Adapter for mounting bicycle taillights on an aero seatpost

If you ride time trials or triathlons you have to train on your TT bike. That means attaching lights at least part of the year. But aerodynamic seatposts and seat stays don't provide anyplace to mount conventional taillights.

There are some commercial taillights and taillight brackets that work on some aero seatposts for some taillights. I wanted to be able to use any taillight on my TT bike so I used a different approach. I built an adapter that clamps a piece of round tube to an aero seatpost. Any conventional taillight for a round seatpost clamps onto the round tube. The adapter is easy to install and remove without tools and it is sturdy enough to hold a taillight in place on crummy chip seal roads.

On a bicycle two taillights a few inches apart are much better than one. One taillight steady and one with a long period pulsing flash let drivers see the bike and judge the distance better than a single light. This adapter handles that by clamping in a longer section of round tubing.

Click any of the small pictures to see a bigger version.

 
picture
Parts list:
  • A mounting block cut out of scrap molding. The front slot fits over the tail of a 3:1 aero seatpost.
    The rear slot is round, one inch diameter, and angled at about 75 degrees.
  • A piece of one inch aluminum tubing to act as a round seatpost.
    It is drilled to attach in the rear slot of the mounting block.
    I made two pieces: a short one for attaching one taillight, and a longer one with enough room to attach two taillights.
  • A short strip of female velcro attached to one side of the mounting block
  • A longer strip of male velcro attached to the other side.
    It wraps around the seatpost and attaches to the velcro on this side.
  • Hardware to attach the velcro strips and the piece of tubing.
picture Here are all of the pieces assembled, with a short piece of tubing to mount one taillight:
  • The velcro strips are attached with contact cement and wood screws with trim washers.
  • The short piece of tubing is bolted in place.
    It sticks out far enough to attach a seatpost taillight bracket.
picture Here are all of the pieces assembled, with a longer piece of tubing to mount two taillights:
  • The longer piece of tubing is long enough to mount two taillights about three inches apart.
picture A conventional taillight bracket for a round seatpost fits over the piece of tubing.
Here the short piece of tubing is installed pointing down to lower the taillight.
picture Conventional taillight brackets for a round seatpost fit over the piece of tubing.
Here the long piece of tubing is installed with brackets to mount two taillights about three inches apart.
picture Here it is installed with one taillight along with a tire and tool bag on a TT bike with a 3:1 aero seatpost.
The short piece of tubing is installed pointing up to raise the taillight.
picture Here it is installed with two taillights along with a tire and tool bag on a TT bike with a 3:1 aero seatpost.