The perfect kit

[Ravi Junior]

Hello all!

I've been thinking about electrifying one of my two bikes that I use every day for commuting. After a few months of research (btw, this forum is awesome), I would like some advice regarding what to buy.

The options:

1) There's a local shop that sells 36v front hub geared kits (MXUS). They have 2 motor options, 350w and 500w and only install front wheel setups (I attached a picture of both motors side by side).
2) Buy the above kit without the battery and buy a 48v battery from ebay.
3) Order a TSDZ2 mid drive directly from China and buy the battery from ebay.

My commute is short, ~15km total + 4km to and from the gym 3x a week, entirely flat but with strong headwinds most of the time. The problem that I'm trying to solve is that my work place doesn't have showers and I sweat more than most people, even on light walks. I love to pedal and an electric motor appeals to me for two reasons: 1) I won't get all sweaty when I get to work; 2) I can get to work faster. The plan is to go to work pedal-assisted and come back on leg power alone (I really enjoy the workout a bike ride provides).


About me:

I use my bike as my main mode of transportation. Male, 85kg, very fit. I have no problem with a front hub. Never tried a mid-drive.

So here are my questions:

1) I use my 700c road bike 90% of the time, since it's newer and much more efficient than the 26 MTB (it's more of a backup bike). Should I convert the MTB and leave the road bike for days when I don't want any assistance or just convert the bike that I use more often (road bike)?
2) Should I go for 48v or 36v? Is the 36v kit enough to cruise at ~35km/h with pedaling? I don't see the point of spending a lot of money for a kit that is slower than my legs (I usually cruise between 28km/h and 32km/h).
3) Should I buy the local front kit or the China mid drive kit? The local kit comes with a 1 year warranty.

The thing is I really enjoy the workout my bikes and what I'm looking for is just a bicycle that goes faster and is easier to pedal with strong headwinds, not a motorbike. Thanks and sorry for the long post!

 

[Nealh]

Welcome to the forum Ravi,
For easier work commute & cruising at your desired speed then 48v makes sense. Also makes sense converting the bike you use most, pointless converting if you are not going to use it.
Hub for commute and mid drive for mtb off road.

A rear hub is a better ride then a front hub.

The Mxus smaller 350w makes sense ( depending on its rpm) for any issues that may crop up or generally China kits are easy to get hold of and reliability isn't usually an issue.
The Q128C version is about 3kg run the 36v 201rpm hub (actual 260rpm) at 48v, running at 48v it will be about 328rpm. Speed means reduced battery range but not an issue for your needs.

 

[Deleted member 4366]

If you want to fit a front motor, you should only fit it in steel forks. You can fit a 250w one in aluminium forks as long as the drop-outs are strong, you use eccentric washers or file the dropouts to re-centralise the axle, and you use at least one properly anchored torque arm.

A rear motor gives better handling, better traction, is quieter and a lot safer.

 

[Aarongriffin999]

You mention not wanting a motorbike, but both kits are above 250w and so legally they will be classed as one. I agree with d8veh that the rear drive would be better, front is possible but it is need a torque arm.

 

[Woosh]

but both kits are above 250w and so legally they will be classed as one.

you misunderstand the 250W specification. It is 'maximum continuous rating'. It is tested under labs conditions, measured at the motor's spindle as mechanical output at 25kph, after allowing 10% for road/tyres friction loss. There is no gradient or headwinds in the labs.
The electric assistance is limited to 25kph, above that speed (15.5mph), the motor will turn off. On flat roads, your bike will need about 200W at 25kph. For most of the time, on flat roads and even when riding against moderate headwinds, the motor will not need to supply anymore than 250W plus friction loss. The controller only lets through as much current as needed to maintain your speed, so it never is going to let in more than 250W, it will never fall foul against the law.
You are however permitted to exceed 250W momentarily when riding against headwinds or climbing hills, as long as you stay below 25kph.
You only break the law if you derestrict your bike, allowing it to output a lot more permanently as if you were climbing a steep hill continuously. Then the motor would exceed what it is legally allowed to do, as the high power is no longer temporary.

for more info:
http://www.pedelecs.co.uk/electric-bike-guides/uk-electric-bike-law/

 

[Benjahmin]

Aww streuth! No wonder it's difficult for folk to get a grip on this legality thing.
A bloke can go out and buy a Bugatti Vaeron and have no restriction on where he drives it, even though he'd break the speed limit every time he booted it in 1st gear.
Yet pedelecers have to put up with all this meaningless fudgy put a sticker on it carp that just wastes everyone's time and brainpower. Not to mention the poor bu***rs in N.Ireland who can't even take them out of the shed. All this kerfuffle and, as far as anyone knows, there's never been the hint of a prosecution.
The older I get, the more I come to the view that the most dangerous and useless thing in the world is a Government.
Amen.
Morning rant over. Thankyou and have nice day.

 

[Aarongriffin999]

Thanks for the clarification @Woosh that is the clearest anyone has explained it to me so far. I'm feeling my comment hijacked the original post so let's head back to that. Sorry Ravi.

 

[anotherkiwi]

Aww streuth! No wonder it's difficult for folk to get a grip on this legality thing.
A bloke can go out and buy a Bugatti Vaeron and have no restriction on where he drives it, even though he'd break the speed limit every time he booted it in 1st gear.
Yet pedelecers have to put up with all this meaningless fudgy put a sticker on it carp that just wastes everyone's time and brainpower. Not to mention the poor bu***rs in N.Ireland who can't even take them out of the shed. All this kerfuffle and, as far as anyone knows, there's never been the hint of a prosecution.
The older I get, the more I come to the view that the most dangerous and useless thing in the world is a Government.
Amen.
Morning rant over. Thankyou and have nice day.

