New Commuter Build

[Michael Jacobs]

Newbie here, completed a new build 3 weeks ago and have ridden to work 5 times so far. Some observations and questions:
The build: Surley LHT, 10 speed (11,12,13,14,15,17,19,21,24,28), BBSHD, 5 PAS, Luna Eclipse 42T, 52v-13ah Shark Pack.
The commute: 16 miles one way, 4 decent hills the longest being 1.6 miles. Before the build it would take me about 70 minutes, now I can do it in 40 minutes! What a blast! I can now ride up the hills at 18-21 mph instead of 9-10 mph. On the flats I'm going 28-31 mph. On the first commute I intentionally did not charge the battery at work to see what kind of milage I could get out of a charge. Lost power at about 29 total miles, does this seem about right? Thought I would get a little more. On the hills I'm ussually in PAS 5, 15t rear. On the flats PAS 5, 11t, and I can barely keep up with the motor. Would I be better off with a 50-52t chainring? The best chain line is in the 15t or 17t. In the current set up I live from 11t to 15t with gear inches from 99.3-72.8. With a 52 chainring, I could get a little bit wider range of gear inches using 13t-21t (104.0-64.4) and have an overall better chain line with the 5 gears. It would also give me 2 more gears for the flats and 2 gears for extreme hills.
Gear inches:
42 chainring: 11-28(99.3,91.0,84.0,78.0,72.8,64.2,57.5,52.0,45.5,39.0)
52 chainring: 11-28(122.9,112.7,104.0,96.6,90.1,79.5,71.2,64.4,56.3,48.3)
Any flaws to my logic? Any issues that I'm over looking in going with a 52t chainring?
I'd post pictures of the build, but I can't figure out how. Help with this is appreciated as well!
Thanks in advance for any advice.
Michael

 

[George S.]

With the BBS02 a 52t chainring was asking for trouble in hill country. You needed to keep that motor spinning or you could do damage. The BBSHD is much more durable so just use climbing gears to the extent you can.

The 29 miles sounds about right. You are moving at speeds that chew through a battery very fast, maybe 800 watts or more. Better to charge at both ends or use two batteries. The harder you push a pack, the quicker it will lose enough capacity to be a problem.

You have that set up as a racing bike, apparently, with drop bars. Very few people have done that. Brakes OK?

 

[Douglas Ruby]

I am not working with a mid-drive, but with a Specialized Turbo. I re-geared so from a 48T, 11-32 to a 44T, 11-36. Thus my gear range went from 42" - 122" to 34" - 112". My bike has much less torque than yours and is not pulling through the driveline which makes the chain line less of an issue. Further, I have no option for a throttle mode at speeds above 12 mph.

I would gear your bike so that you can "use" all of the first 9 gears with the 10th gear (11 tooth rear) reserved for descents or extreme tail wind. That said, I would suggest either a 46T or 48T drive sprocket. The 46T would give you a speed of 29.4 mph at a cadence of 90 rpm and a 48T would give you a speed of 30.4 mph. I believe the Bafang can run up to a cadence of 130 rpm, but that is not usually sustainable by a recreational cyclist. If you are comfortable sustaining a cadence of 100 rpm, I would go with the 48T.

If you max out the bike in throttle mode, (say 120 rpm), you could be doing 35-40 mph in 8-10 gear.

 

[Michael Jacobs]

With the BBS02 a 52t chainring was asking for trouble in hill country. You needed to keep that motor spinning or you could do damage. The BBSHD is much more durable so just use climbing gears to the extent you can.

The 29 miles sounds about right. You are moving at speeds that chew through a battery very fast, maybe 800 watts or more. Better to charge at both ends or use two batteries. The harder you push a pack, the quicker it will lose enough capacity to be a problem.

You have that set up as a racing bike, apparently, with drop bars. Very few people have done that. Brakes OK?

Brakes seem fine, the bike really slows down when I stop pedaling. The thought with the gearing is that I don't even use the top 5 gears so if I had a larger chainring I would use a larger range in the back and a more centered range. I think I can still keep a good cadence on the hills with a 52-21 vs the 42-15 I'm using now. Any idea when Eric at Luna is going to make a 52 Eclipse?

 

[George S.]

Going by this, I would say Eric thinks the 46 is too high. He just brought out a 30t, for off road. Paul at EM3ev has the 42t Bling, plus the stock one. Given that it's being sold into the fatbike, snow and trail market, it may be a while.

https://www.electricbike.com/battle-of-the-bafang-bbshd-chain-rings/

That build seems to work. They say using the drops is 15% more efficient, especially at higher speeds.

 

[JoePah]

Id stay away from the 52T on a mid drive... It will load your battery on the hills causing voltage sag....Better to pedal a little faster with a lower gear ratio.

 

[Michael Jacobs]

Id stay away from the 52T on a mid drive... It will load your battery on the hills causing voltage sag....Better to pedal a little faster with a lower gear ratio.

I don't think it would be a lower ratio. If you look at the gear inch numbers at the top of the post a 42t-15t equals 72.8 gear inches(5.4 gear ratio). This is the current combination that I'm using on the hills. If I switch to a 52t chain ring and use the 19t on the rear it's 71.2 gear inches(5.3 gear ratio). Aren't these basically the same? It seems like I would be able to achieve the same cadence in either of these combinations.

 

[JoePah]

I don't think it would be a lower ratio. If you look at the gear inch numbers at the top of the post a 42t-15t equals 72.8 gear inches(5.4 gear ratio). This is the current combination that I'm using on the hills. If I switch to a 52t chain ring and use the 19t on the rear it's 71.2 gear inches(5.3 gear ratio). Aren't these basically the same? It seems like I would be able to achieve the same cadence in either of these combinations.

The problem with the 52T is that you will tend to use it with the smallest freewheel gear.. Trust me that's what most ebike riders do. And that will load up your motor and battery more than it was intended.

 

[Michael Jacobs]

The problem with the 52T is that you will tend to use it with the smallest freewheel gear.. Trust me that's what most ebike riders do. And that will load up your motor and battery more than it was intended.

If I use the 52/11 on the flats and still maintain a cadence around 90, does this still load up the battery?

 

[Douglas Ruby]

52-11 @ 90rpm w/26" tires (your nominal based on earlier gear inch table) is around 33 mph. I would expect that the Bafang is putting out a goodly amount of power at that speed and RPM. The issue will be that shifting with a mid drive under load is MUCH harder. If you have a tendency to avoid shifting and stay in the 52-11 and then slow down, the load will become much higher as the bike tries to accelerate. I would still aim for a high of around 108" 112" gear and then get keep a lower 1st gear for climbing. A 123" top gear is VERY high.