Converting a Boardman 8.6 hybrid

[mtjnr]

Currently exploring different options for my first ebike. Thought about getting a Boardman 8.6 and adding a tongsheng mid drive. Don't want to spend more than 500 on the donor bike, looking for light weight, good brakes and a bit of an all rounder for commute and weekend rides. My question is would the tongsheng mid drive work with this bike or would there be any issues?

https://www.halfords.com/bikes/hybr...-bike-2021---green---s-m-l-frames-366230.html

 

[bonzobanana]

I'm sure the Tongsheng will work fine with it. I guess the issues are if you were close to the maximum weight limits of the Boardman which I think is 120kg rider weight or you were a very strong cyclist then the extra stresses of the motor could be an issue. The Tongsheng peaks at about 80Nm and the average rider is between 20-50Nm output depending on age and fitness. I'm personally more of a fan of hub motors for ebikes mainly used on the road because of their huge benefits in reliability, simplicity and extending the life of the drivetrain well beyond of that of a normal bicycle. So safer for longer rides. However apart from a few cables needing re-routing I can't see an issue with that Boardman bike. The hydraulic brakes means you'd have to buy the little stick on hydraulic brake lever sensor wires if you wanted the brake levers to cut off the motor but with a torque sensor this is less of a requirement as when you stop pedalling the motor will stop however it will stop quicker with brake lever sensors.

The Boardman is a light bike at 11.2kg for its price point but why do you need a light bike for a ebike project when the motor will easily compensate for a 100kg rider let alone a couple kg in the bike itself. The bike will not be super comfortable with a alloy fork.

Tongsheng motors need a high discharge rate from the battery to generate that 80Nm of peak torque. You are looking at somewhere around 18A at 36V or 48V, at least over 600W output. Mid-drives take huge current to generate their high torque. You need a pretty heavy weight battery to allow for that current output. Maybe something that comfortably does 20-25A for safety and to prevent fires. That's a heavy battery typically. You are probably looking at a 48V 12Ah or 36V 15Ah minimum battery. Despite mid-drives making up only niche of all ebikes sold they have a disproportionate number of ebike battery fires because too many underspec the battery for mid-drive motor kits. Better to use a stronger heavier cheaper bike and give yourself more money for the battery in my opinion.

One other thing is the current gearing on the Boardman. I think the Tongsheng comes with a 48T front chainring typically and the Boardman has a 36T largest cog on the rear so your peak torque would be 60Nm (36/48 x 80) but you have to allow for a couple Nm lost through the chain so probably more like 58Nm which is down to higher hub motor output levels. So to get that full 80Nm peak torque you will need a larger rear cassette like a 50T rear cog to give you that 80Nm output. That's why mid-drives work best with mountain bikes because they typically have the lowest gearing.

 

[chris667]

I agree with @bonzobanana - there is little point spending out on a very light bike if you're attaching an enormous battery and motor to it.

Better to get a cheaper hybrid like this one:

https://www.halfords.com/bikes/hybr...ike-2020---grey---s-m-l-xl-frames-346126.html

Then, spend the extra money on handbuilt wheels. This bike will be hard on wheels, so it makes sense to build stronger ones. Go for a cassette hub, 36 spokes and Andra rims. A dynamo hub front wheel would mean you had lights even if your batteries were out.

And mudguards. Hub motors put the electric bit of the bike in a place that attracts muck, so a mudguard with a long flap is useful.

I also agree that a hub motor is probably a better choice if it's just a "commuting" bike. There's less to go wrong.

 

[Jameshow]

Might the mid drive damage the light tubing if attached to it. DAMHIK! (Child seat on scottcx!)

 

[chris667]

Might the mid drive damage the light tubing if attached to it. DAMHIK! (Child seat on scottcx!)

I doubt it, but my feeling is there's little advantage when you consider the potential weight saving is so little. Better to make it a bit stronger.

I like the subway because it has a steel fork. I know ali forks are probably fine too, but it strikes me steel is a better material for this application.

You'd know for sure when the alu fork cracks and your chin is hurtling towards the pavement.

 

[cyberknight]

daft question apart from the fun of building the bike the cost of the bike and kit is coming close to just buying an e bike with warranty ?

 

[CXRAndy]

Currently exploring different options for my first ebike. Thought about getting a Boardman 8.6 and adding a tongsheng mid drive. Don't want to spend more than 500 on the donor bike, looking for light weight, good brakes and a bit of an all rounder for commute and weekend rides. My question is would the tongsheng mid drive work with this bike or would there be any issues?

https://www.halfords.com/bikes/hybr...-bike-2021---green---s-m-l-frames-366230.html

Yes it will, I'm doing this conversion for my daughters bike which is a HYB 8.6. The only issue is re routing and probably fitting outer cable covers to the derailleur and delete the front derailleur.

