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Bracket For Using Seat Post Bicycle Lights On Your Rack

Picture of Bracket For Using Seat Post Bicycle Lights On Your Rack
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This Instructable will show how I built a bracket that allows me to attach seat post mounted lights to the back of my bicycle's rack.

After researching to find the best rear flasher, I decided upon the Planet Bike Superflash. Unfortunately, it's designed to be mounted to the seat post, or by using a clip, to a saddle bag, backpack, or anything with a loop. The clip on the Superflash isn't strong, as some reviewers of the product write. Also, the Superflash does not have a screw for mounting to a rack.

I use a rear rack on my bike to mount pannier bags and the occasional package. I also use a saddle bag to carry a tool kit, cellphone, and other necessities. With all of this stuff on my rack and under my saddle, mounting a light on my seat post isn't an option.

My rack has a tab on the back where I can mount a light or reflector using a single screw. Using a handful of spare parts, I was able to construct a bracket that extends from the back of my rack and provides a tubular structure where the seat post mounted light can be attached.
 
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Step 1: Gather your tools and supplies

Picture of Gather your tools and supplies
I used the following tools and supplies:

PVC pipe that approximates the diameter of a seat post
Seat post mounted rear light
Hex key/Allen wrench set
Screwdrivers
Pliers
Metal brackets or any scrap metal that could be bent into desired shape. Note: hardware stores carry metal straps that have holes pre-drilled in them.
Hacksaw for sawing the pipe and bracket
Drill or knife for making holes in the pipe
4M hex screws with split lock washers and wing nuts

As luck would have it, I found a piece of PVC pipe on the side of the road. All I had to buy for this project was a handful of screws, nuts, and washers.

Note that I don't have my Superflash yet. I'm substituting my current Trek Flare 7 light in the meantime.

Step 2: Make a bracket to hold the pipe to the rack

Picture of Make a bracket to hold the pipe to the rack
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I got lucky when I bought my rack in that it came with several different sized and shaped metal mounting brackets for securing the rack to the eyelets on the back of my bike. One of the brackets was suited perfectly for this project. All I had to do was make an extra bend or two to get the shape I needed.

Using your favorite clamp (Vise grips, pliers, C-clamp, etc.), bend your bracket to suit your particular rack. You may need to use a hacksaw to cut the bracket. If so, consider using a file to smooth out any sharp edges or burrs.

Step 3: Prepare the pipe to accept the seat post mounts

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Test fit the seat post mounts to the pipe to ensure a good fit. Use extra rubber spacers if you need to add more girth.

Put the light on the pipe and hold the pipe up near the rack and bracket to eyeball the fit and position. Decide where to cut the pipe based on the best fit. Be sure to leave room at the top and bottom of the pipe for the nuts that will receive the screws. You'll need to be able to reach the nuts on the inside of the pipe with your fingers or by using pliers.

Use a hacksaw to cut the pipe. Then hold the pipe on the bracket and mark where the screw holes should go.

Step 4: Attach the bracket to the pipe section

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Use a drill or knife to make holes where you will attach the bracket to the pipe.

You will be inserting the bracket on the inside of the pipe and running the screws from the outside of the pipe to the inside. Manipulating the nuts on the inside of the pipe can be tricky. I used pliers to hold the wing nut in place while I turned the screw to get it threaded.

I used split lock washers on the outside of the pipe, but I am not sure if they will work. Due to the pipe's plastic composition, I wasn't able to tighten down the screws as much as I'd like, since the force warps the pipe and could potentially break or crack the plastic.

Step 5: Attach the new bracket to the rack, add lights and reflectors

Picture of Attach the new bracket to the rack, add lights and reflectors
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Finally, attach the entire bracket assembly to the rack and add your seat post mounted lights and reflectors. Depending on how much room you leave on your pipe section, you could attach additional reflectors.

Notice that the entire bracket with light attached should be lower than the deck of the rack. This is to ensure that the lights won't be in the way of an oversized package that is put on to the rack.

I also used this opportunity to add a piece of self-adhesive D.O.T. standard reflector strip to my rear fender.

In my opinion, having the lights and reflectors behind the rack, rather than under the seat increases visibility greatly from the side as well as the rear. However, this should never be a substitute for super cautious riding. Be careful out there.
jet_ski5 years ago
this is an awesome idea!! now i'm wishing I kept that bit of seatpost that I hacked off my bike a couple of weeks ago! :P
seb11886 years ago
Thanks very much for this, I'll be trying it out very soon. I will however make one small modification. You say you couldn't have it tight in case you broke the PVC pipe, so perhaps it would be better to shape the pipe by cutting a strip off the top at the back and gluing on a flat piece of PVC, so that it is the flat surface that is in contact with the rack, allowing you to securely attach it. Or to save the hassle of solvent glue, use a piece of wood and do the same.
scottredd (author) 6 years ago
After my first test ride it was obvious that the bracket was moving up and down too much every time I hit the tiniest bump. It even threw my light off of its mount. I used two little zip ties to lash the bracket to the back of the rack, and so far, it's making a big difference in keeping the bracket steady.
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Germy6 years ago
Great Instructable. I lost my rear reflector by using a crappy mount. This one seems infinitely better.

As a note, I would remove all the photos except the first two on the Intro step. On some pages (and maybe only for some people), viewing photos on later steps won't work unless that photo is active in the Intro. If you use a photo in a later step, it might be a good idea to remove it from the Intro.

Image Bug
scottredd (author)  Germy6 years ago
Thanks Germy. I was up too late writing this and not sure why I thought I needed to put all photos there. I just uploaded them all at once. :) I don't know if all racks have a place to mount a bracket, but I am sure using P-clips one could rig up something.