Help! Perfect elusive donor bike

[Bari Gadgi]

Hi everyone
I'm still on the hunt for the perfect donor bike.
Ideally want a hardtail with plus tyres and a decent fork.
No problems finding 73mm bb's however most "good quality" bikes have external bb's. This means that the distance between the non drive crank and the chain ring is much greater than having an internal bb.
Any ideas, as its the one major thing I can't get my head around.
I could post a few photos showing exactly what I mean on my current hardtail if that would help anyone.
Best regards
K

 

[vfr400]

Why are you concerned about the BB? All decent bikes have BBs like that. Nobody else complains.

 

[Bari Gadgi]

Why are you concerned about the BB? All decent bikes have BBs like that. Nobody else complains.

Thanks for the reply.
Apologies, as this wasn't intented as a complaint, just an honest question.
I realise that bafang motors come in different widths to accommodate different bb's my question I suppose is do you get a 73mm to fit a 73mm bb or a longer one to accommodate the extra width of having an external bb, and still maintain the chain line of the original.

 

[Woosh]

don't worry about that.
if you are going to fit a BBS motor, you have to remove the external ball bearings. The measure that matters is the length of the bottom bracket shell, minus the bearings.
The chainline on the BBS kits is 50mm. Same chainline you have with most bikes.

 

[vfr400]

The only complication to fitting these motors is when you have a press-fit BB. The screw in type, whether external or internal are removed and don't play any part in the installation. Normal shells (not PF or fatbike) are 68mm or 73mm. If you have 73mm, you leave off the locking ring and fix the lock-nut with Loctite or centre-punch it to stop it from coming undone.

For a hard-tail bike, I'd always fit a rear hub-motor unless there are exceptional circumstances. Hub-motors are more reliable, cheaper, have lower running costs and are more user-friendly.

 

[Bari Gadgi]

Thanks vfr400
The reason for the mid drive was to maintain the use of the gears.
The bike would only really be used for it's hill climbing ability and hopefully 30miles + range in the local cheviot hills.
Broadly speaking what I've learned from the "net" is that hubs are better on road if you like, whereas mid drives can do both but by maintaining gearing they perform better on serious hills.
My original bike to convert was going to be a whyte 905v3 but since buying it I haven't had my full suspension out as I like it so much. So my intention is to sell my full suss and buy another whyte or a similar orange to convert.
Really rate the whyte, we've got 4 now and with an electric motor and + size tyres it would make a cracking off road machine.
Cheers
K

 

[Bari Gadgi]

don't worry about that.
if you are going to fit a BBS motor, you have to remove the external ball bearings. The measure that matters is the length of the bottom bracket shell, minus the bearings.
The chainline on the BBS kits is 50mm. Same chainline you have with most bikes.

Thanks Woosh
Very useful diagram. I've just been and measured my bike (whyte-909 v3) and yes the centres are indeed 50mm. I'll add a photo of my bb which I've annotated just to confirm.
I bought this with the fullest intention of converting however enjoy riding it compared to my full suss, that it's being sold to fund another whyte or an orange.
If you have any specific experience of any of these or this type of bike I'd appreciate any help you can provide.
Essentially I would like to motorise (using a bafang 750 or 1000w motor) a very capable hardtail that would get some hard of road usage.
Cheers
K

 

[peter.c]

The width will not be a problem ,but the internal cable route might but you could re -run the gear and brake cables outside a side view pic would help

 

[Bari Gadgi]

Hi Peter
Thanks for your reply.
I'll attach the images that I have on my phone.
The bottom bracket has quite a "bulge" to allow the cables to exit the shell. I'd thought that the motor axle might have passed through and still allowed the cables to exit. God knows how I'd re-route the cables, there's also a dropper post actuator cable in there. I assume it goes over the top rather than around the bottom.
See what you think.
Cheers
K

 

[vfr400]

Thanks vfr400
The reason for the mid drive was to maintain the use of the gears.

I think you got that the wrong way round. You can keep your gears with a rear hub-motor, but you lose them with a crank-motor.

You need to measure the diameter if the BB shell in the wider middle bit. It looks too wide for a normal crank motor like a BBS**. The maximum you can have is about 13mm from the inside of the BB shell (where the thread is) to the outside of the tube. The cables and the guide will definitely have to go.

Also a 42T chainring is 21mm beger in radius, so your 19mm clearance is not enough, assuming that you end up with the same chainline. You'll still need some clearance in case of run-out or if you want an elyptical chainwheel. 42T is already a bit small for an electric bike, so you don't really want to go much smaller. The standard 46T one is about right for the 250w BBS01. For a BBS02 or HD, I'd want something bigger, especially on the road.

 

[Nealh]

With a BBS/ mid drive you can fit a 2x up front thought smallest inner ring will only be 36t other any smaller a chain will foul the final drive cover. There are spiders available for the 5 fixing drives, chain line may be affected but I had no issue albeit I used alfine 8 on the rear.

