The promised arrival of 32″ wheels is being accompanied by an endless ream of speculation. From those that know, and those that are guessing. All kinds of technical talk about how much of an advantage the big wheels will be compared to their diminutive predecessors. We’ve talked to pro riders about their own 32″ bikes, we’ve consulted the tire designers responsible for helping create the actual tires for 32″, we’ve consulted the oracles and looked to the stars to try see the future.
But when the rubber hits the dirt, what are the actual differences between 29″ wheels and 32″? Are they actually faster? Where are they faster? And how much faster?
The findings are not what you’d expect. At least, not entirely.
Hype versus cold hard facts
I hit my local trails with a power meter and two bikes. One prototype 32″ xc bike from an unnamed, but large brand. And, in the 29″ corner, a race-proven Canyon Lux World Cup. Same trails. Same Favero power meter pedals. Same semi-fit editor’s legs. All combined for an empirical, real-world comparison to find out the cold-hard truth about which tire size rules supreme.
Okay, maybe it’s more like a lukewarm, semi-empirical, real-world comparison. The real world isn’t a laboratory. I’m not fit enough to produce perfectly matched efforts and only had time for a couple of runs on each bike. But these are trails that I know well. And some differences were quite obvious, with the empirical and experiential findings lining up in a way that is hard to deny.
The method
Our search for cold hard facts led to an admittedly lukewarm truth. The head-t0-head match up was less of a blowout than expected, with no real K.O. punch landing in either direction. But here’s how we achieved those findings and, then, what murky vision of the future that leaves us with.
The test ride is divided into three sections. Three very different stretches of climbs. Or, two timed segments, with the longer, latter segment being divided into two. With power meter in hand, or at foot as it were, the two bikes were compared on time vs power and effort.
Why am I equivocating so much before even showing the numbers? Well, the two bikes have very similar suspension designs, but not identical. They both had fast tires (Maxxis Aspen vs Pirelli Scorpion XC RH) but not the same tire. The bikes had different suspension, with the 29″ floating on RockShox SID/SIDLux and the 32″ on a Fox Float SL and the unreleased Fox fork that showed at Sea Otter and MADE bike show. And, due to circumstance, the rides took place on different days.
So, semi-empirical. But anyway, on with the show.
photo: Liam Wallace
The Trails
In Cumberland’s extensive trail network, I opted for two very different stretches of trail.
First, the lowest section of Sobo No Michi, a winding, mostly smooth, mostly low-angle climbing trail that isn’t exactly technically challenging but, crucially, is defined by many switchback corners.
Second, Climbmax. This segment was ridden as one effort, tying together lower and upper. While both are far more technical than Sobo, the sections have very different flavours. The lower section has more space between features and is less technical. The upper is constantly, repeatedly punishing with steep, often loose stretches connecting frustrating steps up logs and rocks, finishing with two bigger rock faces that, I hate to admit, force me to my feet as often as I make it up them cleanly.
The results: Gimmie some numbers
Sobo no Michi
29: 2:38 (11.5 km/h) – 352 W/175bpm
32: 2:53 (10.5 km/h) – 339W/154bpm
Lower Climbmax
29: 1:56 (10.1 km/h) 314 W 184bpm
32: 1:52 (10.5 km/h) 356 W /177bpm
Upper Climbmax
29: 3:02 (10.9 km/h) – 327 W/187bpm
32: 2:47 (11.9 km/h) – 358 W/187bpm
Both Climbmax (upper and lower combined)
29: 5:19 (11.0 km/h) 326 W/186bpm
32: 5:00 (11.8 km/h) – 361 W/183bpm
Deciphering the results
So, that’s all a bit messy. But there’s a couple takeaways.
One: the 29″ was faster on Sobo, with just a small difference in Watts (13). By 15 seconds over less than 3 minutes. That is kind of surprising. I’d expected the 32″ not to be a huge advantage, but I didn’t think it’d be slower.
Two: the 32″ was faster than the 29″ on Climbmax, by 19 seconds over five minutes . But almost all of that difference (15 seconds) was on the upper section, despite a smaller differences in wattage between efforts on upper and lower (31 vs 42). This lines up with the purported advantages of 32″ tires. More grip for steeper, looser surfaces made it easier to put down power on the big wheels while better roll-over made it easier to stay seated and stay on the gas at times where I was forced to stand and surge my way up shelves of rock and roots on the 29″.
Looking at heart rate, it was identical on upper Climbmax and actually lower when riding the 32″ on lower Climbmax. Why? Well, if my theory holds, I was able to stay seated and put in a much more even effort on the big wheels versus having to stand, surge, and re-accelerate more often on the ‘little’ 29-er.
