My own 4 bikes consist of 3 classic mountain bikes with old school 26″ wheels and one more modern bike with 27.5″ wheels. In the last century you had no choice. If you wanted an MTB you were getting 26″ wheels but in 1999 the first 29″ tires for off road use became available. It wasn’t exactly a revolution as I remember. 29″ wheels seemed to somehow be just too big. The look of a bigger wheeled bike was different and it was easy to find reasons to stick with 26″. 29ers were a rather quirky choice. Frame geometry at that time was still of the modified road bike school of thought and wasn’t adapted to better suit larger wheels. Because 26″ seemed too small to some and 29″ too big to others a compromise was found. An old European wheel standard, 650b, had been tried by MTB pioneers Gary Fisher and Charlie Kelly around 1980 but the difficulty of acquiring the Finland made Hakkapolitta tyres meant that the project soon ground to a halt. From 2007 some were experimenting with the compromise size and by 2013 several manufacturers were offering 650b wheels which have a tyre diameter of 27.5″. The takeover was very fast and soon 26″ wheels were confined to low end bikes. For serious mountain bikers the choice was between the 2 larger sizes with 27.5″ being dominant. Since then a lot of effort has been put in by manufacturers to radically change frame geometry. Bikes are longer and lower with less steep steering head angles to promote stability. You don’t feel nearly so perched on top of a bike as you used to and are far less likely to go over the handlebars. All good news. Over the last couple of years 29″ wheels have gained a lot of ground on the middling size. They are the standard for cross country race bikes but are also appearing in enduro racing which involves a trail ride with timed, downhill segements to determine the winner. After my wife and I visited our son on the south coast, where he now lives, he said I could bring his 29″ wheeled bike back with me since he hadn’t been using it. It’s a 2014 Trek Fuel EX8 and whilst not totally modern it’s quite similar to Trek bikes you could buy today. I rode the bike last week, mainly on the road but today had the chance to ride it on familiar terrain back at home. So what differences stem from the different wheel sizes?
Firstly it’s obvious that the bigger a wheel is, the more it will weigh. Heavier is always going to be disadvantageous. The weight is compounded by the fact that most of the weight of a wheel is concentrated in the rim and tyre. To speed the bike up the wheels obviously need to turn more quickly and getting those bigger rims and tyres spinning is resisted by their inertia, the is resistance to movement which is directly related to weight. There are, however, some compensations. Firstly a bigger wheel has a bigger contact patch of the tyre on the ground. This may offer more grip, particularly on a dirt surface where more knobbles can claw into the terrain. Secondly the bigger contact patches spread the weight so you can run lower tyre pressures, cushioning the ride and smoothing things out. The inertia to movement works the opposite way once the wheel is up to speed. It carries more momentum to keep the bike rolling when the ground resists. Finally a bigger wheel has an additional way in which it smooths the ride on bumpy ground. The longer tyre contact patch touches a stone, tree root or whatever before a shorter one. The wheel may still need to move up by the same distance but with a longer contact patch there’s more time, at the same speed, for the wheel to rise. This translates to a less harsh feel to the ride over broken ground. I gave all this some thought during today’s ride.
I know that the best way to test an unfamiliar bike is to ride it on familiar ground which you’ve experienced many times before. I rode to Healey Nab and completed 3 laps of the man made trail in rather damp conditions. It would have been nice to try some fast segments for comparison but with today’s mud any figures were likely to be meaningless. Instead I concentrated on the feel of the bike. I definitely found that the bike was smoother on rocky climbs. The middle size of 27.5″ feels closer to the way the 29er rides than it does to my older 26″ bikes but the 29er definitely smooths the ride a little more. Early 29er were often said to be harder to get into sharp turns because of the greater gyroscopic effect of a big, heavy wheel. I get this but think you can generally help matters out by being more forceful when steering into a turn. The bigger wheels add stability so you can afford to muscle the bike around more without flinging it off line. I found that I certainly had to push the handlebars down into the turn to get it going the way I wanted. It took a few corners to get the feel of things but then I was flicking the bike around as I would my 27.5”. On a downhill I wasn’t noticing it been especially smoother than the 27.5” wheels but both of the larger sizes are a distinct improvement over an old 26er.
So for me, on our local, fairly rocky, root infested terrain I see advantage for the 29er over any other wheel size. If it was all about fast acceleration on smoother surfaces a 26” bike might seem better. There’s also the excitement which comes from the more “on the edge” feel of smaller wheels, which is why I love my 3 classic bikes. What’s certain for me is that there’s no point in compromise. If I was buying a new trail bike today it would be a 29er. How have others found the recent evolution of the bikes we ride?