Frebike
As we enter the third week of the Tour de France, we have had loads of time to take a look at the bikes of the riders already, and there was loads of trigger for tech dialogue at this 12 months’s race. There’s been tyre discuss, as the talk of tubular vs tubeless was usurped by clinchers. Wheels have had their time within the highlight too, as Jumbo Visma and Ineos Grenadiers shunned Shimano in favour of non-sponsor choices, regardless of our suggestion that Shimano has something new coming.
At the moment it is the flip of one other wheel-based part, the disc brake rotors. Riders together with Julian Alaphilippe, Marc Hirschi and Adam Yates have been utilizing mountain bike rotors.
The rotors they’ve been choosing are the Shimano RT-MT900 rotors from the model’s mountain-bike-focussed XTR vary. That is as a substitute of the SM-RT900 rotors that come a part of the road-focussed Dura-Ace groupset that the riders have been utilizing.
There are numerous variations between the 2 units of rotors, essentially the most noticeable of which is that the cooling fins are smaller in dimension on the XTR rotors and go away sizeable holes between the rotor’s centre-lock physique and braking floor. Conversely, the Dura-Ace rotors function a lot bigger fins which make the rotors nearly stable in look. This extra sparing use of fabric means the XTR rotors weigh much less; 9 grams much less for 140mm rotors, 10 grams for 160mm.
The holes drilled into the rotor’s braking floor are bigger, too, which whereas untested on this software, can result in higher chew, higher wet-weather efficiency, and elevated cooling properties. Thirdly, the physique of the rotor – which incorporates the centre-lock adaptor and the arms to hook up with the rotor’s braking floor – is constructed otherwise; the Dura-Ace rotors have thinner arms which curve according to the rotation of the wheel, whereas the XTR rotors use double-strutted, almost-triangular-shaped arms which might be bulkier in look. Whereas that is unconfirmed, it is a truthful assumption that the outcome is a rise in stiffness and sturdiness.
There was loads of hearsay and hypothesis round why, which we will dive into, within the hope that we will discover some solutions.
We’ll preface this with a disclaimer: We do not have the solutions. Mechanics and groups preserve these choices near their chest, however we’ll dive in nonetheless with the intention to see what the more than likely causes are.
Weight
The primary and most evident distinction is the burden. As talked about, the distinction is to the tune of 19 grams for a pair of 160mm entrance and 140mm rear – the commonest mixture.
Regardless of the minor potential advantages of rotating weight, few Tour de France groups want to save lots of 19 grams with the intention to hit the UCI’s restrict of 6.8kg. We all know from our Specialized Tarmac review {that a} 58cm Tarmac SL7 weighs 6.89kg, drop that right down to the 54cm body that Alaphilippe is using and also you’re already at (or beneath) the UCI restrict. This implies to us that whereas weight might be a part of the equation, it is unlikely to be the complete story as to why groups are utilizing the rotors.
So, what about cooling?
Each rotors utilise ‘Ice Applied sciences’ which primarily pairs an aluminium layer sandwiched between two metal layers, and ‘Freeza’, which extends this aluminium layer into cooling fins, these are then painted with heat-dissipating paint. With bigger fins, one would assume the Dura-Ace rotors are higher at cooling, albeit offset considerably by the bigger holes on the braking floor of the XTR rotors. Riders within the Tour de France are extraordinarily unlikely to be dragging their brakes all the way in which down a descent, so it is unlikely that cooling has ever been a problem, so even when there’s a distinction, it is unlikely to have been an element within the resolution.
Higher braking?
With the bigger holes drilled into the XTR rotors’ braking floor, one might predict a slight improve in braking efficiency, particularly within the moist. A idea compounded by Maciej Bodnar’s choice to use the XTR rotors on the highway world championships in Yorkshire final 12 months.
This may very well be a consideration for assured descenders similar to Hirschi, however in all probability and expertise, the Dura-Ace brakes provide such excessive efficiency already that we will not envisage any riders going to such lengths for extra.
Aerodynamics?
There in all probability is a distinction, however with the turbulent air coming off the entrance wheel and the minimal thickness (round 1.8mm) of the rotors, any distinction might be small, and it is unlikely to have been an element within the resolution.
Crosswinds?
When Roval launched its Rapide CLX wheels, they made claims concerning the stability of their entrance wheel in crosswinds and that by decreasing these moments of panic the place your wheel is swept off-line, it could scale back the variety of instances a rider has to decelerate with the intention to regain stability. With the elevated gaps within the rotors, the XTR rotors will doubtlessly be much less affected by crosswinds, and with that, they’re sooner… proper?
Probably. It could clarify why Adam Yates used it on the entrance wheel solely on the Dauphine, but additionally, it in all probability is not the complete image, as a result of in nearly each different case they’re getting used each back and front. And a 160mm rotor might be a lot much less affected by wind than a 622mm wheel.
Is it as a result of they’re stronger?
The tolerance for clearance between a rim and a rim brake pad is roughly 3mm. Whereas that of a disc brake rotor is significantly smaller at round 0.5mm. Subsequently, if a rotor is ever misaligned, broken or bent, there’s a lot much less free house earlier than the brake pads begin to rub.
With the elevated bulk within the physique of the rotor and its arms, it may very well be conceivable that the rotor is stronger, sturdier, and higher at withstanding impacts.
With the quantity of using, crashing, travelling, transportation and manhandling, it is simple to think about a state of affairs the place a wheel is knocked, dropped, crashed or somebody’s bike leans in opposition to one other, pushing the disc out of true. It is smart that if a workforce is ready to use a rotor that may higher stand up to such impacts, riders would require fewer bike modifications in the long term.
Or is it a easy case of availability?
With the COVID-19 pandemic closing factories all over the world for months earlier this 12 months, and with rumours rife about if and when Shimano plans to replace Dura-Ace, might it merely be that Shimano’s shares are working low?
We reached out to Shimano for a solution, and the response suggests in any other case, as Ben Hillsdon tells us: “Groups are additionally supplied with Dura-Ace rotors so they’re free to decide on.”
He then went on to reiterate the purpose of weight: “Our workforce liaison officers inform me that some groups nonetheless wrestle to get the 6.8kg weight restrict so that is the rationale why they request XTR rotors.”
The doubtless reply is a mix of the above, as WorldTour groups are not often single-minded of their method to gear developments. Weight is clearly a consideration, however the elevated sturdiness might effectively be a part of the equation, and the possibly improved wet-weather efficiency might be a bonus.
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