The 26mm Issue


Vintage French seatpost sizes..or simply called “why didn’t they just make one bloody size of seatpost?”  Yes, beware the French bike, for there are a surprising number of difficulties that can easily stand in your way to building that great project. If you’re not exactly sure of the sizing and the threads of your frame, or if you’re not certain that the parts you have are correct, then you’ll be really riding your luck. You’ll probably get stuck, an have to fork out for new parts. In this blog I want to look at the seatpost sizing issue, albeit briefly, as it is a very common problem when building a French bike.




The First Dilemma


Look at the three seat posts in the first photograph. Only one of them has its size stamped on it. Two of the three, therefore, practice the dark arts,  the first problem when trying to work out what post to fit: many french seat posts don’t have a size stamped on them. So even if you do know the correct size of seatpost that you require, you may well buy a post from someone who has guessed its size. The Simplex post in the picture above is again unmarked, and I’ve never understood for the life of me why these manufacturers didn’t bother stamping them.






The Second Dilemma


This the difficult task of finding out for certain the size of your seat tube. There are three likely scenarios: it could be a 26.2mm, a 26.4mm, or possibly a 26.6mm. I’ve heard a case of a Swiss bike ( which took the traditional French threading ) taking a 26.8mm. Now, 0.2mm may not seem very much at all, but it’s surprising just how much of a difference it makes. A 26.2mm in a 26.4mm tube will feel loose, and a 26.4mm post won’t fit in a 26.2mm.  Unless you start faffing around with shims, the seatpost that you may have bought off Ebay may be the wrong size. Put simply, French bikes built before 1982 had no single standard for seatposts. A Motobecane with Reynolds tubes could have a 26.6mm, and one from the same catalogue could just as easily have a 26.2mm. C’est ça. It’s a simple as that.






Measuring It


Unless you’re a real whizz with precise instruments, I wouldn’t bother measuring seatposts to check their sizes. I’ve tried it. It’s frustrating. If you do have an electronic calliper, you may be able to get a good idea of its size, but it’s always better to buy a seatpost that has a stamp on it. Thankfully some were stamped, like the Sugino and the JPR above, which just makes it so much simpler. It’s a fact that there’s a utilitarian aspect to Japanese parts; they are nearly always stamped, to provide the necessary practical information. Unlike Simplex, Spidel, Ava and Pivo, embarking you on an unnecessary investigation into the befuddled world of 2mm differences. I suppose that’s why Shimano rule the roost today.






A General Idea of Sizes



Lower-end French bikes, without Reynolds, Vitus or Columbus tubing:  26.2mm 

Better quality French bikes with Reynolds 531, Vitus and Columbus tubing:  26.4mm; some will be 26.6mm

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