MTB Wheel size, what is the big differences?

In the beginning, 26" MTB wheels were all that was on the market.  During the last 10 years the choices and option of MTB wheels has exploded and make for much confusion when choosing your machine. After a few years, mainstream dirt wheels have settled down to 27.5" for aggressive riding and 29" for cross country (XC)– but with plenty of crossover in between.

Here are the pros and cons of each size:

26"

• Inherently lighter and stronger than a bigger wheel
• Highly maneuverable
• Easy to find spares and or parts
• Easier for rough ground to slow or even stop
• Less stable

27.5"-650B

• Roll on rough ground better than the 26", without the weight/clumsiness penalties of 29"
• Bigger contact patch for more grip
• Almost as maneuverable as 26" but more stable
• Could have been an unnecessary middle ground

29"

• Superior rolling performance on rough ground – maintains the best speed
• Superior stability
• Creates surprising grip from unpromising tires
• Heavier with more flex than smaller wheels
• Frame geometry needs rethinking to accommodate
• Tough to fit on small frames and/or long travel forks

The 26", 27.5" & 29" are basically just names at this point and are not actually correct measurements.

In reality, the BSD (bead seat diameter) of 29in wheels is 622mm, 27.5in are 584mm and 26in are 559mm. That’s 24.5in, 23in and 22in respectively! So never mind the jargon – today they’re all really just labels, not accurate measurements.

Making bigger wheels work

Taller wheels are basically longer levers, so they flex more. Reducing this without adding excessive weight, especially at the rim, is the tricky part.

Lengthening the axle and spreading the hub flanges (the bit the spokes lace to) is a great way to bring strength back to the wheels. 

Your frame and fork dictate the axle width in most cases. Originally, all wheels were 135mm rears and 100mm fronts Hollow 12/15/20mm screw-thru axles also add significant stiffness (and safety). Good wheels convert between the sizes with simple spacers.

Boost sizing- 148mm rear & 110mm front axles is slowly gaining ground, it does require a compatible frame and fork. 150mm-plus rears remain the preferred of downhill bikes.

Bigger rims must be stronger too, but that adds weight. Carbon fiber is ideal for both reducing weight and adding stiffness. Extra width also brings greater tire support and more aggressively square profiles which allows for more strength and better cornering.  For years rims were stuck at 19mm or even 17mm widths, leaving 2.35in tires pinched.

Be sure to select wheels with the correct axle spacing for your frame and fork as well as the correct size. As you increase the size of the wheels you will want to look into lighter rims (carbon) and wider axles (thru-axles) to maintain the strength when riding hard. 

Hope this helps in your decision making process, always feel free to reach out to us and ask questions to find what is right for you and your machine.

Enjoy the ride!