Hello everyone,
Here is my situation: I've had a geared (500W Bafang) front hub drive for almost 5 years now. Put several thousand miles on it, some pavement, some offroad. For the most part it does the job but it's not easy to transport in a car of course. It's not super heavy at 55 lbs, and I do have an old GMC Yukon I could take it around with but it's still a pain to have the motor on the front instead of the center or rear.
So the plan is to get either a 500W Bafang mid-drive or a 500W Bafang geared rear hub drive. This would be mostly for offroad including steep climbs. Now...before you immediately say "Buy a mid-drive for that, silly", let's talk about some issues with mid-drives:
CHAIN: Most mid-drive mountain bike motors are 250W, I assume so they can be sold everywhere including Europe and Asia. I don't think 250W is going to cut it for me when climbing grades over 7%. Yes, you can boost most of those to around 400W but I know some local dudes that boost their mid-drives all the time and they go through motors pretty fast. Like every 1000 miles. That just seems ridiculous. Yes, Bafang does make a 500W or 750W BSS02 but then you get the risk of the chain snapping. I plan on doing a 34t chainring and an 11-52t cassette. If I'm in the granny gear that means a gear ratio of 0.65, not super low but pretty dang low for e-power, and pretty high for torque. Will the 11 speed chain survive a 0.65 gear ratio and 400-800W up something steep? I know a geared hub drive can...and a rear hub drive should be able to handle a lot more watts than a front hub due to the extra weight on the back of the bike, and I can normally get about 300-400W up something steep with a front hub. So that means with a rear hub I'm hoping for more like 450-600W or more up steep hills, assuming of course I have the traction and can keep the handlebars straight.
TRACTION: A gazillion people out there say mid-drives can effortlessly climb stuff all day long, but I'm talking about specific 8-18% grades on either singletrack or fire roads with some loose dirt/gravel. That's not so easy with any setup, I know that, because any loose dirt or gravel will threaten tire traction. Loss of tire traction = bike stops. Doesn't matter if it's a mid-drive or a hub drive, no tire traction = no climb. If mid-drives are so great, why are many of them sold with large 44-52T chainrings? And why are there smaller aftermarket chainrings for climbing steeper stuff? It's obvious that a higher gear ratio will result in a poor climb even with a mid-drive. And more than one person has snapped a chain with a smaller chainring and increased torque setup. You don't have that issue with a hub drive. For a geared hub drive, the only things limiting success up a steep hill or mountain are tire traction, battery life, and making sure not to overheat the system including the controller. Is that incorrect? If so, how?
So here's the real question: are you 100% confident that a 500W mid-drive with an 850W or so peak power option can handle a long 9-10% climb of say 1000 feet on loose dirt singletrack? Will it shrug off tire slippage; will the chain survive large fluctuations of torque if and when the wheel slips on loose stuff up the hill/mountain? Will the mid-drive motor shed that extra heat fine? If so, then I'll take the mid-drive. If not, a geared rear hub drive seems the best option because the drivetrain is not a factor that could limit climbing success. Only traction, battery power, excessive heat (and of course my own pedaling stamina) could threaten the climb, not the drivetrain itself. Good or bad argument?
Here is my situation: I've had a geared (500W Bafang) front hub drive for almost 5 years now. Put several thousand miles on it, some pavement, some offroad. For the most part it does the job but it's not easy to transport in a car of course. It's not super heavy at 55 lbs, and I do have an old GMC Yukon I could take it around with but it's still a pain to have the motor on the front instead of the center or rear.
So the plan is to get either a 500W Bafang mid-drive or a 500W Bafang geared rear hub drive. This would be mostly for offroad including steep climbs. Now...before you immediately say "Buy a mid-drive for that, silly", let's talk about some issues with mid-drives:
CHAIN: Most mid-drive mountain bike motors are 250W, I assume so they can be sold everywhere including Europe and Asia. I don't think 250W is going to cut it for me when climbing grades over 7%. Yes, you can boost most of those to around 400W but I know some local dudes that boost their mid-drives all the time and they go through motors pretty fast. Like every 1000 miles. That just seems ridiculous. Yes, Bafang does make a 500W or 750W BSS02 but then you get the risk of the chain snapping. I plan on doing a 34t chainring and an 11-52t cassette. If I'm in the granny gear that means a gear ratio of 0.65, not super low but pretty dang low for e-power, and pretty high for torque. Will the 11 speed chain survive a 0.65 gear ratio and 400-800W up something steep? I know a geared hub drive can...and a rear hub drive should be able to handle a lot more watts than a front hub due to the extra weight on the back of the bike, and I can normally get about 300-400W up something steep with a front hub. So that means with a rear hub I'm hoping for more like 450-600W or more up steep hills, assuming of course I have the traction and can keep the handlebars straight.
TRACTION: A gazillion people out there say mid-drives can effortlessly climb stuff all day long, but I'm talking about specific 8-18% grades on either singletrack or fire roads with some loose dirt/gravel. That's not so easy with any setup, I know that, because any loose dirt or gravel will threaten tire traction. Loss of tire traction = bike stops. Doesn't matter if it's a mid-drive or a hub drive, no tire traction = no climb. If mid-drives are so great, why are many of them sold with large 44-52T chainrings? And why are there smaller aftermarket chainrings for climbing steeper stuff? It's obvious that a higher gear ratio will result in a poor climb even with a mid-drive. And more than one person has snapped a chain with a smaller chainring and increased torque setup. You don't have that issue with a hub drive. For a geared hub drive, the only things limiting success up a steep hill or mountain are tire traction, battery life, and making sure not to overheat the system including the controller. Is that incorrect? If so, how?
So here's the real question: are you 100% confident that a 500W mid-drive with an 850W or so peak power option can handle a long 9-10% climb of say 1000 feet on loose dirt singletrack? Will it shrug off tire slippage; will the chain survive large fluctuations of torque if and when the wheel slips on loose stuff up the hill/mountain? Will the mid-drive motor shed that extra heat fine? If so, then I'll take the mid-drive. If not, a geared rear hub drive seems the best option because the drivetrain is not a factor that could limit climbing success. Only traction, battery power, excessive heat (and of course my own pedaling stamina) could threaten the climb, not the drivetrain itself. Good or bad argument?