I understand rolling resistance, tire pressures, rotational weight scenarios but it was very enlightening to read the intricate details of this article from a Finland based research lab. I hope you find it as captivating as I did. Enjoy…
Tucked inside a small industrial complex in Nastola, Finland, is the nondescript grey building of independent third-party tyre testing facility Wheel Energy.
Using a battery of custom purpose-built machines, founders Petri Hankiola, Veijo Pulkkanen, and Marko Savolainen are addressing some of the common questions surrounding bicycle tyres and they’re coming up with some interesting answers that no longer have to rely on word of mouth, tradition, or intuition for their veracity.
Take these conclusions for example:
Wider tyres roll faster than narrower ones: Many riders have argued for years that narrower tyres – especially on the road – are faster and more efficient than wider ones when in fact, the opposite is true. According to Wheel Energy, the key to reducing rolling resistance is minimising the energy lost to casing deformation, not minimising how much tread is in contact with the ground.
All other factors being equal, wider casings exhibit less casing ‘bulge’ as a percentage of their cross-section and also have a shorter section of deflected sidewall. How big a difference are we talking about here? For an equivalent make and model of tyre, Wheel Energy claims the 25mm-wide size will measure five percent lower rolling resistance on average – the supposed average limit of human detection – than the more common 23mm-wide one.
Unless you’re a pure climber and solely focused on weight, the takeaway message here is that you’ll go generally faster on wider rubber even if it’s slightly heavier.
Larger diameter wheels roll faster than smaller ones: Yep, ’tis now been confirmed in the lab – 29ers roll faster than 26ers. Wheel Energy says the effect here is similar to that of tyre width in that larger-diameter tyres exhibit less casing deflection and thus, less energy loss.
In the case of 29ers, there’s the additional factor of 29er’s lower angle of attack for anything other than a perfectly smooth ground surface. The longer effective lever requires less energy to overcome whatever tyre bulge exists at the contact patch so more forward momentum is maintained.
In addition, Wheel Energy’s analyses of tyre contact patch have confirmed that 29″ tyres don’t have a bigger footprint than otherwise identical 26″ ones. While the total area is the same, the shape of the patch is longer and narrower on 29ers, though.
Higher thread counts aren’t always better: According to Wheel Energy, higher thread count casings are generally lighter and suppler than tyres with lower thread counts since they absorb less rubber during the vulcanisation process (non-vulcanised tyres such as most high-end tubulars exhibit their own characteristics).
However, they also suffer from decreased puncture resistance since the individual cords are thinner and easier to cut. Interestingly, Wheel Energy claims medium-count casings (around 60tpi) may offer the best all-around performance for everyday use. As compared to 120tpi casings, they can actually roll faster and are much more resistant to cuts while often carrying just a slight weight penalty.
If cut resistance is highest of your list of priorities, 30tpi tyres are apparently the way to go but you can also expect them to be heavy and slow rolling.
Puncture-resistant belts work but they’re not created equal: Nylon, aramid, and other belts placed under the tread do help ward off flats but there are benefits and trade-offs to the various materials.
Tougher ones like aramid are durable and highly cut- and puncture-resistant but their stiff nature also sucks up a lot of energy, thus contributing to rolling resistance. More flexible ones like nylon aren’t as bulletproof but offer a better compromise if you still want to retain good performance.
Tread pattern matters, even on the road: The importance of tread pattern is no surprise to the off-road world but common wisdom often says it’s a non-factor on pavement where slick treads presumably would deliver the greatest surface contact with the ground and thus, the best grip. However, asphalt is far from a perfect – or even consistent – material. In those cases, certain tread designs can provide some measureable mechanical adhesion with the ground.
Inner tubes matter: Think there’s no point in that expensive lightweight tube? Think again if you’re trying to go faster. According to Wheel Energy’s data, latex tubes roll ten percent faster than common 0.6mm-thick butyl tubes though today’s ultra-thin butyl models come admirably close. Just in case you’re wondering, the claimed limit of human detection for rolling resistance is about five percent.
How they do it
Wheel Energy’s constantly evolving collection of testing machines are no miracles of design innovation or elegance but the fact that they exist at all is noteworthy in that as far as we’re aware, it’s the only independent test facility of its type in the world.
Currently, there are dedicated stations for rolling resistance, crown and sidewall puncture resistance, friction, and contact patch characterisation with additional apparatuses being designed and built as necessary. Each machine is fully custom-designed, built with computer-controlled hydraulic loading and fitted with industrial load cells for precise and accurate measurements.
Rolling resistance tests are conducted on large-diameter drums with various types of surface treatments, friction tests are done with a wide range of ground types (asphalt, concrete, etc.), and puncture tests can be performed using interchangeable tip sizes and radii. Conditions are kept constant throughout to foster repeatability.
Why it matters
Tyre development can be a notoriously black art and with development cycles reportedly taking around a full calendar year for a single model, it’s easy to lose an entire model year if something goes awry. And once a mould is cut, it’s more or less a done deal whether or not the tyre is actually any good.
As such, companies such as Specialized, Trek, and Vittoria (and whoever else is willing to pay) now commission Wheel Energy to provide valuable data to aid the process.
Specialized is especially open in how Wheel Energy’s information has improved its range – and exposed the flaws. By Specialized’s own admission, the company had been falling behind in recent years in the tyre market – where, ironically enough, it first got its start in the industry back in the late seventies.
“In particular, it even says its previous-generation S-Works Mondo road flagship was a whopping 25 percent slower than most of its competition… Ouch.
That’s supposedly all changed now. Thanks to data from Wheel Energy, Specialized tyre product manager Wolf vorm Walde claims the Mondo’s replacement – the Turbo – is now on-par with the rest of the high-end road tyre market in terms of rolling resistance.
Among the changes are reduced rubber around the shoulder of the tread and reduced rubber thickness in the casing, both of which help minimise the amount of energy lost in casing deformation as the tyre rolls down the road.
In the case of Specialized’s revamped Roubaix clinchers, it was also found that sidewall puncture resistance could be improved without hampering rolling resistance by simply increasing the casing ply overlap in that area.
Based on our initial test rides on a pair of pre-production samples, we’d say that data has been put to good use as they feel notably lively for tyres that aren’t necessarily intended for racing – and perhaps even better than Specialized’s previous-generation Mondos though we still need to put more testing time in before drawing any firm conclusions.
If other Wheel Energy clients can make similar improvements in efficiency both in terms of tyre development and performance then ultimately we all stand to gain in terms of the quality of tyres on the market as well as the pace at which they improve – not bad for a little nondescript grey building in the middle of the woods in Finland.