Pump track
The pump track provides information in two respects when it comes to tyre formats. Firstly, the inertia of the system is immediately noticeable, as you have to accelerate the bike without pedalling, and secondly, extremely high forces act on the tyres in the banked curves, which provoke lateral buckling if the air pressure is too low or the rim is too narrow. With the minimum pressure that can still be ridden on the pump track, the tyres generally have sufficient lateral stability in any terrain situation. In combination with the 28 millimetre wide rim, the 27.5 and 29-inch tyres were at a pressure of 1.5 bar. With the Plus tyres, we were able to lower the air pressure in combination with the very wide 45 mm rims (rider weight 70 kg) to just 0.9 bar at the front and 1.0 bar at the rear without any stability problems. The air pressures determined in this way served as the basis for all subsequent driving and laboratory tests.
Asphalt
For most bikers, the minimum pressure that can still be ridden on tarmac is more practical. Here too, the perfect grip can provoke high lateral forces when cornering. However, the minimum pressures determined on the pump track do not deviate from this test. Here too, the Plus tyres are still rideable at a very low 0.9 bar at the front and 1.0 bar at the rear and offer good stability and therefore safety in extreme situations.
Riding stability: 27.5+: 1 | 27.5: 0 | 29: 0
WEARABILITY
The inertia of a wheelset has a significant influence on the feel of a bike. Agile and sprinting, or sluggish and sluggish.
Accelerating, braking, turning in, changing bends, actively jumping off. When it comes to changing speed or direction, the inertia of the rotating wheels is particularly noticeable. It is not only the mass itself that is decisive, but also its distribution. The further away the mass is from the hub, the more noticeable the effect. Due to the lowest weight and the smallest diameter, the two 27.5 wheels are by far the most agile. The jump from 29 to 27.5+ is huge on the Specialized (15 watts more for acceleration). Due to the big weight difference of 264 grams per tyre, the Plus tyre feels much more sluggish. With Schwalbe, the additional weight of only 124 grams per tyre and the significantly smaller diameter result in a smaller deficit when accelerating, as confirmed by the measurements with the Auditor Inertia Chronograph.
Inertia: 27.5+: 0 | 27.5: 2 | 29: 1
To get a feel for the inertias determined, we have calculated
how high the power (watts) is for a 5-second sprint from 0 to 36 km/h. Regardless of
differences in the measured data, the psychological effect can be much greater.
effect can be much greater. As soon as something feels slower, the brakes also kick in in your head.
COMFORT / ROLLOVER BEHAVIOUR
Only the larger tyre volume and the better support of a wide rim make it possible to reduce the air pressure of plus tyres by around 0.5 bar. What the coasting test (point 1) proved by travelling a further distance is also confirmed by the smoother ride feel. Thanks to the low rideable air pressure of 1.0 bar and (depending on the model) almost the same diameter as the 29er, the plus tyres offer noticeably more comfort and are less likely to get stuck on obstacles. As you can see in the high-speed videos from our tests, the plus tyres absorb more of the impact energy due to better deformation and do not bounce off the obstacle as high as the thinner tyres with an air pressure of 1.5 bar. The bike and rider are lifted less, and the tyre retains more ground contact between the individual obstacles. The plus tyres also show their advantages on demanding, rooty uphill climbs thanks to more ground contact and lower braking torques. To a lesser extent, the 29er also stands out favourably from the smaller 27.5er in terms of rollover and comfort.
Comfort: 27.5+: 2 | 27.5: 0 | 29: 1
PUNCTURE PROTECTION
Plus tyres can only make the most of their advantages if they are ridden at low air pressure. To check whether this increases the risk of punctures, we carried out a puncture test.
The laboratory values
Which offers better protection against punctures? The Plus tyre, which is inflated to just 1.0 bar but has a much higher volume, or a thin 27.5/29er with a tighter 1.5 bar? The tests on the Schwalbe guillotine confirm that the heavy Specialized Plus tyre offers the best snakebite protection, closely followed by the 27.5 and 29er. The significantly lighter and thinner Schwalbe Plus tyre performs slightly worse than the 27.5. Here too, the 29er tyre runs out of air the earliest. Due to the larger volume of the Plus tyres, there is no disadvantage in punctures despite the lower pressure. How robust the wider, but weight-conscious Plus tyres perform on sharp-edged gravel remains to be seen in practice.
Puncture protection: 27.5+: 1 | 27.5: 1 | 29: 0
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