Belt drive Brompton G Line folding bike upgrade kits have finally arrived! This is thanks to Kinetics, a Scottish bike shop and custom bicycle fabricator. I’ve previously covered this shop’s custom Brompton work in a video and written article.
The Brompton G Line is an all-new folding bike with bigger 20” wheels and the widest handlebars and tyres of any Brompton before it.
The Brompton G Line has been designed to ride like a typical bike across varied terrain, thanks to a more stable frame geometry and modern features such wide tyres, hydraulic disc brakes and an 8-speed internal gear hub.
This is in contrast to a typical 16″ Brompton, which is a short-distance bike that folds into a tiny form suitable for busy public transport.
Kinetics has now developed various upgrade kits for the Brompton G Line. They offer belt drive upgrade kits, as well as special dropouts that allow you to fit the ultimate internal gear hub – the Rohloff Speedhub, which has 14 gears and a 526% gear range.
Let’s start with a quick overview of the benefits of belt drive bicycles.
Benefits of Belt Drive Brompton Bikes
Belt drive folding bicycles mean you never have to clean or lubricate a chain. This keeps your bike clean, and you’ll never get grease on your hands or pants again.
Belts are typically longer-lasting than chains too. Most cyclists go years without needing to replace a belt or sprocket – expect to ride three to four times further with a belt than with a chain.
Belts are also great in adverse conditions. This is partly due to the sprocket design, which effectively sheds debris from its surfaces. In addition, a belt drivetrain is usually paired with an internal gear hub, which also helps to seal away your critical gear components from the elements.
Ultimately, belts save you a lot of time. You will spend less time maintaining your bike, sourcing replacement parts, or dropping your bike at the shop for repair.
You can read more about why I think belts are better than chains HERE.
Brompton Frame Modification
The Kinetics G Line belt drive kit is simple to fit, however, it will require permanent frame modification. This will void your frame warranty.
As a bicycle belt is one piece (it cannot be split in two), cutting your rear dropout is necessary. Kinetics uses an angle grinder with a 1mm cutting disc to make this modification, but customers also use a hacksaw or a Dremel with a cutting disc. Now, the belt can be squeezed through the gap.
The dropout is reinforced with a stainless steel “joining plate” that connects the two dropout mounts with the rear rack mount. This plate can be seen in the image below.
Customers should apply touch-up paint over the cut to prevent surface corrosion. This corrosion would only be cosmetic, but it is best avoided.
Belt Drive Brompton Tensioner
Kinetics has also created a special belt tensioner for the Brompton G Line.
The smooth “snubber roller” pushes the belt firmly onto the rear sprocket to prevent skipping. It can be adjusted up and down to ensure the belt stays in place.
A second “tensioner sprocket” has been printed with the Gates Centertrack design. This sprocket keeps the belt tracking straight and features side plates to guarantee the belt will not fall off when the bike is folded.
If you need to remove the rear wheel for a puncture, it’s similar to chain drive. You can half-fold the Brompton, unhook the tensioner, and remove the belt from the front sprocket to remove the rear wheel. The big advantage is that you’ll never get grease on your hands.
Brompton G Line Joining Plates & Dropouts
Unique stainless steel joining plates and dropouts have been developed by Kinetics too. These are different for Alfine and Rohloff hub owners.
The belt tensioner goes on the inside of the frame for the Alfine hub, and the joining plate mounts to the outside. A 5mm bolt connects the joining plate to the rack mount for extra reinforcement.
The belt tensioner mounts on the outside of the frame for the Rohloff hub, and the joining plate goes on the inside. The Rohloff rear sprockets sit further out than the Alfine rear sprockets, which requires the tensioner to match the belt alignment.
A great thing is that Kinetics also offers a Rohloff OEM dropout to suit the Rohloff OEM axleplate. This makes wheel installation and removal very easy with Rohloff hubs.
Belt Drive Brompton Gearing
A front belt sprocket replaces the front chain sprocket. The 60-tooth front belt sprocket can be used with 22 and 24-tooth rear sprockets on the standard Shimano Alfine hub to provide gear ratios similar to the standard Brompton G Line gearing (54-20T or 50-20T).
The gear ratios are much lower when you upgrade to the Rohloff 14-speed hub. With a 63-tooth front sprocket and 19-tooth rear sprocket, the low climbing gear is under 20 gear inches (~1.55 development). This is similar to the climbing gear you’d find on a mountain bike!
Belt Drive Brompton Upgrade Kit Pricing
The belt drive Brompton upgrade kits cost £395.
This isn’t cheap but includes the full belt drivetrain (~£270 by itself) along with the special components required to make a belt drive Brompton G Line. Kinetics is happy to modify your frame and fit the kit if you live in the region.
You can get the Kinetics belt drive kits HERE.
