Why aren't 16" wheel city bikes more common?

Question

I love the Brompton with its obvious folding capabilities. However the best part of the bike for me is not the folding but the fact that it's small with its 16" wheels and light/compact frame. I can easily bring it up the stairs even without folding it or really quickly lift it from the frame to get across complicated obstacles on the road (say up a curb or past construction work areas).

Which got me thinking, why are most bikes so "big"? Why the 26/29" wheel ratio? I understand the benefit of such wheels and frames for performance - obviously a larger wheel is better for mountain biking and road racing by taking more impact off of you and onto the wheel. But for city commute/errands I wouldn't imagine something the size of a Brompton making much difference. And in fact the Brompton is truly successful and loved by its users.

So my question is, why is the market full of bigger bikes instead of more compact ones (not necessarily foldable)? Is it purely a market/fashion/ease-of-production thing or are smaller wheels more problematic than larger ones?

Answer 1

I have ridden bikes with different sizes of wheels, from 29" MTB/622 Road wheels, through 20" folder, 12" scooters, and one folding A-bike with 6" wheels.

My perception is that the bigger the wheel's radius, the better it is at rolling.

The smaller wheels will hang up much more easily on small obstructions like stones, cracks/joints, or similar. Gravel is another example of a surface that is really hard for a small wheel to roll over where a large wheel simply... "rolls over" things.

You can test this yourself - scootering a bike takes the gearing and transmission out of the equation. Imagine scootering over a patch of gravel on a large wheel vs a small one, and how far you can glide before having to put a foot down.

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For a folder, the additional value of a small wheel is in the space it saves when folded. For a non-folding bike, that's not adding anything useful so a larger wheel works better.

Answer 2

I cycle round a city (Chester) every day, typically covering five to ten miles in a trip. Even though this is on allegedly high quality roads the reality is that there are a lot of potholes and other rough surfaces. Indeed, some of the roads are cobbled and inherently rough.

I use a road bicycle (no suspension) with 700C wheels, and even with the large wheel size I frequently find myself having to stand on the pedals to avoid damage to my undercarriage, and with 16" wheels this would be a lot worse.

If you want your bicycle to fold up into a small space you have to use small wheels for the obvious reason that the wheels don't fold, and this is why Brompton opted for small wheels. But in Chester, and I assume Chester is fairly typical, the larger wheels are superior in every other way.

Answer 3

I can easily bring it up the stairs even without folding it or really quickly lift it from the frame to get across complicated obstacles on the road (say up a curb or past construction work areas).

Wow, you can get across curbs on the road by lifting your bike? Wonderful! It's very useful that as a cyclist you have the capability to tackle curbs. Otherwise you'd have to turn back, ride back home, abort the plan to use your bike and use a car instead because of those damn curbs.

However, let me tell you something even better. I have the capability to ride over curbs without having to lift my bike, on my full-wheel-sized bicycle. I just ride over curbs. No matter whether it's sloped or straight wall, no matter if it's low curb or high curb, I can always ride over it. Maybe for a very high curb that is a straight wall, I have to reduce my speed to avoid pinch flats and rim damage but that's it. I never lift my bike over curbs.

However, on my Brompton I can't get over curbs except if the curb is very low and sloped as opposed to straight wall, and even then I have to reduce my speed to practically nothing and still I can really feel the bump. Otherwise I have to dismount, lift the bike and re-mount.

Also on my Brompton the ride quality on general roads is very poor. It has a suspension block and I presume the ride quality would be even poorer without the suspension block. All the suspension block can maybe do is bring the ride quality of a 16" bike to the same level as a ride quality of a 20" bike, while at the same time making the bike horribly wobbly. My Brompton wobbles a lot, stealing a significant fraction of my pedaling power.

No way with the wobbliness and the horrible ride quality and the inability to ride over curbs would I be a cyclist if all we have are Bromptons. I almost never use my Brompton, except if I need to combine different means of transportation such as bike + car or bike + public transit. For that the Brompton is perfect. For everything else a Brompton is crap.

Which got me thinking, why are most bikes so "big"?

Because big wheels have low rolling resistance, very good ride quality and ability to ride over curbs at speed. Bike wheel size works generally like this: the bigger the wheel the better (because of low rolling resistance, good ride quality and ability to ride over obstacles), except when the wheel becomes so big it's difficult to design a frame around it. Bike wheel sizes are 622mm because approximately 95%-98% of adult riders can be accommodated with that wheel size, and the rest have to buy special purpose bikes with reduced wheel size.