The most dangerous thing is BAD government. Many countries get on just fine with theirs but I fear there are more bad ones than good ones in this world.

 

[DynatechFan]

OP looks to be in Argentina - a most gorgeous and windy country, but presumably a country without the same silly laws we have in the UK./EU

FWIW my commute home is uphill and often nasty headwind, a decent geared hub motor makes both of them go away

The other joy of ebikes is you can pootle if you want to arrive fresh, or press on and build up a sweat, either way the bike plays too

 

[Deleted member 4366]

Thanks for the clarification @Woosh that is the clearest anyone has explained it to me so far. I'm feeling my comment hijacked the original post so let's head back to that. Sorry Ravi.

It's a good explanation of how motors work, but doesn't explain correctly what's allowed. You can use any motor that's rated at 250w by the manufacturer. You can use that motor in any way that you want. There's no limit to how much power you push through it - only practical limits that would damage it.

Note that some manufacturers rate their motors much lower than what they can run with. Heinzmann make/made a 200W motor that they supplied with a 33 amp controller at 36v. That's a maximum of 1320 watts of power from the battery and something like 1000w of actual output power.

All the tests called up by the various standards for ebike motors only deal with over-rating. There's nothing to stop any manufacturer under-rating their motor, which is why it's possible to get powerful "250w" motors and why the torque from Bosch, Shimano, Yamaha, etc. motors increases nearly every year.

In 2011, the Bosch 250w motor made about 50Nm. Their latest CX produces 75Nm. Brose claim 90Nm and I heard of 110Nm from someone recently. The bikes all do 25km/h. Therefore, the 250w Brose is making 80% more power than the original 250w Bosch or double the latest 250w Bosch 40Nm Active Line motor.

 

[Ravi Junior]

Welcome to the forum Ravi,
For easier work commute & cruising at your desired speed then 48v makes sense. Also makes sense converting the bike you use most, pointless converting if you are not going to use it.
Hub for commute and mid drive for mtb off road.

A rear hub is a better ride then a front hub.

The Mxus smaller 350w makes sense ( depending on its rpm) for any issues that may crop up or generally China kits are easy to get hold of and reliability isn't usually an issue.
The Q128C version is about 3kg run the 36v 201rpm hub (actual 260rpm) at 48v, running at 48v it will be about 328rpm. Speed means reduced battery range but not an issue for your needs.

Thanks for the great advice, Nealh! As I suspected, 48v seems the way to go.

I am leaning towards converting the MTB mainly because my road bike has drop bars and this makes it impossible to install a throttle and brake sensors. What do you think?

 

[Ravi Junior]

If you want to fit a front motor, you should only fit it in steel forks. You can fit a 250w one in aluminium forks as long as the drop-outs are strong, you use eccentric washers or file the dropouts to re-centralise the axle, and you use at least one properly anchored torque arm.

A rear motor gives better handling, better traction, is quieter and a lot safer.

The road bike has a steel fork, I'm not sure about the drop outs... They seem strong enough though (it's a decathlon triban bike).

I brought the bike to the local kit seller and he didn't seem worried about the drop outs. Should I? Would it be dangerous to run the motor at 48v on the front wheel?

I'd rather install on the rear wheel but when I asked the local seller for a rear hub mount, he said he only installs front hubs and I don't think I'm technical enough to install a rear hub on my own.

This is one of the reasons I've been looking into the TSDZ2 mid drive; it seems easier to install myself and mid drives seem generally safer than hub motors.

 

[Ravi Junior]

Thanks for the clarification @Woosh that is the clearest anyone has explained it to me so far. I'm feeling my comment hijacked the original post so let's head back to that. Sorry Ravi.

Hah, no problem, that was actually a very interesting discussion although, as @DynatechFan observed, I live in Argentina and there are very few restrictions on e-bikes around here.

 

[harrys]

I would convert the mountain bike, because I believe you never want to ruin a good riding fast bike with 12 pounds or more of motor and battery. Some motors here in the power hungry USA weigh more than 12 pounds alone

 

[Deleted member 4366]

A 48v motor in a front fork is definitely on the dodgy side. You get 33% more torque at 48v than 36v.

The problem is the drop-outs, not the forks. The whole torque of the motor goes through a 1cm radius, so it's a massive force. It tries to twist the motor out of the drop-out, so you need a lot of metal around that to resist it. Road bike drop-outs are normally small to save weight, so have very little resistance to twisting forces.

On aluminium forks, the problem is slightly different. They still need to be strong enough to resist the twisting forces, but, additionally, they suffer from metal fatigue, so everything can be OK for months, then suddenly, without warning, they pop, which sends you straight over the handlebars to land on your face. I've personally witness that once, and I've seen two other sets of aluminium forks with popped drop-outs, even though the motor had been installed very carefully with torque arms. That's why I wouldn't recommend a front motor unless you have proper steel plates holding the motor, like these, which you can see is 5mm steel plate welded to the bottom of the slider. This is a case where cheapest is best. You can get that whole bike for about £120 new. I found one in a rubbish skip and gave the guy £5 for it. I upgraded the brakes to hydraulics and upgraded the BB to a cartridge one for a total of £60, so for £65 I had a really good donor bike:

 

[Ravi Junior]

@d8veh thanks for the insightful reply. You just reminded me of an old MTB that I have that might be a better donor. The fork seems to be steel (I tested it with a magnet and it stuck) and the dropouts look just like the one above (see attached photos). Would this be a better option for conversion?

 

[Deleted member 4366]

Yes, that looks a lot better for a front motor.

 

[Deere John]

I have actually a similar fork but in aluminium. Have had it for two years and about 12000km riding now (!). Front motor also. Very satisfied with my bike. It's the simplicity I like. Almost maintenance free. Have thought about mid drive instead but when I think of above I don't wanna change [emoji3]

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