2025 is a big year for Brompton as it marks their 50th Anniversary. And, Brompton is bringing the party with a radical overhaul of their original 16″ wheeled bikes and a brand new 20″ wheeled bike called the G-Line. From our perspective, 2025 marks a generational shift in Brompton’s product line, outdating all previous model years in one fell swoop. This change especially affects the popular Brompton C-Line model. So, is the 2025 C-Line better? Heck yes! Let’s dig in and see what’s up.
Outdated versus Obsolescent
As we trace in this article, 2025 might mark a revolutionary year for Brompton, but such revolutionary talk must be checked. Brompton is a wildly interesting company and for Brompton, the new never erases the old. Different years of Brompton models might become outdated, but they never become obsolete. One thing that makes Brompton very special is that most of its improvements are “backwards compatible.” That’s why most parts from the current model year will famously interchange – and upgrade – Bromptons that are decades older. That’s pretty amazing.
Until 2025, backwards compatibility on a Brompton meant that the same frame could accept different decades of parts. The only exception to this was the last big change to the frame in 1987. In 1987, Andrew Ritchie – founder of Brompton – realized he could increase the unfolded wheelbase of his bike while maintaining the small folded size. The longer wheelbase increased the footprint and stability of the bike. But, it also meant that very few parts from 1988 and forward were backwards compatible. Unless you changed the frame. And, that’s so expensive that it’s rarely worth it.
This is the exact same situation in 2025. While nothing has changed on the Brompton P-Lines and T-Lines, the rear-frame on a 2025 Brompton C-Line – their best-selling models – is completely different from a 2024 model. This new frame is called the MK6 and replaces the older MK5 frame. As of 2025, all models of Brompton (excluding the G-Line) use the MK6 design. This new frame is wider and accommodates a wide range of gears along with several key improvements. The only difference between the various MK6 frames? The C-Line rear frame continues to be made of steel and the P-Line and T-Line is titanium.
Forward Compatibility
What does this mean? It means that any C-Line prior to 2024 represents an entirely different generation of Brompton bike. It might be backwards compatible, but it’s not forward compatible. That means that many sundry parts continue to be interchangeable with the MK6 frame, but many essential parts are not. Take for instance, the gears. Let’s say you buy a 2024 C-Line and come to realize that you really prefer more gear range. To upgrade this would mean an entirely new MK6 rear frame, rear wheel, shifter, derailleur, and cog-set – plus labour – at an estimated added cost of $1750. Ouch!
Is there a massive price difference for these improvements? Not at all. If you’re looking for a 2024 C-Line 6-Speed at regular price, that will cost $2400. In comparison, a new Brompton 12-speed C-Line will set you back $2650. That’s a $250 difference that buys you some pretty revolutionary improvements, not to mention forward compatibility for at least another decade or two. Let’s take a peek at all these new improvements.
Advanced Frame
One of the greatest improvements in the new M6K frame is the design of the bridge that holds the roller wheels. What are the roller wheels? The roller wheels are awesome. Instead of having to carry the bike from place to place when folded, the roller wheels allow you roll the bike much like a suitcase. We all know that carrying a heavy suitcase is no fun, but when you roll a heavy suitcase it feels light. Same with a Brompton – only a Brompton isn’t heavy. That said, a Brompton will start to feel heavy if you’re carrying for a sustained time. That’s why the rolling wheels are so great.
Above is a picture of the older MK5 frame, from 2024 and earlier. If you follow the dashed line in the image above, you’ll see the roller wheel at the top of the dashed line. You’ll also see that each roller wheel is attached to a different frame tube, a fairly thin tube that bends towards the pedals. The problem with this design is twofold. The first is that you’re limited by the roller wheel size. The small roller wheels on the MK5 frame tend to get stuck in sidewalk cracks and can often feel like they defeat the purpose. The second is airfreight. When the bike is folded and put into a case, these roller wheels rest against the case and tend to be the first line of defence in turbulence, or typical baggage handler abuse. We’ll let the picture below tell the story.