Once my motor arrives from the States.

 

[CXRAndy]

daft question apart from the fun of building the bike the cost of the bike and kit is coming close to just buying an e bike with warranty ?

The TSDZ2 is a great motor, with torque sensor. Super smooth delivery (especially if you get open firmware version). Parts are plentiful, no expensive proprietary markups. Works with variety of battery types and voltage (open firmware version)

Bike can returned to stock and motor fitted to another donor bike

 

[Pale Rider]

Torque sensor crank drives give a much more natural cycling feel, which an existing cyclist will certainly appreciate.

Less relevant to a non-cyclist whose only concern will be that the ruddy thing helps up hills.

Apparently, some hub motors now come paired with a controller which mimics torque sensing.

I'm not sure how effective that is, but it's worth considering if the OP goes the hub route.

 

[CXRAndy]

Currently exploring different options for my first ebike. Thought about getting a Boardman 8.6 and adding a tongsheng mid drive. Don't want to spend more than 500 on the donor bike, looking for light weight, good brakes and a bit of an all rounder for commute and weekend rides. My question is would the tongsheng mid drive work with this bike or would there be any issues?

https://www.halfords.com/bikes/hybr...-bike-2021---green---s-m-l-frames-366230.html

Yes it will, I'm doing this conversion for my daughters bike which is a HYB 8.6. The only issue is re routing and probably fitting outer cable covers to the derailleur and delete the front derailleur.

Once my motor arrives from the States.

 

[CXRAndy]

I'm sure the Tongsheng will work fine with it. I guess the issues are if you were close to the maximum weight limits of the Boardman which I think is 120kg rider weight or you were a very strong cyclist then the extra stresses of the motor could be an issue. The Tongsheng peaks at about 80Nm and the average rider is between 20-50Nm output depending on age and fitness. I'm personally more of a fan of hub motors for ebikes mainly used on the road because of their huge benefits in reliability, simplicity and extending the life of the drivetrain well beyond of that of a normal bicycle. So safer for longer rides. However apart from a few cables needing re-routing I can't see an issue with that Boardman bike. The hydraulic brakes means you'd have to buy the little stick on hydraulic brake lever sensor wires if you wanted the brake levers to cut off the motor but with a torque sensor this is less of a requirement as when you stop pedalling the motor will stop however it will stop quicker with brake lever sensors.

The Boardman is a light bike at 11.2kg for its price point but why do you need a light bike for a ebike project when the motor will easily compensate for a 100kg rider let alone a couple kg in the bike itself. The bike will not be super comfortable with a alloy fork.

Tongsheng motors need a high discharge rate from the battery to generate that 80Nm of peak torque. You are looking at somewhere around 18A at 36V or 48V, at least over 600W output. Mid-drives take huge current to generate their high torque. You need a pretty heavy weight battery to allow for that current output. Maybe something that comfortably does 20-25A for safety and to prevent fires. That's a heavy battery typically. You are probably looking at a 48V 12Ah or 36V 15Ah minimum battery. Despite mid-drives making up only niche of all ebikes sold they have a disproportionate number of ebike battery fires because too many underspec the battery for mid-drive motor kits. Better to use a stronger heavier cheaper bike and give yourself more money for the battery in my opinion.

One other thing is the current gearing on the Boardman. I think the Tongsheng comes with a 48T front chainring typically and the Boardman has a 36T largest cog on the rear so your peak torque would be 60Nm (36/48 x 80) but you have to allow for a couple Nm lost through the chain so probably more like 58Nm which is down to higher hub motor output levels. So to get that full 80Nm peak torque you will need a larger rear cassette like a 50T rear cog to give you that 80Nm output. That's why mid-drives work best with mountain bikes because they typically have the lowest gearing.

View attachment 694970

My wife's bike has a TSDZ2 on her shopper. The original bike is a Columbia Ladies shopper with a Shimano Nexus 8 hub gear. Mated to the Tongscheng it works perfectly, it has a 52v battery. She has plenty of gearing to get up 15% gradients with a decent cadence.

