Not since dual-suspension mountain bikes debuted has there been so much
controversy and confusion surrounding a mountain bike technology. We are
talking about the wheel-diameter war. Mountain bikes were originally designed
around 26-inch diameter wheels, and these wheels had a long, unchallenged reign
as mountain biking’s recognized “standard.” This meant that tire, rim,
suspension and frame design and technology all started and ended with 26-inch
Then came a group of frame designers who questioned the superiority of
26-inch wheels. The best-known advocate for breaking the 26er mold was Gary
Fisher, who championed a larger-diameter wheel that would deliver more contact
with the trail, be less affected by the trail surface, lower the bottom-bracket
height in comparison to the wheels’ axles, and, once up to speed, roll like a
runaway freight train.
The early 29ers had very limited support from tire companies and even
less support from suspension suppliers. Accepted frame geometry, intended to
work around 26-inch wheels, needed modifications to take advantage of the larger
hoops. Early adopters of 29er technology got bikes with heavy wheels, heavier
steering response, hook-and-ladder-long wheelbases, mediocre fork performance
and tires that were too big and heavy. Most riders went right back to their
26ers after a demo ride on one of these early creations. There were, however,
enough riders who rode in desert (sandy), winter (snow) or wide-open (fire
road) conditions to keep the glowing ember of the 29er alive.
Today, 29ers are no longer an ember, but a forest fire. They enjoy
plenty of wheel and suspension choices, and their geometry has been dialed to
take full advantage of the 29-inch format. There are even companies that only
produce 29er bikes. Niner and Fisher Signature Bikes from Trek are only
available with 29-inch wheels. The final proof that 29ers have arrived may be
their growing acceptance by our European counterparts, who avoided 29ers like
the bubonic plague. Riders who speak negatively of the larger wheels have not
ridden one recently or prefer more than four-inches of rear wheel travel.
THE NEW GUY
The MBA wrecking crew fields more questions about 29- vs. 26-inch
wheeled mountain bikes than any other technical feature, and that includes
suspension and drivetrain questions. With so much confusion and
misunderstanding about the two wheel sizes, certain powers in the mountain bike
universe have decided to make things even more con- fusing by offering a third
wheel size, halfway between the 26er and the 29er wheel—the 27.5-inch wheel
(also referred to by bike geeks as 650b). The advantage of the mid-sized format is that it is supposed to deliver
the benefits of a 29-inch wheel while making it easier to eke out clearance for
rear suspension travel and for the action of the front derailleur.
WHEEL TECH 101
Think of the wheel as an inclined plane—a ramp. When the wheel contacts
a bump, say a two-inch block of wood, a triangle is formed from the top edge of
the block to the ground and back to the point where the tire contacts the
trail. The steeper the triangle, the harder it is to get the wheel up and over
the block. The smaller the diameter of the wheel, the steeper the triangle
becomes, until it reaches the point where the wheel is too small to get up and
over and stops dead in its tracks. The difference between the strike angle of a
26-inch wheel and a 29-inch wheel (over the wooden block) is only about 5
percent, but the cumulative effect of rolling up and over a 5-percent steeper
angle thousands of times a mile adds up quickly. The larger-diameter 29-inch
wheel has noticeably less rolling resistance.
Another benefit of a larger-diameter wheel is the relationship between
the bottom bracket center and the wheel axles. A lower bottom bracket lowers
the center of gravity, and gives the chassis a more stable feel while
cornering. The bottom bracket heights of 26-, 27.5- and 29-inch designs are
about the same, but a closer look reveals a secret that might explain the
highly lauded cornering ability of 29-inch chassis. At 12.5 inches, the bottom
bracket center is only a half inch lower than the axles of a 26-inch bike, but
the bottom bracket is 2 inches below the wheel axles of a 29er. Weighting the
pedals of a 29er puts much of the rider's weight well below the axles, which
has a profound stabilizing effect.
26 VS. 27.5 VS. 29
Jamis Bikes covers their bases by offering steel-framed hardtails in the
three wheel size formats. When they offered us three similarly priced bikes to
try back to back, we jumped at the chance for the ultimate demo ride. You can
argue with hype, crunch all the numbers, and show up with years of bias, but
when you ride bikes back to back, things become clear very quickly.
Although all the Jamis frames measured 17
inches from the center of the
bottom bracket to
the top of the seat tube, the 26er felt like a minibike
compared to the other two bikes. It was the easiest to straddle and had the
nicest fork. Jamis spec’ed this 26er with a 6-inch-diameter front brake rotor,
the smallest of the three.
Pros: Excellent on steep and stepped climbs. Easy to accelerate out of momentum
sapping situations. Braking was strongest, especially at the bottom of
descents. By far the
most responsive to pumping
the trail. A light-feeling
that encourages the rider to hop
over or around obstacles.
Cons: Descending is intimi
dating, especially after spending
time on the other
two wheel sizes.
