bolt on brake disc adaptors, any good?

jimmyhackers

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these things?

https://www.ebay.co.uk/itm/185216785924?var=692975752168

im planning on retrofitting a rear disc to my 20" hub motor bmx thing. im laxy, and wondered if these are any good?

if not it'll be making a bracket then welding it to the swing arm.
 
jimmyhackers said:
these things?

https://www.ebay.co.uk/itm/185216785924?var=692975752168

im planning on retrofitting a rear disc to my 20" hub motor bmx thing. im laxy, and wondered if these are any good?

if not it'll be making a bracket then welding it to the swing arm.

I have one of those in my parts box. The orientation of the dropout slot doesn't align with any frame that I've seen, but I think it's best suited for a horizontal dropout, if any.
 
Whenever I see used examples of those (I work in a donation supported community bike shop), they're bent. I strongly doubt you can use one without having the rotor rub all the time.

These seem a little less hokey, and are designed to fit rear opening dropouts:

https://www.ebay.co.uk/itm/283419290000
s-l400.jpg
 
Chalo said:
Whenever I see used examples of those (I work in a donation supported community bike shop), they're bent. I strongly doubt you can use one without having the rotor rub all the time.

These seem a little less hokey, and are designed to fit rear opening dropouts:

https://www.ebay.co.uk/itm/283419290000
s-l400.jpg
Made in Florida, so I thought I would add the US ebay link (shipping is a lot less for those of us in the colonies) ....
https://www.ebay.com/itm/283419290000?

I have never been able to find the documentation of the appropriate dimensions for a disk caliper mount relative to the axle. I am certain that is probably due to my ignorance. I might order one of these just to reverse engineer the those dimensions.
 
LewTwo said:
Made in Florida, so I thought I would add the US ebay link (shipping is a lot less for those of us in the colonies) ....
https://www.ebay.com/itm/283419290000

OP is in Old Blighty, so that's why I grabbed him a .uk link.

I have never been able to find the documentation of the appropriate dimensions for a disk caliper mount relative to the axle. I am certain that is probably due to my ignorance. I might order one of these just to get the those dimension.

View attachment is_e_09-12-02_11.pdf

Screenshot_20220627-161501.png
 
Chalo said:
is_e_09-12-02_11.pdf
Thank thee :thumb: :D

Edit, 5 August 2022:
What I failed to understand (something that everyone else likely already knew) was that the inside surface of the disk mount and the inside surface of the dropout were to be the same surface/offset.
Bicycle Disk Brake Dims 07.jpg
 
You can get them at Bikeberry for $13 plus a few dollars shipping.

https://www.bikeberry.com/products/bbr-tuning-billet-aluminium-disc-brake-caliper-bracket?variant=36268020564134&/?utm_source=google&utm_medium=cpc&utm_campaign=PMAX%20high&gclid=CjwKCAjwquWVBhBrEiwAt1Kmwp5hVOQYF9G0JyX8O5U-vUo0oITvMs_aDz1Uio_BoZGRdqw1Ew5HIRoCVK8QAvD_BwE

They were designed, I think, for gas powered bikes. I have one on a steel frame fat tire bike, and I recently installed one on a front fork of another bike. A lot of cutting of excess metal was involved. but I have a sawzall. The picture shows a failed brace that I didn't use. as the hole spacing was wrong.


fab_work.jpg

It's pretty solid, anchored at the axle and the fork prvents any further movement, but I added the bracket to be sure. I also added a torque arm which is not in the picture. I can drop the motor, and the bracket stays aligned on the fork.

P4230809.JPG
 
Note that add-on disc tabs alter the spacing of your hub, and will make the rim run off center if not accounted for. They'll also require you to spring the fork or frame ends wider to install the wheel, unless you remove an equivalent amount of left side axle spacing to make room.
 
I don't think I saw much of a problem with the wheel being off center. Before I had the disk adapter, I was using rim brakes and I had to dish the hub wheel to center it. I can certainly do that again.

I ran a 135mm rear hub motor for a brief time in the front fork of a fat tire bike, I was surprise that it could be dished, but I centered it.

