E- Bike kit for Tern A7 Link
 

Essentially, I want an E-Bike kit for power to get up the occasional
hill I may have to climb when riding my Tern A7 Link folding bike
around my beautiful island of Puerto Rico. I need enough power to
help me pedal my 180lbs up any incline or hill.

Most of the time I will not be using any motor assist, so I'm
concerned about using a gearless hub motor, because I understand there
is some drag in pedaling when the motor is not engaged. I also
understand a geared motor does not have this issue, so I prefer a
geared hub motor kit for my Tern bike. Having said that, I do prefer
a front hub motor kit for ease of installation.

My Tern A7 Link folding bike has 20 inch tires. I have a Shimano
MF-TZ21, 14-28T, 7 speed freewheel. The rear frame dropouts are
139.7mm wide (equal to 5.5 inches) and the front fork dropouts are
76.2mm (equal to 3 inches.

Which E- Bike kits would you suggest for my needs?

Your spacing is actually 135 rear and 74 front. Those are what you'll need to keep in mind when looking for motors. As for using a front motor, you should consider two things... 1: It will likely void any warranty you have since the fork is for probably not designed for that use in mind. 2: Even if you don't care about the warranty, depending on how much torque you're generating on the fork, you're trusting that the fork can take it. Up to you if that risk is worth it. Personally I wouldn't take that risk.
Rear motor would be a safer choice. But you say you want it to "help you up ANY incline". Well, hub motors already are at a disadvantage for hill climbing compared to mid-motors, although the smaller 20" wheel size will help in that regard. You'll need to look at motors that have enough power/torque for serious hill climbing. Grin (ebikes.ca) has a simulation program that can help you figure out which motors are capable of the inclines you're facing without overheating.
Mid-drives are more flexible when it comes to hilly terrain. Are those in consideration?
What are the laws in PR for ebike motor systems? Do you have limitations on watts or anything?

I bought my kit with those concerns in mind. As a friction drive, there is zero drag when not used as it doesn't touch the wheel. The weight is minimal so you can just leave it on the bike and ride like normal and then use when you need it. Happy to answer questions if it interests you at all. PAS and/or throttle options. Onemotor.co.

Thanks for the reply Nightdiver. Puerto Rico follows U.S. Federal law which allows a motor of up to 750 watts (1 h.p.), whose maximum speed on a paved level surface, when powered solely by such a motor while ridden by an operator who weighs 170 pounds, is less than 20 mph.” The federal law permits e-bikes to be powered by the motor alone (a “throttle-assist” e-bike), or by a combination of motor and human power (a “pedal-assist” e-bike).

I plan to focus on hub motors which are suitable for my limited budget. I am retired and have a limited income.

Bill

ebikesca has a "Brompton" kit that should suffice, but has relatively low power. (look at their simulator to get an idea of what to expect) They're very easy to deal with AFAIK, technically proficient and good CS. Their prices are high, so you might want to look at what BMS Battery, a much less reliable supplier, has to offer.

The Tern at 74mm can't accept many motors, and t wouldn't do another front drive kit anyway. The added risk of fork breakage outweighs any convenience, plus front drives tend to slip on wet surfaces. Now Grin sells a cool G10 rear motor kit for a 20" wheel, but it's like $615 w/o battery, Grin's always been too rich for me.

I've built up three 20" wheels using the Q100H motor from BMSBattery. Good motors. No problems. I bought the bare motors and put them in the rims myself. About $200-220. I didn't save any money, but feel I had better parts and a stronger wheel. The electrics came from PSWpower - motor controller , throttle, brakes, PAS, etc for $90. So we're talking $300-330 for the motor/electrics.

Looking on ebay and amazon, here's a geared motor kit on ebay.for 20" rear wheel.
https://www.ebay.com/itm/Ebike-Conve...xcXj2lsqDUGfOg

If I had to buy one though, this one from China via aliexpress.com has a controller that is much easier for a novice to wire.
https://www.aliexpress.com/item/3296...a71d7a6cE44CMF

Batteries are a different subject. Reliability , safety, and it has to fit somehow on your bike. I'm not able to tell you how to solve that problem.

