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The Kinetics MTBrompton is a new off-road version of the Brompton folding bike.
Normal Bromptons use tiny 16″ wheels with 35mm (1.35″) wide tyres. This wheel size is key for providing the famous small fold, but it also compromises the performance of the bike in some situations – namely on rougher surfaces such as cobblestones, gravel roads and forest trails.
But you no longer need to compromise – you can now trade some of your Brompton’s folded size for a much more capable bike.
This is thanks to the Scottish bike shop and custom bicycle fabricator, Kinetics, who have created the MTBrompton upgrade kit. I covered this shop’s custom Brompton work in the video above (written version here).
The Kinetics MTBrompton upgrade kit is essentially two things: a taller and wider fork, and a longer and wider rear frame triangle. These pieces will bolt directly to any Brompton frame.
With this upgrade kit, your Brompton will also be compatible with disc brakes, various high-end internal gear hubs and even Gates Carbon belt drive.
And if you don’t currently have a Brompton, you can purchase one through Kinetics and they can customise it to your every need.
Why Off-Road Bromptons Are More Capable
While Brompton folding bikes typically use 16″ wheels with 35mm wide slick tyres, the MTBrompton offers 20″ wheels and 60mm wide off-road tyres.
Don’t worry, the MTBrompton still folds up just like a normal Brompton. However, with the new big wheels, it can handle much rougher off-road tracks.
This is partly due to the larger diameter wheels having a smaller ‘angle of attack’ over obstacles. Larger wheels allow you to maintain higher speeds when the surface is rough, and the extra voluminous tyres will deform more over bumps and depressions in the road, providing a much smoother ride – and more traction to boot.
The larger wheel format also gives you access to off-road tyre treads. You can pick from fast-rolling touring and gravel tyres with minimal tread, right through to sticky mountain bike tyres that have the maximum grip and traction possible.
If you want to achieve the highest average speeds on the road, the 20″ option is about as fast as it gets for a small folding bike. You can even get Schwalbe’s top-of-the-line Pro One road bike tyres in the 20″ size, which literally halve the rolling resistance of a typical Brompton tyre.
The MTBrompton Drivetrain Options
The MTBrompton is incompatible with typical Brompton gears, but that’s ok because you now have the opportunity to upgrade to a higher-performing internal gear hub, and belt drive too!
I’ve written extensively about Shimano Alfine 8 and 11-speed hubs, which are amazing value for money and are definitely recommended on an MTBrompton build.
However, if you want the most efficient and the most durable hub available, you will want to invest in the infamous Rohloff 14-speed hub. This has been my hub of choice for over 150,000km of bicycle touring now.
The MTBrompton Bottom Bracket Height
One compromise that you need to make with an MTBrompton is the height of the bottom bracket shell (BB).
As the Brompton mainframe is unchanged through the upgrade kit, the BB sits around 350mm off the ground, which is 30-40mm higher than a hardtail mountain bike (and 80mm higher than a regular Brompton).
This isn’t a huge deal, in fact, it will help prevent both pedal strikes with the ground, and front chainring strikes on obstacles. But the additional ride height will feel a bit like you’re riding on top of the bike, rather than in it. And your saddle will now be 80mm higher off the ground, making it a bit harder to get on.
This will certainly be noticeable if you’re coming from a 16″ Brommy, but you probably won’t realise it if you spend time on mountain bikes.
The MTBrompton Folded Size
You can expect the folded size to be around 140mm longer, 45mm taller and 80mm wider than a regular Brompton, which is still a very manageable size for an apartment or public transport use.
Kinetics include some “ears” for the bike to stand on when folded. The folded bike is said to roll nicely on the back wheel, so it doesn’t need the typical Brompton rollers.
The MTBrompton Weight
The Rohloff hub version pictured above with Schwalbe Big Ben tyres comes in at 14.6kg (32.2lb).
This is not particularly light for a folding bike, but the Brompton steel frames are known for their durability, and the Rohloff 14-speed internal gear hubs are as tough as they come.
The MTBrompton Price
The MTBrompton upgrade kit is a niche, handmade product that’s made in very small quantities in the UK. The result is an expectedly expensive price tag.
