Condensed Answer: 29″ wheels have great roll-over-ability and can therefore be faster on climbs and descents than smaller wheels.
That said, the wheel size of a bicycle is only one of the characteristics that determine climbing ability – tires, weight, gearing, and drag are also crucial.
29″ wheels won’t turn a machine into a monster climber if it lacks on the aforementioned accounts.
The Climbing Advantages of 29″ Wheels
The main advantage of 29″ wheels, not only during climbs but in general is their ability to roll over obstacles. This is the main practical reason for the existence of 29″ wheels – the bigger the wheel is in relation to an obstacle, the less the irregularity matters.
This quality of large wheels is more important when descending or riding on flat surfaces, but it gives a boost even when climbing because the rider can cut corners by passing through obstacles instead of surrounding them.
- Faster (potentially)
If the wheels of two bikes are making the same number of rotations per unit of time (e.g., 50rpm), then the bike with the bigger wheels will be moving at a greater speed because its wheels are larger. (The larger the circumference of a wheel, the further the bike moves.)
|Wheel Size||Tire Width||Wheel Circumference|
The table above contains example data of two bikes using different wheel sizes and the same tire model.
When two bikes are in the same gear, and the riders are cycling at the same RPM, the rear wheels are rotating the same number of times too.
For example, if the gear is 42:12 (the chainring has 42 teeth whereas the rear cog has 12 teeth), the gear ratio will be 42:12 = 3.5:1.
This means that in that gear, one revolution of the cranks/chainring will spin the rear wheel 3.5 times.
Thus, if the riders of both bikes are spinning the cranks at 80 RPM, the rear wheel will have to rotate 80 x 3.5 = 280 times in 60 seconds.
If that’s the case, Bike 1 will move 2.18m (wheel circumference) x 280 (number of wheel rotations) = 610.4m.
In different, Bike 2 will move 2.3m x 280 = 644m. Or in other words, Bike 2 will cover more ground in the same amount of time and will therefore move at a greater speed.
The speed of Bike 1 will be at 36.6km/h or 22.75mph.
The speed of Bike 2 will be 38.6/km/h or 24mph.
Conclusion: 29″ wheels make a bike faster in every gear low or high thanks to their extra circumference. In order for a bike with smaller wheels to match the speed, the rider will either have to rotate the cranks at a higher RPM or shift up.
All The Factors Affecting a Bike’s Climbing Capabilities
The wheel size of a bike is not the only element that influences climbing capabilities.
The characteristics below are also very important:
- Tire Type
If the tires aren’t right for the terrain, the bike will lose speed. For example, if you’re using knobby tires on asphalt, the bike will be slower due to the extra rolling resistance.
Conversely, if you’re relying on slick tires when riding off-road, the bike will have poor grip and will force the cyclist to ride slowly and take fewer risks.
The weight of the bike matters the most when climbing. The lighter the bike is, the easier it is to climb on it.
A very light bike with smaller wheels can outclimb a 29″ model that’s as heavy as a cart of bricks.
The geometry of the bicycle matters too. In general, MTBs with very slack head tube angles aren’t the best climbers because the rider is too upright and thus in a non-aerodynamic position.
Also, the slack head tube angle positions the front wheel too far forward. This results in reduced front wheel traction and increased rear wheel traction. For that reason, the front wheel may pop up as in a wheelie during the climb.
The extra weight on the rear end makes it more difficult to spin the rear wheel and move forward. Hence why people often naturally shift their weight forward during a climb.
A bike may have ideal components for climbing (including 29″ wheels equipped with the perfect tires for the terrain), but if the gearing is inadequate for the climb, the rider will experience difficulties.
If you want to build a serious climbing machine, you need low gearing. This could be achieved fairly cheaply by using a triple chainset. Alternatively, you can go for a 1x drivetrain with a massive cassette, but keep in mind that this route is notably more expensive.
The gearing of a bike makes it easier to ride uphill by reducing the number of times that the rear wheel rotates per one revolution of the cranks. As a result, it’s easier to spin the pedals.
For example, if the gear is 22 (chainring) : 34 (cog), the gear ratio is 0.65. Or in other words, the rear wheel doesn’t even make a single full revolution per one spin of the cranks.
- The Rider’s Shape
It doesn’t matter what bike you’re riding if you’re out of shape. At the end of the day, the engine of the bike is the cyclist, and if his lungs and legs aren’t strong enough, the wheel size becomes irrelevant.
Summary: What You Need To Know
- 29″ wheels could make a climb easier thanks to their ability to roll over very rough terrain.
- Bigger wheels are potentially faster because they move the bike a greater distance for the same rotations per minute.
- The geometry, weight, tires and gearing of the bike greatly influence its climbing capabilities too.
- The fitness prowess of the rider is ultimately the most important performance factor.