The Future of Plus-Size Tyres

Plus-size tyres might be the bike world’s current hottest trend but so few of us have had the opportunity to properly try out these tyre widths. From pros we hear an echoing cry of: “Yeah, plus-size tyres have their advantages, but they’re not for me.” So, just who are these tyres made for then? What are their advantages and disadvantages? Where is the concept headed? Here are the answers.

The ultimate resource, the Cambridge Dictionary, defines a trend as ‘a general development or change in a situation or in the way that people are behaving.’

With this in mind, plus-size tyres can certainly take on this label. Since 2015’s Sea Otter Festival the bike world has gone through a mass of emotions including indignation, disbelief and excitement about the new widths. Back in March, we carried out exclusive tests in the South of France with plus-size tyres from Specialized. Then came a flurry of product launches from various manufacturers over the following weeks and months, proclaiming how they’d united the benefits of fat bikes with those of 27.5 models. This prompted yet more questioning and raised eyebrows: where had these assertions come from? Given that so few tyres were out on the market when these frames had been designed, what were these claims based on?

New parametres have to be set for plus-size tyres. What’s the best tread profile? What’s the perfect carcass? The industry is still getting to grips with fundamental research.Die Industrie ist noch im Stadium der Grundlagenforschung.

EUROBIKE saw the industry split into two opposing fractions: those who’d been pushing plus-size tyres from the get-go now revealed extensive new collections; while others maintained staunchly that they lacked the expertise to present several such bikes all in one hit. These firms kept to just one model, or even deigned to reveal any bikes with the new wider tyres.

The various approaches were evident as we carried out yet more tests, this time under the wing of the Design & Innovation Award 2016. No two plus bikes are the same it transpired, and despite having almost identical figures on paper, these bikes couldn’t have given more diverse rides. However, some parallels naturally existed; and here are a handful of fundamental findings:

How they ride

The marketing hype proved substantial when they claimed that plus-size tyres offer an as yet unrivalled level of grip combined with an agile handling package (when compared to fat bikes). On loamy ground in particular, the term braking point takes on a whole new meaning, and any rooty off-camber sections are gobbled up by the massively grippy tyres to give the rider a serious sense of confidence. For both pros and amateurs, these situations are ones to throw your arms up in glee about. But naturally, as we’ve come to learn, every high has its low, and the tyres have a tendency to wallow on berms and compressions regardless of your level of riding. Given the bigger surface area, they can be sluggish through mud and loose ground. The plus-size tyres gain approval on climbs, particularly on technical terrain thanks to the enormous traction they deliver and the barely noticeable increased rolling resistance. Yet the scales are tipped once more when you take the extra weight – and subsequent slower acceleration – into consideration.

The right air pressure

The decisive parametre for a plus-size tyre revolves around its air pressure. Quite frankly, nothing else can impact on their performance more than the air pressure. Even 0.1 bar, or less than 1.5 PSI can turn a perfectly set-up bike into an unrideable beast – and vice versa. It’s difficult to make any sweeping recommendations here, as the correct air pressure can vary drastically from the tyre model, the rim width and even your air pressure gauge. Even in our testing we had discrepancies of up to 0.2 bar purely based on how we measured the pressure. Judging by our Flaig pressure gauge, the optimal air pressure (depending on the tyre, rims, rider’s weight and style) was between 0.9 and 1.2 bar. To nail your own personal set-up, we recommend increasing and decreasing the pressure by 0.1 from the starting point at 1.0 bar. Using the same pressure gauge, try and bridge the perfect compromise between grip and sponginess.  

Is bigger really better?

There’s one trend floating around at the moment that can’t be ignored: wide rims. As the tyres have more support, there’s less chance of them deforming and the air volume can be increased. During this test we used rims with an inner diameter of 30 – 50 mm and tyres of 2.8” to 3.0” from various manufacturers. Our result: Wider doesn’t necessarily mean better for plus bikes. Why? With 50 mm rims, the weight increases and the handling becomes sluggish. Moreover, the side knobs end up being too high which negatively impacts on the tyres’ ground footprint. The tyres on the 50 mm rims also kept trying to deform. The optimum consisted of a 40 mm rim with a 2.8” tyre, although the 30 mm models worked a treat and proved better at accelerating (due to the lower weight).

Where the fun ends – the weight

Our test fleet showed one thing for certain: bikes with plus-size tyres will only really work if their weight is kept to a minimum – but that comes at a cost. Carbon bikes proved far more agile, more nimble on the descents and more efficient on the climbs in comparison to the 2kg heavier and half-the-price aluminium bikes.

The crucial aspect – the tyres

The point of contact to the ground and at the heart of any plus bike: the tyres. In our test we didn’t just put various tyre models through the wringer, but we looked at multiple widths. The findings: 3.0” tyres barely offer any more grip than a 2.8” model, which – given their extra weight – rules out our interest in them. Even flat-profiled tyres offer huge amounts of grip and if you’re not into mending a puncture every five minutes then tubeless is mandatory.

Who are plus-size tyres for?

Mountain bikers who prefer comfort and stability over weight and those who don’t have a calendar crammed with hardcore races for the season can already get a good deal out of riding plus-size tyres. But you’ve got to be willing to do three things: firstly buy high-end products to ensure that you achieve a decent payoff between weight and performance; secondly suss out the air pressure issue; and thirdly, go tubeless. The same applies to the world of e-performance, although weight is further down the priority list here.

Plus-size tyres offer huge advantages but there’s still a long way to go until they reach their full potential. In our opinion, there’s a road to improved performance by choosing a supreme front and rear tyre option and setting up the ideal tyre-wheel combination with the optimal tyre and rim widths. Similarly, tyres with a width of around 2.6” on 30-35 mm rims could be the dream set-up for traction and agility. Running the correct air pressures is another tricky issue for plus-size tyres. And given that bikes are already becoming ever more complicated, we would love to see things simplified and a bit more user-friendly.

Words: Christoph Bayer Photos: Christoph Bayer/Trev Worsey

Design & Innovation Award 2018 E-MTB Trends

What will the e-bikes of the future look like? What are the key trends and biggest challenges of the upcoming year?

Design & Innovation Award 2017: Application

This year the DI.A makes a return to San Vigilio – Dolomites, and is set to be bigger, better, more exciting and more varied than ever.

Expert Discussion | Redefine Performance of E-MTBs

What do we need to do to give E-MTBs more performance and make E-Mountainbiking the next big thing?

Expert Discussion | Crossing the Divide between MTB & Road

From the simple bicycle, a plethora of variations has been borne, but are they really so different and is there still something they can teach one another?