A disc brake upgrade is a necessity on the MTBrompton, as the regular rim brake calipers don’t offer enough tyre clearance for 2.4″ tyres. And the original Brompton hubs are incompatible with disc brakes, so you will need to shell out for a new internal gear hub too.
Here’s the minimum price for the full Kinetics upgrade:
1x MTBrompton rear triangle with a Shimano Alfine 8-speed internal gear rear wheel (£795)
1x MTBrompton fork + 2x TRP Spyre disc brakes + 1x front wheel (£565)
2x Schwalbe tyres (£100)
Total: £1460 (~US $1840)
If you do not currently have a Brompton bike to upgrade, the bike itself adds £1200 to the purchase price. The total for a complete MTBrompton starts at £2660 (~US $3350).
It’s worth noting that Kinetics also offer Kindernay 14-speed, and Enviolo CVT gear hubs for an extra cost. In addition, you can upgrade the Shimano Alfine hubs to electronic shifting (Di2).
If you’re shipping a MTBrompton internationally, you can remove 17% from the purchase price. You don’t have to pay UK VAT, but you will have to pay shipping plus some tax or import duty when the package reaches your country.
Similar Off-Road Folding Bikes
The MTBrompton isn’t the only folding bike with 20″ wheels and wide off-road tyres.
Eerder Metaal over in the Netherlands is making some beautiful custom off-road Bromptons. These bikes have a touch more tyre clearance (2.6″), and the option for derailleur gears, fenders, luggage adapters, travel bags and more.
Eerder Metaal even shaves down the head tube of the main frame. This allows the fitment of a long fork that clears a wide tyre and fender, but all while keeping the bottom bracket at a reasonable height. As a result, the Xplorer has a 30mm+ lower BB compared to the MTBrompton (315mm with 2.25″ tyres), and a slacker head tube angle for better off-road bike handling too.
Additionally, there are no “ears” for the Xplorer to stand on when folded. It instead sits on four rollers that are neatly integrated into the rear triangle and fender. This allows you to easily roll the Xplorer about with a front bag attached (see video).
The waitlist is significantly longer from Eerder Metaal, and they are priced a bit higher due to the extra custom work (€5500 as pictured above).
Bike Friday offers a model called the All-Packa folding bike, and it has the same wheel and tyre specification as the off-road Bromptons.
The All-Packa is a fair bit cheaper (US $2495) and lighter (12.5kg/27.6lb). As the frame has been designed from the ground up, the bottom bracket height is 75mm lower than the MTBrompton. This height is ideal for gravel riding (the bike’s intended use) but could be a bit low for riding over obstacles.
The Bike Friday All-Packa has a slower and larger folded size (if that matters to you) and uses a typical derailleur drivetrain. The bike is made in the USA and gets a lot of praise in online reviews.
Birdy is the original off-road folding bike company.
While the wheel diameter is a bit smaller (18″ rather than 20″), Birdy uses front and rear suspension to provide a smooth and fast ride over rough terrain. You can expect the Birdy GT to ride just as well off-road (if not better) than the Bromptons with wider tyres.
In comparison to other folding bikes I’ve mentioned, the bottom bracket height is 60mm lower than the MTBrompton and a touch higher than the All-Packa.
Thanks to the monocoque aluminium frame, the Birdy GT is the lightest folding bike of the lot (11.4kg/25.1lb). It’s available in a bunch of colours at prices starting at US $2600 and jumping up to US $4900 if you’d like a Rohloff 14-speed gear hub.
Bromptons are some of the smallest folding bikes available, and their ingenious design allows them to fold down in just a handful of seconds (the world record is five seconds).
However, the 16″ wheel size with narrow slick tyres is limiting for mixed-terrain riding. And the available gear systems are frankly quite clunky compared to other gear systems available.
The Kinetics MTBrompton upgrade kit allows you to have it all. You can ride comfortably on the dirt and cobblestones without losing the great Brompton fold. And you get a much more refined internal gear hub and brakes too.
For more info, head over to Kinetics-Online.