 

[Bari Gadgi]

As I understand you keep your gears on both however a hub doesn't have the advantage of the gearing provided by the rear cassette whereas a mid drive does.
I

 

[vfr400]

As I understand you keep your gears on both however a hub doesn't have the advantage of the gearing provided by the rear cassette whereas a mid drive does.
I

Not correct. You don't have to change your gears with a hubmotor as long as you get the right sort of motor - cassette motor for free-hub gears and freewheel motor for freewheel gears. With a crank motor, you nearly always need to do something with your chainwheels, i.e. lose them if 2 or 3 or change size if 1. Also, crank motors wear out fancy 11 and 12 speed cassettes and chains very quickly, so you wouldn't want to keep them, especially as they offer no advantage when you have a motor. 9 speed would be better for reliability and durability. The same applies to fancy derailleurs. They're great until you mess up a gear-change and the torque from the motor wraps it around the fancy cassette. those things are great on a pedal bike, but a liability on an abike with a crank motor, as you'll probably find out.

 

[Bari Gadgi]

OK folks thanks for the input.
I'll see if I can find another bike. As mentioned this was my first attempt at finding a bike to convert and its obviously not a good fit.
To sum up;-
Older bike.
Cable runs from the top, down seat stays avoiding bb area.
2/3 front ring operating a x7/8/9 cassette.
Do homework regarding the correct hub motor.

 

[vfr400]

You can replace cables with continuous ones and re-route them around the motor. If there are brake hoses there, you have to disconnect from the caliper to reroute them. That's not the biggest obstacle.

When you look for a donor bike, all the things that make a non-electric bike good aren't so important. The best donor bikes are high spec MTBs fro 10 to 15 years ago. Make sure you get disc brakes. Air suspension and hydraulic brakes are also good.

As I already said, the bike you have would work really well with a rear motor, which would be better than a crank motor. Crank motors are arguably better for full suspension bikes. They can also be better for towing or exceptionally heavy riders or heavy riders with steep hills. For everything else, a hub-motor wins hands-down.

 

[Bari Gadgi]

You can replace cables with continuous ones and re-route them around the motor. If there are brake hoses there, you have to disconnect from the caliper to reroute them. That's not the biggest obstacle.

When you look for a donor bike, all the things that make a non-electric bike good aren't so important. The best donor bikes are high spec MTBs fro 10 to 15 years ago. Make sure you get disc brakes. Air suspension and hydraulic brakes are also good.

As I already said, the bike you have would work really well with a rear motor, which would be better than a crank motor. Crank motors are arguably better for full suspension bikes. They can also be better for towing or exceptionally heavy riders or heavy riders with steep hills. For everything else, a hub-motor wins hands-down.

Cheers v

You can replace cables with continuous ones and re-route them around the motor. If there are brake hoses there, you have to disconnect from the caliper to reroute them. That's not the biggest obstacle.

When you look for a donor bike, all the things that make a non-electric bike good aren't so important. The best donor bikes are high spec MTBs fro 10 to 15 years ago. Make sure you get disc brakes. Air suspension and hydraulic brakes are also good.

As I already said, the bike you have would work really well with a rear motor, which would be better than a crank motor. Crank motors are arguably better for full suspension bikes. They can also be better for towing or exceptionally heavy riders or heavy riders with steep hills. For everything else, a hub-motor wins hands-down.

Thanks very much for the reply.
I've spent a wee bit of time having a look around on the net, and discovered that whoosh has a bike shop! Should have realised by his/her membership.
Lots of interesting things to look at and loads of info too.
I think it would be almost sacrilegious to dismantle my current 905 however the hub does sound interesting. One question though? From what I've seen the torque output for hubs seem to be quite low. Does the working action of a hub allow lower torque to perform as well as a mid with higher outputs. This is a worry for me where most climbs in the local hills are serious granny ring jobs.
This is probably where I appear to be getting mixed up with the mid using the existing gearing.

Anyway got to say a massive thank you to everyone who has responded to what are probably daft newbie questions.
Think whoosh might be getting a call at some point, god help them!

Cheers
K

 

[vfr400]

At any voltage, torque is proportional to current - more or less, so if you want more torque, you get a system that can supply and handle the current. 15 amps at 36v is enough for most people, especially if you have the 15.5mph limit. 20 amps is better for heavy people that have moderate hills, and 30 amps can drag heavy people up steep hills.

You also get more torque if you increase the voltge. If you take a standard geared hub motor and run it at 48v, you get 30% more torque than you would at 36v, so a motor running at 15 amps and 48v is equivalent to a 36v one at 20 amps.

It doesn't really matter what the nominal voltage of the motor is because it's a meaningless characteristic. The nominal voltage is only a base to specify it's rotation speed. A lot of people worry that running a 36v motor at 48v might over-stress it. That's not so. It's the current that stresses it and a higher voltage allows you to run less current.

