General Bike Tech
Comparison of 27.5 and 29er wheels
First off I should explain the 650B or 27.5 label. The 650B wheel size has been around for a long time and was used on bikes at the end of the 1800s and early 1900s. The bead diameter for 650B (584) is roughly midway between 26”(559) and 29” (622) so the label of 27.5" has been attached to the 650B wheel size for simplification when discussing the three sizes of tire. From this point on I will use the 27.5 label for this size.
The 29” wheel size is the same diameter as road and hybrid bikes and because of this there are many road type tries that will fit on 29er rims.
This article implies that the 26” wheel size for mountain bikes has gone the way of the dinosaur. For the most part this is true except for youth bikes, which some companies have utilized the cast off 26” wheel as another step before moving into the full sized 27.5” or 29”. Few companies are using the 26” wheel on adult sized mountain bikes at this time. The reason(s) will be explained later in this article.
First a short history lesson on mountain bike wheel size. When mountain bikes as we know them were first being created by those guys in Marin County (there were probably others around the world doing something similar but the Marin county boys just got famous for it) they used old beach cruisers to plunge down the dirt roads on Mt. Tamalpais and these beach cruisers had 26” wheels. These bikes were used because they had the large tires that were desirable for this type of riding. As the mountain bike evolved no one really thought much about the wheel size until the late 1990s/early 2000s.
There were a few custom builders doing 29” hardtails but there were no suspension forks and few knobby tires/wheels available for this wheel size. Since the 29” mountain bike rim is the same diameter as 700c road wheels there were a few narrow rims and knobby tires on the market.
To my knowledge the Gary Fisher Bicycle Company was the first production bike company to introduce the 29” wheel on a large scale. This created a market for the parts necessary for adoption of the 29” wheel.
Advantages of the 29" wheels
One word that describes the ride of 29” wheels is momentum. They roll over terrain more efficiently and deflect less while riding slowly over rough terrain. This is very important when climbing steep, loose trails. It can be frustrating when you are working really hard on a climb only to be bounced and forced to zig zag from side to side because the front wheel is getting deflected off small rocks because of the slow speed. 29” wheels tend to roll over these same obstacles instead of being deflected. This allows the larger wheel size to improve your climbing efficiency.
There is also a larger tire/dirt contact patch due to the larger diameter tire. This allows greater traction and braking capability.
Disadvantages of 29" wheels
The first disadvantage with the larger wheels is bicycle sizing for shorter riders. Due to the large wheels the bike frames need to have longer top tubes and chain stays for the large diameter wheels to fit. The longer top tube makes for a larger fitting bike even in the smaller sizes. Typically the smallest size 29er is 15” whereas the small 26” bikes could go down to 12” and still have a nice handling bike. This can lead to shorter riders having a hard time correctly fitting on a 29er.
The front of the bike is also higher because of the additional height of the tire which can also cause fitting problems for shorter riders. They are great for riders taller than say 5’ 6”, but below that the smallest 29er can feel like a big bike. Consequently for taller riders there is a greater opportunity for a good fit. Where fitting a person 6’4” on a 26” bike was always problematic it is now easy and the 29er looks very natural with taller people.
The second disadvantage with 29” is they are slower to accelerate from a stop. This is really only a problem in certain competitive events where there are many low speed turns followed by quick acceleration.
Advantages of 27.5" wheels
The 27.5” wheel size allows some of the benefits of the larger 29” wheel while retaining some benefits of the 26” wheel.
In my mind the primary advantage of the 27.5” wheel is the ability to fit smaller riders. If you don’t fit comfortably on your bike in the first place you will not enjoy riding and that is the greatest travesty of all.
Beyond fit there are design considerations with full suspension bikes. The 27.5” wheel seems more appropriate for longer travel all mountain and downhill bikes, even for taller riders. 29ers still have advantages for hardtail and cross country bikes.
Disadvantages of 27.5" wheels
Ultimately there really are not any serious disadvantages with this wheel size accept for fitting taller people. The same problems fitting shorter riders on 29ers is mirrored for taller riders on 27.5s.
This wheel size is actually closer to the 26” wheel than to 29. This allows the 29 to still have the momentum advantage once up to speed.
As of this writing there are not as many tire choices available for 27.5 wheels (especially street tires) but that will quickly change as this size becomes widely adopted in the industry.
The reason for this article is certainly not to confuse or create the idea that one size is better or worse, only to explain the differences between the two primary mountain bike wheel sizes on the market at this time.
Ultimately we are all different people with unique aspirations. It is important to remember there are no right or wrong choices, only the one that allows you to enjoy life and maybe forget about the daily grind for awhile.
A test ride at your local bike shop is the best way to experience either wheel size and determine what works for you.
It was not long ago that the only option was 26” and everyone had a great time riding all over the world on those. Either size will enable you to get outside wherever you live and experience the wonder of riding a bike.