Choosing the right wheel-size in a touring bike is very important. Getting it wrong could mean being stranded in the middle of nowhere with a broken wheel and no way to repair it. So which wheel size is right for you? To get a better idea of the effects of different wheel sizes imagine two very different wheeled vehicles.
The first is a bicycle with wheels six feet (about two metres) in diameter, rather like a penny-farthing but with both wheels the same size.
The second is a skateboard with wheels of about two inches (roughly 5cm) in diameter.
Assume for the moment that the wheels on both vehicles have the same hubs and thickness of tyres. In reality this would be highly unlikely, if not impossible, but for this thought experiment it helps to ignore the effects from these parts.
Imagine how the different wheel sizes would affect the vehicles.
The huge six-foot bicycle wheels would be very heavy and take considerable effort to start moving. But once up to speed their inertia would help them roll along easily with little effort from the rider. The height of the wheels would be much greater than any obstacles they would likely encounter, like bumps and potholes, and so the ride would be relatively smooth. The wheels would cover a considerable amount of ground with each revolution (about 20 feet – 6 metres) meaning that friction in the hub would be minimised. This would give a fast, smooth ride and long hub life. However, to be strong enough to support a rider the wheels would need to be heavy, due to the very large rim diameter. If the weight were notably reduced the wheels would become very weak. Large wheels also have naturally high gearing. This, combined with their weight, would make riding uphill a struggle so low gears would be needed.
The small wheels on the skateboard could be made very strong yet light. They would also have naturally low gearing. These factors would allow very fast acceleration and make for easier climbing. However the small rim diameter means the wheels would only cover a small amount of ground (about 7 inches – 20cm) per revolution. The lack of inertia combined with increased friction in the hub bearings mean the wheels would slow down fast and the hubs wear out quickly. The wheels would also be very sensitive to bumps in the road and even small bumps or potholes could stop the skateboard dead.
This gives a rough idea of the differences wheel-size makes to strength, ride-quality and wear, though they are obviously far less pronounced with realistic wheel sizes. The two main sizes used on touring bikes are 700C (622mm) and 26” (559mm). There are other sizes but they are generally regarded as non-standard and harder to get parts for. You may have good reasons for going with a different size, for instance if using a recumbent or folding bike, but otherwise it’s best to stick with the two most common sizes. 700C wheels roll more smoothly and tend to be slightly faster than 26”, which are stronger and have better acceleration. Bear in mind also that 26” wheels with very fat tyres can actually have an effective diameter as great as 700C wheels with thin tyres. In fact, the choice of tyre will likely have more effect on ride quality than the wheel size itself, but the wheel size will influence the choice of tyre.
Besides strength and ride-quality the most important things to consider about wheel-size are the availability, size and type of tyres, tubes and spokes. It is generally easier to find these for 26” wheels than 700C and in many parts of the world 700C parts are essentially impossible to get hold of. For this reason, and for greater strength, most heavy-duty trecking bikes use 26” wheels. It is possible to build very strong 700C wheels but they will be heavier than 26” wheels of similar strength. Tyres for 26” wheels tend to be more focused towards off-road, mountain biking and commuting with few fast road tyres. 700C have a much greater range of lightweight racing tyres and fewer off-road varieties though these are available. However, there is a huge amount of overlap in tyres for different wheel sizes and good quality touring and commuting tyres are available for both 700C and 26” wheels.
So which is the best wheel size for touring? If you are sure you will only be cycling with light to medium loads on good quality roads in developed countries then go for 700c wheels. Otherwise go for 26”. The difference in speed on a loaded touring bike is generally not all that great but the 26” wheels will be stronger, have lower gearing thus making hill climbing easier, be easier to get spares for in almost any country, and, will be better suited for cycling off-road and on cycle paths – which can be surprisingly rough. On the other hand, many people have cycled round the world with heavy loads on 700C wheels so if you’re absolutely set on this size go for it. If you’re still not sure go for 26″, as you’re less likely to run into problems with this size even if the ride isn’t quite as smooth and fast as you’d like.