Light, fast and cheap urban commuter.

I am thinking un an urban commuter, based on and old steel frame street bike i bought really cheap (70€). I am thinking in a small rear hub motor (XF08), paired with 6 fet sinewave controller and 14S battery. Some of the objectives are it to be stealth, light and secure to leave on the street without any parts easily stolen. I would like to commute at about 40kmh pedaling without hills, and 25kmh with 7-8% hills. My goal is to stay below the 15kg the whole bike including battery.

I would appreciate some help to improve the idea as much as possible.

That is the bike:



Here is the parts I plan to use:

- Rear small geared hub (Mxus XF08 or similar)
- 6 fet sinewave controller
- 14s battery in a box in the frame, with LCD and buttons on it (lights, PAS level, on/off, etc...)
- No throttle
- No display on handbard
- PAS activated
- Front and rear light connected directly to the battery

I also plan to upgrade some part of the bike:
- Handbar (something more commuter instead of the street bike style)
- Brakes levers with motor-off option.
- Maybe fiber carbon fork, handbar and seatpost to take some weigh out.
- Tyres for something wider for a more secure commuting.

The most important part of the ebike will be the battery case, located in the lowest part of the frame, where I plan to fit the battery, controller and all the switches needed. It should be water resistant and secure locked so I can leave the bike on the street.

My doubts are:
- Can the XF08 hold 500-750w or would the planetary gears self destruct? I will pedal always, and I don't expect that power to be continuous. Maybe I can add a temp probe to the motor to check the temperature.
- Battery configuration, 14s? 13s? 10s?
- Battery case material: crystal fiber, aluminium, steel?

Any other idea, more than welcome.

looks like a good idea to me. I would love to build a bike like that off of a frame like yours. Take a look at the bikes in my signature for some of my experience.

my road bike goes 25 miles, at 25mph, and weighs 25lbs (plus 4lbs for a battery). sound similar to what you are looking to build.

Pick two of the three? Light, slow and cheap is easy.

Whether you fry a small motor like that running 48v,, which likely means you can pull up to 1000w, depends a lot on how heavy you are, do you really pedal hard, and how long that hill is.

36v,, or cutting down to 15 amps max,, both should work,, but there went fast.

Slightly heavier 500w rated motor will work for a bit less light, fast, and well,, is any e bike really cheap? If you really want the light and fast,, the larger geared motors are only about 2 pounds heavier than typical smaller ones. But they can get you up the hill a lot better, able to handle more watts.

If you reallllly pedal, and you weigh under 150 pounds, then the small motor pushed all the way to 1000w will work for you. but if you weigh 250,,, you might need to consider the smaller motor expendable. Cheap enough to take that approach.

Well, I am 90kg, which is near to 200 lbs. I plan to pedal, as I said, nearly legal bike (only the final power will be ilegal), so no thottle, only PAS mode to make it work.
Talking about the speed, I should say that "fast" in this proyect would be something near to 40kmh (25mph), because it would be a bike to use on the city, where you can't go any faster becoming dangerous to pedestrians and other bikers. My idea was to be in the 500-750w range, as I have had a XF07 frontal small geared motor running at 24v 20A (first ebike I built to myself) and it worked during 2 complete years without problems, till the fork broke down (was aluminium type).


I recently knew about the Xiongda 2 speed motor. It feels as a good option at 3.3kg instead of the 2.7kg of the XF08 with that 2 speed feature that would help a lot pushing some more watts in the up-hills parts of the travel without forcing it too much. But I have read that some people had problems with this motor and broke their planetary gears twice. However, I think it should be easy to fit all the kit in the battery frame box with some hand work.

Fast would be a relative term. 25 mph is not usually called fast in the USA. So I was thinking you were aiming for 1000w or more, and 30 mph.

I'd say most of those tiny motors can easily handle 750w,, provided you are not a huge guy trying to avoid pedaling up hills at all.

So go for it, you can get all three, if max speed possible with 750w is all you want.

light, moderately fast, and cheap compared to 2000w setups, is definitely possible.

dogman dan said:

Fast would be a relative term. 25 mph is not usually called fast in the USA. So I was thinking you were aiming for 1000w or more, and 30 mph.

I'd say most of those tiny motors can easily handle 750w,, provided you are not a huge guy trying to avoid pedaling up hills at all.

So go for it, you can get all three, if max speed possible with 750w is all you want.

light, moderately fast, and cheap compared to 2000w setups, is definitely possible.

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Yeah, my bad explaining as people in this forum tend to think on 3kw as a normal bike. We can't be street legal in Europe if the motor assists over 25kmh and over 250w. I don't plan to be that legal, but don't need a moto neither. I got a Cromotor running at 6kw (13kw peak) and I will use that bike on weekends, while the "light" the rest of the days.

I'll try the Mxus XF08 first at 750w peak (48V 15A). If the motor breaks down, I'll go for the Xiongda 2 speed.