Here is another bolt on adapter I'm using. They clamp onto the frame, and are intended for a thru-hole skewer or axle/nut. I am using one like that with a non power rear wheel.

PICT0011.JPG

For ebike wheel, I cut a slot so I could drop in the motor axle, and while you cannot see it, I put holes in the dropout so it's screwed to the frame, but I still have some bracing to resist twist.

IMG_2024.JPEG
 
LewTwo said:
What I failed to understand (something that everyone else likely already knew) was that the inside surface of the disk mount and the inside surface of the dropout were to be the same surface/offset.
Bicycle Disk Brake Dims 07.jpg

That's true only for the rear brake tabs. Front tabs are offset 4mm outboard of the inside surface of the fork tips.
 
Here's another option:
https://www.chasertech.com/disc-brake.html

RJ the Bike Guy reviews several adapters and installs the Chaser Tech adapter on a regular bike:
https://www.youtube.com/watch?v=emW7M-ZD0Pw

I was researching this topic because I'd like to install a cable actuated hydraulic disc brake on the rear wheel of my Trek 7300 which has a Grin SX2 rear hub installed. I'm more interested in eliminating the wear on the rim than I am in greater braking power.

I had just given up on the idea because the Chaser Tech adapter plate that attaches to the dropout appears to be too thick, the adapter posted by docw009 is designed for QR, and I'm not trusting my life to the adapter posted by the OP.

So to docw009 I say "Cool Beans!" I'll be returning the Shimano rear V brake I just ordered and will be ordering the adapter featured by docw009 and a TRP HY/RD brake.
 
brash54 said:
be ordering the adapter featured by docw009 and a TRP HY/RD brake.

I have neither observed nor heard anything good about HY/RD brakes. Seems like a lame way to have all the drawbacks of both kinds of brake, plus the drawbacks of a hokey add-on disc adapter, instead of getting better braking from a simpler, lighter, better looking, and much more maintainable V-brake.
 
Thanks for your advice. Appreciate the feedback from someone with insight into the particulars. I had read some positive feedback for the TRP, Juin, and one other cable actuated hydraulic disc brake. I need to put the computer away and go ride my bike.

After taking another look at the dropouts on my bike, I see that they're not flat, and I have no intention of filing them down or drilling holes in them. I'll be installing the Shimano V brakes after all.

Cheers!
 
Kool Stop pads would be a big upgrade from stock, if you feel you could use more braking power. Also if the seat stays spring apart when you apply the brake hard, you can add a booster arch to reinforce the brake bosses.

https://www.ebay.com/itm/265804020625
s-l400.jpg
 
I am trying to design a generic rear dropout disk brake adapter. I had difficulty finding some of the dimensions I needed for this effort. Most notable is the distance between the inside face of the dropout and the front surface of the disk rotor. Ultimately I had to measure it from the one sample I had. As close as this old redneck can come is 14.80 mm but I decided to call it 14.75. In this picture the critical dimensions are noted with red letters on a yellow background. The dimensions in blue are for reference.
(picture removed)

Update:
Well I screwed that up ... I used the radius lengths for the front fork on the rear hub.
See the updated version below.
Generic Disk Adapter Clearance Dims(22 Aug 2022).png
 
LewTwo said:
Most notable is the distance between the inside face of the dropout and the front surface of the disk rotor. Ultimately I had to measure it from the one sample I had. As close as this old redneck can come is 14.80 mm but I decided to call it 14.75.
is this useful?

https://endless-sphere.com/forums/viewtopic.php?f=2&t=88269&p=1287983&hilit=rotor+face#p1287983

Chalo said:
If I remember correctly, International Standard bicycle disc brakes specify a rear rotor mounting surface exactly 15mm from the hub lockout face/inner dropout face. If your hub and a threaded six bolt adapter can be made to provide that amount of offset, then a disc brake caliper should be able to mount normally to engage the rotor.
 
amberwolf said:
is this useful?
Yes, thank thee :D

I was guessing that they were shooting for 15 mm but decided to err on the side of caution. I would rather have a bit of extra clearance than a bit of interference.
 
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