The clocks are ticking faster in the bike industry. While many bikers haven't even realised that 27.5 inches is the norm, a new trend is already pushing its way into the shops. 27.5-Plus, 27.5+, 650B+ or B+ for short. Different terms, but they always mean the same thing: wheels with a diameter of 27.5 inches, paired with wider tyres of around 3.0 inches.
For fear of missing out, every manufacturer wants to be involved right from the start. Very few of them have extensive experience to fall back on. The bike manufacturer often lacks the test tyres or rims, while the tyre manufacturer usually lacks the corresponding bikes for testing. Nobody can therefore say with certainty at the moment what the optimum tyre width for the new Plus width is.
27.5+: theoretically sensible
In terms of the idea, Plus makes perfect sense. Anyone who has already gained experience with a fat bike knows how much traction a wide tyre with little air offers. However, anyone who has ridden a fat bike also knows what wider and therefore heavier tyres feel like. Sluggish, doughy, undefined and sometimes quite bumpy due to the lack of damping. Not to forget: the wider Q-factor of the cranks, which can be hard on some knees.
So why not take the middle path, the golden one? What has already been tried and tested with wheel diameters is now happening with tyre widths. The 26" and 29" tyres have become the compromise 27.5", while the traditional widths of 2.2" and 4.8" for fat bikes have become 3.0". Semi-fat or Plus, as the additional width is called. The essence of both compromises (diameter and tyre width) is therefore 27.5+ or B+. At least most manufacturers are focussing on this dimension. The market also offers 29+ or even 26+ tyres in homeopathic doses. So we can be curious.
Weight, diameter, tyre contact area and volume - in terms of the actual figures, the new Plus format differs significantly from the existing sizes and is closer to 29 or 27.5 inches in diameter, depending on the model. However, in order to get an objective feel for the Plus tyres, BIKE also tested all relevant criteria such as rolling resistance, traction, riding stability, inertia, comfort and puncture protection in laboratory and field tests - with surprising results.
Weight
As you would expect, the 27.5-inch complete wheels weigh the least on the scales. The 29-inch wheels only weigh four percent more, while the Plus combination weighs 25 percent more for Schwalbe (2.8" width) and 44 percent more for Specialized (3.0" width) due to the wider tyres and rims. If, contrary to the test setup (all tubeless with 100 ml sealant), a tube is used (208-284 g), the difference is even greater.
Tyre contact patch
With the same load on a tyre, the contact area (the contact area with the ground) depends solely on the air pressure used. With a tyre pressure of 1.0 bar for the plus tyres and 1.5 bar for the narrow tyres, the calculated contact area is 33 percent larger with the same carcass flexibility.
Volume
Three litres separate the Specialized 27.5 from the fat Plus tyre. With Schwalbe, the difference is only 1.8 litres. The comparison shows just how much leeway there is within the new Plus size. Schwalbe-Plus and Specialized-Plus are also separated by one litre. Due to the large volume, the Plus tyres feel relatively firm even at low pressures and make for thick arms when pumping.
CONCLUSIONS: There is undoubtedly a lot of potential in the new Plus format, as our tests show. However, the measurements also show that the ride feel and design of the plus tyres can be extremely different. If we had only carried out the tests with the much slimmer and less cushioning Schwalbe Plus tyres, the conclusion would be the same: There are hardly any disadvantages in terms of weight, inertia and rolling behaviour, but the traction does not stand out significantly from a good 29er tyre. With the heavier and significantly better damping Specialized Plus tyres as the other extreme, the conclusion would have to be: Plus tyres offer a noticeable gain in traction, comfort and safety, but significantly curtail the agility of a bike. Due to the dimensions of the new plus tyres, the differences in tyre construction and rubber compound are even more noticeable than before. However, as with all new products, the optimum tyre and rim width, outer diameter and rubber compound have yet to be determined.
The question also arises as to for whom the new tyre format is a real asset. As the Plus bikes clearly stand out visually from a normal bike, the innovation can be marketed well. However, whether every touring rider can really benefit from more traction and therefore safety, but has to carry more weight, depends heavily on the respective area of use and the personal requirements of a bike. Even if tyre technology continues to advance, wide tyres will always remain heavier than narrow ones. In addition, the lack of compatibility with existing bikes due to tyre clearance and the installation width of the hubs is a real point of criticism for the new Plus format.
Peter Nilges BIKE test editor: "Viewed objectively, the Plus tyre scores the most points in the equally weighted test criteria. If other points such as weight or higher demands in terms of riding dynamics are added, the lead of the plus tyres crumbles. It also remains questionable whether tyre widths of up to 3.0 inches are really necessary, as many bikers do not yet exploit the full potential of the current tyres. "
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