A fairly recent innovation in mountain bike riding is the evolution and growth of the fat bike (and the tyres it touts) into the relative mainstream of mountain biking. Whilst true fat bikes are never going to be an everyman choice the bike industry is pinning its hopes on a new plus sized standard that is a whole lot more marketable.

27.5+ This is a ~3 inch wide tyre on a 27.5 inch rim. This is compatible with some existing 29″ frames if clearance allows as it is almost equivalent in diameter to a standard 29er.
29+ This is a ~3 inch wide tyre on a 29 inch rim. This nearly always requires a specific 29+ frame and fork.
Surly produced the famous Krampus model in 2012 with 3 inch wide tyres on a 29er frame. This bike made the first rumbles between standard mountain bikes and fat bikes – the latter of which having made a massive surge of profit in the bike industry of late. So where does the problem lie? Fat bikes are known for their all-terrain 4-6 inch wide tyres. These tyres are penetrable to almost any surface and provide comfort, grip, smiles and a few odd looks. Although we don’t have many opportunities to use them as originally intended, they are some of the most talked about bikes in the industry. Now, if we take a 29er frame and add 27.5+ tire sizes, we will usually have a snug but acceptable fit. This means the compatibility with existing frames is promising, especially given the new range of extra wide forks the industry is busy preparing for their 2016 model ranges. However, when we start thinking about 29+ the immediate market is much smaller due to the lack of compatibility. 29+ is a big wheel when you consider the tyre height – for smaller riders this is likely to be off-putting for the ‘perched’ feeling and the extra wheel-base length that is required. Some brands will certainly take up the 29+ wheel size but 27.5+ is going to dominate the plus sized trend.

So for now, it seems 27+ tires are the next in-thing. For terms of compatibility, they can easily be converted and placed on most 29er frames for those willing to try out. One problem which has been recently discovered about the sudden influx of these tyres is that there is no industry standard system for defining widths and breadths of the tyres. The 27+ tyres we have encountered are of slightly different thickness and widths – something which will definitely affect the way you ride. This seems glamorous, but one has to consider the problematic space issues with thicker rim tyres. With limited stay available in the rear triangle, it is essential to clear up and ensure your ride can take modifications.

The industry has been preparing. The Boost 148 axle heavily pushed by Trek brings in more space in the back and is being adopted as the new MTB standard by many brands. Up front, 110mm wide hubs are coming and the fork manufacturers such as RockShox, Fox and Marzocchi have these wider 27.5″ forks prepped and ready for release just weeks from now.

Be certain, the big brands are getting on board with 27.5″ for their 2016 bike releases. Also be prepared for a surge in independent and relatively local level bike brands preparing their specifications to attract the wave of customers. With the state of the bike industry as it is, bike companies are not going to want to miss out on a lot of isolated and independent interest in their companies – so we think you’ll see quite a few other brands getting on board. Only a few years ago fat bikes were a pretty rare breed but every major manufacturer now offers them. 27.5+ is a much more marketable concept than fully fat ever was.