Donor bikes - what to look for?

[Egon]

Just wanted to put together a checklist for a donor bike.

Is a steel frame best? Especially for higher powered motors?

Is there any preference between 26” or 29” wheels?

I guess disc brakes are also best.

Anything else important to consider?


Also, any recomendations for older steel framed bikes to look out for secondhand.

 

[Alan Quay]

Just wanted to put together a checklist for a donor bike.

Is a steel frame best? Especially for higher powered motors?

Is there any preference between 26” or 29” wheels?

I guess disc brakes are also best.

Anything else important to consider?


Also, any recomendations for older steel framed bikes to look out for secondhand.

You don't need a steel frame (below 1kw anyway), any frame with a rear hub motor will be fine. If you want front wheel drive, go for rigid fork (normally steel) or fit torque arms to suspension fork.

Disks are best, but mech disks area pain in R's. Unless you are very heavy, or want top performance, V-brakes are fine.

Look for a quality second hand bike. Some of the older GT's have a nice steel frame. The more modern ones are Alu, and are are also nice.

Carerra and Trek are normally good second hand bets, Specialized and Kona also good but don't expect an eBay bargain.

I think 29'er is a bit of a niche market. Very little about second hand so you'll be a bit limited on choice.

 

[Alan Quay]

Oh, and don't EVER, no matter how tempting, or new, or cheap or shiny, ever, touch an Apollo. Ditto Trax & Shockwave.

Stick with a half decent brand and you won't go far wrong. It normally won't cost you any more either.

Add Dawes to the 'half decent' list. Also most Claud Butler's.

 

[Egon]

You don't need a steel frame (below 1kw anyway), any frame with a rear hub motor will be fine. If you want front wheel drive, go for rigid fork (normally steel) or fit torque arms to suspension fork.

I think 29'er is a bit of a niche market. Very little about second hand so you'll be a bit limited on choice.

Thanks Alan.

I'm considering a 1000w rear hub, so maybe steel would be advisable then.

I'm not limited to just secondhand, but I want to get the best value for what I do spend. I've also been looking at some 2015/14 models and ex display stock.

Most of the newer steel frame MTBs seem 29ers or 27.5. But I don't think anywhere is selling 27.5 hub motor/wheels. Which is a shame as it looks a nice size for a converted ebike as they they come in slightly wider sized wheels as well.

 

[anotherkiwi]

You can lace or have a motor laced into any size of wheel. There are motor kits with bare motors.

I found a kit with a 1000W motor in a 27.5 rim just now

P.S. this is an English language forum so it is a "host" bike (the bike hosts the kit it isn't giving anything away...)

 

[Egon]

You can lace or have a motor laced into any size of wheel. There are motor kits with bare motors.

A bare motor is something I've considered, the fact it's another hurdle and another expense is putting me off a little.

I found a kit with a 1000W motor in a 27.5 rim just now

Care to share??

 

[anotherkiwi]

http://www.ciclotekstore.eu/b2c/producto/9822033/2/nitro-e-bike-motor-kit-48v-without-battery-

 

[Alan Quay]

Thanks Alan.

I'm considering a 1000w rear hub, so maybe steel would be advisable then.

I'm not limited to just secondhand, but I want to get the best value for what I do spend. I've also been looking at some 2015/14 models and ex display stock.

Most of the newer steel frame MTBs seem 29ers or 27.5. But I don't think anywhere is selling 27.5 hub motor/wheels. Which is a shame as it looks a nice size for a converted ebike as they they come in slightly wider sized wheels as well.

When you say 1000w I am assuming you mean a direct drive hub? These are low torque, so ally frame should be fine.

Are you sure DD will suit your requirements?

 

[Egon]

From what I've read online about the various options it seems like a suitable choice. Are you not a fan? Do you favour mid drives instead? I guess the mid drive would make a better hill climber.

On a related note. How important is the 'host bike's gearing system? Is 10 enough? Or is it a case or more is more? With mid drive motors I can see it making a difference, but is the same true of a DD rear hub?

 

[Alan Quay]

From what I've read online about the various options it seems like a suitable choice. Are you not a fan? Do you favour mid drives instead? I guess the mid drive would make a better hill climber.

On a related note. How important is the 'host bike's gearing system? Is 10 enough? Or is it a case or more is more? With mid drive motors I can see it making a difference, but is the same true of a DD rear hub?

Somewhere between the two is a geared hub motor. It's single speed, but has a gearbox enabling the motor to run at its most efficient, while generating plenty of torque. The Bafang BPM/CST models are good examples.

The 500w CST will assist up to about 23mph and climb like a mountain goat.

DD's are good for high speed, but not very good on hills.

As for gearing, I do most of my miles on a 4 speed hub geared bike. 3 is enough.

 

[Egon]

Thanks for all the advice Alan. There's some much choice it can seem somewhat overwhelming.

Just been reading this guide to mid drives - https://www.electricbike.com/mid-drive-kits/ The GNG drive on there looked interesting, checking out their website it seems they're now selling a 2000w capable dive.

 

[Alan Quay]

Mid drives have never been my thing, so I can't really comment.

As I understand it, mid (aka crank) drives are more suited to the cycling enthusiast.

D8veh has a good ready reckoning method to determine if CD is a good idea for you: When you ride a bike do you wear special clothing?

If the answer is yes, CD is for you. If not, a geared hub drive might suit you better.

So what is your intended use?

