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Belt + 3-speed IGH + Seattle Hills = TSDZ2, BBS02, BBSHD, or mistake?

Posted: Apr 06 2021 12:29pm
by argosnotch
I've been reading these forums for a few weeks now as I'm contemplating adding a mid-drive to my bike (for only recreational riding in the city on roads and some paths). I currently own a 2010 Norco Ceres It's a belt drive with an Alfine 8 IGH. I really liked the belt drive, and am trying to keep it if I can overcome its drawbacks. Reading about the builds people have done with the belt drive, it seems ditching the Alfine for a Sturmey-Archer cs-rk3 3-speed with spacers, solves the belt line problems. I've not owned a 3-speed before, so am concerned the gear range isn't enough.

I only rode recreationally (3-4 times a month, 6 months out of the year), but stopped riding about 5 years ago as the Seattle hills (plus age, fitness, and injuries) became just too hard and not much fun. It's five years later, and the hills look 5x as steep today. For context, I live at the top of a 1 mile, 450 foot elevation hill, and any riding I would do ended with that hill. Not to mention, going anywhere in the city is up/down/up/down hills (lots of them quite steep at 9-15% or more.

With the hills here, and my lack of fitness, is trying to go to a 3-speed a mistake? Ideally, I'd like to pair it the with torque-sensing TSDZ2 but worried it wouldn't have enough power. With either Bafang motor, I'm also concerned about the cadence required. Being an older, recreational rider, my "cruise" cadence is slower (60-75). It seems these motors are happier spinning a lot faster. Is this a recipe for disappointment?

If the hill issues can be solved by gearing, is the 3-speed going to be just be too slow (or spinning to fast) when not on hills? Bike currently has 50T/22T. I don't think smaller than 50T fits on the mid-drives. The largest rear cog is only 24T.

I'd also need to upgrade my wheels (for the 3-speed plus existing wheels are too narrow), brakes (have lower end mechanical discs), and Gates drive system (currently have the original non-centertrack system). Given all this, would I be happier buying an new off the shelf ebike that includes a belt drive like the Priority Current.

Thanks in advance for any insights,

Re: Belt + 3-speed IGH + Seattle Hills = TSDZ2, BBS02, BBSHD, or mistake?

Posted: Apr 10 2021 5:41am
by dogman dan
Pretty much the only easy way to do what you want here, is to put a front hub motor on the bike. I'm not familiar with Seattle, but I've climbed hills 10 miles long that averaged 8% grade with pretty ordinary 1000w hub motors. (48v)

The other way you could do a mid drive is to put a motor on the bike that drives a belt or chain to the left side of your rear wheel, like gas bike kits do. The fun here is the fabrication of it.

The best idea, is to scrap the idea of using that particular bike. Put a decent mid drive kit on a bike with regular chain, and a 7 speed gear in the back. You won't need expensive, lighter, 9 or 10 speed. With the motor, bigger jumps between each gear will work fine. Heavier, steel frame bike of decent brand will do fine. Even a beach cruiser with compatible bottom bracket would be a good choice. Something like a townie.

Re: Belt + 3-speed IGH + Seattle Hills = TSDZ2, BBS02, BBSHD, or mistake?

Posted: Apr 10 2021 7:32am
by spinningmagnets
I don't know if it's a good idea or a bad one. For hill climbing, put on the smallest chainring that will fit on your selected drive unit. The fact you want to convert a belt drive complicates things.

The TDSZ2 will climb very steep hills, but because it has less power than the other two you mentioned, you have to have very low gearing available to the drive. Small chainrings on front, and large sprockets on the back. You will have to slow down quite a bit on the worst hills, to keep the motor RPM's up.

Re: Belt + 3-speed IGH + Seattle Hills = TSDZ2, BBS02, BBSHD, or mistake?

Posted: Apr 10 2021 8:50am
by Stealth_Chopper
Sincerely, why reinvent the wheel? OK if that's what you want to do of course it's fine.
You need max torque, and can always take it easy.
Maybe when you are happily tired some day: You might just want to motor up a mountain on the way home
'just because'.
It's later than you think, I imagine you want to ride now?
Creating your own semi custom eBike with a kit might be rewarding or 'Maybe not so much'
Good Luck