Hi MBA, I’m in Brisbane and have been shopping around for a new mountain bike. I’m thinking I will get a 29er dually but I’m hearing a lot of stuff from sales people that sounds like ‘BS’.
They tell me that 29ers are better up hills but don’t accelerate as fast, then they say that 29ers have more surface contact with the terrain—this part in particular is first class BS. I ride GT at the moment and have been really happy with it. Is there any truth to what I’m being told?
To keep it simple, let’s call it big wheels versus little. In the big camp are the 29ers while we tend to lump 26 and 27.5-inch together—they are very close in size and possess a very similar ride feel. In most cases the radius of a 27.5 wheel is only 10-12mm greater than the equivalent 26er (based on our measurements which include the tyre). The radius of a 29er is around 33mm greater than a 26er so the difference is pretty clear. On the trail it’s quite easy to mistake a 27.5 bike for a 26er but 29ers are visibly different.
Anyway, there are many misconceptions surrounding the different wheel sizes and it’s usually boiled down into a simple statement such as, ‘29ers are faster’ or 29ers climb better. In reality it’s far more complex. Big wheels will do some things better and other things less so. Likewise small wheels have their own shortcomings.
At the end of the day you need to consider which option better suits your trails and terrain, as well as your riding style and personal preferences. Of course the wheel diameter is only one factor and the bike itself has a range of design elements that will have a greater bearing on the ride than the wheel size in isolation; there’s the frame geometry, suspension design, tyre selection and so on.
Now, to briefly address some the points you’ve mentioned:
• 29ers are better up hills.
Bigger wheels are heavier which works against you when climbing, so in this respect it’s a myth. However, if the climb is littered with rocks and steps, the bigger wheel will roll over these momentum sapping obstacles with less effort. Of course a skilled rider on small wheels may be capable of pumping, popping and hopping over the trail and maintaining their momentum, but this in turn requires energy and will wear you down over time. So big wheels usually climb better at low speed on a rough surface but the smaller/lighter wheels may hold the advantage on smoother hills or stop/start style switchback climbs.
• 29ers have more surface contact with the terrain.
For a given air pressure, the size of the contact patch remains constant. Only the shape of the contact patch varies with big wheels forming a longer but narrower footprint. Debates may rage over the significance of the footprint shape but we won’t bother going there—it won’t make or break your day and plenty of World Cup XC races have been won using smaller wheels.
The added air volume of a 29er (for a given tyre width) does have a small bearing. As it’s approximately 10% greater, there’s more air in the tyre to support your weight. Because of this you can run 3-4psi less in a 29er when compared to a 26-inch wheel, and this in turn will offer a slight increase the footprint size and traction.
In reality, I feel that most of the traction and rolling advantage comes about from the bigger wheel being more likely to stay grounded over uneven terrain, as it’s less prone to being bumped around. Of course you can get similar results from longer travel suspension, which also improves traction, and smaller wheeled bikes do tend to offer more suspension travel.
So take whatever you hear with a grain of salt, especially when someone tells you that one wheel size is simply ‘better’.