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I have an Electric Bike with rear brakes which are not as strong as front disc brake (countless amount of tweaks never solved it well without rubbing the wheel too much). So, I am looking at converting to disc brakes

Is it possible? Using which products? I was thinking of a start with those two: http://www.aliexpress.com/item/MTB-Disc-brake-flange-disc-tray-adapter-screw-thread-switch-disk-disc-tray-refires-disc-brake/32312668990.html

And since I cant post more than 2 links, search on AliExpress for "brand new hs1 brake rotors" - the one from "Store:Carbon-Bicycle Co.,Ltd" for 9$ is the one that was recommended.

But I lost contact with the guy who guided me to those once in a train, so I don't know how to proceed what else do I need...

The frame is made of aluminium, and below you can see pictures of the read wheel, to understand the construction and my options...

Second image

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Note: The question referred to: Disc brakes on leader doberman which has no tabs and adaptors

Deals with question on how to piece together parts for the specific branded Doberman frame, while in my case, I am not entirely sure which parts do I need, and my frame is Chinese generic no-brand frame, making it much more difficult to find the correct parts that would fit together well.

  • Second picture: i.stack.imgur.com/9PIZ0.jpg – Carmageddon Jan 31 '16 at 11:11
  • The main thing to remember is that those bolt on mounts are trying to achieve by friction something that framebuilders struggle to achieve with welded metal. It's disturbingly easy to make a disc tab that's almost strong enough. The good news is that when those fail they're likely to stop the wheel going round altogether, so you will still stop. Also, they look really flimsy, welded mounts are normally at least twice as thick as those tie-on ebay ones. – Móż Jan 31 '16 at 11:17
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    Having worked on am electric bike, two things occur to me: dealing with the back wheel is hard enough without disk brakes getting in the way; you barely need back brakes - the back wheel is so heavy it's never going to lift off the ground so you can brake very hard with the front brake with no fear of going over the bars. In addition cheap disk brakes are no better than good rim brakes. I suggest you put really good pads on first. – Chris H Jan 31 '16 at 12:08
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    My earlier comment has gone missing, but I found the kool stop dual compound pads where the metal back is fixed and only the rubber replaced are very effective and hard wearing. The previous XLC pads I had aren't much less effective even in the wet, but wear faster. This all assumes alloy rims. – Chris H Jan 31 '16 at 13:39
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    Most of your braking power is from the font. Pretty evasive and costly for little benifit. I can lock up the rear wheel on any of my rim brakes on the street. – paparazzo Jan 31 '16 at 17:27
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In general, on electric bikes, the rear hub is an essential part of the electric motor/drivetrain in order to power the bike and is very different from rear hubs on standard 'manual' bikes.

Because of this, in order to have a rear disc brake system you'd need to replace your hub (or whole wheel if this isn't possible) with one that has disc brake rotor mounts. You won't be able to use the screw on aluminium one linked to in your question.

Secondly, you'll have to install a retrofit device onto your frame to mount the disc brake caliper. These are available with vary degrees of quality but looking at your frame, you'd need to remove the pannier rack which I assume you probably don't want to do.

I think it may be fruitless to pursue this conversion to be honest and if you have a disc brake on the front of your bike this is where to majority of effective braking should be happening anyway - simple rule is that you should use the front brake to slow your bike down until the point where you can use the back brake to bring your bike to a stop.

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  • Yes, the chances are good need to get the wheel professionally rebuilt, quite possibly by an electric bike specialist, even if you can get the parts. – Chris H Jan 31 '16 at 13:01
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    Thank you for your reply Adam. I don't understand why do you say I would need to replace the hub motor? If you look at the first picture again, you would see that right after the hub motor shiny cover ends on the left, there is an external thread, which apparently suits the Adapter Block linked on Aliexpress. – Carmageddon Jan 31 '16 at 13:06
  • @Adam: About your final comment, I think you missed this piece in my comments on the question: "my problem is not whether rear wheel lifts off ground when I use forward disc brake, but that I CANT use forward brake at full force without significant risk of the front wheel dangerously loosing fraction, and end up slipping and falling with the bike! I had this happen to me, which is WHY I want the rear brake to be much more powerful than the current V brake is" – Carmageddon Jan 31 '16 at 13:07
  • @ChrisH: Why do you say its likely that I'd need to rebuild the wheel? – Carmageddon Jan 31 '16 at 13:09
  • See other comments on whether adaptors would fit, and how well they'd work if so. Consider how a rotor could fit next to a hub like you've got. – Chris H Jan 31 '16 at 13:37
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I would not try to change to disc brakes. The Late, Great Sheldon Brown did write an article on braking, and it covers things better than I could: SheldonBrown's Braking Article

You may want to try a different compound on your existing brake. I have had good luck with KOOL STOP dual compound pads in the past, but shimano makes some good ones too. Don't use generic brands, they don't stop as well. Also, degrease the rim, it looks dirty in your pictures.

If you 'must have a rear disc', the best path forward is to swap to a disc-frame and get a new rear wheel/hub. Assists are very 'invasive' to the whole bike design, so an upgrade that impacts the assist is usually more economical to implement by changing the entire bike. Sometimes, in these cases, the best answer is 'no'.

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  • I have left the bike today at a store who can straighten the rear wheel - it has bends on it which prevent perfect read brake calibration so that it can stop the wheel, but also not rub it all the time. Hopefully this will resolve my problem. I also spoke to one mechanic, he says those KOOL STOPs where the pads are removable/replaceable are not holding well, and escape especially in electric bikes.. so he doesn't recommend those. – Carmageddon Feb 1 '16 at 10:35

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