At the forefront of plus-size: the US bike and accessories manufacturer Surly, here the Dirt Wizard 26x2.75 tire, also available in 29x3.0

Variety vs. confusion
Three wheel sizes for mountain bikes: that already exists and the fat bike trend is once again pushing forward new standards for hubs, bottom brackets and tire widths. And now - as if the variety wasn't enough at the moment - the first bikes with tires in so-called plus sizes could be seen in the 2014 season, mainly at the Eurobike, but also at the Bike Days.

This plus size refers to widths between 2.75 and 3.25 inches. This means that the outer diameter (including the tire) of the wheels is not only wider, but also higher. (Established mountain bike tire widths usually range from 2.25 to 2.35 inches to 2.5 inches, with fat bikes this is around 4 to 4.8 inches). There really aren't many products of this plus size on the market, let alone available for purchase; the plus-size products from Rock Mountain, Surly, WTB and Vee Tire are above the radar.

Also at the forefront: Taiwanese tire expert Vee Tire, here with the Trax Fatty tire, available in 29x3" and 27.5x3.25"

War of the St...andards
With wide tires, the issue of the chainline comes into play - because if the roller is really wide, the chain and tire lugs get in each other's way. For fat bikes, the new bottom bracket/Q-factor and hub widths have provoked this, and for plus sizes, the Boost 148 rear hub standard is now being brought into play. (Boost 148 was introduced by Trek with Sram in summer 2014 to make 29er rear wheels stiffer, axle width 148mm, for axle format 12mm) The wider rear hub provides a suitable chainline that leaves more space for the tire. With wider hubs and a larger flange distance, stiffer wheels can also be built, which is certainly advantageous with wide rollers. Especially with a 29+ wheel, a stable wheel construction is important so that the wheels are not "spongy" to ride.

Already on show at the Bike Days 2014 in Solothurn: Rocky Mountain's Sherpa concept bike, which relies on plus-size tires and is available in the
the "Adventure" area of application

.

The vision
With the plus size, several trends could come together and virtually multiply. Wide rims are popular in enduro sports and are a prerequisite for plus-size tires. With the three current wheel sizes, bikers are already aware of and sensitized to this topic. For example, 650b+ wheels could be ridden in a 29-inch bike - and give one and the same bike with two wheelsets (i.e. 650b+ for rough terrain and unrivaled traction uphill and at the limit when cornering and the conventional 29er wheelset for the faster pace) a very wide range of use. The same is conceivable with a 650b bike that brings the trendy fatbike feeling with 26+ tires.

A possible conclusion
Once the confusion of wheels is over for the end customer (and reduced to the 27.5 and 29 inch sizes), the additional plus width standard including the new hub axle size has arrived on the market and wider rims with rim widths of around 30 to 35 millimetres have long been normal on bikes - then the mountain bike could make a quantum leap in terms of riding fun, range of use and versatility.
The plus size could bring the egg-laying wool-milk sow on studded tires a good deal closer to reality.