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
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
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!