Help. Ebike conversion

[slowbutsure1936]

Hi

I have a Carrera Subway bike and bought a rear wheel conversion on the internet from a shop. All seemed to work fine until I picked up the bike and the back wheel fell out. I took it to a local bike shop as they said on the phone they could grind the rear forks a bit to make it fit. Having looked at it they said, because of the construction of the bike they can't grind it because it would affect the integrity of the forks and will likely snap.

Any thoughts on how to get over this?

Thanks,

Trevor

 

[Bonzo Banana]

Going to need more information ideally. Halfords have been doing the Carrera Subway model for at least 15 years and have had various different models plus they have changed manufacturers many times. Also which kit is it.

It may simply be that you need a torque arm kit to secure the hub motor. This type of thing. The Carrera Subway is a very generic type of bike, nothing proprietary not the sort of bike that should throw up too many issues. I'm sure you will get there in the end. It's a very generic derailleur hanger they fit to the frame one of the most common to replace. Also might be worth checking a few videos on youtube about Carrera conversions. The Subway is a model with rigid steel front forks but many Carrera mountain bike models have used pretty much the same frame as the Subway except they come with front shocks. So if you search for Carrera ebike conversion you may find some useful info if there are no videos about converting a standard Subway because effectively the rear of the bike will be the same and you have a rear motor. I personally wouldn't start grinding an aluminium frame the heat from grinding can undo the careful heat treatment of the frame that adds strength to it. It could slightly weaken it so I would avoid that if possible. In contrast the front forks are pretty much indestructable with normal use and you can hack those about a bit more. I'm sure I've watched videos on youtube of both direct drive and geared hub motors fitted to Carrera mountain bikes with great success.

 

[Andy-Mat]

Hi

I have a Carrera Subway bike and bought a rear wheel conversion on the internet from a shop. All seemed to work fine until I picked up the bike and the back wheel fell out. I took it to a local bike shop as they said on the phone they could grind the rear forks a bit to make it fit. Having looked at it they said, because of the construction of the bike they can't grind it because it would affect the integrity of the forks and will likely snap.

Any thoughts on how to get over this?

Thanks,

Trevor

How about a few photos of the forks and any damage to them caused by the wheel dropping out. Sizes too and lengths.
regards
Andy
PS. Close and sharp, from several useful angles....

 

[slowbutsure1936]

Thanks, im not sure a torque arm will help as the wheel just pops out, there isn't enough depth in the rear forks to hold the new wheel. The kit is a cycletricy kit 250/1000w dual power, 48v. Im going to pick it up now from the shop and will then take some pictures. The subway is about 5 years old.

 

[slowbutsure1936]

Pics attached.

 

[slowbutsure1936]

Having said the forks / drop outs are not deep enough, it’s only by about 3mm, but obviously enough to cause the wheel to pop out.

 

[Andy-Mat]

Pics attached.

Excellent Photos and very clear, many thanks.
I am reminded of the saying that a "picture is worth a 1000 words!"
The fork looks tiny to me personally, and I am not surprised that you are having problems.
But I am also interested in opinions of other here too.
My only thought, but not easy to achieve, but how I would go about it, would be to generously cut off the same piece from a scrap bike, and weld it securely and accurately in place of what you have now.
Or find another frame, and scrap the one you have now......
I am sorry for you that you have such a problem, hopefully someone here knows a proper fix.
Best wishes and happy Easter to all Pedelecers.
Andy

 

[slowbutsure1936]

Excellent Photos and very clear, many thanks.
I am reminded of the saying that a "picture is worth a 1000 words!"
The fork looks tiny to me personally, and I am not surprised that you are having problems.
But I am also interested in opinions of other here too.
My only thought, but not easy to achieve, but how I would go about it, would be to generously cut off the same piece from a scrap bike, and weld it securely and accurately in place of what you have now.
Or find another frame, and scrap the one you have now......
I am sorry for you that you have such a problem, hopefully someone here knows a proper fix.
Best wishes and happy Easter to all Pedelecers.
Andy

Thanks. Welding bits on is an interesting option I hadn't thought of. I think the frame is aluminium? which can be tricky to weld I think. Not impossible though. The opposition might be to return the kit and go for a mid-kit. As the shop assured me the kit would fit my bike because it was a "universal" kit, I would hope they would take it back.

 

[Andy-Mat]

Thanks. Welding bits on is an interesting option I hadn't thought of. I think the frame is aluminium? which can be tricky to weld I think. Not impossible though. The opposition might be to return the kit and go for a mid-kit. As the shop assured me the kit would fit my bike because it was a "universal" kit, I would hope they would take it back.

