Lightweight Trekking Bike Build

[Deleted member 4366]

Here's the donor bike:

It's supposed to be a gravel bike, but it doesn't quite have the relaxed geometry of a good one. It's good points are that it has disc brakes and it didn't cost too much. It's bad points are that the brakes don't work. I think this is an added arrangement, which might have something to do with that. It's convenient, but no good if it reduces the braking:



Not that it matters because all that's going to go. I'll be fitting carbon fibre straight bars and Shimano Hydraulic brakes. I'll be using the Shimano XT M766 integrated shifter/brakes because I love them and they take less room on the handlebars. This is all the stuff that's going to be added:



The motor weighs 1.5kg with its wheel nuts, etc. The stuff I took off weighs 1.5 kg, leaving the bike without brakes and bars weighing 7.95 kg. The total weight of what I'm adding is 3.0kg, so the finished bike without the battery will weigh 9.5kg. I'm looking at a battery weight of 2kg for stage one, then later, I'll go down to a 1.5 kg one. I think I can lose another 0.5 kg at least by changing the cranks and pedals to lightweight ones

 

[Tabs]

Looking forward to the build

 

[Deleted member 4366]

The first minor problem was that the bracket for the LCD was too small to fit the handlebars. The actual LCD is fixed by two screws, so previously I've fixed them with an aluminium plate fixed to the stem cap:



but I had a bracket left over from that S-LCD3, which has the same fixing hole spacing as the Bigstone one, so I used it on this one:



This is as far as I can go for now. I need to shorten the brake hoses:

 

[mxer]

Nice build! Like that little motor 1.5 kg wow, do they make a rear? Can you tell me more on the equipment, screen motor and controller, is this all plug and play BMS battery stuff?.

I'm always drawn to your post/ threads D8veh, nice work, great stuff! Cheers for sharing..

 

[Deleted member 4366]

Yes, they make a rear one. Awol will no doubt be posting on that shortly, as I'm just sending the one I bought with my front.

Yes, it's sort of all plug and play as long as you buy a throttle with the small black connector and get your own PAS and battery. The controller has bullet connectors for the battery, which you'll probably want to change for your favourite.

I have a brilliant solution for the battery - details to follow later in the build.

 

[awol]

Yes, they make a rear one. Awol will no doubt be posting on that shortly

I'm feeling under pressure now and need to sort a bike out for it quick.

 

[chris_n]

How many spokes, 32 or 36? Looking forward to this as I have a few ideas of my own.

 

[Deleted member 4366]

36 spokes. I forgot to ask whether they did other arrangements. Now my rims won't match. Mind, you, these motors are so cheap (about £125 with controllers and LCD - even less for just the motor), if it does the job, I might see if they do a 28 hole one to get matching rims.

 

[anotherkiwi]

What windings do they have? You asked that question for sure! Then we just need to know if it will handle 44.4 V at 17-18 Amps...

 

[Deleted member 4366]

It's wound to hit peak power at 15 mph with 36v. The power rams down after that. That means 20 mph at 48v. It's a tiny motor. Don't think about it hauling heavyweights up hills. If I can find a decent controller, I'll try it at 48v, but no more than 12 amps.

The motor outputs about 350w at peak. I've been trying my present bike on level 3, which is 250w input power and something like 200w output. I find that that's enough for what I need on my MTB, though I have to pedal hard to get up the steepest hills. With a weight saving of 10kg (10%) and 50% more power, this new build should be more than adequate. After all, I can do all my rides on my road bike, so having 300w to help me with only a 3kg weight penalty should be pretty good.

I opened the standard 11 amp controller. The main capacitor is 50v, so it won't work with 48v directly, but if you're going to make a custom battery, 12S could be an option.

 

[anotherkiwi]

Thanks. That is kind of confirming my thoughts.

After reading your advice on other threads I have come to the conclusion that 2 hub motor wheels is the ideal solution for my problem: if I go north (to visit sons) it is flat so the tiny motors would be fine, if I go south I need more power for hills so a Q128, CST or BPM is the better choice.

My inner bad boy petrol head would also like a transmission fluid cooled BPM with steel planetary gears running 72 V @ 20 Amps... For Saturday night

It's wound to hit peak power at 15 mph with 36v. The power rams down after that. That means 20 mph at 48v. It's a tiny motor. Don't think about it hauling heavyweights up hills. If I can find a decent controller, I'll try it at 48v, but no more than 12 amps.

