Last year, South Africa's Greg Minnaar (Santa Cruz Syndicate), a three-time UCI World Champion, won a record extending 20th Downhill World Cup in Fort William, Scotland, adding a 21st win later in the season in Lenzerheide, Switzerland, site of the 2018 UCI Mountain Bike World Championships presented by Mercedes-Benz. What made these wins unique was that they were the first World Cup events to be won on a bike with 29" wheels. This year, French rider Amaury Pierron (Commencal/Vallnord) became the first rider to win the overall Mercedes-Benz UCI Downhill World Cup series on 29" wheels.
So does this mean the debate is over, and 29" wheels have replaced 27.5" ones? Not so fast - both the Elite Women and Men reigning UCI World Champions, Miranda Miller of Canada and Loïc Bruni of France, both riding for Specialized, won on 27.5" wheels, as did the 2018 Women's World Cup winner, Great Britain's Rachel Atherton (Trek Factory).
Greg Minnaar has won with both wheel sizes over the years, but, as a taller rider, points to bike fit as the biggest benefit of the larger wheel size: "I think one of the benefits to running bigger wheels has nothing to do with the actual wheel size. In my opinion, the bigger wheels have forced the bike manufacturers to lengthen the wheel base, letting the rider sit more centred on the bike. There is not one thing my 29" [Santa Cruz] v10 can't do that I've done on previous [27.5"] v10's. Whether racing, cornering, back flipping .... my 29" V 10 has done it all."
Pierron, on the other hand, isn't convinced that either wheel size has a clear advantage, "For the debate on 27.5" / 29", I don’t know what to think. I think each has its advantages and disadvantages. It also depends on riding style, and the size of the rider. We still see wins with the 27.5", so that’s a sign that wheel size isn’t everything!"
The final word goes to UCI World Champion Loïc Bruni: "Yeah, it's a tricky question; and there are a lot of people who won't agree with me. I'm not the biggest fan of 29ers. I think they have some benefits for sure; they roll really well and for sure carry the speed better. But in terms of your [cycling] position and the fun aspect, I'm not convinced yet. It's not scientific, no one has shown me yet that one is faster than the other. People have different tastes and expectations, like pretty much anything - ride what you love and what you have the most fun with! For tall riders, for sure it's an advantage to race a big bike that fits you. I will trust Specialized with what they think is best, but 27.5" ain't dead. A good rider is fast on any wheel size."