Tutorial: DIY Top Tube Bosses
Jan 26, 2015
article & images by Nick Salazar
I'm a huge fan of the relatively new direct-mount top tube storage "standard." And I put that word in quotation marks because it was never explicitly intended to be a standard, but became one by industry practice. Introduced in 2009 by Trek on the original Speed Concept, the standard basically just consists of a pair of M5 water female threads, spaced 63mm apart, allowing you to bolt things on to your top tube. This happens to be the exact same threading and spacing used for standard water bottle cages. It's a simple, elegant, and aerodynamically-clean way to add storage to your bike without resorting to Velcro, zip ties, or adhesives. I love it. And while many other players in the industry have adopted this feature to make it something of a de-facto standard, there are still some holdouts that have yet to implement this brilliant, no-brainer solution.
In the past, I've often worked with athletes to do special bike builds and modifications in what I call our Service Course Treatment. Recently, I built up a Blue Triad SL for Aussie pro triathlete Paul Matthews. One of the changes I made to his bike was to add top tube storage bosses in order to bolt on a TorHans Aerobento box, providing him with some aero storage and also completely hiding his cables. A LOT of readers asked me how I did that, and this article is the answer. It's a brief tutorial on how to install your own top tube bosses to any bike. The bikes in this tutorial are made of carbon fiber, but it works the same no matter what material your bike is made of. Also, keep in mind that we will be drilling holes in the top tube, which will void your warranty and possibly cause structural damage. Personally, I have no trepidation about doing that to my bikes, and I have confidence that it won't cause any problems. But if you're worried that your bike will fall to pieces if you make a tiny hole in it, then you'll want to avoid this kind of mod.
The solution is, in a word, Rivnuts. Specifically, M5 Rivnuts, the size used for water bottle cages as well as top tube storage boxes. These special threaded inserts allow you to add an anchor nut into a blind hole (a hole for which you have no back-side access), and in most cases this is what your bike already uses for its other bottle bosses. The pictures and video in this article are worth a lot more than 1,000 words of description, so I'll be brief in my writing. But in short, a special installation tool threads into the Rivnut, then pulls the insert against itself while you push it against the hole. This causes the outer casing of the Rivnut to deform and spread out behind your blind hole, effectively pinching it in place against the wall of your sheet (in this case, the top tube). I bought two tools, in the interest of thoroughness. First was the Astro 1442 tool - this one requires two handed operation, develops a LOT of pull force, but is a quite a bit trickier to set up and use. The second was the Westward 5TUW4, which is a convenient one-handed tool, and very easy to set up, but develops slightly less pull force. Ultimately, I prefer the Westward. Another nice feature is that it comes with mandrels for M3, M4, M5, and M6 Rivnuts, a more useful set for bike-related jobs than the M5, M6, and M8 mandrels that come with the Astro.
You can get Rivnuts in both steel and aluminum, and the right material depends on the tool you're using. The Astro 1442 develops a LOT of torque, and is best for steel inserts - it will easily strip an aluminum one. The Westward 5TUW4, really doesn't develop quite enough torque to deform a steel Rivnut (I was able to do so, but with a lot of effort) - this tool is best with aluminum inserts, which it can deform with ease. Fortunately, each tool already comes with a starter pack of Rivnuts, in the appropriate material for the tool. And that starter pack includes M5 Rivnuts, which is what you'll need for this mod. Either material will work just fine and have no problem installing on the wall of a bike, be that bike carbon or otherwise. Ultimately, I slightly prefer the Westward tool, but either tool or any similar alternative will work just fine.
Beyond that, the only info you really need is how to prep your bike for the installation. Basically, you just line up your intended top tube storage product, mark out where the bosses need to be, drill your pilot holes, and finally install the Rivnuts. It's all covered in the video, so make sure to check it out. The gallery below provides a bit more detail. Enjoy!
Rivnuts + Tools
Here's the business: all the shots of Rivnuts and the installation tools used for this mod. We've included some shots of Rivnuts installed onto a carbon sheet (and one of a squashed Rivnut installed onto nothing), so you can see what the underside will look like after you've done this to your own bike.
And here's the final product; two of my bikes with new top tube storage bosses. They work perfectly!