Can bigger really prove to be better?
Plus bikes promise to deliver more traction, more control and more comfort. They’re being billed as the next big thing in trail riding, and all the key brands are jumping on the fat-tyre bandwagon.
Let’s make one thing crystal clear: Plus bikes aren’t just for plus-size riders. That’s because the Plus part actually refers to the tyre width, not the size or strength of the bike.
To confuse matters further, Plus bikes come in two distinct flavours: 27.5 Plus and 29 Plus, both rocking tyre widths in the range of 2.8in to 3.0in. That’s compared to regular 2.2-2.3in models commonly found on most current bikes.
Plus bikes explained
For now though, we’ve got two new wheel sizes in the mix. Unsurprisingly, they come with their own unique set of design issues and standards. Is the upheaval worth it? Well, if manufacturers’ claims of increased traction and control are to be believed, the fatter Plus tyres sound like they could catch on.
There are still plenty of unanswered questions though. Such as, are they just for beginner riders? How soft can you run the tyre without puncturing? Is there an increase in the rolling resistance, and can they cope with mud?
It sounds obvious, but it’s important to understand that wheel size is a product of rim diameter and tyre width. Fit a 2.0in tyre, or a 2.5in tyre, to the same rim and you get two different wheel sizes. Taken to the extreme, this is in essence what Plus wheel sizes are all about.
Plus size wheels use rims with the same diameter as regular 27.5in and 29in rims, but the massive 2.8-3.0in tyres give two new wheel sizes that require dedicated frames and forks.
Given that one tyre manufacturer’s 2.8in tyre can look more like a 2.6in, while others have profiles that measure up closer to 3.0in, there’s a lot of variation between brands.
Fatter tyres need wider rims for extra support. So, even though the Plus size rim diameters are the same as 27.5in and 29in, the rim widths need to increase in proportion to the tyre width
According to Schwalbe, a 2.8in Nobby Nic at 15psi has a 21 per cent bigger contact patch than a 2.35in Nobby Nic at 25psi. More rubber on the ground equates to more grip, and with all other things being equal, wider tyres with more air volume should let you run lower inflation pressures while still providing the same level of support.
Unfortunately, things aren’t equal. To stop the weight of the bigger tyres from creeping up, tyre manufacturers are using thinner casings, with less rubber. In practical terms this means you can’t run some Plus size tyres as soft as you think, as they have less inherent support and damping. It also means that the sidewalls are more prone to cuts and will degrade more quickly.
The bottom line is that, while tyre construction is important on any bike, it’s going to prove even more critical on Plus bikes.
Before we dismiss Boost as yet another exercise in obsolescence, let’s take a closer look at the advantages. By increasing fork dropout spacing from 100x15mm to 110x15mm, the hub flange spacing can be increased by 10mm.
This reduces the spoke angle relative to the hub, resulting in stiffer, stronger wheels. On the rear it’s a similar story, only this time it’s only a 6mm improvement as the dropout spacing grows from 142x12mm to 148x12mm.
The extra width of Boost dropouts was necessary for the additional clearance required by the wide 3.0in tyres. And painful as progress can be, Boost will ultimately be better for all bikes, as stiffer, stronger wheels are an advantage.
If you’ve been paying attention, you’ve probably worked out that if you increase the rear hub spacing, and move the hub flanges further apart, the cassette has to move further outboard and this will mess up your chain line.
Fortunately, crank manufacturers are on board with the Boost standard too, so companies like SRAM are producing dedicated chainrings, with 3mm extra offset, that shifts the chain ring further away from the BB. This corrects the chain line without the need to change the BB standard or crank spacing.
Bolt-on spiders and single ring designs have made this the least painful step in the shift to Plus-size tyres. Also, the wider chain line is needed so the chain actually clears the tyre.
The best plus sized bikes
Specialized Stumpjumper FSR Comp 6Fattie
While the Stumpjumper Comp 6Fattie is more sluggish than bikes with regular tyres, climbing traction is a revelation and this largely makes up for the slightly less responsive ride elsewhere. The Stumpy is still a blast to bounce around on (literally), and it’s stacks of fun on the right terrain. It’s playful, it’s planted on steep descents, and the massive grip levels improve balance and braking, making it really sure-footed over rocks and roots. Given that you’re getting the latest tech at a fair price, the Stumpy 6Fattie offers some significant advantages while also keeping entertainment levels high. Just don’t expect it to cut through mud.
