Demystifying mountain bike wheels!
Like it or not, 650B mountain bike wheels—often called 27.5"—have arrived in a big way. Most manufacturers now offer their trail bikes in a 27.5" version instead of, or in addition to, the traditional 26". Devinci is no exception, offering each of its bike options with 27.5" wheels. But what does that really mean for you? Here’s the full story on 27.5" wheels.
Products used for comparison
Tires: Schwalbe Racing Ralph TL Ready Evolution Line, 26x2.25, 27.5x2.25, 29x2.25 Tubes: Maxxis Presta Welter Weight, 0.90 mm thick
Wheels: Stans ZTR Arch EX black (white adds 20 grams)
Bike wheel sizes
First off, we tend to say that 27.5" or 650b bike wheels are exactly halfway between 26" and 29" and therefore offer the best of both worlds. Looking more closely at the actual dimensions, we see that this isn’t quite true. In fact, 650b is 1" larger than 26" and 1.5" smaller than 29", so it’s actually closer to 26" than to 29".
| Wheel size | BSD (Bead Seat Diameter) | Absolute difference vs 27.5" |
|---|---|---|
| 26 x 2.25" | 559 mm (22") | -1" |
| 27.5" x 2.25" | 584 mm (23") | N/A |
| 29 x 2.25" | 622 mm (24.5") | +1.5" |
Static weight
Static weight, or the weight listed on manufacturers’ websites, is a metric bike buyers are often curious about. Comparing the same wheels, tires and tubes in different sizes, we can see that a 650b wheelset is about 6.8% heavier than its 26" counterpart, and that a 29" set is nearly 12% heavier than the same equipment in 26".
| Wheel size | Weight of a pair of tires (g) | Weight of a pair of tubes (g) | Weight of a wheelset (g) | Total weight (g) | Absolute difference vs 26" | Difference in % vs 26" |
|---|---|---|---|---|---|---|
| 26 x 2.25 | 990 | 322 | 1615 | 2927 | N/A | N/A |
| 27.5 x 2.25 | 1060 | 382 | 1685 | 3127 | 200 | +6.8% |
| 29 x 2.25 | 1070 | 400 | 1775 | 3245 | 318 | +11.9% |
“Dynamic” weight
Static weight is great for impressing your friends, but what really affects how your bike behaves on the trails is the wheel’s “dynamic” weight. To better understand the impact of using different wheel sizes, we use the moment of inertia formula. This formula gives us an estimate of the difference in acceleration and deceleration when using 26", 650b or 29" wheelsets. To do this, we calculate the moment of inertia = Mass × Length2, the product of the mass and the square of its length. The lower the result, the easier it is to accelerate, which means more responsive acceleration. Conversely, a higher number also means it will be harder to slow the movement, so momentum will be more easily maintained.
| Wheel size | Weight in kg | Crank length (m) | Moment of inertia (mass x length) | Absolute difference vs 26" | Difference in % vs 26" |
|---|---|---|---|---|---|
| 26 x 2.2.5 | 2.927 | 0.559 | 0.91 | N/A | N/A |
| 27.5 x 2.25 | 3.127 | 0.584 | 1.07 | 0.16 | 18% |
| 29 x 2.25 | 3.245 | 0.622 | 1.25 | 0.34 | 38% |
There you go! Hopefully these few numbers will help you choose the right wheel size on your next ride!
Enjoy the ride!