 

[Egon]

Primerily leasure. I live west of you, in the middle of the countryside in Cornwall. So I guess my primary prerequisite is that it can handle some pretty steep hills and muddy fields. But I'd also like it to have enough power to be able to take most of the strain if necessary.

 

[Alan Quay]

DD is not for you then. Not enough torque, unless you are very light.

In my opinion, BPM/CST would suit you best.

It s important to understand that power and torque are different things.

Power = Speed x Torque

So, for a given amount of power you can have lots of one, lots of the other, or a balance.

 

[danielrlee]

If you're not concerned about remaining legal, don't be so quick to dismiss a DD hub. They give plenty of torque if you feed them enough power and they'll withstand far more power than any geared hub will.

 

[Egon]

Hmm. Well that's given me more to think on.

Are there any good articles on BPM & CST drives so I can get a little more clued in about them? Or a comparison of the speed / torque ratings of various systems.

I know people on here rate the Bafang mid drives as good hill climbers, the 02 especially. What do I need to be looking for if I want to compare the possible performance of that to the BPM / CST?

BBS02 500w
Voltage: DC 48V
Power: 500 Watts
Current Limit: 18A (controller is 25A version, reprogrammed to 18A)
Motor Weight: 4.22KG
Controller: 9 Mosfet, Sine Wave, Intergrated With Motor
BB Length: 68mm
Max torque: ≥120N
Max Efficience: ≥78%
Waterproof Grade: IP65

BBS02 750w
Voltage: DC 48V
Power: 750 Watts
Current Limit: 25A
Motor Weight: 4.22KG
Controller: 9 Mosfet, Sine Wave, Intergrated With Motor
PAS Sensor
BB Length: 68mm
Max torque: ≥120N
Max Efficience: ≥78%
Waterproof Grade: IP65
http://www.eclipsebikes.com/motor-kits-bafang-8fun-drive-motor-c-73_130.html?osCsid=71c0922582598b2d3fc769428e393247


BPM 500w
Rated Voltage (V) 36/48
Rated Power (W) 500
Max Diameter (mm) ￠180
Max Speed (rpm) 36V(280) 48V(230)
Rated Efficiency (％) ≥78％
2P 16
Reduction Ratio 1:5
Weight (kg) ≤4.5
Open size (mm) 138
Drive and freewheel type 7s
Spoke Specification 12G
Cable location Shaft center, righ
Hall sensor sensor
Integrate speed sensor
Connector
Brake type V/Disc (>￠160)
Surface Silver/Glossy black painted
Noise (dB) <55
Salt fog test (h) 24/96
Water proof Grade IP54
Certification CE ROHS
http://www.elifebike.com/peng/iview.asp?KeyID=dtpic-2012-59-Q25J.1A2QG

 

[Egon]

If you're not concerned about remaining legal, don't be so quick to dismiss a DD hub. They give plenty of torque if you feed them enough power and they'll withstand far more power than any geared hub will.

Road legal is not an concern no.

I have seen footage of a 1500w DD hub power it's way up a hill, so I know it's capable. But will they not suffer from other issues like overheating or struggle with the strain of constant hill climbs.

 

[Kinninvie]

I have a DD front motor (1Kw Dillenger) fitted to Trax mtb and although the bike handles it easily its useless at steep hills .
It has a range of between 10 and 18 miles on a 10Ah battery.
I also have a BBS02,750W fitted to a Cannondale Trail 6 and it romps up the steepest of hills with ease and gets between 35 and 50 miles to a 15A battery.
I live up on the moors so similar to Cornwall with steep hills in all directions.
BBS motors are also stealthier and quieter than big hubmotors and can be fitted to any size wheeled bike,mines a 29er and originally it was on an Apollo Evade mtb.
The one thing I have done with all my ebikes is put hydraulic disc brakes on.

 

[danielrlee]

Road legal is not an concern no.

I have seen footage of a 1500w DD hub power it's way up a hill, so I know it's capable. But will they not suffer from other issues like overheating or struggle with the strain of constant hill climbs.

Yes, no and maybe.

I am a big fan of big rear-mounted DD hub motors. I love the simplicity, durability and reliability of them. Nothing else comes close in these aspects. Generally speaking, they can also handle far more power than most other types of motor.

Mid-drive motors will always be more efficient hill-climbers as they give the option of massive gear reduction, leaving you able to climb a hill of almost any gradient at a snail's pace. This doesn't necessarily translate into faster hill-climbing, but they will always remain cool while performing in this manner. For extreme gradients, they will be the most reliable, but are not without their own issues.

My most used bike features a 1000W rated Crystalyte 3540 DD hub, driven at around 3000W. I recently tackled Wiltshire's highest peak (Milk Hill) with this bike and it performed beautifully, absolutely flying to the top. The motor was quite warm at the peak, but I am running a fairly sophisticated system through a Cycle Analyst with thermal-rollback that will automatically dial-down the power to keep the motor within a pre-specified temperature range. There's no way an off-the-shelf mid-drive motor would have got me up there quicker anyhow. This isn't a riding style suited to everyone though.

If you are still considering a hub motor, you should take a look at this motor simulator to give you an insight on how a given system would handle:

http://www.ebikes.ca/tools/simulator.html

I'm not sure how far you like to take things, but as a DIY'er, you might also be interested in recent advances in DD motor cooling as detailed here:

http://www.ebikes.ca/statorade.html

 

[Alan Quay]

As I said before, I suspect a geared hub motor would be the best answer.

How far and fast do you want to go, and how much do you weigh?