26" BMX DK Legend Build

[BallHarder]

This is my first "build" so I wanted to document the process.

I'm starting with a DK Legend 26" BMX bike.



This has been a really fun bike. It has been my main mode of transporting my daughter to the playground and I've taken it to the pump track a few times. Seems very sturdy and well built. Excuse the redneck bike stand setup and cluttered garage.

I bought a 2000w 4t hub motor and 60v 30ah battery all from Leafbike. I placed the order and paid on December 13, 2023 and received the hub motor kit on December 27.


Everything was packed very well.



Here's everything I was sent. The motor/wheel, two throttles, 16t sprocket, controller, charger, pedal assist ring, brake levers and the display. I was too excited to wait for the battery.


If only I didn't need a battery! I'm happy with the look so far. I temporarily used zip ties until I can get some cable wraps for the brake lines and LCD wires.

I did notice that the axle on the wheel is smaller than the OEM wheel. I'm curious if you all would recommend some kind of spacer? Or would some aftermarket torque arms make sure the wheel stays on?

 

[neptronix]

Let's see a picture of this axle mis-fitment.

You will want a pair of torque arms on a motor like this even if you didn't have axle problems.

 

[BallHarder]

Here's a couple pictures of the axle and drop out. Is there a universally recommended torque arm for bikes that don't have the disc brake nuts welded to the subframe?

 

[neptronix]

Yikes. I don't feel confident about saying to use that even with a pair of torque arms.
The problem is that the torque arms are going to handle all of the axle torque and weight themselves basically.

You got the wrong axle motor for the bike and whatever you are going to do to make this work will involve drilling into, maybe welding the frame to turn that dropout into a 10mm dropout.

This looks like maybe a 14 mm axle which i have not heard of a single hub motor working with.
There exist hub motors that fit 12 mm axles but not 14 mm.

 

[BallHarder]

That’s very frustrating. I emailed back and forth with Peter at Leafbike quite a few times before placing my order. I sent him the specs and link to my bike.

I’ll email the company and see what they say.

 

[BallHarder]

What about these?

HUB AXLE ADAPTER KIT-14mm TO 3/8″(10MM)

HUB AXLE ADAPTER KIT-14mm TO 3/8″(10MM) Machined from super hard 7075 aluminum, these 3/8″(10mm) axle to 14mm dropout adapters are much lighter than a steel version, but just as strong! -Price is for a set (2-alum adapters & 2-steel washers) Weight: 16g/.56 oz Shipping to the Contiguous US is...

www.profileracing.com

 

[calab]

Get a machinist to make you some beefy steel inserts to bolt onto the dropout and keep the power down, dont do jumps and look for another bicycle.

 

[neptronix]

What about these?

HUB AXLE ADAPTER KIT-14mm TO 3/8″(10MM)

HUB AXLE ADAPTER KIT-14mm TO 3/8″(10MM) Machined from super hard 7075 aluminum, these 3/8″(10mm) axle to 14mm dropout adapters are much lighter than a steel version, but just as strong! -Price is for a set (2-alum adapters & 2-steel washers) Weight: 16g/.56 oz Shipping to the Contiguous US is...

www.profileracing.com

That might actually work in addition to torque arms. I would personally consider running two torque arms on one side, 1 torque arm on the other, to make up for the fact that your axle isn't holding any of the torque itself.

I can't vouch 100% for that though.. let's see what others think

 

[Chalo]

What about these?

HUB AXLE ADAPTER KIT-14mm TO 3/8″(10MM)

HUB AXLE ADAPTER KIT-14mm TO 3/8″(10MM) Machined from super hard 7075 aluminum, these 3/8″(10mm) axle to 14mm dropout adapters are much lighter than a steel version, but just as strong! -Price is for a set (2-alum adapters & 2-steel washers) Weight: 16g/.56 oz Shipping to the Contiguous US is...

www.profileracing.com

Problem with any such stepped washer is it has a 3/8" or 10mm round hole, and your axle is 14x10mm. It won't fit.

If you get or make a custom torque arm, put the axle hole oriented vertically in the slot, to fully occupy its width.

 

[neptronix]

Damnit, he right..

It might be possible that adapter this works with the grin all axle motor. It has a different kind of torque arm. You might want to check with ebikes.ca.

 

[amberwolf]

V7 Regen Torque Arm 14mm

V7 Torque Arm with Machined Clamping Block for Regen Hub Motors. Fits M14 Axles in both Front and Rear Installations.

ebikes.ca

V7 Regen Torque Arm 12mm

V7 Torque Arm with Machined Clamping Block for Regen Hub Motors. Fits M12 Axles in both Front and Rear Installations.

ebikes.ca

 

[neptronix]

Interesting.. too bad you can't stack them on top of each other to get a hopefully strong enough dropout that is stronger than the OEM dropouts.

I would feel better about some 1/4 inch steel torque arms bolted into the frame..

