronson or OUST. Grease will create heat and these bearings will be spinning in the range of 1-18krpm depending on speed. These bearings are half the size of the 16T motor pulleys, so it’s effectively 2:1. 190kv motor on 12s is about 9krpm at the top which is almost 18krpm on the bearing. Service your wheel and idlers every 150-250miles(15-25 charges depending on your range). Cover your idlers to prevent large debris from binding between idlers and motor pulleys.
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Hopping on the Idler train! Figured I post a pic as I was able to fit an in an idler with a 72t pulley and pneumatic wheels. It can be done! I am loving the idler btw.
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Looks great. Did you have belt skips during braking prior to the idler pulley added?
@E1Allen Oh yeah definately. I wasn’t using this exact setup before, I added the idler pulley when I switched to pneumatics, but when I switched my belt wrap on the motor pulley would have gotten worse (had I not added the idler), so I can only imagine that the skipping would have gotten worse.
That setup looks stressful for the belt, because of the sharp bend. I would make sure to run that belt SUPER loose to avoid premature failure.
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I think running it loose is kind-of the point. Also, belts are cheap 
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Awesome contribution @PatRocks & @JuniorPotato93! I’ve been trying to resolve some skipping that I’ve been experiencing at the lower end of rpms/acceleration curve. I’m now having to be very cautious when accelerating as I’ve skipped and been thrown off my board. I also have the same experience as you when braking. Even after taking everything apart and make sure the pulley was centered and the tension was as hard as possible, I still had the same challenges. This is a wicked solution. Appreciate the time and testing that you’ve done! Now, to give it a try!
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unnecessary imo.
i’m still confused on how you make belts with teeth…
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Magic! 
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Nice modeling!!
Idler pulleys are not necessary, but they are useful! My belts are several hundred miles old, and they’re still in great shape. I can still read the writing on them 
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So, are you saying that idlers major advantage is belt longevity? more than belt skipping or efficient torque (grabbing more teeth)?
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To me, the main point for a longer longevity (and others equipment like motor shaft bearings) is the belt tension. The belt can run with less tension thanks to the great coupling with the motor pulley. I really felt the difference switching from a 6355 no idler to a 6374 with idler.
Before, I couldn’t trigger an emergency braking without having the belt slipping.
Now, even with a stronger motor, I can do so, with a belt less stressed.
The downside however is a worst coasting.
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Exactly what @Pimousse said. Being able to go slack on the belt tension is beneficial to not only the hardware, but to the overall ride quality as well.
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@Deckoz any recommendation on belt size? I’m currently using the 265mm belt on the TB V4 foward facing motor mount.
Will the cleaning schedule (removing every 2 weeks) create any unnecessary wear on your motor threads? Are you using locktite on these motor mount bolts?
Thanks for your help!