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Until a few years ago, choosing the right wheel size was easy. There were only mountain bikes with 26-inch wheels. But 26-inch MTBs are slowly dying out. The major MTB manufacturers have been developing new wheel sizes for several years now. No more new 26-inch mountain bikes. Even for downhill bikes, the 26-inch standard has had its day. 27.5 inches is the new 26 inches. Mountain bikes in 26 inches (559 mm) can only be found on children's and youth bikes and on the second-hand market.
In order to achieve more traction and better rollover behaviour, the bike engineers equipped the new models with 29-inch (622 mm) wheels. However, some bikers lacked the agility of the small wheels. In order to combine the advantages of both worlds, there were soon wheels with a size of 27.5 inches - often referred to as 650B (584 mm). Today, the 26-inch mountain bike is extinct - except for children. This is because the advantages of large wheels predominate - from hardtails to downhill bikes.
Not established for mountain bikes: 27.5 inch plus format
A few years ago, a number of manufacturers entered the market with 27.5-inch bikes that relied on so-called plus wheels, which meant that the 27.5+ bikes was born. Behind this are wheels with a diameter of 27.5 inches, paired with wider tyres of 2.8 to 3.0 inches, which are supposed to provide more traction and riding comfort. However, bikes with XXL tyres have not caught on. Bikes with a 27.5+ rear wheel are often found on e-mountain bikes, while the plus-size format is hardly ever found on classic mountain bikes. Although the diameter of 27.5+ comes close to 29 inches due to the wider tyres.
Which is better: 27.5 or 29 inches?
The last few years have shown a clear trend: 29 inches has gained ground on a broad front against 27.5-inch wheels has prevailed. Better rollover behaviour, more traction and a very smooth ride 29-inch wheels have established themselves across all mountain bike categories. Bikes in 27.5 inches are much rarer, mainly in the enduro segment. However, there are also many manufacturers who rely on 27.5 inch bikes, especially for smaller frame sizes.
Pro 29 inch: Advantages of large MTB wheels
Mountain bikers are regularly confronted with obstacles such as stones or roots. With small wheels, the front wheel has to be lifted even in the case of medium-sized obstacles. Large wheels, on the other hand, simply roll over them. The rider does not have to worry about this, but can concentrate fully on the trail. The good roll-over ability of large wheels also increases smoothness. The bike remains smoother, even with many successive bumps from the ground and at high speeds on downhills.
Pro 27.5 inch: Disadvantages of large MTB wheels
The smoothness brings great advantages on rough passages, but is more of a hindrance in tight, technical passages. The large wheels increase the wheelbase and therefore the effort required by the rider to turn the rear wheel. The additional weight and the larger diameter increase the rotating mass. As a result, larger wheels react somewhat more slowly. This is particularly noticeable when accelerating. Due to the higher rotating masses, a 29-inch bike requires a little more power when changing direction and the bike's playfulness decreases. This disadvantage is even more serious for smaller riders. Many manufacturers are responding with adapted wheel sizes. For example, small frame sizes are often fitted with 27.5-inch wheels (sizes XS and S) and the larger frame sizes (usually from M to XXL) with 29-inch wheels.
Conclusion on the right wheel size for a mountain bike
29-inch wheels have established themselves in all mountain bike categories, as the advantages clearly outweigh the disadvantages. Only in the enduro segment and for small frame sizes are there still bikes with 27.5-inch wheels. Bikes with a mullet or MX construction are relatively new. Here, a 29-inch front wheel is fitted to the front of the bike and the rear frame holds a smaller 27.5-inch rear wheel. The aim is to combine better rollover behaviour on the front wheel with more agile handling on the rear wheel. This concept is already familiar from motocross sport.