I forgt about Alumium, sorry.
But a good way of joining alumium without welding, is to do as I said before, but with very generous overlapping joints, and then rough up with sandpaper, then clean well with Meths (not petrol as it leaves residues), not touching with your fingers either, and then glue using a high quality epoxy for metal.
Finally, with fine Fiberglass bandage, or Carbon Fiber bandage, Epoxy that on the outside neatly.
That will be stronger than welding if done correctly, and does not care which part is Alu and which is steel also! And does not need painting except for show!
Best wishes.
Andy

 

[Bonzo Banana]

Those look like normal dropouts to me. Remembering that aluminium is softer material I think you will need at least one possibly two of the torque arms which will be steel and far stronger. There is a video here with another Carrera model with possibly similar rear dropouts on the frame. I only had a quick look so there may be better videos but this one looks useful. Also because the steel plate is on the outside of the dropout you will be able to tighten the nut a little bit tighter. The torque arm will stop the axle turning in the dropout if correctly installed and you can share the load if you install two torque arms so both sides won't drop. Maybe I've got the wrong impression so could you do a image of the axle in the dropout as far it will go if necessary removing any washers etc that might prevent it fully going in (make sure you remember their position) and then we can see how much of the axle is protruding around the rear dropout.

A front motor hub would have been the much easier option because of the steel forks but even on those you would want a torque arm fitted with a 1000W hub motor. I realise you may have it only set to 250W but its still a heavy direct drive motor hub of quite a few kgs extra over a geared hub motor.

I think the only type of hub motor where you don't need a torque arm is a weak small geared hub motor and bikes that come pre-configured with a hub motor may already have strengthened and deeper dropouts. You have to make yours suitable with a torque arm.

 

[Andy-Mat]

Those look like normal dropouts to me. Remembering that aluminium is softer material I think you will need at least one possibly two of the torque arms which will be steel and far stronger. There is a video here with another Carrera model with possibly similar rear dropouts on the frame. I only had a quick look so there may be better videos but this one looks useful. Also because the steel plate is on the outside of the dropout you will be able to tighten the nut a little bit tighter. The torque arm will stop the axle turning in the dropout if correctly installed and you can share the load if you install two torque arms so both sides won't drop. Maybe I've got the wrong impression so could you do a image of the axle in the dropout as far it will go if necessary removing any washers etc that might prevent it fully going in (make sure you remember their position) and then we can see how much of the axle is protruding around the rear dropout.

A front motor hub would have been the much easier option because of the steel forks but even on those you would want a torque arm fitted with a 1000W hub motor. I realise you may have it only set to 250W but its still a heavy direct drive motor hub of quite a few kgs extra over a geared hub motor.

I think the only type of hub motor where you don't need a torque arm is a weak small geared hub motor and bikes that come pre-configured with a hub motor may already have strengthened and deeper dropouts. You have to make yours suitable with a torque arm.

That all makes good sense to me personally.
Thanks
Andy

 

[Nealh]

The 1000w hubs usually have a 14 x 10 axle so getting the 14mm depth to sit in a std 9mm qr d/o doesn't work hence the axle simply rolls out. The difference is approx.2.5mm needs to be filed out of the d/o, fi possible. The brake side isn't an issue it's always the hanger/gear side. Ideally one needs all of the flat of the axle to bare within the d/o and then add two torque arms if possible, anti rotation washers are not enough on there own.
Most hubs geared hubs used don't cause much of an issue as they only need 1.5 -2 mm motor taken out but more power full hubs with the larger axle need a bit more work.

 

[Nealh]

Use a dremel tool with course milling bit and one should be able to take out about3 mm from both sides (or enough so the axle flat sits wholly within the d/o) , just be careful and match the axle seat profile for a snug fit. For torque arms make you own one piece arms out of steel 2 - 3mm should be thick enough (make sure the piece of steel is over sized) machine out the hole so it again match's the axle shape and use the tapped hole( up and slightly to the rear of the drop out) as the sole fixing point. Once one has the axle shape snug and it fits nicely over the axle, mark and drill the fixing hole. Once this is done one can then reshape the over sized plate to a nicer looking size.

 

[Bonzo Banana]

There is a lot of information on the Grin site regarding torque arms and some handy diagrams. They don't mention filing the dropouts on the page.

Torque Arms - Grin Products - Product Info

For every force there is an equal and opposite force, and for every torque there is an equal and opposite torque. Sadly with import hub motors this opposing torque is often born entirely by bicycle dropouts that are not up to the task, allowing the motor axle to spin out. Grin has pioneered the...

ebikes.ca

I'm sort of between Grin and Nealh regarding this but I have to bow my head to Nealh's greater experience. I have only fitted hub motors to steel dropouts and I prefer a front hub motor as I'm a very heavy rider and get 95% of my punctures in the rear wheel so want to keep that standard so I can quickly sort punctures. I do have a hub motor to install for a rear wheel but again its going into a steel folding bike frame so I have more flexibility and strength at the rear dropouts.