Differences in power throw off those numbers a little bit, I’ll admit. But they’re backed up by supporting rides. A less powerful 32″ effort on the Climbmaxes still produced a significantly faster time on the upper section and a similarly equal time on the lower section. A less powerful 29″ effort on Sobo still produced a faster time than on the 32″.
Then there’s how those ride’s felt.
The company you keep: some context and some B.S. beyond the numbers
As I said, the numbers are a little murky. But some context might help make the picture a little clearer. Or, as I’ll get into below, a little differently murky.
While the numbers are a little murky, how those rides felt clears the water a little. At least in terms of explaining the numbers. First, I thought my 32″ climb on the fast, flowy Sobo was going to blow Strava leaderboards out of the water. I was genuinely surprised when the 29″ was significantly faster, as the efforts felt similar.
At the opposite end, I fully expected upper Climbmax to be faster, based on how the ride felt. But I wasn’t expecting it to be that fast. I also thought lower Climbmax would be faster than it was.
Looking at the trails themselves, those experiences on Climbmax make sense. On the lower section, there were parts where the big wheels made a big difference but, back on the 29″, I still felt fast. That changed on the upper section. I was bouncing around on the ‘little’ wheels, fighting to keep power on the pedals, sliding on dirt and, at the end, couldn’t make the big rock despite trying as hard as I could. On the 32″, the experience was totally different. It felt easier to keep putting down power, it rarely felt like I was running out of grip. Even on the big rock move at the end, when I was totally gassed, it wasn’t a struggle to get to the top. So the power numbers are higher, in part, because it was easier to keep putting down power.
Then there’s the company. On Sobo and lower Climbmax, I completely failed to make a dent in the Strava leaderboards. On upper Climbmax, I suddenly vaulted up past the locals and into the ranks of visiting pros. To be clear, I’m under no illusion that that’s my own efforts as, just minutes earlier, they were still virtually putting the boots to me (and I’m aware that they rode those times in the middle of a much longer BC Bike Race Stage at the end of a long week). Instead, I’ll stick to arguing that, on the really technical trails, the 32″ started to shine, carrying me above my own abilities.
The Tipping Point: Grip and roll-over versus rotational mass and acceleration
Which brings us to some conclusions. Or some more questions. Instead of being a knock-out, this little quasi-scientific game proved that the advantages of 32″ aren’t quite as clear cut as it might seem. Except where they are. Which makes the move to bigger wheels less clear cut than the move from 26″ to 29″.
When 29″ rolled out, the improvement’s in roll-over were so huge compared to 26″ wheels that any drawbacks to the increased rotational mass were quickly (or eventually) forgotten. But, the move from 29″ to 32″ isn’t as clear cut. Even moderately technical trails it was close while on easier, faster trails the faster acceleration of 29″ was a significant advantage. On really technical or loose trails? 32″ a huge advantage. The improved grip and roll-over made it perceptibly easier to clean hard stretches of trail, with that experience being backed up by numbers.
But how often are we all riding very difficult stretches of trail? And is that worth the trade-off on easier trails, even in a racing environment?
Put another way, when do we hit a tipping point between the gains earned by adding more grip and roll-over speed versus the downsides of adding rotational mass and loss in acceleration? Is 32″ too much for most riding situations, even when it’s significantly better in more extreme situations? Or, god forbid, should we start talking about 30.5″ as potentially striking a better balance?
It’s not all about climbing
All of those notes apply in different ways when you point the bike downhill. While cross country types will be most concerned about climbing efficiency this weekend in Solider Hollow, descending is equally important (or more important) when you’re just riding for fun. It also matters to racing, even if it doesn’t look like a huge gap. But being able to descend more easily means more recovery which then means you can hit the next hill harder. So, I guess it matters to everyone.
I won’t get into time differences between riding the 29″ and the 32″. And I do get into the details of how the big bike feels different in far more detail in my ride impressions story. But I will say the 32″ does make riding any kind of technical sections far smoother and, therefore, easier. This is especially relevant for traditionally more steep and sharp-steering cross country bikes. It was just less work, mentally and physically, to ride hard trails on the big wheels than on a 29″. The 29″ was more fun, though. It corners faster, it is easier to move around in the air or to play around moving between lines on the trail. But that’s what we all said about 27.5″ and 26″ wheels, too, and now 29″ are reasonably fun.
So, what are the conclusions? Well, first off, the power and efficiency debate isn’t as clear cut as some, myself included, would have assumed. 32″ are not a universal K.O. blow for 29 wheels, perhaps even in XC racing. There are ride, trails and races that will suit the little wheels better. But also, 32″ are more of an advantage, in some respects, than anticipated on descents. So this could be an interesting battle. Hold on, it’s about to get weird.