You never get near peak torque due to the gearing. First photo battery fitment, then completed in the 2nd. This was done in summer 2019, still going strong, original battery, no faults at all

 

[CXRAndy]

I'm sure the Tongsheng will work fine with it. I guess the issues are if you were close to the maximum weight limits of the Boardman which I think is 120kg rider weight or you were a very strong cyclist then the extra stresses of the motor could be an issue. The Tongsheng peaks at about 80Nm and the average rider is between 20-50Nm output depending on age and fitness. I'm personally more of a fan of hub motors for ebikes mainly used on the road because of their huge benefits in reliability, simplicity and extending the life of the drivetrain well beyond of that of a normal bicycle. So safer for longer rides. However apart from a few cables needing re-routing I can't see an issue with that Boardman bike. The hydraulic brakes means you'd have to buy the little stick on hydraulic brake lever sensor wires if you wanted the brake levers to cut off the motor but with a torque sensor this is less of a requirement as when you stop pedalling the motor will stop however it will stop quicker with brake lever sensors.

The Boardman is a light bike at 11.2kg for its price point but why do you need a light bike for a ebike project when the motor will easily compensate for a 100kg rider let alone a couple kg in the bike itself. The bike will not be super comfortable with a alloy fork.

Tongsheng motors need a high discharge rate from the battery to generate that 80Nm of peak torque. You are looking at somewhere around 18A at 36V or 48V, at least over 600W output. Mid-drives take huge current to generate their high torque. You need a pretty heavy weight battery to allow for that current output. Maybe something that comfortably does 20-25A for safety and to prevent fires. That's a heavy battery typically. You are probably looking at a 48V 12Ah or 36V 15Ah minimum battery. Despite mid-drives making up only niche of all ebikes sold they have a disproportionate number of ebike battery fires because too many underspec the battery for mid-drive motor kits. Better to use a stronger heavier cheaper bike and give yourself more money for the battery in my opinion.

One other thing is the current gearing on the Boardman. I think the Tongsheng comes with a 48T front chainring typically and the Boardman has a 36T largest cog on the rear so your peak torque would be 60Nm (36/48 x 80) but you have to allow for a couple Nm lost through the chain so probably more like 58Nm which is down to higher hub motor output levels. So to get that full 80Nm peak torque you will need a larger rear cassette like a 50T rear cog to give you that 80Nm output. That's why mid-drives work best with mountain bikes because they typically have the lowest gearing.

View attachment 694970

That is a Bafang BSHD motor. By the looks of it the wiring is terrible, same could be for battery connections.

I used XT90(90A) connectors for the battery and limited peak current to less than 10A

 

[chris667]

daft question apart from the fun of building the bike the cost of the bike and kit is coming close to just buying an e bike with warranty ?

No, not at all.

A conversion is nowhere near as expensive as a bike with similar quality parts. Even if you buy a cheap new bike!

As to warranty, there are warranties and there are warranties. I would always suggest Wooosh, I had such good service from them and I'm much more confident they'd help me if I had an issue compared to most complete ebike retailers.

 

[mtjnr]

Thanks all for the advice. Everyone seems to have a different opinion when it comes to this subject lol.

I'm also looking at the Specialized sirrus X2.0 which has steel fork instead of alloy and only a 1x drivetrain which might be more suitable with the mid drive?

If I were to go with a rear hub instead would anyone have any recommendations? Looking to keep the bike light just for lifting as I had a test drive of the crossfire e and having to lift it over a few gates wasn't much fun!

I think the factory built ebikes come with potential issues in terms of availability of parts and while a bike and tongsheng will cost c1.2k to get a bike with spec and motor as good would cost at least double of not more.

I see woosh are now doing the tongsheng with a saddle bag battery that doesn't weigh much at all and gives 50 miles. That seems ideal if true but didn't think a battery that small could give that much range?

 

[bonzobanana]

Torque sensor crank drives give a much more natural cycling feel, which an existing cyclist will certainly appreciate.

Less relevant to a non-cyclist whose only concern will be that the ruddy thing helps up hills.

Apparently, some hub motors now come paired with a controller which mimics torque sensing.

I'm not sure how effective that is, but it's worth considering if the OP goes the hub route.

There is nothing unique about the torque sensor used in a mid-drive ebike you can have exactly the same setup in a hub motor drive system. Typically a torque sensor in the bottom bracket that feeds information to the controller and smoothly controls output power. Yes a higher ratio of mid-drive motors have torque sensors but it works just as well with a hub motor. Yes the fact the mid-drive has its power scaled through the gears might seem better but even on a hub motor the torque sensor will sense when you have gone to a higher or lower gear by your efforts and scale the power output to the motor. In that way there is no difference. The main advantage of a mid-drive motor is you can benefit from the lower gearing of mountain bikes to get higher torque output and of course many mid-drives seem to get past the 250W rating and consume 600-800W of power when hill climbing.