This blog is a repository for all my the bike-related studies over the past 20 odd years. The content ranges from modelling and analytical studies, to hacks and bodges made to my bike equipment. It's all been done in an attempt to make myself faster on a bike, to make the most of my mediocre fitness.
Blog posts have been written from 2020 onwards. The dates of the posts reflect when the work was originally done.
It’s almost complete now, with just a few older posts still to write up.
This is another 3D-printed bike part that I've designed recently.
During the spring this yea I had the idea to make a number of aerodynamic improvements to my road bike, in time for the summer time trial season. Sadly (and as usual) I've had less spare time than I wanted. Also, the CAD design work has taken me longer than I had anticipated.
Anyway, this mount for my Garmin Edge 840 computer is the first of several minor aerodynamic improvements that I'll create for my road bike.
What aero improvements are possible?
I have always been intrigued by the claims made several years ago by Wahoo about the aerodynamic efficiency of their Wahoo Elemnt Bolt. Those claims are summarised nicely on DC Rainmaker's site. Wahoo claimed that the Elemnt Bolt had 50% less drag than the leading competitor (i.e. Garmin) with those drag savings equating to a 1.5 Watt saving (although they didn't quote what speed that was for) but apparently that corresponds 12.6 second savings over a 40km time trial. Those savings are fairly small but not negligible. To put that in context, 12.6 seconds is about half the penalty of having a round bottle on the down tube, according to Specialized's wind tunnel testing (see here).
DC Rainmaker also performed some wind tunnel tests of his own though, which showed that the savings for a Bolt are actually much smaller than Wahoo's claims, more like a 1 second saving, instead of 12.6 seconds, when the computers are mounted horizontally. That's very small, a truly marginal gain.
Still, despite this very small saving, it's something I wanted to do. I felt that the integration with my stem and handlebar could be improved too, which I felt could yield some additional drag savings. Therefore, I pressed ahead and designed the mount.
Mount design
What I wanted from the mount was to something that: 1) Had a more aerodynamic profile at the leading edge.
2) Covers the Garmin's side buttons, which disturb the flow and aren't needed during a ride.
3) Was blended into my stem and the circular section of my handlebar.
The design consists of a 'sleeve' into which my Garmin 840 easily slips into, and separately a mount that bolts onto the handlebar. Once the Garmin is inside the sleeve, it can be fitted to the mount so that it's perfectly flush. The front and back of the sleeve are shaped to help keep the sleeve perfectly flush with the mount, in addition to a central Garmin quarter turn mount (also designed and 3D-printed) that ensures it won't fall out. All of this is quite difficult to describe with words, so I have uploaded a video to YouTube (see below) that shows it in action:
The sleeve and the mount have two cut outs at the bottom left and bottom right corners. This allows me to press the start/stop button on the right and the lap button on the left, as shown in the second video below. There's also a small C-shaped cut-out in the left hand side of the sleeve's thin sidewall, that allows the on/off button to be pressed. I felt that these three buttons were the only three that really needed to be pressed during a ride, with the other computer functions being available via the touchscreen.
Apart from hiding the protruding buttons via the sleeve, what makes this mount aerodynamic is the shape of (1) the leading edge of the fairing and also (2) the blending of the mount around the stem and handle bar.
The mount smoothly curves into the stem face plate and into the round profile of handlebar at the centre. A lot of trial and error was required to get a shape that fits closely to double curvature shape of my 3T stem. This is undoubtedly the most fiddly part of creating 3D designs - getting them to fit with existing parts and geometries that I don't have the CAD surfaces for.
For the leading edge of the mount, I chose to use a NACA 0024 aerofoil profile. This is a general purpose aerofoil with a 24% thickness to chord ratio. NACA's double-0 series aerofoil profiles are used for all sorts of things and I judged it to be a good choice for this kind of application.
The Garmin quarter turn mount and the handlebar mount are connected using M3 machine screws and nuts. I used these dome-headed stainless bolts from eBay, which have dome-shaped heads that have a 6 mm diameter and a depth of 1.8mm.
A few more photos
I'm pleased with how it turned out. I've attached a few more photos below.
The design at the moment is customised to the shape of my 3T Apto stem, so it won't fit to many other stems at the moment. However, if you are interested in printing one of these for yourself, for your bike, then leave a comment below. If I get enough interest, I'll create a generic version that will work with most alternative bar and stem set-ups and will upload it to Makerworld.
I've worked in the aerodynamics department of a large aircraft manufacturer for over 20 years. In my day job, I'm responsible for the prediction, modelling and measurement of the drag and lift of our aircraft. Much of my interest and knowledge of engineering and aerodynamics spills over into my main hobby, which is cycling (Road, MTB, cyclocross and time trialing).