Stronger
The new MK6 frame radically improves this. Instead of two thin frame tubes that bend to hold each roller wheel, the new design features a single burly cross-tube that cannot bend or crack. Take flight without worry!
The MK6 design also allows for much larger roller wheels, which makes rolling the bike so much better. Another cool little feature? On the MK5 frame the only way you could roll the bike was by towing with the handlebars up. On the MK6 frame you can roll the bike by using either the seat or the handlebars. This has to do with a revised placement of the Brompton stop-disc – yet another small improvement!
Waaaaay More Gears
The biggest reason to grab a 2025 Brompton C-Line is the massive – and we mean massive! – improvement in gear range and intermediate gearing. This deserves some explanation.
First, what is gear range? Gear range is best expressed using numbers. The numbers used to express gear range are called “gear inches.” We’re going to keep it simple. On one side of a gear range you have gears that are designed for climbing monster hills. On the other side you have gears designed for that perfect day with the wind on your back. The gears in-between are called intermediate gears. Have you ever ridden a bike and felt like it couldn’t climb or go fast enough? That’s a matter of gear range. Have you ever ridden a bike and kept switching between gears, because one gear feels to0 hard and the other too easy? That’s a matter of having too few intermediate gears.
The little chart (above) helps illustrate the difference between the MK5 C-Lines of 2024 and earlier, and the new MK6 C-Line of 2025. Again, the 2-speed and 6-speed represent the older MK5 frame while the 4-speed and 12-speed represent the new MK6 frame. At the bottom of the graph, for comparison’s sake, we have the gear range of a modern gravel bike. You don’t have to know what a gravel bike is, but it’s helpful to know that they tend to have the widest gear ranges of all bikes out there.
Geared for Anything
And so, what does this all mean? In the case of the new 12-speed this bike has the gears to do anything. And, you’re never lacking for comfort with the number of intermediate gears. This bike blows the 2024 6-speed out of the water. Besides a limited gear range, the other problem with the six speed is a lack of intermediate gears. The chart tells the story – the 6-speed gear range has quite a few missing teeth.
Meanwhile, the new 4-speed solves a problem Brompton has been stewing on for years. The 2-speed Brompton has always been a fairly poor seller, partly because it’s really just a glorified 1-speed. The difference between the two gears was negligible. But, for those who want a minimalist platform, the new 4-speed answers all questions. Sure, it might still demand more legwork on bigger hills, but it gives you a lightweight option without the same price tag of a T-Line or P-Line. A great bike if you have a lot of stairs in your life!
Rack em up!
The other really nice thing about the new Brompton MK6 frame is the optional rear rack that it uses. The older design of the Brompton rack was klunky, to say the least. And, at 3.8 lbs, it wasn’t exactly light either. This is what it looks like:
The new Advance rack (below), which is optional for all 2025 bikes, is a thing of beauty. At just 1.34 lbs it has the same 10kg weight capacity as the older rack, but is 65% lighter. The older rack was made from cast aluminum and – while it had gone through several revisions over the years – recalled the inelegant aesthetic of early Brompton models. The new rack is made of tubular heat-treated aluminum, the same stuff that all high quality bicycle racks are made of. And, the best thing about this rack is how it accommodates the new and very large 66mm roller wheels. If you find yourself rolling the bike a lot, the 2025 bike is a rolling dream.
Will the new Advance rack fit on older Bromptons? No it will not. The Advance rear rack, alas, only fits on the newer MK6 frames – so it is not backwards compatible but it is forwards compatible. Another good reason to consider a 2025 model.
In Conclusion
Should you buy a 2024 or 2025 Brompton C-Line? Well, obviously this is up to you, but we hope that we helped illustrate the generational wedge between the 2024 and 2025 model of C-Lines. Again, this generational wedge is best described by each bikes forward and backward compatibility, alongside the massive improvements in gearing, strength and little things like rolling the bike when folded.
Is the new 2025 C-Line worth the wait? We think so. At the time of writing there are plenty of 2-speed and 6-speed C-Lines in the Brompton USA warehouse, and we have no plans to order any. We honestly can’t wait to see the new generation of C-Line bikes!
