montana2436 said:
I have to commute 12 miles only one way.
So 24 miles total?
2.5 miles - going up a long 10-15 degrees hill.
A 15 degree hill is fairly steep. Do you mean 15% grade?
Is it that steep all the way up? Or are there any parts that are steeper? You'll want to plan for the worst case so you have enough power to go up it at a speed that will let you keep the motor from overheating.
YOu can check out the http://ebikes.ca/simulator to try out different motors and controllers and batteries to see what will work for that hill without overheating it. It'll also give you a guesstimate of wh/mile. I recommend simulating using one of the 9C 280x motors, and a 20A controller first, with a 52v or 48v battery.
1.5 miles - open area with 10-12 mph headwind common.
I was thinking about a front wheel 500W dd motor (or rear wheel would be better?) and a 15ah battery. Will this be enough to get me home at average speed of 20Mph with minor pedaling (don't want to get sweaty)?
Keep in mind that maintaining 20MPH against a 10-12mph headwind means the bike must be capable of 30-32MPH, which takes a lot more power than 20MPH does, and will eat up your range faster. If you don't need to maintain 20MPH while in the headwind or hill zones, it won't take nearly as much power, or use up nearly as much range.
If you have to have an average of 20MPH and you ride in traffic, you're going to have to go significantly faster than that for your cruising speeds, especially if you have to go uphill slower, or against hte headwinds slower, or if you can't accelerate quickly (or take your time accelerating). You might have to go 30MPH (or more) to get an average of 20. (I have to go 20MPH to maintain an average of 13-14MPH in many places here in Phoenix traffic).
If you're always on open roads with no stops and no traffic, and can quickly get up to speed and maintain it, you may only need to go 22-25MPH to average 20. (when I'm on streets with no traffic and few stops, I can average 16-17MPH while only going 20 max).
How much battery Wh you actually need will be determined by the amount of power you use, by the Wh/mile your trip will require. The higher the voltage battery, the more Wh you get for the same Ah.
Most of my regular bicycle type ebikes have taken around 20wh/mile for a 48V-52V battery, for riding at 20MPH top speed, averages as noted above. But I'm riding entirely on the flats, with little wind, though there are usually a lot of stops and starts.
So at 20wh/mile, needing to go 24 miles, and adding in a few miles of range for both detours or worse winds than expected, and aging of the pack reducing it's capacity over time, call it 30 miles total range, is 30 miles x 20 wh/mile = 600wh. Assuming a 52v pack (14s lithium) then 600 wh / 52v = 11 Ah.
So if you are not using more than 20wh/mile, that 15Ah pack would work fine.
However, I expect you'll use more than 20wh/mile because of the faster speeds you need to go to maintain 20MPH average.
Front or rear wont' really make that much difference in most cases:
--front is usually easier to install (and remove when tire changes/etc are needed)
--front may affect suspension more, depending on design and quality of suspension and bike.
--rear may mean changing out shifters/derailers to match the new freewheel type (if it doesn't match your existing one).
--both need torque arms to ensure no axle spinout.
etc. There's threads about "front vs rear" hubmotors with a lot of discussion about the pros and cons of each.