I do think a 36V pack is good enough to run a folder. We can get 20 miles easily out of a 8AH pack, and I'll take on a 30 mile ride with a spare pack.
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I've had both 350w, 36V & 1200w, 52V front hub motors on steel forks (with a single torque arm) without incident (of course that doesn't guarantee they're completely safe, but I never experienced any problems). Your bike spec specifies a steel fork, so you should be safe with a front system if it satisfies your other requirements.

Thank you linberl, but the friction drive at Onemotor.co is just expensive for me.


Bill

Thanks 2old, the ebike.ca company has a stellar rep, but the prices are a bit high for me. BMSBattery has reasonable prices and I will check them out as you suggested.

Bill

Thanks Doc Wui for addressing the cost of the ebike conversion. I am a retired 66 year old living with a limited income. BMSBattery prices for motor look good for me, but did you have to modify the electrical component connectors from PSWpower to connect to motor? How was the customer service at BMSBattery?

Bill

If friction drives interest you, there is a very inexpensive one, just missing all the bells and whistles but otherwise very functional. Could be fun to try. Outrunner Rear Drive - Pe-Drives There are front and rear wheel models.

The Q100 motors use a 9 pin modular connector, along with a extension cable that terminates with 3 bullet connectors and 2x3 plug for the sensors. If they don't include the cable any more, then you have to add it. The KT-controller from PSWpower.uses the same connector. I've never communicated with BMSbattery. Bought three Q100H motors at separate times and two other motors. I hear they're hard to deal with when theu screw up an order.

You might look at this vendor. They can sell the controller with the "waterproof" connectors. Also a finished wheel. These are the same connectors used in commercial bikes and are better from an install/reliability,
AKM-100CST 36V250W Rear Hub Motor 36holes with 20/26inch/700CC wheel rim [AKM100CST 36V250W motor 26/700cc] - $119.00 : Zen Cart!, The Art of E-commerce

There's some people on the pedelecs forum in the UK that have built folders recently. Might have more recent vendor feedback,
https://www.pedelecs.co.uk/forum/for...discussion.42/



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I don't know iff you got my previous reply. I am new to Internet forums. Anyway, I saw ebike motors on front wheels made for an 83mm for. My bikes front fork is 76.2. Will the wheel made for 83mm fork fit my bike? Would I have to spread my front fork to fit the 83mm wheel?

Steel is malleable and you shouldn't have difficulty spreading it the seven or so mm. One small motor I looked at was 75 mm, but AIR it was the "expensive" Grin one.

Thanks 2old. Any special tool to spread the fork?

The "special" tool some use is a 2 X 4 (ha ha); I've only spread (or constricted) rears (hope that doesn't sound dirty); to do it well, a solid axle with nuts on the inside that you "turn out" would be my choice since it can be done equally and incrementally. Make sure you have a torque arm on the fork (even two if, but probably not, feasible). Look at endless sphere for set-ups with small hub motors (like the Q 100); I think the S06P controller can be matched with the small motors easily, but I haven't done it. My front conversions have been Dillenger (which doesn't seem to service the US like they used to) and eBikeling (which doesn't have 20" systems AFAIK).

One other thing that might factor in: AIR, Tern had front fork problems breaking with some of their bikes. If by chance you have one of those models, I wouldn't even consider a front hub system.

Thanks a lot 2old. I will check out what you have suggested. By the way, Merry Christmas.

FYI, that's not spreading it 7mm, it's 9mm since the actual fork OLD is 74mm nominal, so if you found a hub for 83mm wide (which would be a very strange width to produce for a bicycle), then you're looking at cold setting 9mm. That is quite extreme for a DIY situation, especially with such relatively short lengths of tubing. If you're committed to using a front hub motor on your stock fork, then get a 74mm front hub.

Thanks nightdiver. After doing some research I believe my best and safest bet is to get a rear wheel hub motor. My Tern bike limits me as to the availability of front hub motors, because the 74mm front fork is not as common as what seems to be the standard 100mm front fork in the bike world. I am also concerned about the durability of the front fork with a front hub motor mounted. I have read some horror stories from bicyclists where the front fork has failed under the stress of the front fork hub motor. I may not happen to me, but I prefer not to take a chance.

Great thinking! Kudos for taking the safe route even if it isn't your ideal solution.