Condensed answer: The top speed of a bicycle is determined by its gearing rather than the size of its wheels. Thus, it’s inaccurate to conclude that smaller wheel sizes such as 26″ are slower than larger ones (e.g., 700c) in every case.
Bicycle Gearing and Speed
If bigger wheels equaled more speed at all times, then tractors should be faster than cars, right?
Ultimately, the speed of a bike or a vehicle is determined by its gearing (the system through which the rider/engine transmits power to the wheels) and the power output of the engine/rider.
Race cars are faster because they have high gearing and powerful engines that can effectively generate power for the high gearing to operate.
The drivetrain of a bicycle consists of chainrings found at the front and small cog(s) at the back. When the rider spins the cranks, the chain transfers power from the front of the bike to the rear.
The larger the chainring and the smaller the rear cog, the more power can be produced and transferred to the rear wheel.
There’s a term known as gear ratio which refers to the relation between the chainring and the cog.
For example, if the chainring has 44 teeth and the rear cog has 11, the gear ratio is 4:1.
This means that for each full revolution of the front chainring, the rear wheel would spin 4 times.
The larger the gear ratio is, the faster the bike can be because each spin of the cranks equals more revolutions of the rear wheel per minute and thus a greater traveled distance.
The formula for speed is Speed = Distance/Time.
Therefore, a bike that covers more distance in the same amount of time than another bike is moving faster regardless of wheel size.
The table above contains data for two hypothetical set-ups. Both bikes have the same tire width, but different wheel sizes.
In 44/11, the rear wheel spins 4 times per 1 crank revolution.
Since the rider is pedaling at 80rpm, the rear wheel makes 4×80=320 turns per 1 minute/60 seconds.
The traveled distance can be calculated by multiplying the wheel’s circumference by the number of wheel turns.
In this case, the distance is 320 x 207.50 cm = 66400cm = 664.00 m = 0.66km
In 34/11, the rear wheel spins 3.09 times per 1 crank revolution.
At 80 rpm, the rear wheel makes 3.09 x 80 = 247.2 revolutions.
Thus, the traveled distance is 247.2 x 215.3cm (wheel circumference) = 53222cm = 532.22m = 0.53km.
The formula for speed is: Speed = Distance/Time.
In the example case above, we have the following speeds:
Bike A’s speed = 664m / 60s = 11.0667m/s = 24.75 mi/h = 39.84 km/h
Bike B’s speed = 532.22m / 60s = 8.87 m/s = 19.84 mi/h = 31.93 km/h
Bike A has the potential to be 24.7% faster than Bike B despite having smaller 26″ wheels. The potential for extra speed comes from the higher gearing.
However, if both bikes have the same gearing, then Bike B will be faster than Bike A.
Conclusion: 26″ bikes are slower only when compared to bikes with larger wheels and identical or higher gearing.
Smaller wheels are easier to spin from a dead stop. Consequently, bikes with smaller wheels tend to accelerate faster. For that reason, a bike with 26″ wheels is easier to get up to speed than a bike with 29″ wheels, for example.
Smaller wheels may be easier to accelerate, but they have smaller inertia and require more effort to keep spinning.
In different, larger wheels are more difficult to get up to speed, but once there, they maintain the speed with less effort. Hence why larger wheels are considered better for covering long distances.
Another parameter that directly impacts speed is rolling resistance. The lower the rolling resistance of a tire is, the less effort is required to maintain a higher speed. Higher rolling resistance, on the other hand, is detrimental when speed is the goal.
If a 26″ wheel is equipped with slick tires, it will have a lower rolling resistance on paved roads but reduced grip on off-road terrain.
Conversely, knobby tires offer more grip when riding off-road by digging into the ground. On paved roads, however, knobby tires are slower and noisier.
FAQ: If 26″ wheels aren’t necessarily slower, why do they feel slow?
Many people who go from 26″ wheels to 700c/29″, for example, immediately feel faster.
The explanation is fairly simple. First, 26″ bikes are either retro MTBs, large BMXs, or old commuters. Meanwhile, 700c wheels are found on road bikes, touring bikes, commuters, and modern MTBs (700c = 29″).
Road bikes and even touring bikes tend to have much higher gearing than retro MTBs for example.
Thus, a road bike provides a much higher speed potential not only thanks to its larger wheels but thanks to its high gearing too.
Also, when switching to larger tires, the user will have to produce less torque to keep them rolling on flat roads. The reduced energy requirement will make you feel faster and lighter even when you’re not technically moving at a higher speed than before.
FAQ: I want maximum speed. Will 26″ wheels work for that?
The practical answer is no. If you want a fast bike, nothing beats a dedicated road bike. The aggressive geometry in conjunction with high gears, light weight and large tires with low rolling resistance facilitate the maintenance of decent speed levels.
While 26″ bikes can be very fast, a standard road bike will always dominate them when riding on the road.