arthurtuxedo
100 W
I posted back in February to get input on a setup for hauling heavy items. I'm still brainstorming the idea, but today I was able to borrow a Bullitt with the Shimano STEPS mid-drive to test it out. Basically I'm looking for a cargo bike that can deliver small but heavy items (think ~200 lbs of car batteries) around San Francisco, and have decided that a front loader is the way to go. I liked the Bullitt, but I can't see most of the field guys being willing to use it because a lot of the deliveries are on streets where bikes are effectively banned. There is no bike lane, the roads are full of pot holes, and drivers have been in miserable traffic all day so they're stressed out and competitive. When they see something with pedals in front of them, it is like a red matador cape in front of a bull and they are liable to make aggressive, dangerous passing maneuvers but lack the driving skills to do it safely. I need something that can beat most cars being driven with a heavy pedal, but only for the first 10 MPH. An initial burst of acceleration should cause them to back off and not try to aggressively pass.
I was thinking that the best bet would be a Yuba Supermarche (20" wheels front and back) with a slow-wind rear DD hub and about 3 kW. That should provide enough acceleration to make our employees want to use it, tackle hills, and allow for extra-heavy runs hauling a Bikes at Work trailer (different part of town, so fast acceleration is not necessary when using the trailer). Top speed is not important, and in fact I'd like to keep it around 25 MPH or below, both to keep our employees out of trouble and in order to avoid needing front and rear suspension. I'm looking for torque to get off the line at slightly greater acceleration than car traffic (but only from 0-10, after that it's OK if it doesn't keep up) and to get up our famous SF hills, which is why I am thinking about a slow-wind motor and 20" wheel. The battery will be 72V, not sure what the current rating is but I think it's quite high, definitely 40A and probably more like 100. We have a lot of these lying around for reasons I won't get into. We also have some BAC 2000 and 3000's that I can press into service, so phase current limiting and field weakening are on the table. The batteries are easy to swap and we have a surplus, so efficiency is not very important.
My main concern is that with heavy loads and steep hills, even a slow-wind motor will just turn into a space heater rather than a mode of propulsion. I could be talked into a mid-drive like the BBSHD, but I really don't want to put that kind of strain on a bicycle gear system on a regular basis, especially since if the thing breaks in the middle of someone's shift, they're going to be on the clock the whole time and that's a lot of $$ to pay someone to wait for the van to come pick them up. It would also put the kibosh on this whole project since the end goal is to replace the van for 95% of trips, not to need a van rescue itself. A hub-motor should be more reliable, and if it does crap out we'll provide a nice low gear ratio so they can limp back to HQ.
Am I right to lean toward the 20" Supermarche, or could the same goals be accomplished with a Bullitt or similar 26" rear wheel? Does a mid-level DD like the Crystalyte 3525 make the most sense, or could I accomplish the same thing with a lighter one like the 9C 2707? Are there additional considerations that I'm not taking into account?
I was thinking that the best bet would be a Yuba Supermarche (20" wheels front and back) with a slow-wind rear DD hub and about 3 kW. That should provide enough acceleration to make our employees want to use it, tackle hills, and allow for extra-heavy runs hauling a Bikes at Work trailer (different part of town, so fast acceleration is not necessary when using the trailer). Top speed is not important, and in fact I'd like to keep it around 25 MPH or below, both to keep our employees out of trouble and in order to avoid needing front and rear suspension. I'm looking for torque to get off the line at slightly greater acceleration than car traffic (but only from 0-10, after that it's OK if it doesn't keep up) and to get up our famous SF hills, which is why I am thinking about a slow-wind motor and 20" wheel. The battery will be 72V, not sure what the current rating is but I think it's quite high, definitely 40A and probably more like 100. We have a lot of these lying around for reasons I won't get into. We also have some BAC 2000 and 3000's that I can press into service, so phase current limiting and field weakening are on the table. The batteries are easy to swap and we have a surplus, so efficiency is not very important.
My main concern is that with heavy loads and steep hills, even a slow-wind motor will just turn into a space heater rather than a mode of propulsion. I could be talked into a mid-drive like the BBSHD, but I really don't want to put that kind of strain on a bicycle gear system on a regular basis, especially since if the thing breaks in the middle of someone's shift, they're going to be on the clock the whole time and that's a lot of $$ to pay someone to wait for the van to come pick them up. It would also put the kibosh on this whole project since the end goal is to replace the van for 95% of trips, not to need a van rescue itself. A hub-motor should be more reliable, and if it does crap out we'll provide a nice low gear ratio so they can limp back to HQ.
Am I right to lean toward the 20" Supermarche, or could the same goals be accomplished with a Bullitt or similar 26" rear wheel? Does a mid-level DD like the Crystalyte 3525 make the most sense, or could I accomplish the same thing with a lighter one like the 9C 2707? Are there additional considerations that I'm not taking into account?
