Interest check for >50T wheel pulleys compatible with BN/SR125

So, as the title states, trying to gauge interest here for a run of wheel pulleys for larger urethane wheels. These will be compatible with the wheel interface part of Boardnamics pulleys, giving you more options than the normal 36/40/44T, while also supporting the new M4 on 35mm spacing pattern of the new SR125 wheel core developed by Radium. This means a single set of these teeth can support everything from kegel, to abec, to SR125’s. They’ll likely be made of 7075 aluminum, and cost is looking like around $80/set of two currently, but will be brought down with more buyers. Currently looking at a 55T, but im entirely open to a different tooth count if that helps with interest.

  • Yes, count me in
  • Yes, but the price needs to be cheaper
  • Maybe
  • No
0 voters

And for a reference of how it looks as a complete unit - Here’s the 55T on a BN Kegel wheel interface

And here it is on a set of BRP wheel hubs i’m making that have the SR125 bolt pattern.


The MAD 125mm will be released soon. I think 55t will be too over geared but I am not quite sure. How about a 50t pulley?


I’m not opposed to going down to a 50T, but my logic was that if you’re overgeared at 55T, you can just bump up the motor pulley - whereas if you’re undergeared at 50T, you can’t really drop the motor pulley tooth count haha. I’m guessing here that anyone needing a more significant reduction on thane is probably trying to push a pretty high motor rpm, either through high kv, high voltage, or both - because that’s why i’m doing this haha.

For reference, here’s how the 55T looks on a 125mm diameter wheel - roughly 16mm of clearance.


So, just a quick update on pricing - if i can get three sets sold, i can get the price to about $60/set + shipping, or i can maybe consider anodizing

I don’t know much about manufacturing mechanical parts, but would it be cheaper if it was in two parts that bolt together like the BN pulleys? So one piece that engages the core, one that has the pulley profile. I thought making small parts out of smaller billets helps with cost

Its already modelled as that. The system reuses the front half of the boardnamics pulleys for the wheel core interface, or bolts straight up to the SR125 wheel core.


Gotcha! Idk if that was the edited part or I just didn’t read but that makes sense

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You can definitely get three sets sold. All 3 to me, if need be.


Just for curiosity, what does the 55T look like modeled on a 110mm wheel? What about a 53T on both wheels?

How wide is the HTD-5M tooth profile? Is it 16mm or 21mm?

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I would definitely go as high as practical for exactly the reasons @Ac53n mentioned.

It would also help if it was a number that minimized divisors with popular motor pulleys (15, 16, 18, 20) and that means my vote goes to 53 which is prime.


Cant be much if any clearance, the Savage 50t leave not a great deal… like ~5mm from memory… fuck all for street but could be managed on good surfaces… from memory… i could measure in the morning.

Is there any benefit to a prime number?

@Dinnye said it better than me

but that’s for cogs.

If I had a pulley tooth that had been hit by a rock or something, or a rock stuck in the belt, I’d want the wear spread evenly around the belt and other pulley so as to maybe avoid a weak spot. But I think it may be less important with belts. I don’t know. The number of teeth on the belt is also at play here.


It’s more important for a gear drive I think but even for belt drive it makes sense to go for relative prime numbers whenever it’s not inconvenient.

If a rock gets stuck in one of the pulleys, it’s gonna hit the belt on the same few teeth again and again if the greatest common divisor is not 1. If it’s 1 meaning the gears are relative primes then the wear will be distributed equally meaning no weak spot is created and you have much more time to remove the rock before the belt gets damaged too much.

I am not interested in buying personally, but if I was my vote would go to 53T. That’s a size that’s still borderline possible to run on 105-110mm wheels as well, while it’s a prime and allows larger ratios for the 125mm wheels than available currently.


I have it modeled for 15mm belt width (17mm of actual tooth width), as the next build im making these for is a low profile build, but if theres interest i can make a couple in 20mm width.

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One moment, ill have that mocked up momentarily.

55T on 110mm (8.5mm of clearance from wheel to exterior of pulley flange)

55T on 125mm (16mm of clearance from wheel to exterior of pulley flange)

53T on 110mm (10.1mm of clearance from wheel to exterior of pulley flange)

53T on 125mm (17.6mm of clearance from wheel to exterior of pulley flange)


All of those look fine IMHO