New wheel build - am I biting off more than I can chew ?

[Paultr]

I have recently put a rear wheel with a hub motor on my brand new hybrid bike (see another thread). Unfortunately the wheel does not match the front one cosmetically so I have come up with an idea which I would appreciate some feedback on please.

I now have a 250W motor but quite fancy a 350W one. I love the one I have but a little bit more speed might be nice . Also I would like to have a wheel to match the front one (matt black rim and spokes).

So my idea is to buy a 350W motor in a wheel and take it out and remove the spokes. I would then remove the black spokes from my original wheel and cut them to match the length of the spokes I have taken off the new wheel. I then reassemble my original wheel and hey presto I have a bike with matching wheels with a nice turn of speed.
I then take my old 250W motor and put it into the wheel that came with the 350W motor. I will have to buy new spokes because the 350W motor has a larger diameter than the 250W one. I then give the 250W wheel and motor to my wife and put it into the new bike I am going to buy her for her birthday. This will ensure she can come riding with me with motorised help but at any time I can just turn up my power and leave her in the dust

As to my skill levels they are pretty much none when it comes to bikes but I have the Park Tools bike book, the Internet, a good set of tools and plenty of time on my hands.

Is the above idea doable or can someone think of a reason why it can't be done and also, if it is doable could a newbie do it if he/she took their time ?

Thanks for any feedback
Paul

 

[Woosh]

how about spray paint the spokes and motor to match?

 

[Richardab]

Wheelbuilding is made out to be a bit of a black art. There is certainly some skill and more importantly patience required, but its not impossible to do DIY. I've done a dozen or so wheels in the last few years basically just using the internet as a guide, there is an excellent guide on Sheldonbrown.com, but you need to follow it to the letter or you will make mistakes and there is also several spoke length calculators available. Tensioning can be done by ear to get equalized, there are even apps that listen to plucking noise and tell you the tension, in the end I bought a tension meter.

I'd forget cutting down old spokes, by the time you have found someone to do this and redo the threads you are probably in for more than new spokes.

But in reality most people would sensibly just pay a shop to build a wheel, its not that expensive and you know it will be done right.

 

[Paultr]

Wheelbuilding is made out to be a bit of a black art. There is certainly some skill and more importantly patience required, but its not impossible to do DIY. I've done a dozen or so wheels in the last few years basically just using the internet as a guide, there is an excellent guide on Sheldonbrown.com, but you need to follow it to the letter or you will make mistakes and there is also several spoke length calculators available. Tensioning can be done by ear to get equalized, there are even apps that listen to plucking noise and tell you the tension, in the end I bought a tension meter.

I'd forget cutting down old spokes, by the time you have found someone to do this and redo the threads you are probably in for more than new spokes.
... .

Sounds right up my street. I am most definitely no spring chicken but love finding out about things I have no experience of. Got your point about buying new spokes - also has the added advantage that I will have a lot to practice on ! I should imagine it is like a lot of things - first time takes forever and there are mistakes but second time is dramatically quicker and easier.

 

[Paultr]

how about spray paint the spokes and motor to match?

Yes, I considered that but although part of the rim is black there is a stainless part for use by people with rim brakes. To be honest it is not that noticeable - I have got that many gadgets and bits and pieces on the bike and the back wheel is surrounded by a rack, a motorcycle type box and two panniers so that you can hardly see the wheel anyway ! It is the 350W I want

 

[wheeliepete]

A 350 watt motor will not necessarily give you more speed than a 250 watt one, it's the winding speed of the motor and the voltage you give it which effects that. Be aware though that a higher rpm motor will not give you the same torque for hill climbing. It's always a compromise between the two, you can't have both without more amps and higher voltage.

 

[Paultr]

A 350 watt motor will not necessarily give you more speed than a 250 watt one, it's the winding speed of the motor and the voltage you give it which effects that. Be aware though that a higher rpm motor will not give you the same torque for hill climbing. It's always a compromise between the two, you can't have both without more amps and higher voltage.

My idea is to keep all the ancillary components from my existing hub. So the voltage will be the same as will be speed controller. So what do you think will be the effect of the larger motor in terms of torque, speed and battery usage ?
(Note to self - must get around to fully understand how electricity works )

 

[Woosh]

So what do you think will be the effect of the larger motor in terms of torque, speed and battery usage ?

larger motor has more and larger magnets, the coil has more magnetic poles compared to the smaller motor, which is translated to a higher level of magnetic saturation. All that means is the coils on a larger motor can take higher current and more efficiently and delivers more torque at the same rotational speed.
Motors cannot convert 100% electricity into kinetic energy. The useable yield of e-bike motors is between 50% and 86%. Below 50%, the motor converts more electricity into heat than kinetic energy, it will overheat in minutes.
Manufacturers publish regularly the experimental measurements of power versus a range of RPMs, I use the motor simulator at ebikes.ca for a quick look up if I can't wait for manufacturers' replying to my request for information.
http://www.ebikes.ca/tools/simulator.html
If you compare the XF07 against the BPM (the power v RPM data is already available on the site), you will find the yield at 50% in this condition:

at 50% yield (green plot):

MXUS XF07: gradient 13%, speed 12kph.
Bafang BPM: gradient: 17.5%, speed 9.4kph

Clearly, everything else equal, the Bafang BPM can climb steeper gradient albeit at lower speed.

