I am going to have to disagree very strongly with a lot of what you are saying here
@Smaug.
the BEST case, if you are mechanically-inclined, is that you will burn weeks and weeks getting everything sorted out.
That is a *gross* overstatement, so far out of line that it is just flat out untrue. You have to remember that, first of all, plenty of people build up fat bikes with the motor we are discussing here. The problems are known, as are the solutions. What is not known (simply because I haven't personally done this exact one) is how the chainring choice is going to shake out. That will be solved with direct experience, but truly... its not brain surgery. There are a lot of words on the screen here, but those are here to keep someone from doing much in the way of error, when it comes to trial-and-error. Certainly, in no circumstance is someone going to spend "weeks and weeks" figuring out the solution. There's so little to have to fuss with here.
The WORST case is that you'll realize you bit off more than you can chew and now you have hundreds of dollars sunk into a project that never materialized.
But he has more or less solved that by asking people with experience what the solution is. I'm not sure if this made it into the thread or was only in my DMs with the OP, but he consulted a Bafang dealer who told him straightaway what he needed to do for an ICT and that it was easy. And it is. But chainring choice is where you can end up throwing money away and as you can see above much attention was paid to describing the cheap - and maybe free - way to get past that. Regardless my advice was to budget in a do-over on the chainrings. A 28T Lekkie is $75.
- That bike was not designed with eBike speeds in mind. (esp. re. braking performance) You are thinking of at least doubling its speed compared to its design envelope. (as well as adding extra weight that needs to be slowed down)
The implication here is that braking performance is an issue and this is wrong. First of all, note the OP is talking about an e-MTB and he is interested in small chainrings. That translates to slow speed in the woods, on singletrack etc. It will also keep speed down on the street. Sure, downhill speeds will be fast but the 'e' in 'emtb' will not affect gravity's pull on a bike speeding down a hill unpowered. 15 lbs of battery and motor on a bike are meaningless in that regard. Next... he is purchasing a quality mtb. Take a moment to read the specs and understand the brakes it has on it. They are more than strong enough to handle a frat bike careening down a hillside, and so they will also be just fine on a fat bike going down the street.
- There is also the question of whether the frame can handle the extra power. If you go with the mid drive arrangement that m@ is suggesting, you'll put probably quadruple the power through the drivetrain that it was designed for.
I'm sorry but this is lack of experience doing the worrying here. That chromoly frame is more than strong enough to handle a BBSHD or something even bigger. Surly frames border on being the gold standard when it comes to strength. There is no reason for concern here. For that matter, even the dirt cheap Mongoose Dolomite frame is plenty strong and thats a $250 bike. There is no issue with the frame, period.
However there is a potential issue using 12s. Plenty of people do it (the ones who do are all hi-po singletrack rider), but 12s chains under BBSHD power have been known to snap when being rode (rided? ridden?) hard on trails. The solution is to bring along a spare chain, which EVERY mid drive rider in the woods should do right next to their tire irons and patch kit. But thats not the frame.
- Best case is that chains & sprockets wear a lot faster. Worst case is that it snaps and strands you God knows where with your mobility issues and a disabled 100 lb. bike.
Here again, this is inexperience talking. I follow best practices on builds and I do NOT get any additional wear and tear on my drivetrains. I also follow best practices on riding, and as thanks for that, in all the years I have been riding, despite the fact I take along a spare chain without fail, I have never snapped one. Further, I get roughly 3000 miles out of a chain, and sometimes more, although the 'more' is on a bike with 2wd which extends chain life almost indefinitely it seems. Anyway, 3000 miles on a chain is as good or better than analog riders get.
Just today I put a 28T Lekkie front chainring on my Surly Big Fat Dummy. A few days ago I swapped out the 11-46T cluster for an 11-51T, and to follow best practices, I also changed the chain to match the new drivetrain. The old 11s chain has 1679 miles on it and the gauge still doesn't show any wear. But I'm changing it anyway since its a best practice with a new cluster.
Re. buying a fatbike that was designed from the start to be electrified, I see that the price of the Surly ICT is $2k. You could pay up to $200 to return ship the ICT and buy the Aventon Aventure and break even.
And have a vastly inferior bike. Mass-merchandise ebikes in this class have components that most cyclists would recognize as junk. Starting with an ICT, you get a chromoly frame of the highest quality short of a custom frame, along with quality hubs and wheels. Same for the derailleur and shifter although 12s is going to be iffy on chain durability. But not so iffy I wouldn't give it a try and see how it fares. You can change a chain from a spare in your bag in ten minutes.
I have an Aventon and can vouch for their quality. The Aventure has a hub motor, so all the extra power wouldn't be put through the chain & sprocket drive train; it's applied directly from within the hub.
There is a reason
quality e-mtb's are all mid drives. Hub motors are awful in the mtb segment. On the street and no more than low rolling hills, hub motors that cannot take advantage of gears and are single-speed as a result are in their element.
You can tell I'm a little more risk-averse than m@. The way it's going, it sounds like you'll be 100% reliant on his help to get this done...
There is nothing short of an enormous amount of self-help out there in terms of how-to's. And yes, I wrote some of the popular references on the subject, including
Mid drives up the ante on the required competence of the builder. Read this so your bike lasts without things breaking or wearing out early.
talesontwowheels.com
and taking it a couple of steps beyond what is needed here:
You want to build an ebike, but the project seems overwhelming. Lets de-mystify the entire process, including planning, parts and perfecting the end result.
talesontwowheels.com
I went to those lengths specifically because there is so much misinformation out there.
