Advice for Surly ECR conversion for some assist

Hello,

I've been following rabbit holes on various sites and forums and would like to pick some other brains for advice.

I have a Surly ECR that I would like to add a front hub motor. Why? Well I want the electric power components to be easy to remove for bikepacking trips. I'm mostly looking for some assist on some uphills (nothing crazy less than 1/10th mile and maybe 6-8% grade) and to have AWD for snow in the shoulder seasons. I run Dirt wizards with added studs for the winter and Extraterrestrials in the summer for commuting.

I'm 200lbs and carry 10-30lbs of stuff with me back and forth to work depending on the day.

I mostly want to pedal for exercise but want some assist on moderate hills and maybe to help out on rainy days to make the commute faster.

Budget is $800-$1200

I'e been eyeing the LunaCycle mac motor 12t kit (https://lunacycle.com/mac-motor-asi-high-performance-hub-kit/) but it may be overpowered for my actual needs. I'd be happy to down-tune the wattage if that's possible with their asi bac 800 controller.

I've already purchased two torque arms from ebikes.ca (http://www.ebikes.ca/shop/electric-bicycle-parts/torque-arms/torqarm-v2.html)

I have a velocity dually rim (29x45mm) with 36 spoke holes ordered to fit the vast majority of font hub motor spoke requirements.

Looking at schwalbe big apple for my new front tire or running another surly ET 29x2.5

Please let me know if I've forgetting or overlooking anything. Thanks!

A 29+ bike is the single worst choice for use with a hub motor. It keeps the motor at the lowest possible speed, but demands the highest possible torque to propel the bike. But given that, your prospective MAC 12t is probably the best choice of hub motor to drive a 29+ bike.

If you only want a push, and don't want the motor as full-time sole propulsion, you can also consider a Q128 motor-- the 201rpm version-- which would reduce the weight and cost of your project.

What battery are you going to use? The battery more than anything determines the capabilities of your system.

Thank you for your insight. The battery is actually where I'm the most unsure. I was looking that lunacycles wolf pack... but honestly that might be overkill. I know it will be the single largest expenditure for my system.

Major overkill and maybe not available. Go to the MAC seller in business building batteries and MAC wheels long before Luna. EM3 ev. Mac experts, best built batteries!

tomjasz said:

Major overkill and maybe not available. Go to the MAC seller in business building batteries and MAC wheels long before Luna. EM3 ev. Mac experts, best built batteries!

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Thanks for the recommendation! Any suggested setup of their kits for my plans? One of the 36v sets?

Is the Grin 8T all-axle hub a possibility?

Fellow noob here, I had similar requirements as you and just bought the 9C hubmotor kit from Grin (48v, 1000w front hub).

I think a lot of the concern about a hub motor’s inefficiency for larger wheels like yours can be mitigated by the fact that you intend to pedal, a lot. Someone correct me if I’m wrong, but if you pedal the bike manually up to about 10mph before hitting any throttle, then a lot of the heat/inefficiency can be avoided, correct?

Keep us posted!

81forest said:

Someone correct me if I’m wrong, but if you pedal the bike manually up to about 10mph before hitting any throttle, then a lot of the heat/inefficiency can be avoided, correct?

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While that's true to some degree, it still leaves two problems. First, a hub motor's torque is divided by wheel size to determine tractive force. There's no getting around the bigger wheel providing less thrust to push the bike. Second, you want the motor to be able to cruise in its efficient speed range of 50-80% of free speed. Using lower voltage lowers the free speed, which brings that efficient range within closer reach. But it also reduces the power available to accelerate up to and maintain such speed. You can wind up in a situation where the motor bogs down to an inefficient speed range unless you pedal vigorously.

The moral of the story is that you have to choose carefully among motor windings, battery voltage, and controller amp ratings to match wheel size, road speed, power required and torque available. The smaller the wheel, the more forgiving these factors are.

My first hub motor bike was a 29er, with a big direct drive front hub running on 36V. It worked adequately, cruising at about 22-23mph compared to 28mph free speed. But I wouldn't do it that way again. Its acceleration and climbing were needlessly lazy for a bike that could draw up to 1400W of electrical power.

Good info Chalo!

I find with 48V in 4T direct drive winding on 26" that its adequate for take off torque, but sometimes I like thump stumping torque on take off, and a better hill climbing experience. The only way to do it is to go to a smaller wheel diameter of 22-24" then of course if I want to keep my speeds the same, I have to up the voltage to say 60 or 72V. Which is my next step, laced into a 16x1.60 in Shinko tire. Sure it'd be heavy.

81forest said:

Someone correct me if I’m wrong, but if you pedal the bike manually up to about 10mph before hitting any throttle, then a lot of the heat/inefficiency can be avoided, correct?

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That may be true, but in my experience it isn't a particularly enjoyable way to ride. Also, it doesn't take much time to get from zero to 10 mph. So I really don't care a whole lot about that inefficiency. Maybe I'll make up for it a bit with a somewhat longer coast to a stop.

Brisk acceleration from a stop without killing your legs is one of the major benefits of of having an ebike IMO. So I'd only give that up in special circumstances and not in regular day-to-day riding.