 

[Blunderbuss]

Hi Paultr - this could give you all the skills needed for the proposed job:

http://www.cambridgewheelbuilding.co.uk/index.html

 

[Benjahmin]

The higher wattage motor is not more powerful, it is merely capable of having a higher current passing through it for a stated time, without overheating. So I don't think you'll be going any faster.
One way to achieve higher speed and torque is to run a 36v motor at 48v. 33% increase (nominal) in both.

 

[awol]

For a little bit more power (not speed) from the existing motor maybe put a bit of solder on one leg of the controllers shunt.
More speed, you will need more volts so that depends on whether your controller will take more volts and whether it restricts the speed too.
I generally black out the rim's unpainted rimbrake edges with a black touch-up paint pen to colour them in and that looks nice.

 

[Benjahmin]

Agree with all that's been sais on the batteries. I'd say, if you're carrying both , use them both, don't keep one as a spare. It stresses the batteries less and range anxiety disappears into thin air. Suddenly you can take that lane, on a whim, that you've always wondered where it came out, and still get home.

 

[Paultr]

For a little bit more power (not speed) from the existing motor maybe put a bit of solder on one leg of the controllers shunt.
More speed, you will need more volts so that depends on whether your controller will take more volts and whether it restricts the speed too.
I generally black out the rim's unpainted rimbrake edges with a black touch-up paint pen to colour them in and that looks nice.

That's a good idea - I assume you mean car touch up paint - do you think that would that stick to the spokes if I decreased them thoroughly ?

 

[awol]

This paint pen was recommended by @Fordulike and is really good for around the rim, with some patience it could do the spokes too but I would probably lay the wheel in a larg box mask it and and spray it all would be easier. Do degrease it all first though.

https://www.ebay.co.uk/itm/Pentel-Permanent-Cellulose-Paint-Marker-Pens-MMP20-Single-Buy-4-Pay-For-3/351763259099?epid=1660707124&hash=item51e6b95edb:m:mKDs4MX_abILjJ8AQY8iHhg&var=620691211480

 

[Paultr]

Thanks awol - wait for a rainy day I guess !

Re. the motor change, I think I have got my head round it now. So the only way to reliably get more speed would be to move to a higher voltage system with a bigger battery or less range and more importantly more weight Having spent some time thinking about it I reckon I am happy with what I have now. Even if I change everything and get another 5-10mph I will then want even more. The times I have enjoyed most on the bike so far are when I have been relaxed and just tootling along. Before I had the motor, 15mph felt fast by pedal power and being able to do that with the minimal or no input is a great feeling as is contributing energy when I feel like it. I haven't yet tried my most challenging local hill but I think I should be OK and even if the bike struggles it is located in a suburban setting and there are alternative routes with more gentle inclines.
Thanks for all the replies to the thread
Time to get painting !

EDIT: awol, how glossy is that Pentel touch up pen ? I might have a problem with car specific products as my wheels are matt black. I might be better off with Humbrol modelling enamels which presumably come in matt

 

[Benjahmin]

As per another post.........Marathon Plusses.

I too find that pootling along at 12ish mph is mostly satisfactory. It still nearly doubles what I would be doing unassisted, especially around here. I am up to about 5200 miles on my conversion now and I'm finding that the legs, on some days, feel a lot more capable than even in my younger years which, at 65, is something of a surprise. Salutations to the e-bike!

 

[awol]

how glossy is that Pentel touch up pen ?

It's not full on gloss but got slightly more of a sheen to it than matt. Also it takes 2 or 3 coats to get a nice looking finish. You get maybe 3 or 4 wheels out of a pen.

 

[Paultr]

It's not full on gloss but got slightly more of a sheen to it than matt. Also it takes 2 or 3 coats to get a nice looking finish. You get maybe 3 or 4 wheels out of a pen.

Thanks awol. My Cannondale is most definitely matt apart from the name which is in gloss (you can hardly read it !) so I will have a hunt around for a matt solution. Going to get one of those Pentel pens though to touch up my old racing bike prior to selling it.