Can a 1000w mid drive do hills, or does it always needs MTB gearing to get high Nm?

m@Robertson

Well-Known Member
Region
USA
I wouldn't worry about straining the motor, and changing the chainring won't really affect the motor much anyway. From the POV of the motor (so to speak) it's how fast you go up the hill, not how fast the chainring is turning that matters, at least over a much broader range of outputs than a human.
Stepping into an old thread I know, but the above is in error. Changing the chainring will affect the motor quite a lot. The issue is if you are climbing a steep hill and bogging the motor. A bigger ring will be a potential disaster in the making. As @tomjasz noted, the BBS01 and 02 are very sensitive to gearing, and this is because you can literally fry them if you bog them and subject them to load. Like going up a steep hill with a chubby rider and a load of groceries.

I typically use a 42T front chainring. Its the smallest possible that still gives you that steep offset. I recently built a bike that used the Lekkie 40T - but that needs a special motor cover to let the smaller ring fit and still have its steep offset. Not a thing for the beginner to tackle. My longtail Big Fat Dummy uses a 36T ring because it runs VERY steep hills ... but that longtail means a 215+ link chain which lets me lose the offset without losing my big gears in back... a special case. The 36T allows the motor to survive the punishment it gets. And my Bullitt cargo bike which lives only on flat land can take a 52T ring... but only because I run it 2-4 cogs in for straight chainline.

My Envoy runs in hill-strewn Monterey and I positively crawl up hills right now with its 42T ring (46T big cog in back), coming back from the store. I'm going to switch to a 40T (I can't lose my offset on this one) to ease the motor's life a bit, but of course thats a full weekend project since I have to do the main gear swap inside the new motor cover, then file down the nub on the motor casing, clean every bit of metal shaving off etc. etc. etc.
 

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
I guess I think of the chain ring as another tuning tool. If you see yourself using just one end or the other of the gear cluster/cartridge/freewheel, a chain ring change in the proper direction can center the range of gears you're using most frequently, avoiding the potential for situations where you run out of range/available gearing. -Al
 

m@Robertson

Well-Known Member
Region
USA
I guess I think of the chain ring as another tuning tool. If you see yourself using just one end or the other of the gear cluster/cartridge/freewheel, a chain ring change in the proper direction can center the range of gears you're using most frequently, avoiding the potential for situations where you run out of range/available gearing. -Al
Yeah for sure picking the proper chainring - both with tooth count and offset in mind - is *super* important for a mid drive builder who is building smart.

Part of the misperception on front rings, I think, is from people who don't know better and assume a 'powerful' mid drive has enough oomph to overcome a bad chainring choice. Particularly one where you go too big. They don't, and bog down big time if you make the mistake of say picking a 46T when instead a 42T. Doesn't take much. I have been there and done that sooo many times, nowadays I don't need to buy chainrings for a build to see whats going to work. I have a pile of the things to pick from after all the mistakes adding up over the years.
 

AHicks

Well-Known Member
Region
USA
City
Snow Bird - Summer S.E. Michigan, Winter Gulf Coast North Central Fl.
So much has to do with the weight of the bike and the load, the size of your motor, the area you ride, tire size in use, and the speed you like to run at. So many variables. I don't know how you would ever calculate all the different factors - or be interested in trying for that matter. Much easier in this shade tree mechanic's mind to just put it together and ride it. Shouldn't take too long to get a good idea of where you are at, and which way you need to go.... -Al