Conflict: Give Me the Girth

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One of my favorite things about these “CONFLICT!” articles is that they’re written blind - I have no idea what arguments Andrew is going to employ. There’s no “responding” instead, we’re trying to anticipate each other's rationales. As one of my friends likes to say “you only get to ride a trail blind once” and we only get to yell at (or past) each other on the internet about any topic once. So here’s my impassioned (but also logical) argument for why I vastly prefer bikes with seat tubes that are 34.9 mm in diameter vs. those with 31.6 or, even worse, 30.9 mm openings.

The short version is quite similar to my argument for 200 mm post mounts on frames and forks vs 203: It’s very easy to shim a 34.9 mm tube down for smaller diameter posts, but good luck fitting a girthier post in a more svelte seat tube. If I’m looking for maximum compatibility out of a frame, I want it to be able to fit any post.

But there’s more to it than that, and we’re going to have to take a deep dive into pseudo-engineering and early 2000s American evangelical purity culture to get to the bottom of this. So buckle up!

Internet Engineering

Beyond the compatibility argument, there’s a simple engineering angle in play here. In the good old days, when I was just a wee lad pushing a big bike up steep hills, there were a bunch of different seat tube diameter standards, and that was, generally, ok. Seatposts were simple and affordable, they didn’t have any moving parts, and while you could purchase more expensive ones, at the end of the day, it didn’t really matter who made the post your saddle rested upon.

And then along came dropper posts, and everything changed. Instead of a simple tube, we needed to fit seals, bushings, cartridges, actuators, and all manner of gadgetry into this limited space. Because mountain biking is always complicated, we didn’t just solidify all of those diverse rigid posts into one standard. Instead, four distinct flavors of dropper post emerged: 27.2 mm (mostly for drop bar bikes, often externally routed, not really relevant to this conversation), 30.9 mm (the subject of my ire), 31.6 mm (probably the most common size), and 34.9 mm (what I think should be the standard size.)

Logistically, 30.9 and 31.6 mm dropper posts generally share the vast majority of components, sheathed in a differently sized outer tube. The difference is small – all it takes to shim a 31.6 mm tube to a 30.9 mm dropper is a cut up beer can.

But 34.9 mm posts give manufacturers enough extra space to make changes. OneUp’s 34.9 mm droppers integrate the collar into the post so that you can slam them further into the frame and get more drop for your buck. And BikeYoke’s excellent Revive MAX uses that space to bump the upper stanchion from 25mm to 28mm, making for a stiffer, more durable post. That’s awesome.

After an unfortunate saddle-on-tender-bits incident that led to an Urgent Care visit complete with pre-warmed ultrasound gel, I’m all in on 200+mm droppers. When I’m not reviewing, I prefer to run 240 mm droppers on both my bikes. But with my weight suspended that high above my seatpost collar, the deficiencies of smaller diameter tubing shine through. It’s just a lot of man meat sideloading a spindly support. If bumping to a 34.9 mm tube allows manufacturers to make more robust and reliable posts, sign me up! Remember how bad dropper posts used to be? Let’s keep moving away from that paradigm.

I don’t care for your compliance (or weight)

Back to the “good old days” of rigid posts: Folks with job titles similar to mine used to go deep on the flex patterns of their rigid posts, and a key piece to that puzzle was the diameter. Smaller diameter posts flexed more, giving a more compliant and comfortable ride when you were seated, hammering over bumps or chunder.

But the whole point of dropper posts is that we no longer have to hover our taints over our saddles when we’re in those situations. I’m hard pressed to come up with a single situation where a modern mountain biker needs to worry about the compliance of their seatpost. So while that was a valid argument in the old times, it just doesn’t hold weight anymore.

Which, speaking of, yes, bigger diameter dropper posts weigh more. You’re gaining over 100 grams when you jump from a 31.6 mm diameter, 210 mm travel OneUp dropper to a 34.9 mm option with the same length. Even if you run an adaptor with a smaller post in a wider tube, you still gain 30ish grams. It makes sense that bikes like the new Epic Evo come with a 30.9 mm dropper. Shave weight where you can. But, when your 160 mm bike comes stock with DoubleDown tires and CushCore (*cough Rocky Mountain cough*) does shaving a few grams at the seat tube really make sense?

Purity Culture

Our college men’s group leader was chewing gum as he led us in prayer. That wasn’t out of the norm – he was a 5 Gum guy, complete with puka shell necklace and cargo shorts. But when conversation turned to “sins of the flesh” which it often did in that cultish and testosterone-heavy environment, it turned out the gum was a prop. With one promise-ring-clad finger he fished the wad of used gum out of his mouth and held it up for us all to behold.

“Ok guys, every time you sleep with someone outside of marriage, it’s like taking a piece of gum out of their mouth and popping it into yours. And everyone they’ve ever slept with has chewed that gum too. Isn’t that disgusting!? Just think about that any time you’re tempted to lust.”

From that startling opener, the conversation then devolved into the perceived value of locks that can be opened by any key versus keys that can open any lock, typical American evangelical purity culture misogyny. As a metaphor for relationships, it was, quite honestly, ineffective. Here I am after all. Partners are not locks to be opened or conquests to undertake.

But dropper posts? That’s a different story. A bike with a 34.9 mm seat tube that can fit any size dropper post with shims is more valuable than a severely limited 30.1 mm option.

Because I am a leggy person, I have a 200 mm dropper post, with a saddle mounted at hand at all times, ready to swap onto short-posted review bikes. It’s not a big deal, and it makes reviewing those bikes much better. That post has a 31.6 mm diameter because that’s the size of the vast majority of the bikes I review. Sometimes they’re 34.9 mm, in which case, I’ve got a handy shim to swap in. This system works great, until I’ve got a bike with a 30.1 mm post in for review. Sure, I could change my default to 30.1, but then I’d have to shim it on almost every bike I swap it to. That’s stupid. Just like purity culture.

My Utopia

Where does that leave me? In a perfect world, most new bikes would come with 34.9 mm seatposts. We’re two for three on the big three: Trek and Specialized are fully onboard. If we want to move slowly toward that, let’s start to eliminate the 30.1 mm standard gradually. We can shim those posts up to work in 31.6 mm tubes. But in the meantime, let manufacturers reap the benefits of girthier posts. Give us droppers that are more durable, more reliable, and less flexy.

I need to go read Andrew Major's take, but something tells me it's going to leave me unable to fit my favorite dropper into my most bikes.