"A Treatise on Belt Sizes," Or "Is HTD3M Really All That Bad?" Or "Some Thoughts on Belts"

ESK8 Mechanics
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I’ve recently been having some trouble with belt skipping during hard braking, and it got me thinking about different belt pitches and why we use 5m pitch over 3m pitch.

As many of us know, the standard belt size we use is 5mm HTD, where each tooth is 5mm tall (?) and the teeth are spaced 5mm apart. However, Boosted, probably the earliest brand to make a super reliable, (relatively) high-performance board, uses 3mm. I think it’s safe to say that the boosted board has really powerful brakes that are extremely reliable, and i rarely if ever hear about bboard owners having belts skip while braking. Either way, if 5mm is so much stronger (what seems to be a safe assumption given the larger teeth), why don’t they use it?

A thought occurred to me: Each 5mm tooth can individually bear more load, but if you have 3mm teeth, you have almost 67% more teeth in mesh at a given time because they each take up less space (1.666 times more teeth, to be exact). Therefore, if each 3mm tooth can withstand at least 3/5ths of the load of one 5mm tooth, it stands to reason that 3mm belts can transmit more power. I checked spec sheets from the same manufacturer for HTD5M and HTD3M to find out what the exact numbers were. Guess what? a 5mm tooth

Screenshot%20(35)

Has a shear strength of about 27.21 N/cm (with the cm representing the width of the belt of course) at 0 RPM, meaning that for the 3mm belt to be “stronger” it would have to have a shear strength of at least 16.326 N/cm. So, I checked the 3mm belt spec sheet and

Screenshot%20(36)

it has a shear strength of 17.30 N/cm, which is actually an improvement of about 5% over what would be expected of a 5mm belt of the same dimensions. Additionally, this spec sheet lists the minimum number of teeth per pulley for both of these belt sizes to be 16, but i’m running 15 and some people on this forum go as low as 12. With smaller teeth, i could run 20 or something and still have a smaller pulley than I have now (i’m trying to push my max speed down to about 25mph with 190kv, 12s, and 107s and just keep the torque to tow my friends around). This makes sense, because 3mm belt should be more flexible, which in theory means we won’t have to pull it as hard to keep it meshed with as many teeth as possible so lower belt tension should be possible, because it won’t naturally curve away from the pulley as much. Especially for how small our motor pulleys are, i think running 3mm belts might actually be better than 5mm belts.

In conclusion: I think there might be some advantages to running 3mm belts like boosted does instead of 5mm belts like basically every other belt drive on the planet. Namely, I think flexibility, size, straight-up shear strength, number of teeth meshed, noise, and belt tension could all stand to benefit from a downsize in our belt pitch. I think 5mm belt probably wins on durability and ease of creating pulleys, but we should seriously consider 3mm as an option.

What are your thoughts on this? Did i miss something? Anyone have experience with both belt sizes want to comment? Thanks guys!

– Joe

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intersting question. I feel that 3m belt would be good especialy for +12mm wide puleys.

I upgraded my board to a 5m 15mm wide but quickly came back to the original 5m 9mm belt because it was quieter and more efficient (more flexible).

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tldr: 9mm not enough, 15mm too much: try 12mm? :thinking:

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the boosted board doesn’t output nearly the amount of power that most of our boards do. i have trouble with my benchwheel skipping too. 3m is much easier to get a hold of and much cheaper too, that’s my suspicion on why they used it

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That’s true, but I’ve ridden boosted boards and they seem to brake much harder than my board without slipping. Could that be the gearing ratio, the wheel pulley size, and the belt width (mine are dual 9mm because i can’t fit 15mm)?

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i’ve never had skipping issues with full -120a braking (-60a motor min and -12a batt min per vesc) with properly tensioned 15mm belts and 15/36.