I won't deny it does worry me about removing too much material with regard a aluminium rear dropouts. I've always recommended the Carrera Subway as a great basis for converting to an ebike but that is because of its super strong chromoly forks which are ideal for a front hub motor. I did assume there wouldn't be too much difficulty in also fitting a rear hub motor though because so many have already been fitted to Carrera frame rear dropouts. Looking at those dropouts which are pretty standard actually for QR it seems less than ideal.

My instincts would be to just shape the dropout to be a perfect fit for the hub motor axle i.e. just remove a tiny bit of material and then rely on the torque arms but I admit this may be the wrong advice and maybe should be ignored.

If you end up with a rear wheel that is time consuming to remove when you get a puncture then consider a tyre liner and using a ultra thick downhill inner tube plus use sealant in the inner tube.

 

[Benjahmin]

I agre, I think you're going to have to deepen the dropout. I've used these in the past, they are very sturdy and can be configured many different ways
:https://www.ebay.co.uk/itm/144327018082?var=0&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338268676&toolid=10044&customid=Cj0KCQjw0umSBhDrARIsAH7FCoe_sayR9Gy6POPVUWYVkTOU1oI9YOGhJTlSDWBmFZn37E7Qks8FwTsaAt7XEALw_wcB


I would try to use two but, as Nealh says, the gear side is going to be tricky.
Alternatively, sell that great hulking direct drive and buy a geared hub. It'll give you an all round better experience and be much kinder to your battery - and be legal.

 

[Bonzo Banana]

I agrehttps://www.ebay.co.uk/itm/144327018082?var=0&mkevt=1&mkcid=1&mkrid=710-53481-19255-0&campid=5338268676&toolid=10044&customid=Cj0KCQjw0umSBhDrARIsAH7FCoe_sayR9Gy6POPVUWYVkTOU1oI9YOGhJTlSDWBmFZn37E7Qks8FwTsaAt7XEALw_wcBe, I think you're going to have to deepen the dropout. I've used these in the past, they are very sturdy and can be configured many different ways:
I would try to use two but, as Nealh says, the gear side is going to be tricky.
Alternatively, sell that great hulking direct drive and buy a geared hub. It'll give you an all round better experience and be much kinder to your battery - and be legal.

There is nothing illegal about a direct drive hub motor configured with a controller giving out 250W nominal and only assisting up to 15.5mph. In fact many commercial mid-drive motors like Bosch peak at far higher watts, over 700W. It has to be large due to the simple design internally without planetary gears. Yes they are heavier but you don't have the small power loss in the planetary gears or the large power loss of mid-drive which has more significant losses through the drivetrain. I think the most efficient motor was a geared hub with the freewheel clutch disabled so it could have regen and that was something like 7W a kilometre (or possibly mile) and the most efficient direct drive was 9W I think. However a geared hub without regen was something like 9-10W. Anyway there is a fair comparison here between the different systems;

For many the extra strength, simplicity and reliability of direct drive makes its the ideal choice and with regen enabled it can significantly reduce brake pad wear and of course unlike mid-drive it extends drivetrain lifespan like all hub motors.

The issue here is the aluminium frame QR rear dropouts. No reason to think this won't be a fantastic ebike when sorted.

 

[slowbutsure1936]

Thanks everyone, this is certainly the place to be!

I’ve ordered a Dremel tool from Amazon. I have one torque arm that came with the kit. The problem I’m going to have is getting a torque arm on the non-geared side as there is no room on the spindle, but plenty of room on the geared side, oddly! The whole wheel is a difficult fit, you have to prize the forks apart and use spacers.

I do like the idea of making my own torque arm with steel but my skills are very rudimentary in that area. I guess it doesn’t have to be pretty.

I’ve always loved my subway and am nervous about grinding it but I’ve come this far so feel I’ve reached the point of no return

 

[Nealh]

Though filing isn't mentioned the Grin page diagrams shows the axle filly in the d/o with the flats of the axle well covered by the d/o, ali can and will over time spread/wear if no torque arm/s are used to counter the rotation. No standard bike frame will have drops outs that deep whereby no milling/filing is required, most are to accommodate 9mm axles.

Rear ali d/o's are better for fitting then front ali for d/o's which have little strength in them.
The reason for the axle flat to sit in well is to prevent the roll out effect if not done so, given the chance the roll effect will cause miute spread and fracture of the ali d/o.

 

[Nealh]

At all costs avoid securing a torque arm using the hose clip method, a secure fixing via a threaded bolt hole or a through hole with a snug bolt and nut fixing.

Both sides of the d/o'd need to be milled out equally so the axle sits horizontal, don't rush the job. Better to take a little at a time out then go mad.

 

[Nealh]

The D/D hubs axle are 14mm deep, I have yet to find a d/o this deep unless it is horizontal one used for hubs geared bikes or fixed gear bikes which the design is for whee position/chain tensioning. The grin site diagrams would suggest the drop out is already some 15 or 16mm in depth which one won't find on a standard bike.
Ultimately steel is the best fork material more so a front fork.