Also you have to consider gearing. The only way a Brompton can have reasonable gearing is putting a ridiculously small rear sprocket like 12T, and a huge chainring like 54T that's almost becoming so large it's at risk of being destroyed by ground impact. However, chain drives work poorly on small sprockets. The efficiency sucks. The 54T chainring / 12T sprocket on my Brompton gives the same gearing as 48T chainring / 17T sprocket on a full-sized bike. With a 17T sprocket, the efficiency of a chain drive is far better. When reducing the sprocket size from that, the efficiency quickly suffers.

Maybe for really tall riders like over 2 meters height you could increase the wheel size from 622mm to something bigger. However, less than 1% of riders are above that height so you'll see it doesn't make sense to design special-purpose bikes for less than 1% of riders.

So you can see that a 622mm wheel size is usually the best for 99% of riders.

Answer 4

Besides performance, another issue of small wheels is also comfort. When the state of the road is not good (which is more the rule than the exception), you really feel every bump with a 16 inch wheel (or even 20 inch). Bromptons have rubber suspensions and flex in the frame to mitigate that (in some extent), but they are very very pricey bikes.

I've seen some (small) development of compact ebikes with large tires: large tires address the issue of comfort (and tram rails), and the motor addresses the lack of performance. Some big brands have compact ebikes with large tires on their catalog (Cube, Riese&Muller, Rad Power Bikes), but it's a minority and probably even more of a niche than Brompton and Dahon — and relying on subsidizing schemes (like an up to 2.5k€ grant to replace a car by an ebike in France).

But the answer is probably not in the bike themselves: bikes are part of a system and the system around them must be appropriate for their development. My impression is that folding/compact bikes are niche products that only appeal to people who have storage issues and live in places where bike infrastructure is not well developed. If these conditions are not met, they don't really have an edge over conventional designs.

About infrastructure: bike lanes are the advertised feature of that infrastructure, but parking is even more important. If you can park your bike outside your apartment/office, there's only a very limited benefit of compact bikes over a regular one, you rather have a cheap/"disposable" one. Also, people working in these cities but living outside are leaving a bike at the station, which removes the need of a compact bike that they take with them.

If you don't have infrastructure, compact bikes can be a solution for the storage component, as you mentioned. But if you don't have infrastructure, there is also another big issue for which a compact bike doesn't have any advantage over a conventional one: safety. If safety is the primary motivation to not use a bike (and then own), a compact frame won't change that.

Also compact bikes also face the competition of electric scooters and bike-sharing/renting schemes. Scooters are probably more convenient for the "last 5 mile" part of the equation, as they are more compact (and electric). And bike sharing/renting removes the need of owning a bike in the first place (and thus to store it at home).

So in short, the market is probably too limited to go in that direction, and I'm not sure it will evolve in a direction that will allow this format to flourish. If infrastructure develops, the cheapest will win and due to economies of scale, it is more likely to be with 700C wheels. If the infrastructure doesn't develop, compact bikes are likely to remain a niche product: they will remain expensive because of the lack of economies of scales, and only people fitting the niche will buy them.

Answer 5

The ground clearance is important in the city.

When riding next to the pedestrian pavement that is raised, it is safer to have enough ground clearance so not to hit the edge of that pavement with the pedal. Of course, depending on the height of the edge, this expectation may not be realistic. Still, a bicycle ready to hit anything few centimetres above the ground has disadvantage.

Riding over safety bumps or watering hose protectors is another case: it is a disadvantage to care about the pedal position so not to hit the bumps (also depends on the bumps but some may be quite high).

Sharp turns at low speed, with readiness to stop, are frequent in the city environment, and many people still feel more comfortable when keeping the "wrong" pedal down because they need that foot on the ground when stopped.

Maybe it is possible to design a frame with small wheels and good ground clearance, but looks like bicycles with small wheels somehow naturally get very low.

Answer 6

A big issue is cost. The small wheels themselves add a little to the cost due to rarity value of the wheels and the drivetrain (big chainrings aren't so common). The fact that most small-wheel adult bikes fold adds much more - those joints are complex (i.e. costly) and weaken the frame, also shortening the life of the bike.