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interesting. I guess the solution for me has to be dual 15mm. Still, I want to explore this whole 3m thing, there could be something to it

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eh i guess you need tighter tension and a steeper reduction

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The main problem with 3M is alignment, if any of your pulleys it’s a little bit of center the tension will change as you ride, and since the tooth is smaller it will skip easier

My first board was 3M, since the motor pulley was drilled a bit off center is was unriadeable

But the drag was way way lower than with 5M, if you can guarantee that your mount is solid and everything is almost perfect aligned it would be possible

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3mm v 5mm is good for lower power set ups…

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Good research. You may be on to something. I think (no data to backup) that 3m belts require more tension than a 5m belt. I run my 5m belts pretty loose, for free rolling. My friend has a boosted and his belts are pretty tight, but it doesn’t coast nearly as far as mine. And he rarely has skipping. Actually the only time I’ve heard his skip, is yesterday. He hit the brakes hard to avoid a car, and broke a belt. They were only like a month old. I’ve never broken a 5m belt, over 2000 miles.

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boosted doesn’t coast because they use duty cycle. if you’re not throttling you’re braking.

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I wonder what their range could be without the drag brake.

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Is that a guess or you know about that? When I had a Boosted, releasing the throttle would not result in braking.

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I think he meant that regen switch. it technically does brake when u press it while cost. I feel not much difference on normal use , but on flat road it is really annoying.

or if he meant duty cycle in general brake when neutral he is wrong. it does not

in my experence it honestly feel like a toy. sorry guys but acceleration is just not there. 25% hill claim is not that good, i can run faster than the board.

it just not have the Ump, which is the best part of the esk8. speed also is too slow. belt get loose when u go fast and running hot. thats why 3m is enough for them.

one thing about the sound, I prefer bit of noise because people doesnt notice it. i have to say excuse me like 100 times a day. I can make my board dead silence with belt spray, lubed bearing, foc. U won’t hear me until 1 m from behind.

lastly belt eat through the pulleys, and with smaller pitch it will wear down quickly. boosted is no exception although steel pulley will hold for yrs, but my buddy’s v1 is suffering this and rips belts once a month.

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The Boosted Board? You serious?

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yeah I havent tried the new stealth but I tried boosted v2 plus. maybe extended battery will be better. I’m putting 100amps per motor and speaking from diy perspective, but I can’t quite get the torq Im looking for.

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The key to ‘No Belt SKip’ is teeth in mesh and belt tension. Its a job sometimes to find the perfect combination of motor mount length to increase the mesh and running belts loose to avoid motor bearing damage and wasted energy. A properly tensioned HTD5m belt at 12 or 15mm width will almost never skip.

The difference in Evolve and Boosted is when you slam the brakes on a dual vesc with dual 15mm belts and a 10s/12s 30q pack, you are typically exerting a lot more force than you will with a boosted or evolve board. So your more likely to skip. Just use proper belt lengths and tension and those issue will go away.

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I kind of slightly agree. The boosted board and the app are super polished. But for almost 3 years, Boosted didn’t support Android, I waited and waited, and then the boosted left me.

As well the advertised milage of 7-8 miles really was 4 miles with heavy riding(who doesn’t ride hard?). The torque is lacking compared to most DIY builds. While I do think it has a place, they no longer have a place in my home or esk8 arsenal. Especially after, cracked trucks, and the BMS on original battery going bad - even though they were warranty.

Boosted is a nice entry level board, but with the range and size and lack of power, it can’t fit into the “last mile” category. Android support was non-existent throughout my ownership. It’s hard to categorize a proper place for it. Especially after I sold it, and DIY’d a vanguard that killed it in every aspect except having an odometer.

Anyway back on topic: 20mm belts or bust. can run them superloose for almost no rolling resistance, and they will never skip ever.

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Good luck finding those metal 20mm wheel pullies :wink:

I’d run 20mm in a heartbeat if it was an option. Finding 15mm ones is like pulling teeth, especially if you need more than 36 teeth. @dickyho has some good ones

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