The main thing you need to concentrate on is the motor's max RPM, which will affect various other characteristics like over-heating. Your goal should be to get a motor that will give your bike a maximum theoretical speed that's 25% more than your planned modal speed. 201 rpm is 15 mph (26" wheel), 260 rpm is 20 mph and 320 rpm is 15mph for a 16" wheel. These are the common motor speeds for geared hubs. A 36v 201 rpm motor would be identical in all respects to a 48v 260 rpm one, likewise between a 260 rpm 36v one and a 48v 320 rpm one.

For general use and legal speeds, you want 260 rpm, and for speeds of just over 20 mph, 320 rpm.

In summary, a heavy rider with lots of hills and the 15.5mph limit would want a 260 rpm at 48v with 17 to 20 amp controller, which would blitz a Bosch crank drive in a hill-climbing test. A normal rider without too many hills would be OK with 260rpm, 36v and 15 amps. You have to decide where you are on the spectrum of power required. I'm 90 kg and I have very steep hills on my rides. I have a 320 rpm motor at 48v and 15 amps, which gives me all the power I need. It would be about the same as a Bosch motor on all but the steepest hills. I have a few crank-drive bikes, but they're all rotting in my garage along with various other high torque hub-motored bikes since I found ebiking nirvana.

 

[Bari Gadgi]

At any voltage, torque is proportional to current - more or less, so if you want more torque, you get a system that can supply and handle the current. 15 amps at 36v is enough for most people, especially if you have the 15.5mph limit. 20 amps is better for heavy people that have moderate hills, and 30 amps can drag heavy people up steep hills.

You also get more torque if you increase the voltge. If you take a standard geared hub motor and run it at 48v, you get 30% more torque than you would at 36v, so a motor running at 15 amps and 48v is equivalent to a 36v one at 20 amps.

It doesn't really matter what the nominal voltage of the motor is because it's a meaningless characteristic. The nominal voltage is only a base to specify it's rotation speed. A lot of people worry that running a 36v motor at 48v might over-stress it. That's not so. It's the current that stresses it and a higher voltage allows you to run less current.

The main thing you need to concentrate on is the motor's max RPM, which will affect various other characteristics like over-heating. Your goal should be to get a motor that will give your bike a maximum theoretical speed that's 25% more than your planned modal speed. 201 rpm is 15 mph (26" wheel), 260 rpm is 20 mph and 320 rpm is 15mph for a 16" wheel. These are the common motor speeds for geared hubs. A 36v 201 rpm motor would be identical in all respects to a 48v 260 rpm one, likewise between a 260 rpm 36v one and a 48v 320 rpm one.

For general use and legal speeds, you want 260 rpm, and for speeds of just over 20 mph, 320 rpm.

In summary, a heavy rider with lots of hills and the 15.5mph limit would want a 260 rpm at 48v with 17 to 20 amp controller, which would blitz a Bosch crank drive in a hill-climbing test. A normal rider without too many hills would be OK with 260rpm, 36v and 15 amps. You have to decide where you are on the spectrum of power required. I'm 90 kg and I have very steep hills on my rides. I have a 320 rpm motor at 48v and 15 amps, which gives me all the power I need. It would be about the same as a Bosch motor on all but the steepest hills. I have a few crank-drive bikes, but they're all rotting in my garage along with various other high torque hub-motored bikes since I found ebiking nirvana.

Wow. Thanks vfr400 you certainly know your stuff. Lots to think about and Google.
All this has been rattling around in the subconscious whilst I've been painting the utility room today.
In essence I could use my beloved Whyte with the correct hub motor spinning it's 27.5+ rear wheel and save a lot of heartache. I'd still have the original wheel, freehub and cassette which could be swapped out of things went pear shaped.
Even the specialised stumpy could run a hub if I could sort a decent battery position.
For your info I'm 6'0" and weigh 96kg and as mentioned hit some serious off road hills.
Unfortunately (covid 19 aside) I live in an area of Scotland that doesn't seem to have a great deal of bike convertors. Most bike shops around me are into your standard mega expensive ebikes and wouldn't give me the time of day. I'd love to have a whirl on someone's bike.
If anyone is in and around the Scottish Borders/North Northumberland and wouldn't mind giving me a shot on a bike or do this type of work that would be fantastic.

 

[h1llside]

. I have a 320 rpm motor at 48v and 15 amps, which gives me all the power I need. It would be about the same as a Bosch motor on all but the steepest hills. I have a few crank-drive bikes, but they're all rotting in my garage along with various other high torque hub-motored bikes since I found ebiking nirvana.

Hi vfr400

What motor do you have ?

Thanks

Mo

 

[vfr400]

Hi vfr400

What motor do you have ?

Thanks

Mo

Q128c from BMSBattery. A Bafang SWX02C is also good,, but the Q128c climbs a bit better due to its higher internal reduction ratio. My motor has been completely reliable over 6 years and 6000 miles even though it's spent a lot of time encrusted in salt, like it is now.