This bike requires more rider input and a
Rider position has a bigger effect on how the bike handles and responds. While
a rider can “roll” a techie section on the larger wheels, the 26er rider has to
attack and maintain enough speed to stay on top of the ruts, rocks and
flat-edged bumps. The rider has to work on looking ahead, as the 26er places
the rider lower over the front.
This bike looks and feels proportional. Other
riders didn’t even notice
we were riding 27.5-
inch wheels unless they took the time to read the numbers
on the American Classic rims. It doesn’t have the high feel of a 29er, while
positioning its rider in a more comfortable riding position. This was the only
bike of the three that used a 15-millimeter thru-axle, and there was no doubt
this would give the bike an edge over a similarly equipped model with a
9-millimeter quick-release axle.
Pros: The bike has a
nimble feel that is way clos
er to the 26er than the
but it doesn’t require the
rider to work as hard. Your
always feels neutral.
You can pump the 27.5er along the
trail, and when the
trail heads downward, it allows the rider to remain relaxed. You don’t need to
attack rough sections. These wheels do a good job of staying on top of the
rough stuff, and the front end goes where you want it to go.
Cons: We couldn’t come up with a ride negative. It doesn’t steer as fast as a
26er, but we never found a trail so tight that this made a difference. It
didn’t roll over the rough sections as smoothly as the 29er, but again, it
wasn’t a big enough difference to put the 27.5 rider off the wheel of the 29er.
There is no getting around the fact that this bike feels way different
from the other two. The front
end feels tall, and the rider sits inside the
rather than on top of it. From the first crank rotation, you realize
different forces are at work. The quick response of the smaller wheels is gone.
Pros: The big wheels are great for descending. They smooth out
that would have you puckered on the 26er. The added confidence inspires
remain more relaxed
as the wheels float over
rocky terrain. The big
the best trac
tion of the bunch, both in
corners and on loose
climbs. This bike
the least amount of body
English to stay hooked up (going
up or down).
Crewers noted they
remained seated longer in the 29er. Once up to speed, the bike
holds momentum well—and holding momentum is what the 29er is all about.
Cons: Getting up to cruising speed takes more effort. Steep climbs or
regaining speed following a momentum- zapping misstep is noticeably tougher.
The only plus here is out-of-the-saddle efforts work great because the rear
tire maintains traction. The large wheels don’t respond as well to pumping the
trail, and lofting the wheel requires more effort. This bike doesn’t have that
lively squirt of acceleration you feel on both the 26er and 27.5er when working
the backside of a whoop. The larger rotor up front wasn’t enough to give this
bike the braking power we wanted.
Win: This 27.5-inch-wheeled bike proved to be the most versatile of the three
hardtails. It did an excellent job of blending the best traits of the 29er and
26er with- out ever feeling like a compromise between the two. This bike
scampered away from the 29er on steep uphills or after a speed-zapping mistake.
It then gapped the 26er on the other side of the mountain on the way down—all
the while delivering a very resilient ride that didn’t beat up the rider.
Place: This 29er couldn’t match the 27.5 in a drag race from a standstill or up
a steep ascent. If your riding is wide-open trails with few surprises, the large
wheels will hold an advantage over the 27.5. Our 29er held a slight advantage
on the descents over the 27.5 (and blew the 26er into the weeds), but the
advantage was less than what the 27.5 could throw down going up.
Show: This 26er felt the lightest of the group (it was), and, in experienced
hands, it would beat the other two in acceleration and slicing up or down a
trail. It propelled its rider with pumpatude power and liked to manual, wheelie
and hop around obstacles. The operative word here is “experienced.” An
accomplished rider can pump and manual all day long. The rider who can’t do
those things won’t have as much fun on this 26er as he would on either of the
The shootout winner earned its position by duking it out on the trail.
In the asphalt jungle, there are other factors to consider. The 29er rider will
have plenty of upgrades to choose from in tires, wheels and forks, and the 26er
rider has even more. The 29- and 26-inch hoops are here for at least the
lifetime of the bikes. The 27.5’s future is not so clear. While Jamis and KHS
have both committed to the wheel size (as well as custom builders like Kent
Erickson Bikes and Form Bikes), it is still a format that is found only on the
Mountain Bike Action stated previously that in a perfect world a series
of quantitative tests comparing rolling resistance values over varied terrain
could find a convergence point where the tire's air volume is optimized for
sucking up big hits, the overall wheel weight is minimized, and the diameter of
the tire delivers the lowest possible rolling resistance. This would result in
an exact wheel and tire size that is best suited for the job.
Don’t hold your breath. That statement was made over five years ago and
we still only have 26-, 27.5- and 29-inch wheels to choose from. The fact that
many product managers have never ridden a 27.5-inch wheel is even less
encouraging. Our shootout conclusion doesn’t duck the question in hopes of a
yet-to-be-agreed-to, pie-in-the-sky solution. It is based on what we just rode
and what you can buy today. You just have to understand that going with the
27.5-inch wheels makes you an early adopter of a design, and you are betting on
a dark horse. Of course, that is one very fast, sweet-riding dark horse of a
Reprinted from our March 2012 issue. Like us on Facebook