Trek Stache 9 29+
The Trek Stache 9 is a radical departure from trail hardtail tradition, but it’s certainly no fat bike. Instead, it’s a bold reinvention that’s paid off big time. Despite having the tallest, widest tyres on test, once up to speed, clever engineering and geometry ensure the Stache is an incredibly fast, fun bike that’s somehow almost BMX-like in its playfulness. Sure, the 29 Plus wheel size isn’t without inherent compromises — tyre weight and durability being the key ones. It also has questionable credentials in wet, muddy conditions, but we challenge anyone who loves mountain biking to ride the Stache and not come away impressed.
Specialized Stumpjumper FSR Comp Carbon 6Fattie
With its slack head angle, lower bottom bracket and more active suspension, the Specialized 6Fattie has the edge on most Plus sus bikes, just. It’s been sold short however, as it would be even better if the front end was 20mm longer. Yes, the suspension needs tightening up with the addition of volume reducers, and it’s fair to say, when you’re dropping £3.5k on a bike, someone at Specialized really should have taken the time to ensure that the suspension is totally dialled straight out of the box. Luckily, it’s a super-easy and inexpensive fix that takes the 6Fattie to the next level.
Norco Torrent 7.2
So close to crushing the competition, the Norco gives a glimpse at the potential of Plus tyres. With the imperfections ironed out and a bit more tyre development, the Torrent could be unbeatable.
Specialized Fuse Comp 6Fattie
Given the standout specification, great size range and thoroughly modern geometry, the Specialized Fuse Comp 6Fattie should have easily won this test. It didn’t. That’s because the lacklustre performance of the Suntour fork and the inherent harshness of the M4 aluminium frame beat you down rather than spur you on — the ride quality undermining the remarkable build kit that makes it such an attractive proposition in the first place. Obviously we all want the best specification possible for our hard earned, so while the Fuse gets all of the latest must-have features, it falls short on the most important one of all… ride quality.
Cannondale Beast of the East 3
The Beast of the East 3 is a lightning-fast bike and a blast to ride. This beast won’t be sneaking up on anyone in the woods though, as the chain sounds like it’s tapping out a distress signal in Morse code on the chainstay. Annoying as that is, it’s not enough to detract from an otherwise great bike. With an air-sprung fork, 1×10 drivetrain and comprehensive size range, Cannondale has put together an amazing package for a penny shy of £1,200. All that’s really missing is a chainstay protector and a seatpost quick-release.
Scott Scale 730 Plus
Given that Scott Scale 730 Plus is the most expensive bike here and it doesn’t get a 1x drivetrain, an air-sprung fork or even a clutch rear mech, it’s going to be a tough sell on the shop floor. Get it out on the trail, however, and it will instantly win you over as you carve effortlessly through corners, blast down the rowdiest descents and spin up loose technical climbs with aplomb. In every situation it handles like a charm, so even though the Scale 730 Plus isn’t dressed to impress, it’s hard not to be bowled over by its performance.
Like it or not, the new Boost hub and dropout standard is here to stay. And given that it makes for stronger wheels, rather than simply rendering your current parts obsolete, it’s easy to predict that Boost will quickly become the new norm on most frames and forks. That doesn’t automatically mean they will be Plus-size tyre compatible, though.
The big question is whether or not the Plus-size tyres themselves are ready? It’s clear from testing our three Plus bikes that more rubber on the trail brings some serious, err, pluses. Most notably, the huge increase in climbing traction makes life easier for all riders. Get the balance of rim width, tyre casing and inflation pressure right and Plus-size tyres can be more comfortable too, offering a much larger safety net of increased grip and stability.
So whether you’re just starting out or pushing the envelope at DH speeds, Plus-size tyres definitely bring performance gains to the table.
The flip-side is that the compromises are numerous too. There’s a very small window of optimum air pressure: under-inflate them and the tyres deform too easily; too high and they just bounce around. This is mostly just because the majority of tyre manufacturers use flimsy, thin casings to keep the weight from creeping up. Your only option, then, is to use higher air pressure for support.
This lightweight approach also means the bigger tyres are easily damaged in the very environment they excel in: dry, rocky terrain. If Plus is to prove more versatile, tyres really need to get tougher, better damped and more capable in the wet — and it’s going to require significant, unavoidable added weight with current tyre technology.
Ultimately, it will be you — the end user — who decides whether Plus bikes catch on in the UK. There’s no denying that they have potential, but only after spending a full British winter on them will we know for sure if they really are the next big thing.