 

[amberwolf]

There are options for making those, too--see The Torque Arm Picture Thread for examples and links....

 

[BallHarder]

I guess I should have posted before I bought everything!

Those torque arms look solid. As long as I can find a way to get them to the US I’ll pick them up. I also bought the 10 to 14mm spacers to see if they’ll work.

 

[BallHarder]

If you get or make a custom torque arm, put the axle hole oriented vertically in the slot, to fully occupy its width.

That is a good point and I'll keep that in mind. Thank you.

 

[BallHarder]

Leafbike got back to me saying: "

This shaft is 14mm. Also, you received motor's shaft is 14mm. (The dia. of 14mm)

But, flat should be 10mm that fit for standard bikes' fork. (All of standard bikes 's fork is 10mm)

So, does this mean I would need to buy two of the 14mm version of the V7 torque arm? The Grin website says that you should only use it on the non wire side of the bike.

It slides over the non-wire side of the motor axle, engaging with the 10mm axle flats to prevent the axle from spinning out inside the dropouts.

 

[amberwolf]

Those torque arms look solid. As long as I can find a way to get them to the US I’ll pick them up.

Just order via the linked pages.

 

[amberwolf]

Leafbike got back to me saying: "

So, does this mean I would need to buy two of the 14mm version of the V7 torque arm? The Grin website says that you should only use it on the non wire side of the bike.

In your case, you have to support the axle some way other than the dropouts, so you have to use one on each end. I'd still recommend making something to support the axle in the dropout itself (to fill the space around it), even if it's just a stack of "axle washers" that have the double-D shape at their core (instead of round) that you grind or file so they do that.

Optionally, you can manufacture a torque plate (see The Torque Arm Picture Thread) to do the same job, that you then bolt to your existing dropouts, that adapts your frame to the axle size actually being used.

The size you need depends on the diameter of the threaded portion of the axle (the flats are usually between 9 and 11mm; don't count on them being exactly 10mm as they rarely are).

 

[BallHarder]

Just order via the linked pages.

I'm just dense. I missed the country drop down in checkout.

I just want to be sure. I need a pair of the 14mm V7 torque arms? Leafbike said that the diameter of the shaft is 14mm but with 10mm "flats".

 

[neptronix]

I guess I should have posted before I bought everything!

That's what we're here for!

So, does this mean I would need to buy two of the 14mm version of the V7 torque arm? The Grin website says that you should only use it on the non wire side of the bike.

Two of these are not strong enough to support your wheel alone without the dropout.

When referring to the diameter of an axle, we're talking about this part being 14mm wide: (\\\)
..but with an axle flat section being implied that it's 10mm..

 

[BallHarder]

look for another bicycle.

The problem is I can’t find a single 26” BMX bike that has 10mm rear drop outs. They’re all 14mm or 3/8”.

I think this is a misleading listing on Leafbikes behalf. It’s marketed as a 26” BMX kit but as far as I can tell there isn’t a bike being made today that it would fit. I’m really disappointed that I either have to find someone to modify the bike or accept that I have a $500 paper weight.

 

[BallHarder]

Optionally, you can manufacture a torque plate (see The Torque Arm Picture Thread)

This is intimidating. I have no idea where to find a machinist who would be willing to do such a small job. I’ll ask around.

 

[2old]

Alternatively, you can retain your BMX and procure a 26" steel MTB frame (small if you want it BMX-like). Since you're in CA, there are many on CL. Recently, I built a similar bike with a Specialized aluminum frame, 1000w DD kit and blingy parts from the bin. Interestingly (to me), the rear wheel weighed 18 pounds and the rest of the bike about the same. This isn't the final form since the wires are exposed etc, but it rides fine.

 

[BallHarder]

Alternatively, you can retain your BMX and procure a 26" steel MTB frame (small if you want it BMX-like). Since you're in CA, there are many on CL. Recently, I built a similar bike with a Specialized aluminum frame, 1000w DD kit and blingy parts from the bin. Interestingly (to me), the rear wheel weighed 18 pounds and the rest of the bike about the same. This isn't the final form since the wires are exposed etc, but it rides fine.

That’s a nice alternative. I really like the ergonomics of my big boy bmx but I’ll see what’s around. Thanks for the suggestion.

 

[BallHarder]

Alternatively, you can retain your BMX and procure a 26" steel MTB frame (small if you want it BMX-like). Since you're in CA, there are many on CL. Recently, I built a similar bike with a Specialized aluminum frame, 1000w DD kit and blingy parts from the bin. Interestingly (to me), the rear wheel weighed 18 pounds and the rest of the bike about the same. This isn't the final form since the wires are exposed etc, but it rides fine.

Actually that probably won’t work. The dropouts on my bmx are 110mm and the motor won’t support much wider than that. I think all the mtb dropouts are at least 135mm.

What a mess…