Newbie question about ebike derailleurs

[John Galvin]

Hi

Probably a stupid question.
If I buy a 20" rear wheel prebuilt with a motor, is it guaranteed that my original 9 speed derailleur cassette will fit?
I'm talking specifically about a Tern Link P9. Is there any spec I need to look out for?

TIA

 

[Arbol]

No, it is not guaranteed.

Most motors are for freewheels. There are motors prepared for cassette, but this is usually advertised.

What I do not know is if one could use a DNP 9 speed freewheel with a non-cassette motor, and use a standard 9 speed derrailleur, without further changes. If this were the case, the only disadvantage would be that you could not use your current cassette (and possibly the freewheel has a lower quality).

 

[Deleted member 4366]

Your cassette won't fit unless you get a cassette motor like the Q100CST. Most motors take free-wheel gear-sets. A 7-speed one is about as wide as you can go, and you need a DNP one with 11T top gear otherwise you won't be able to pedal fast enough. Be aware that if you get a Q100CST, you'll probably have to dish the wheel yourself because the Chinese suppliers normally build it with the rim central to the n=spoke flanges, which are off-set from the axle stops.

 

[John Galvin]

Your cassette won't fit unless you get a cassette motor like the Q100CST. Most motors take free-wheel gear-sets. A 7-speed one is about as wide as you can go, and you need a DNP one with 11T top gear otherwise you won't be able to pedal fast enough. Be aware that if you get a Q100CST, you'll probably have to dish the wheel yourself because the Chinese suppliers normally build it with the rim central to the n=spoke flanges, which are off-set from the axle stops.

Thanks for that. It looks like it's a lot more complicated than I thought.
I had a brainwave and I can get a steel fork for the Tern that I'm thinking of using. It doesn't cost much more than the two torque arms I was going to put in and it weighs just 220g more than the aluminium item, which I reckon is around the weight of two solid arms.
Back to a front hub and 2wd.

Thanks

 

[Deleted member 4366]

How wide is the fork. I bet it's too narrow for most motors, but you can open them up a bit seeing as they're steel. So 328 rpm Q100 front motor should e perfect.

 

[Arbol]

Your cassette won't fit unless you get a cassette motor like the Q100CST. Most motors take free-wheel gear-sets. A 7-speed one is about as wide as you can go, and you need a DNP one with 11T top gear otherwise you won't be able to pedal fast enough. Be aware that if you get a Q100CST, you'll probably have to dish the wheel yourself because the Chinese suppliers normally build it with the rim central to the n=spoke flanges, which are off-set from the axle stops.

So, 9-speed DNP freewheels do not fit a freewheel motor?

 

[Cyclezee]

So, 9-speed DNP freewheels do not fit a freewheel motor?

We have fitted up to 10 speed Sunrace freewheels with eZee conversions and many DNP 9 speed.

BTW, our latest torque plates / arms made in the UK are selling like hot cakes and mostly going abroad.
Nice to be exporting a British product

 

[trex]

I am surprised at why you discarded the crank drive option so quickly. For folding donor bikes, crank drive is the best option except when it interferes with the fold (eg BBS01 on Brompton). You get to keep the wheelset, brakes, gears as they are and get better weight distribution, speed and torque in comparison with hub kits. Is it the cost?

[edit]
to John Galvin.

 

[Cyclezee]

I am surprised at why you discarded the crank drive option so quickly. For folding donor bikes, crank drive is the best option except when it interferes with the fold (eg BBS01 on Brompton). You get to keep the wheelset, brakes, gears as they are and get better weight distribution, speed and torque in comparison with hub kits. Is it the cost?

Hi Trex,

I have already explained my reasons in this thread http://www.pedelecs.co.uk/forum/threads/8fun-bbs-01-kits.17365/

If anybody wants one Hatti @ Woosh is the place to go.

 

[trex]

sorry cyclezee, the post should have been marked for John Galvin

 

[Cyclezee]

sorry cyclezee, the post should have been marked for John Galvin

My fault Trex

 

[trex]

No my fault. You are always too polite.

 

[Cyclezee]

No my fault. You are always too polite.

I'm terribly sorry Trex, but I must insist everything wrong in the world is my fault, global warming, wars, the state of the economy, punctures, floods, broken spokes, Scotland failure to qualify for the World Cup, flat batteries the NHS etc., etc.

 

[Deleted member 4366]

So, 9-speed DNP freewheels do not fit a freewheel motor?

You can fit any number of speeds to the motor. The question is whether you can get the assembly in the frame. When you have a frame for 20" wheels, the seat-stays and chain-stays are very short, so not nearly as flexible as a frame for larger wheels. I haven't fitted a motor to a Tern, but it was a tight squeeze to get the seven-speed in my Dahon; however, the Tern frame doesn't look as stiff. I'd need imformation on the stack-heights of the 9 and 10 speed Sunrace ones to pass comment on them. I'd guess that they're about the same width as the 8 speed ones.

 

[John Galvin]

It's weight primarily. I'll have another look but I reckon a mid drive would be a bit heavier, albeit at the bottom of the bike. Would the BBS01 or 02 fit on the Tern?

I am surprised at why you discarded the crank drive option so quickly. For folding donor bikes, crank drive is the best option except when it interferes with the fold (eg BBS01 on Brompton). You get to keep the wheelset, brakes, gears as they are and get better weight distribution, speed and torque in comparison with hub kits. Is it the cost?

[edit]
to John Galvin.

 

[trex]

the BBS01 will look quite nice on your Tern. The motor would be snug in front of the bottom bracket. You should count the number of teeth on your chainring. The BBS01 comes with 46 teeth chainring. The one on the Tern looks like 46T too. If this is the case, pedalling will be same, only assisted.
The battery could go on a seat post rack or front bag.

 

[Deleted member 4366]

The tern has a big chain-wheel - 52T IIRC., so you have to pedal 12% faster for the same speed. You might find that a bit uncomfortable. 46/11 on a 20" ike will be similar to a cheap 26" MTB with 44/14 gearing. They're OK up to about 15 mph, ut you can rarely pedal down-hill.

 

[John Galvin]

I don't think that would be too workable. Besides, the BBS01 is not supposed to be used with a nine speed derailleur. The info on their site says that as they're narrower than normal, the chain can wear quickly.

 

[amigafan2003]

I don't think that would be too workable. Besides, the BBS01 is not supposed to be used with a nine speed derailleur. The info on their site says that as they're narrower than normal, the chain can wear quickly.

Nonsense.

I run my BBS02 on a 10 speed set up. Despite what intuition says, narrow 10 speed chains are no weaker than 7/8 speed chains (and most are stronger, as it's getting harder to find good quality 7/8 speed chains now the market has moved on) and wear is not greater with narrow chains.

 

[trex]

amigafan2003 - I agree with you. I can't see why 9/10 speed chain should be any weaker.
Do you think your BBS02 would win in the Bristol Park Street race?