The Future is Big is emblazoned in black letters on the top tube of the prototype. The slogan hits the nail on the head and is also a declaration of war: the established 29ers could soon be degraded to the new mediocrity. The fully, created under high pressure by the Swiss brand Stoll, rolls on huge 32-inch wheels that not only tower over the editorial dining table, but also the espresso cup placed on top. In short: the bike is huge - despite the M frame size.
Wheel evolution on the MTB
70s until 2015
26-inch bikes have dominated the MTB market for decades and are the measure of all things for small and large riders and across all disciplines. Currently only a kids' and dirt bike topic.
from 2012
The intermediate size 27.5 inch entered the MTB stage well after 29 inches. Nino Schurter piloted a 27.5-inch bike to World Cup victory for the first time in Pietermaritzburg in 2012. Currently only relevant for small sizes and on the rear wheel.
from 2008
Niner came around the corner with 29-inch bikes as early as 2005, and BIKE tested the first 29ers in 2008. But it took until 2010 for the first race wins to be achieved on 29-inch bikes. The big bikes were slow to establish themselves.
from 2026?
Maxxis presents a 32-inch Aspen tyre at Eurobike 2025. Individual companies such as BMC, KTM, Stoll and Bike Ahead are also showing the first prototypes based on the giant wheels.
Drop your trousers in the lab
But before we take the approaching future off-road, we head to our test lab to gather data. The 32 x 2.4 inch Maxxis Aspen tyres measure a massive 817 millimetres in diameter. This means that they outperform the identical 29-inch tyres on our reference KTM by a whole 74 millimetres. A jump that roughly corresponds to that from 26 to 29 inches. However, larger tyres also mean heavier and therefore more sluggish. In order to translate the feeling of "doesn't feel quite as lively as ..." into reliable values, we measured the exact inertia of both wheels in our test lab. The difference in weight between the two wheelsets is 384 grams, with the tyres alone accounting for 150 grams. A 32-inch Maxxis Aspen weighs 75 grams more than its 29-inch brother. Weight that sits as far out as possible and first needs to be set in motion.
27 per cent slower to start
Our measurement series show: The inertia of the 32-inch wheels is 27 per cent higher than that of the 29-inch wheels. Adjustments to the geometry are also necessary to accommodate the additional wheel. The Stoll prototype offers 100 millimetres of travel at the front and rear and has a wheelbase of 1222 millimetres. Almost 50 millimetres more than our reference bike, the KTM Scarp. Even if the distance between the axles is still considerably shorter than on a 29er enduro bike, the overall length of the 32-inch bike is overwhelming. At a whopping 203.4 centimetres long (eleven centimetres more than the KTM!), you wouldn't want to imagine it on the rear rack of a VW Golf - there's only eight millimetres of clearance left and right, measured from the wing mirror!
Déjà vu: like when switching from 26 to 29 inches
The moment of truth has arrived: It's off to the trail. With a weight difference of a proud two kilos in favour of the KTM, the 32 prototype with its 3.5-kilo frame is significantly heavier. Both bikes are equipped with power measurement for an objective comparison. The first few metres in the saddle show that the riding position is consistent. My concerns that the large front wheel would raise the front end too high are offset by the Stoll prototype's stubby head tube and negative cockpit. At 1.79 metres tall, I sit in a sporty position and have plenty of pressure on my hands.
The first key section is not long in coming and leads steeply uphill. I deliberately choose the worst line and constantly pick my way through the loose gravel that has accumulated in the steep gully. Tiring, but doable. On the KTM 29er, the same game takes me back to 2008, which is exactly how it felt when I rode Gary Fisher's first 29er hardtail against a "current" 26-inch hardtail at Bike. Instead of reminiscing, I struggled with the line in the gravel channel. The rear wheel spins at the very first deep section. I lose speed and have to correct with a swerve. And so it goes on. I fight my way up with various foot drops.
More grip, more safety
Despite identical tyre profiles, the difference in grip is huge. The 32-inch bike has more tread on the ground and climbs with more confidence and control thanks to the long chainstays. Short intermediate sprints, on the other hand, confirm the test results from the lab. Weighing just 10.53 kilos, the KTM with its smaller and lighter wheels accelerates effortlessly from a standing start. The 32 requires noticeably more pressure on the pedals. But once the bike is rolling and you're cranking along at a steady speed, you experience the miracle of physics. High steps and arm-thick tangles of roots literally disappear into thin air, while the giant wheels roll over them at almost undiminished speed, preserving the momentum. There's no getting stuck or bouncing as with the small, sorry, normal-sized 29ers.
But can the better rolling behaviour compensate for the higher wheel inertia and, in our case, the significantly higher overall weight? We calibrate the power meters and, in a team of two, simultaneously complete a 200 metre uphill segment with 25 metres of climbing - exclusively on firm forest ground, peppered with a short root section. I sit on the KTM three times, while Max sticks to my rear wheel with the Stoll. We then swap bikes and repeat the same procedure. Max sees the light-footed KTM in front.
Stoll P32 prototype:
12.6 kg1/ 100/100 mm / 32" / aluminium/carbon
- Fork / Shock: Intend Samurai XC / Fox Float Factory
- Gearing / range: Sram XX SL Transmission / 520 %
- Brakes: Shimano XTR 160/160 mm
- Wheels: Bike Ahead Biturbo
- Tyres: Maxxis Aspen Maxxspeed Exo 32 x 2.4" tyres
- dropper post / stroke: Rockshox Reverb / 150 mm
- Special features: currently still a prototype, series bikes available from mid-2026
KTM Scarp Exonic Evo 3:
10.5 kg1/ 110/105 mm / 29" / 12999 Euro / Carbon
- Fork / shock: Rockshox SID SL / SID Luxe Ultimate Flight Attendant
- Gearing / range: Sram XX SL Transmission / 520 %
- Brakes: Trickstuff Piccola C22 160/160 mm
- Wheels: Mavic Crossmax Ultimate
- Tyres: Maxxis Aspen Maxxspeed Exo 29 x 2.4" tyres
- dropper post / stroke: Rockshox Reverb / 125 mm
- Warranty: 5 years
- Max. System weight: 110 kg
- Special features: Handlebar-stem unit
7 per cent better efficiency
But before we start analysing the data, we plunge into the descent. What about the downhill performance and handling of the "big bike"? The long wheelbase and high gyroscopic forces ensure stability. Rough terrain is simply ironed away. It seems impossible to get stuck anywhere or even go over the handlebars, you are so low between the wheels. There is less lateral input on the front wheel. The 32er handles extremely smoothly without being too sluggish or giving you the feeling that you're just a passenger. It masters steep sections in slippery conditions much better. The feeling of safety is significantly higher than on the 29er. One day later, the performance data was analysed. Max was slightly off the mark with his gut feeling. The 32-inch bike completed the climb in the same time, but with seven per cent less power. So it looks like a clear points victory for the new large wheels.
Conclusion Peter Nilges, BIKE Test Manager
More weight and higher wheel inertia speak against the new giant 32-inch size. In almost all other respects, however, 32 inches trumps the current 29ers. Rollover behaviour, riding safety, grip and rolling resistance speak for themselves and will certainly drive the wheel revolution forward.