12S 44.4 V at 12 Amps is a healthy 530 W. With such a light motor 2WD is an interesting prospect.

The LCD-3 lets you limit current quite well (C5 parameter). I ran my mxus at 11.27 Amps for a while (C5 at 05 or 15 / 1.33) to see how the power/range ratio worked for me and 400 W peak proved to be plenty. I think that if I had the GSM mounted to a light weight road frame I might run it with 360 W peak assist and a smaller battery. While I could - age counter just went up a tick again...

 

[Deleted member 4366]

I think they would make a brilliant 2WD bike for off-road use. The light weight motors wouldn't affect the suspension like bigger ones do, and you could run both motors off a single dolphin type battery. the only downside is the free-wheel gears limit what you can do on gearing.

On the road, there's not really any advantage to using 2 small hub-motors instead of one bigger one unless you want or need good suspension. I suppose there's always the stealthiness aspect. At least it wouldn't look like much even though you have 700w of output power on tap.

Annad made and probably still makes a couple of bikes with front and rear Keyde motors, which are a similar size. The Keyde has the cassette spline, so a bit more practical; however, they're a lot more expensive and there were lots of reports of reliability issues.

 

[topographer]

Is a legal motor in each of two wheels legal?

 

[anotherkiwi]

No. EN 15194 says no. Unless you had only one controller and could only use one at a time. I can't think of a special need use where that would be of interest.

 

[Deleted member 4366]

Who's going to notice that it's electric, let alone 2 motors?

 

[topographer]

Two tiny motors and a battery hidden inside the frame. That'd be nice.

 

[fishingpaul]

Here's the donor bike:View attachment 19961

It's supposed to be a gravel bike, but it doesn't quite have the relaxed geometry of a good one. It's good points are that it has disc brakes and it didn't cost too much. It's bad points are that the brakes don't work. I think this is an added arrangement, which might have something to do with that. It's convenient, but no good if it reduces the braking:

View attachment 19962

Not that it matters because all that's going to go. I'll be fitting carbon fibre straight bars and Shimano Hydraulic brakes. I'll be using the Shimano XT M766 integrated shifter/brakes because I love them and they take less room on the handlebars. This is all the stuff that's going to be added:

View attachment 19963

The motor weighs 1.5kg with its wheel nuts, etc. The stuff I took off weighs 1.5 kg, leaving the bike without brakes and bars weighing 7.95 kg. The total weight of what I'm adding is 3.0kg, so the finished bike without the battery will weigh 9.5kg. I'm looking at a battery weight of 2kg for stage one, then later, I'll go down to a 1.5 kg one. I think I can lose another 0.5 kg at least by changing the cranks and pedals to lightweight ones

Out of interest are there any figures available,to how much difference loss of bike weight makes v loss of rider weight,for example if i lost 2 kilos would that help more or less,than losing 0.5 kilos of bike weight when using lower powered motors,obviously shifting body weight can be very hard,but shifting bike weight,can be very expensive.

 

[anotherkiwi]

The motor is in the middle of the wheel so the most difference will be felt by losing 1.5 kg of unsprung weight on a suspended bike. Then the weight difference will be felt when riding over and above the cut off, several kilos less weight to chuck around will also help with handling... This motor is an example of losing weight on the cheap thanks to the very reasonable price.

 

[Deleted member 4366]

I can speak from experience because I've done both. Saving weight from anywhere makes a big difference to handling, braking and how easy it is to pedal. Basically, each 1% mass you lose, makes it 1% easier to go up hills. I've lost 20kg from my own mass and I expect to lose another 10kg from the bike. That makes 30kg reduction from 125 kg, so soon I will only need 76% as much effort to pedal up the same hills. Riding round on my roadbike takes similar effort to get up the hills as my electric bike use to on level 1 assist - maybe even level 2.

When 50kg guys come on here and boast about how well their G-tech goes up hills, you can see why.

Actually, the difference to pedal effort is more than that. If your motor gives 250w, but you need 500w to get up a hill, you have to provide 250w. If you then reduced your mass by about 40%, you'd need 300w to get up the hill. The motor has the same power, so you only need to provide 50w. That means that you have to provide 5 times the effort at the higher mass than at the lower one.

 

[anotherkiwi]

d8veh does the rear motor take an 8 speed freewheel? Or rather does an 8 speed freewheel and that motor fit 135 mm dropouts?