Just to learn, dou you know any small geared hub motor with helical gears? I have read about how they improve the heavy duty resistance (750w continuos for this small motors).

Sr.Agaporni said:

Yeah, my bad explaining as people in this forum tend to think on 3kw as a normal bike.

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LOL, you got that right. Although there does seem to be a small but growing group of the lighter works too e-bikers here. I think you are on the right track. 48v and 15amps should get you around 25mph, if you have the right winding (just over 300rpm no load speed).

Sr.Agaporni said:

- Handbar (something more commuter instead of the street bike style)

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Are you planning on swapping the drop bars for conventional flat bars? If so be careful about it. There shouldn't be any mechanical or safety issues with it if it's done properly but bikes intended for drop bars tend to have different geometry than flat bars and vice versa. You might find you need an unusually short or long stem to compensate for example. You would also need short pull (cantilever) brake levers for the flat bars to match the cable pull of the existing brakes. I've actually done this conversion the other way (flat bar frame to drops) and it can be made to work fine as long as you keep these things in mind.

- Brakes levers with motor-off option.

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I'd advise skipping this and going for a hidden wire brake sensor, it sits inline with the brake cable and does the job without affecting the levers at all.

- Maybe fiber carbon fork, handbar and seatpost to take some weigh out.

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I don't think it would be worth the effort or cost. You're not going to shed substantial amounts of weight off the bike when it's electrified by doing this and carbon tends to be a bit of a thief magnet. Carbon parts also aren't ideal for durability on a commuter bike, carbon can be catastrophically damaged by hard impacts that a steel part would shrug off without issue.

Tyres for something wider for a more secure commuting.

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Absolutely right, I'd go for the widest tyres you can fit. Nothing will let a good bike down more than sketchy tires, be prepared to spend to get solid tyres but they will pay for themselves over and over in the long run. I'm much more familiar with 26" tyres than 700c though so I can't offer much in the way of specific suggestions except for the schwalbe marathon series.

Hello Sr Agaporni,

You might want to read this forum I started since we are looking for very similar bikes. On page 7 i finaly buy a bike (I bought it Saturday) and now in the process of looking at a Q128 or possibly the MXUS. There is a lot of info in this thread that may be applicable to your build as well.

https://endless-sphere.com/forums/viewtopic.php?f=3&t=83886\

Marc

addicted2climbing said:

Hello Sr Agaporni,

You might want to read this forum I started since we are looking for very similar bikes. On page 7 i finaly buy a bike (I bought it Saturday) and now in the process of looking at a Q128 or possibly the MXUS. There is a lot of info in this thread that may be applicable to your build as well.

https://endless-sphere.com/forums/viewtopic.php?f=3&t=83886\

Marc

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Hey Marc. Thanks for the link, I will check.

I am thinking in doing a comparisson between "small" geared hubs. At the moment I am into the 3kg range, so the Mxus is my prefered pick to achive the lowest total weight:
- Mxus XF08 (rear, 250w nominal): 2,7kg
- Bafang SWXH (rear, 250W ): 3kg
- Q128h (rear, 350w): 3kg (not confirmed).
- Xiongda 2 speed (rear, 350w nominal): 3,3Kg
- Mxus XF15R (rear, 350w nominal): 4.2kg
- Bafang BPM 500w (rear, 500w nominal): 4,3kg
- Bafang BPM2 500w (rear, 500w nominal): 5kg

AMC11 said:

Are you planning on swapping the drop bars for conventional flat bars? If so be careful about it. There shouldn't be any mechanical or safety issues with it if it's done properly but bikes intended for drop bars tend to have different geometry than flat bars and vice versa. You might find you need an unusually short or long stem to compensate for example. You would also need short pull (cantilever) brake levers for the flat bars to match the cable pull of the existing brakes. I've actually done this conversion the other way (flat bar frame to drops) and it can be made to work fine as long as you keep these things in mind.
.

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I have a bike that is sold in flat and drop bar configurations. Its not so much the frame and the geometry that is the problem. The key is the brakes, and I think you described that well.

chas58 said:

AMC11 said:

Are you planning on swapping the drop bars for conventional flat bars? If so be careful about it. There shouldn't be any mechanical or safety issues with it if it's done properly but bikes intended for drop bars tend to have different geometry than flat bars and vice versa. You might find you need an unusually short or long stem to compensate for example. You would also need short pull (cantilever) brake levers for the flat bars to match the cable pull of the existing brakes. I've actually done this conversion the other way (flat bar frame to drops) and it can be made to work fine as long as you keep these things in mind.
.

Click to expand...

I have a bike that is sold in flat and drop bar configurations. Its not so much the frame and the geometry that is the problem. The key is the brakes, and I think you described that well.

Click to expand...

As someone who as done drop bars on an ebike... BB7's come in mechanical drop bar disk brakes for road levers. The other option ( more expensive ) is the TRP hydraulic brakes mated to cable operated drop bars. I currently run BB7 Road mated to a shimano sora drop bar setup which is OK, but it doesnt compare to hydraulics by far.