There are various differences between the two rotor sets, the most notable of which is that the cooling fins are smaller in size on XTR rotors and leave large holes between the rotor central locking body and the braking surface. Conversely, Dura-Ace rotors feature much larger vanes which make the rotors almost solid in appearance. This more economical use of material means that XTR rotors weigh less; nine grams less for 140mm rotors, 10 grams for 160mm.
The holes drilled in the braking surface of the rotor are also larger, which, although not tested in this application, can result in greater grip, better wet weather performance, and increased cooling properties. Third, the rotor body – which includes the central locking adapter and the arms to connect to the rotor braking surface – is constructed differently; Dura-Ace rotors have thinner arms that bend according to the rotation of the wheel, while XTR rotors use almost triangular-shaped double-leg arms that are bulkier in appearance. Although this is not confirmed, it is fair to think that the result is increased stiffness and durability.
There has been a lot of rumor and speculation as to why, we are going to delve into it, hoping to find answers.
We’ll start with a warning: we don’t have the answers. Mechanics and teams are keeping these decisions close to their chest, but we’ll dive in nonetheless to see what the most likely reasons are.
The first and most obvious difference is the weight. As mentioned, the difference is in the order of 19 grams for a 160mm front and 140mm rear pair – the most common combination.
Despite the minor potential benefits of weight rotation, few Tour de France teams need to save 19 grams to reach the UCI limit of 6.8 kg. We know from our Specialized Tarmac review that a 58cm Tarmac SL7 weighs 6.89kg, drop it onto the 54cm frame Alaphilippe is riding on and you’re already at (or below) the UCI limit. This suggests to us that while weight will be part of the equation, the full story of why teams use rotors is unlikely.
So what about cooling?
Both rotors use “Ice Technologies” which is essentially a combination of a layer of aluminum sandwiched between two layers of steel, and “Freeza”, which spreads this layer of aluminum in cooling fins, which are then painted with a heat dissipating paint. With larger fins, one would assume that Dura-Ace rotors are better for cooling, although somewhat offset by the larger holes on the braking surface of XTR rotors. Tour de France riders are extremely unlikely to drag their brakes throughout a descent, so cooling is unlikely to have ever been an issue, so even if there is a difference it is little. likely he was a factor in the decision. .
With the larger holes drilled into the braking surface of the XTR rotors, one could expect a slight increase in braking performance, especially in wet conditions. A theory made worse by Maciej Bodnar’s choice to use the XTR rotors at the World Road Championships in Yorkshire last year.
This might be a consideration for confident descenders such as Hirschi, but in all likelihood and experience, Dura-Ace brakes already deliver such high performance that we can’t envision any rider going to such lengths for more.
There is probably a difference, but with the turbulent air coming out of the front wheel and the minimum thickness (around 1.8mm) of the rotors, any difference will be small and it is unlikely that it was a factor in decision.
When Roval launched their Rapide CLX wheels, they made statements about their front wheel’s stability in crosswinds and that by reducing the panic moments when your wheel is swept off-line, it would reduce the number of times that the wheel is swept off line. a pilot must slow down. in order to regain stability. As the spaces in the rotors increase, XTR rotors will potentially be less affected by crosswinds, and with that, they are faster… right?
Perhaps. This would explain why Adam Yates used it on the front wheel only at the Dauphine, but also, this is probably not the full picture, as in almost all other cases they are used both at the front. and back. And a 160mm rotor will be much less affected by the wind than a 622mm wheel.
Is it because they are stronger?
The clearance tolerance between a rim and a rim brake lining is approximately 3 mm. Whereas that of a disc brake rotor is considerably smaller at around 0.5mm. Therefore, if a rotor is misaligned, damaged, or bent, there is much less free space before the brake pads start to rub.
With the increased volume of the rotor body and its arms, it might be conceivable that the rotor would be stronger, more robust, and better at withstanding shock.
With the amount of driving, crashing, traveling, hauling, and handling, it’s easy to imagine a scenario where a wheel is hit, dropped, crashed, or someone’s bike leans against a wheel. other, pushing the disc out of reality. It makes sense that if a team is able to use a rotor that can better withstand such impacts, riders would need fewer bike changes in the long run.
Or is it just a case of availability?
With the COVID-19 pandemic shutting factories around the world for months earlier this year, and with rumors swirling about if and when Shimano plans to update Dura-Ace, could it just be that stocks of Shimano are low?
We’ve reached out to Shimano for a response, and the response suggests otherwise, as Ben Hillsdon tells us: “Teams have Dura-Ace rotors as well, so they’re free to choose. ”
He then reiterated the weight point: “Our team liaison officers tell me that some teams are still struggling to get the weight limit of 6.8kg, that’s why they are asking for XTR rotors. . ”
The likely answer is a combination of the above, as WorldTour teams are rarely resolute in their approach to equipment progress. Weight is clearly a consideration, but increased durability may well be part of the equation, and potentially improved performance in wet weather will be a bonus.