Who doesn't love a new bike ? The other day a new Brompton was released. For those who do not know Brompton is a premium foldable bike manufacturer based in the UK, known for their low-profile once folded, and high quality, bikes.
The thing is, I have had a love and hate relationship with foldable bikes - as they are often great for short distance, but are slow to ride and often heavy. My experience with them as been mostly negative... and I ditched the ones I had for road bikes.
Fall 2024, Enters the Brompton G line serie. A Brompton quality foldable bike, with 20inch wheels (larger than usual for foldable bikes) - and... made for gravel? ... I had to read this a few times. Wider and larger tyres, gravel, disk brakes, and tubeless ready. Crazy stuff.
I tried to learn more about that bike and saw plenty of reviews on the internet. They showed how it folds, how it rides, where it can go. Cool beans. But there are things that I couldn't find. Can I use this to train and travel? Can I justify another few thousands for a new bikes in a way that I would avoid sleeping on the couch?
In order to rationalize my impulsive behaviour, I have to do some maths. So I did some maths.
Can I push enough watts on that thing to get a decent workout?
Smaller bikes, smaller wheels... usually means spinning your watts into oblivion. The the G line comes with bigger wheels than the other Brompton bikes. With 20" wheels - how far can it be pushed?
Looking at the specs we can see that it has a Shimano Alfine 8-speed hub gear, and given that the official website claims a 307% gear range on a 54T chain ring, we can assume that it rides like a 11-28T cassette on the back. There is no traditional cassette per say, but 54 and 11-28 would give us a 307% - So I am going to use that in my calculations.
At a cadence of 90RPM on the flats and on the 54 and 11 configuration (the highest/fastest gear combination), I should be able to ride at 42.41kmh or 26.35mh. Pretty decent for a small bike. We can estimate speed based on gear ratio and cadence - and we have these. But what about the work done? If we factor in aerodynamics - and an aerodynamic drag  (the amount of wind resistance) of 0.3 to 0.4- we would have to push between 347 and 450watts to achieve that speed. 0.3 to 0.4 Cda is not world class as this is not an aggressive aero road bike or a time trial bike. Here we catch a bit more wind, and need to do a bit more work - but since this is what we want. We can get a decent workout at out it without having to spin in the hundreds.
2. Can I climb a hill with this bike?
The G line being sold as a gravel bike, ... I believe that G stands for Gravel... or maybe it just stands for something else... in any case, going on trails surely means having to deal with some hills. Can it do it? Some more mathing...
Let's take the easiest gear. the 54 chainring (there is just one chain ring) and the equivalent of the 28 sprocket and run a couple of case scenarios. Staying at 90RPM seems a little hard with these types of bikes, so let's do some grinding and stay at low RPM without destroying our knees, and without standing - Let's go with 60rpm. One pedal stroke a second, and a blastering speed of 11kmh, or about the speed of a person jogging... but on a slope. Not super slow but going slower would require standing up - so let's keep it at that for now.
Here is a small table I made accounting for different rider+bike and climbing gradient.
T weight\Gradient | 5 | 8 | 10 | 12 |
60+15 (Rider + Bike) | 130w | 200w | 246w | 229w |
70+15 (Rider + Bike) | 147w | 225w | 278w | 330w |
80+15 (Rider + Bike) | 163w | 251w | 310w | 369w |
90+15 (Rider + Bike) | 180w | 277w | 342w | 407w |
Being in between the second and third row - I should be able to climb even challenging climbs with the G - if I am willing to fatigue my legs a bit. 12% seems a little daunting but most climbs are not at 12% in average. if anything they would just have small bits at 12% (usually in the inside of a pin turn).
How about standing up? Let's try to go as slowly as possible at walking speed (about 5.5kmh) and a RPM of 30.
T weight\Gradient | 5 | 8 | 10 | 12 |
60+15 (Rider + Bike) | 63w | 97w | 120w | 144w |
70+15 (Rider + Bike) | 71w | 110w | 136w | 163w |
80+15 (Rider + Bike) | 79w | 123w | 152w | 192w |
90+15 (Rider + Bike) | 87w | 136w | 168w | 201w |
There almost any gradient would work. 5kmh is slow enough to drastically lower the amount of work I would need, and fast enough to maintain momentum and remain on the bike.
In conclusion, short hills are ok almost all the time, but longer climbs need some fitness. Works for me but may not work for all.
How about putting this into context?
Climbing the famous Alpe d'Huez in France with its 13.9km and 1118m of elevation would take me 1hour and 15minutes at 253watts at 60rpm. What if I pedalled faster? I would need some serious broccoli and hold 391watts for 50minutes at 90rpm to make the ascent. That is above what i can hold, even on a good day.
Can the G be used for climbs, yes - but conditionally.
It isn't going to be as comfortable on longer climbs as a road bike with a wide cassette range and a more forgiving front chain ring, where I could maintain a healthy cadence, even on very steep climbs.
My next question - in my ongoing attempt to justify this is...
Can it be transported easily?
28.3" / 72cm (D), 26.2" / 67cm (H), 16" / 41cm (W), about 15kg
These are the dimensions and weight
Usually plane checked-in standard luggage is usually 158cm for D+H+W (you add dimensions and hope it goes below 158cm) and 23kg.
This is more that 158cm folded so it would have to go on oversized. Oversized may be the same price for some companies. For others... it may cost an arm and a leg. (pro tip check oversized and sport transport price before getting a plane ticket - some companies may give you check seat and rob you of your precious-bike-purchasing money on extra luggages).
The G would thus pretty much fly like any other bike on a plane. I would need a small box for it. I checked and some companies do bike boxes for other Brompton bikes, and I expect the G line to have their own very soon.
Looks a little cool.
How about day to day transport?
Day to day transport is where foldable bikes shine, and Brompton's even more so. Even if the G line is a bit bigger, subways, cars, buses, escaltors should not be an issue. It would even fit under a work desk. Pretty sure people in escalators would love to see me taking both the right and left sides... and admire with jealous eyes.
How about power training with it?
Putting it on a home trainer would be a little complicated... no cassette - so no direct drive. And rollers not always accommodate for 20" tires, these are still smaller than standard road bikes and the distance between the roller is not always adjustable.
How about putting power pedals on that thing ?
They have a quick release pedal system so that it can be folded neatly - but can I remove their pedals and put my own pedals with power meter? I got my answer from an email from Brompton:
"The thread on our cranks will be a stand global size, meaning you can instal any third party pedal."
In short - no problems installing power pedals.
In summary
It's a cool bike. I think it is the coolest bike Brompton has made and it does fit many of things I need in a bike.
Is this an option for people who travel? It does seem like a decent option not to have to worry about cars, taxis, etc.
I was thinking about getting a gravel bike... and now this little one is on the short list.
Let me know what you think.
F.
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