Help! Looking for advice: Conversion kit for Surly Big Dummy

[pkht]

Hi all,

Long time lurker, first time poster. I'm looking for some assistance in trying to choose an ebike kit for my cargo bike. I'm very new to ebikes, so trying to learn as much as I can.

Some background: I have a Surly Big Dummy that will shortly be pressed into school run and commuting duties. I’m a pretty fit and experienced cyclist. My commute is 23km in each direction including a slight diversion for school drop off. The big dummy is a great cargo bike, but is very heavy, has quite fat MTB tyres, and needs a lot of human power to get up to speed and up hills. So I’m looking for something to add assistance, so it feels more like my normal bike. I’m basically looking for something to add it’s wattage to mine. My typical cruising output would be around 120-175W.

Here are some priorities I’m looking for:

• It must be road legal, so 250W max I guess.
• I’d like to keep the base function of the bike. So whatever kit it is, I’d like to keep all my existing gears (3 x 10) and still be able to ride it normally without electric power if I wanted to.
• It currently has cable disc brakes, but I’d be looking to upgrade these to hydraulic in the not-too-distant-future. Does this affect the power cut-off methods?
• It has an external bottom bracket, but I would still like to have pedal assist (rather than rely on a throttle).
• Max weight, including bike, rider and human cargo will be in the region of 120-150kg. Take off about 20kg when I'm not carrying the little one.
• Ideally, range would cover the full commute, there and back, so 50km. But it would be possible to charge at work.

What I’ve looked at so far:

• Those Bafang mid drive kits. I don’t like these as it seems remove too many gears, and doesn’t seem to allow it to be used as a proper bike. I could be wrong?
• Cytronex C1 kit - I quite like this, in terms of it’s simplicity, lightweight and minimal impact on the bike. But it seems quite expensive. Also probable range is quite low.
• Dillinger kit - Again, looks good. But pedal assist is only suitable for internal BB. Price seems reasonable.
• Woosh. Not looked into this too much yet. Looks like I would still have the BB/pedal assist problem and it would replace my brake levers. Not sure it has a hydraulic brake option. But I will be getting in touch with them to see what they recommend.

I’m leaning towards front hub systems, since the back wheel needs to support a lot of weight, and mid drive systems will remove the triple crankset I have available for normal (non assisted) riding. But I'm open to suggestions, or resources where I can learn a bit more.

Based in the Bristol area if that affects anything.

Many thanks.

 

[Woosh]

Woosh. Not looked into this too much yet. Looks like I would still have the BB/pedal assist problem and it would replace my brake levers. Not sure it has a hydraulic brake option. But I will be getting in touch with them to see what they recommend.

you don't have to install the sensored brake levers or hidden wire brake sensors if you don't install the throttle.
they are only needed in case the throttle gets stuck.

 

[vfr400]

I can't see any problems in fitting any kit to that bike. You could use a front or rear hub-motor, but my preference would be for a rear one because you get less noise, better traction and better handling. Personally, I prefer 48v to 36v because it gives more torque for the same current, which can be handy on very steep hills and is safer for the motor.

There is no legal limit on the current or power that you put into the motor. The 250w limit is on the "rating" of the motor, which is pretty well meaningless. As long as it's stamped, marked or listed as 250w, it's OK.

Brake switches aren't really necessary if you get the right motor controller. you need one that has a very fast response time to the pedal sensor. Unfortunately most suppliers don't know about that so it's a lottery unless you stick to what's known by users on the forum. I recommend KT controllers that you can buy individually or you get them with Yosepower kits, which are very good.

There are two types of rear motor, which you choose according to what type of gears you have. Cassette motors (usually with a C in the designation) have the spline for free-hub gears and freewheel or normal motors have the threaded boss for freewheel gears.

You have a large triangle, so plenty of space for a Dolphin (also called 09) or Shark (also called 08 or Hailong), or even a Whale battery if you want the extra capacity. You should be able to do the return trip with 600Wh without having to pedal hard.

The pedal sensor isn't a problem. they all work the same and don't cost much. If you have an ordinary 8 or 10 magnet type, you remove the sensor from its bracket (one or two screws) and flip it to the other side. There's normally a joggle in the bracket that reaches backwards. The idea of flipping it is to make it reach forward over the BB bearing holder. If the screw holes are asymmetric, you have to re-drill them. There are loads of other solutions for fitting pedal sensors, but be careful of buying special ones because you can get compatibility issues. It's best to stick with systems that are known to work.

The loss of chain-rings with a crank-drive motor isn't really much of a problem because you don't need all those gears when you have a motor. Generally, crank motors aren't as reliable as hub-motors and they don't give you such a pleasant ride, but many people have them and think that they're great.

 

[Nealh]

The Yose hub is quite good sadly 48v ones are thin on the ground, a better hub imv is the 48v Akiema 128C from BMSB. They are a bit lighter and smaller then the Bafang/8fun bpm/cst.

 

[Woosh]

take a look at this 48V SWX02 kit, it's road legal and has excellent torque:

http://wooshbikes.co.uk/cart/#/product/uid-188-swx02-48v12ah/bafang-swx02-48v-250w-rear-hub-kit-with-48v-12ah-battery

 

[pkht]

take a look at this 48V SWX02 kit, it's road legal and has excellent torque:

http://wooshbikes.co.uk/cart/#/product/uid-188-swx02-48v12ah/bafang-swx02-48v-250w-rear-hub-kit-with-48v-12ah-battery

Thanks. Looks pretty good, couple of questions.

- Is there a version that would support a 10sp shimano cassette (freehub body)?
- Is it possible to get a hollowtech PAS with this kit?

 

[Woosh]

- Is there a version that would support a 10sp shimano cassette (freehub body)?

I only have 8-speed freewheels in stock.
The Sunrace 10-speed freewheel is quite expensive.
Alternatively, I will have the XF08C which has the freehub back in stock next month.

- Is it possible to get a hollowtech PAS with this kit?

yes.

 

[pkht]

Alternatively, I will have the XF08C which has the freehub back in stock next month.

I was just looking at that. I can wait a month no probs. I will email you directly I think.

I see from the manual that you can adapt the brake sensors onto hydraulic levers with just the sensor and a magnet. Is this a separate item, or is it possible just to remove the sensor and magnet from the supplied levers and install them on the hydraulic ones?

 

[Woosh]

is it possible just to remove the sensor and magnet from the supplied levers and install them on the hydraulic ones?

yes, but it's fiddly to do that because the switch used inside the levers are mechanical instead of magnetic.
For bikes with hydraulic brakes, The usual method is to fit hydraulic brake sensors.
http://wooshbikes.co.uk/cart/#/product/uid-196-hdbs-red/pair-of-hydraulic-brake-sensors-for-hub-kits
you only need the brake sensors if you fit the supplied throttle, in case the throttle gets jammed. A simpler method is to use a motocycle kill switch for such an event.

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