Get an idler, they are relatively easy to add after and cheap to make
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if you have space you can also run wider belts
For me, idlers were training wheels until I figured out how to tension properly. That said, they’re helpful in getting easy pulley/belt engagement. As long as your belts are HTD5, no need to look for better belts.
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wasn’t there a boosted board belt that cost like 50+$ but had a lifetime warranty? If i bought it they probably would’ve denied that warranty by now.
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What size is your motor pulley and how wide are your belts?
Also misaligned gears and non concentric pulleys can cause slipping.
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Without going into tensioning, which is king, I would say check the alignment very carefully. A belt that’s not aligned well can slip, as @taz mentioned.
Something else that can cause anywhere from minor to massive slipping in a perfectly aligned and tensioned belt, is broken cords. If your belt has broken cords inside, you will typically not see any indication of this by inspecting it (sometimes you can though) but it will just skip like crazy. In that case, failure is imminent anyway and you need to replace it before many more rides. If you check multiple belts, some new, and the skipping persists…
Then check when the skipping is happening. If the worst skipping is happening any other time besides during hard braking, then I don’t know what’s going on. That’s always when the worst skipping happens.
Alignment – the best way I’ve found to perfectly align belts is
- get motor mount (without motor) snug on hanger, then loosen a tiny bit so it moves
- install wheel and pulley with no speedring (washer) between the hanger and inner bearing.
- push motor mount flush up against wheel pulley so they are touching each other
- keep those held tightly together while you tighten motor mount clamps
- make sure mount is flush against, and touching, the wheel pulley, and there is no gap or misalignment
- finish tightening mount clamp all the way
- make sure again that mount is flush against, and touching, the wheel pulley, and there is no gap or misalignment
- when you’re all done, take the wheel and pulley back off, add a single 1mm speedring (washer) and just like that, the pulley will be perfectly aligned and 1mm away from the motor mount plate
- if you need it further away when you are doing tensioning, then add more washers
And also make sure your pulleys are concentric and don’t wobble at all as @taz mentioned. That’s super important.
edit: was solved below, was using HTD-3M belts/pulleys instead of HTD-5M belts/pulleys
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Thank you everyone for your responses - It sounds like you are all basically in agreement so after reading your posts and poking around a bit I think the problem is motor mount flex. These mounts are custom design, and they worked great for chain drive, but they have just a bit too much flex for belt drive
I’ll be redesigning the mounts rather than messing around with belts or ldlers.
However, on checking the belt is labeled HTD but not HTD5. Did I get the wrong kind of belt? This is the belt I’m using
Thank you again,
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There’s your issue. You want 5M, not 3M.
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Ah, thank you!
Amazon has some but they won’t deliver until June 4-20th. Do you have any recommendations for vendors that might be able to ship more quickly? I need a 312 but it sounds like the standard is 320, so it sounds like a bit of idler is in my future anyway
Update, I found some that will ship sooner
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315 is a commonly stocked length.
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I had this issue for long time on 12s single 45a. Colution - drill additional holes in plate to add 2 tentioning pulleys. Never been happier
vbeltguys for the win if yur US… theres a code here for like 15_20% off somewhere…
this is 10 off: TEN10TENOFF
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@DougM what pulleys do you have? are they 3M or 5M? If they are 3M you would need to find 5M ones to match the bigger belt teeth.
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@SaturnCorp - Good catch - they are 3M pulleys.
This is good because I’ve been meaning to change the ratio anyway - I need a bit more climbing power and bit less top speed.
The current ones (for 6" pneumies) are 72:18 teeth.
Can you recommend a place to order the 5M’s with something like 80:18?
Thank you
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I’m feeling like if u dropped 3 teeth off the motor on 6" that would be a good pop of torque already
That’s about a 4.4 ratio so you’d be looking for a motor pulley with around 15 teeth (15 is the general consensus on the smallest motor pulley that can be run without slippage) and a 66 tooth pulley.
I’m not sure what wheels you have so finding the wheel pulleys will probably be the hardest unless they are a common hub. Any motor pulley with the right size/shape bore for your motor shaft and setscrew or keyway will work. I recommend Torqueboards and BKB for those.
I found a 72 at SDP-SI but they are out of stock. that led me down the rabbit hole of trying to make my own 80T, which I can do, but it will take a long time and I don’t have the right material in stock, so more $$$.
Neither Torqueboards (DIYElectric) nor BuildKitBoards have 72T, but I’ll order a few of the drive pulleys in different tooth counts (15 - 18 as you guys recommend).
I’m running 6-shooters but I can modify any pulley, I just have to find one.
Thank you,
Check this out , https://www.janux-esk8.com/product-page/pulleys-to-fit-6-shooter-hubs . I bought from him in the past and great products fairly priced and responsive seller. The pulleys are made of POM so should last you a while. He might also have some belts in stock and he also have motor pulley 
. Hope this helps.