SweatRocket V2

2026-09-19

Two or three years ago I bought my first bike, an 18kg hybrid I call the Tank. Now I've reached the point where I regularly toy with the forbidden idea of riding fixed in Prague 🤯 And Prague is the anchor in this story. Here's why...

A bit of history

The Tank was a monster hybrid, aka a bike for people who don't know anything about bikes. I got tired of powering it up Prague hills, so I bought SweatRocket, a FabricBike Light Pro - an urban track-ish singlespeed. That's where I got hooked, and where I became a bike mechanic too. Nobody touches my bikes but me, especially MoonRabbit, built from AliExpress parts around a Seaboard CX03 frame. A clear coat one, from Tsunami.

In the meantime the Tank got retired, now it lives as a frame and spare parts for a cargo/shopper ebike build. I was at 2.1 bikes before SweatRocket started dying, which makes it around 1.8 now 😵‍💫 The ebike build I planned for this winter is postponed. The rocket replacement comes first.

New bike build

A month ago I noticed some lateral play in the Fabric's fork. Cleaning and tightening helped a bit. Then the front wheel got thrown between two cobblestones, and I felt it. Not enough to yank me off the bike, but enough to start thinking about the situation. A loose fork is mooshy and rattly, and no fun to ride.

Fabric bikes are fine, and the price/quality balance is decent. Prague's cobblestones are what make this one underspecced. So I gave it a final inspection. Like most bikes, the Fabric has an IS headset. That's "Integrated Angular Contact", or "SHIS IS", if you speak ParkTool or "any manufacturer can do whatever they want" if you speak sarcasm. I can be wrong, but my explanation is that the conical seat for the upper bearing has worn round. I am not surprised - it's a tiny contact patch of hard steel on aluminium, under 26mm tyres, on cobblestones that call for a mouthguard. The city will never admit they need repair.

You can ream the head tube to restore the seat, but there's so little material that I'd just be asking for a problem to repeat. Buying a reamer I hope never to use again isn't worth it either. Time to retire the Fabric and build SweatRocket V2.

Head tube madness

Months before, I was already eyeballing Engine11 Crit-D as a more fun and aggressive frame to ride. Yes, guilty, the Fabric's problem is kind of just an excuse for this whole proceeding. Once I went down to 1.8 bikes, I decided to jump straight into the consumerism part of the story. Procuring that frame in Prague, and it seems even in the EU, turned out to be hard. My best bet was contacting BicycleHero to see if they can ship to CZ. I got ghosted. Look at this beauty though...

With no frame left to obsess over, my brain was free to OCD about the next thing, treating me to two days of research on headset options.

Here's the problem with an IS headset - the bearing seat is machined into the frame itself. When it wears out, the frame is either a write-off or needs a repair with a specialized tool. Headsets with ZS (Zero Stack) or EC (external cup) cups don't have this issue, because replaceable cups take the wear, not the head tube. At least that's how I reason about them! So I wanted a frame without IS.

Which meant a hunt for ZS. It's somewhat standardized, and the head tubes can get properly beefy. The catch though - good luck finding a track frame with ZS. EC is doable on vintage-style steel, which is still popular in fixed circles, but that usually means a steel fork too. So my options were an EC steel frame, or hoping a better-made IS frame survives.

I was about to get a Tsunami EC steel frame when last minute I finally realized there is something strange going on with their bikes. Now fully educated on headset standards I was looking at their TC01 frame that in the photos shows what looks like an EC headset while the description says IS. So... I went to check the TC03 frame that was my best candidate in the IS department. Despite being listed as IS, it has a 44mm straight head tube. And... wait a minute, 44mm straight head tube!? Yes, it is clearly not EC, but I already know ZS looks very close to IS and that diameter suspiciously matches ZS44. I click on that IS headset link in the spec and what do you think!? It lists upper/lower cups that are rather uncharacteristic of IS.

If you check their TC03 now, it should (at least at the time of writing) specify ZS headset and that's because I emailed them asking for clarification and they were all like "oh yeah, thanks, we totally meant to correct that". Since I don't have the frame yet, I can only hope that this is indeed the right correction. By the way, the TC01 frame and I guess the rest of the frames continue to specify IS even though this might not be the case.

Similar things can be said about Crit-D: it also has a 44mm straight head tube and... that's all the spec Engine11 provides. By the looks of it, it might be ZS44 too. Somehow bike manufacturers give no shit about providing complete/truthful specs on their frames. I can somewhat understand this on complete bikes, but clearly people who buy a frame to build their own bike want to know what they are buying? Are we all supposed to be professional mechanics who can infer from 44mm head tube that the only current standard that can match that is ZS44 or perhaps that is some random proprietary IS? Not to mention that makes searching much harder as the right keywords will never be indexed, will never surface in search results.

What's next

So I ordered the frame a couple of days ago: a Tsunami WEAPON TC03. The only non-IS option I could land on given shipping/budget constraints.

And look at it! What's that? Another clear coat Tsunami frame? 🤣 I definitely didn't want to have 2 clear coat steel bikes. The TC03 doesn't come in a lot of colors, so they left me with no choice. But at least it has these black patches, from TIG I guess. And also silly WEAPON branding. I disliked it so much that I even emailed them about that too. Unfortunately they only run these in batches and don't do modifications, so even my humble request to simply omit the WEAPON branding on the tube was denied. So, yeah, I not only continue to ride like an idiot, I'll look the part too. I really don't like to advertise my riding style, but it is what it is! 💥

It should take about a month to arrive. Unless I strip the Fabric I'll need new parts too, and even then, here is the irony: ZS44 cups are an interference fit, so I think I'll need new tooling anyway. I skipped the reamer because I didn't want a tool for one frame, and now I'll be buying a bunch of tools anyway. In my defense - they're for a standard I actually want to stick with. So with all that, realistically I'll be riding SweatRocket V2 in spring.

Closing

So, that's what it feels like to ride in Prague. It is a city that forces you to learn about headset standards! 🤪 With all the crazy stuff going on here riding fixed remains a thought to toy with. Considering it, probably staying at considering, unless TC03 arrives with no brake holes! 🫣