It would be perfectly possible to build a small-wheeled bike that could carry as much as a typical hybrid, city bike, or commuter, but you'd lose the benefits of a compact (already limited if non-folding) bike, or add further cost. Brompton do well for luggage, but I often see people struggling with a folded bike and multiple bags

Answer 7

Comfort has been mentioned several times, and that's also my experience. Also the handling on potholes and kerbs - in fact, just a few weeks ago I fell twice off my Brompton while travelling in an unfamiliar city, when I cycled over a dropped kerb at an shallow angle which never is an issue on my big bike. It can also feel really scary when going down a hill as the steering is much more sensitive.

But a completely different problem, which I can't see in the other answers, is that the smaller frame means it is much harder to transport a bag or your shopping or similar things, so that makes it (for me and presumably many other people) much less practical in daily life.

If such a bike has a rack at all, it is very low. My Brompton has a rack above the rear wheel (the standard model doesn't), but because of the small wheel size the rack is small and very low, so it is really only suitable for some very small bag. It's not high enough for panniers, and anything wider than the rack you will hit your feet when you pedal.

The Brompton has a block at the front for a bag, but you need special bags (or DIY skills) and it can be awkward and unstable and not really suitable for carrying my shopping. I don't like to cycle with a bagpack, so that's out too.

The rack on a my normal bike, with panniers and an optional folding box on top, gives me much more space for whatever I need to carry with me. When I travel with the Brompton, I now have a trailer for the luggage.

Also there are issues with attaching a light. Ok, you can now find lights for the handlebar, so it's not a huge issue, but in my experience the detachable handlebar lights are a bit of a British things, whereas in other European countries many people want a fixed dynamo light (and in some countries a permanently attached light is the legal requirement). This is much trickier on a small frame. On my Brompton, I have a front battery light above the wheel, but because it is so low above the ground, it doesn't light up the path very well.

So, while I like the Brompton, and the low weight is really great, in my normal daily life the weight or size of my full-size bike isn't an problem, but actually an advantage.

Of course it is possible to solve these issues and find clever solutions for luggage and lights, but it can be more hassle and I guess many people just happy with their a normal-sized bike, especially for everyday practical use.

I'm sure there's also a kind of chicken-egg-situation that people don't buy smaller bikes because they are not familiar with them and because shops don't normally have them, and shops don't stock them because people don't ask for them. This could be changing with folding bikes becoming a more familiar sight.

(This all refers to experiences in Europe, mostly UK, France, Germany, I don't know how it is in Africa, Asia or the Americas).

Answer 8

Okay, let's do a little math here.

The larger a wheel is, the greater its circumference. This is critical because the circumference is the part that touches the ground. So the more circumference you have, the fewer wheel rotations are required to move over the same amount of ground. The fewer rotations the wheel needs, the less power you have to put into those wheels to make it rotate enough over a given distance of travel on the ground. (This applies to all wheeled vehicles, not just bikes, but in the case of a car, the power comes from an engine or electric motor instead of your muscles.)

Now obviously your gear ratios are factored into that, but in that case, you're just making a balance between the number of times you have to push the pedals for a given amount of rotation vs. the amount of effort required to push those pedals. Additionally, a larger wheel might be a bit heavier and require more effort, but the difference in weight is not much when you have an open spoked design like most bicycle wheels.

So generally speaking, a larger wheel requires less effort from the cyclist to achieve the same amount of horizontal travel. There's diminishing returns, of course - you don't see many people riding around on penny-farthings anymore for a reason. Above a certain size of wheel, it just becomes wildly impractical and potentially hazardous just getting on and off the bike.

(Note that this only applies to the rear wheel of most bikes since that's the one that you're pushing. In theory, your front wheel could be much smaller and not make any difference in terms of amount of effort required, though you do start having more problems with bumps in the road the smaller you get, as others have pointed out, and I guess it'd also just look funny if the wheels were too different in size.)

Answer 9

I grew up in a city where the roads are poorly maintained and I found that the bigger rims coped better with the pothole edges or the tram tracks sticking out.

Answer 10

The current trend is large wheels, 26 inches and up, as the most popular bicycles nowadays are mountain bikes. Many people though learned how to bike with a 20-incher, like the BMX. IF you have bike-crazy parents, you would have started earlier with smaller ones, 10, 12, or 16 inches. That's where the problem lies. A 16-incher is more likely to be considered a kid's bike, around the time you hit 4-6 years old. Yes, I agree, the 16-in. Brompton doesn't look like a kid's bike but when one has enough cash to buy one of those, he'd more likely get a more popular mountain bike at half the price.