Kelderman on stage 5 of the 2022 Giro d'Italia. Photo: Getty Images

Did Kelderman’s disc brakes break his spokes? No, and here’s why.

Wilco Kelderman blamed disc brake induced spoke failure for his Giro GC demise. Could overheating disc brakes really break spokes or is this a heat of the moment reaction?

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Wilco Kelderman’s overall ambitions at the Giro d’Italia were shattered on Sunday when an unfortunately timed broken spoke left him adrift of the peloton before the ascent to the finish at Blockhaus even began. Kelderman lost over ten minutes on the day and was clear in his post-stage interview with Dutch newspaper, that he believed disc brakes were to blame.

“I broke a spoke in my wheel. Those disc brakes get really hot and my spokes just popped from the pressure,” Kelderman explained. “They just collapsed because from the pressure because it was a very fast descent.”

Disc brakes are undeniably more complex than their rim brake siblings and overheating issues are an all-too-common complaint. Overheating is known to result in warped brake rotors or, worse yet, boiling brake fluid, which can cause brake failure, but this is the first suggestion we have heard of overheating severe enough to result in spoke failure.

Long descents and riding in hot weather accentuate the overheating issues, both of which were in abundance on Sunday’s stage nine of the Giro d’Italia. But of all the arguments against disc brakes – weight, noise, and value, to name but a few – effectively melting spokes is a new one to us. Nevertheless, if true, disc brake induced spoke failure would be a serious issue with extreme implications for rider safety.

Good thing that’s almost certainly not what happened, then.

Can disc brakes overheat spokes?

Let’s start off with an open mind here, as unlikely as the chain of events sounds.

Kelderman and the Bora-Hansgrohe squad race Specialized bikes with Roval wheels and Shimano Dura-Ace Di2 groupsets. Kelderman had opted for the Tarmac SL7 frame equipped with Roval’s new-ish Alpinist CLX II wheels and Shimano’s Dura-Ace R9200 Di2 for Sunday’s stage to Blockhaus. The same combination as the stage winner, Keldermann’s Bora teammate Jai Hindley, plus an additional 14 riders in the peloton, give or take a few for slight variances in setups. It’s a tried and tested setup, with two World Tour teams and a ProTeam all racing regularly on similar, if not identical, equipment this season.

Furthermore, a total of 13 World Tour teams in the Giro rely on Shimano Dura-Ace brake callipers to provide their stopping power. To the best of our knowledge, not a single rider raced Sunday’s stage with rim brakes, including Team UAE-Emirates riders who frequently revert to rim brake setups for high mountain stages but turned to new lightweight disc brake climbing wheels from Campagnolo for stage nine. With so much of the peloton on disc brakes now, it seems unlikely Kelderman, who is far from the heaviest rider in the peloton, could be the only victim of disc brake induced spoke failure.

Although relatively new, Shimano’s new R9200 Dura-Ace disc brake calliper and rotors are already well tested within the pro peloton.

Putting those numbers aside, when it comes to safety and equipment failure, it’s sometimes best to take a guilty until proven innocent kind of approach.

Perhaps unsurprisingly, Roval has now moved to dispel Kelderman’s suggestions of disc brake playing any part in the spoke failure, pointing to a “significant impact” as the culprit. Chris Wehan, Roval’s category leader, told CyclingTips that not only was an impact the cause of the broken spoke, but the spoke in question was actually a drive-side spoke. However That means it was on the opposite side from the disc rotor, so heat would have to travel through the rotor, rotor arms, and then hub shell to get to the spoke heads on the other side.

If we accept Roval’s response that Kelderman’s woes in this instance were the result of an unfortunate and significant impact to a spoke on the opposite side of the wheel, the question still remains as to whether overheating disc brakes could induce some form of spoke failure.

Again, overheating disc brakes is a known issue. So much so, that manufacturers integrate “heat sinks” and cooling aids into disc brake rotors, callipers and even frames to mitigate the issue. Some reports suggest disc brakes can hit temperatures as high as 800°c (1,472°F). What makes Kelderman’s story unlikely is all the failure points that come before the spokes.

It’s a chain of events Glen Leven, team support manager and former lead mechanic with Trek-Segafredo, also has difficulty imagining. As Leven sees it, before a spoke could fail under heat stress, the rotor would be “fire-red” and melting both the rotor and the pads, the mineral oil would have long since boiled off, all of which would result in complete brake failure. If that wasn’t warning enough, and should a rider still be upright and somehow still pulling heavy on the brakes, Leven imagines the hub bearings would expand next damaging the hub shell and providing an additional warning of imminent danger. Whether or not all of that is even possible without losing all braking power is unlikely.

What about the spokes?

Still, though, let’s assume for a second disc brake roasted spokes is possible. Even with a long straight steep descent in hot conditions with a rider dragging the brakes all the way down, and everything mentioned above, there is still one last line of defence.

Stainless steel, as used in many spokes, is highly resistant to heat. Specifically, Roval uses DT Swiss Aerolite spokes in its new Alpinist II wheelset. The 18/10 stainless steel DT Swiss uses in its Aerolite spokes is known for its heat resistant properties and can withstand temperatures up to 925°C (1,697°F) before it starts degrading. Furthermore, unlike other sheltered components further up the disc baked food chain, spokes enjoy some level of a cooling effect as they rotate, putting them at even less risk of overheating.

Can disc brakes break spokes?

The simple answer is, yes. The introduction of disc brakes and the shift in braking torque from the rim to the hub has necessitated a change in the road wheel design and a host of new hydraulic disc brake specific tools. Many manufacturers have had to increase the spoke count and change lacing patterns for the shift to disc brake setups. Furthermore, incorrectly tensioned spokes could succumb to the forces of disc brakes resulting in breakages and wheel failure.

Cadex is using two-to-one spoke lacing on both the front and rear wheels to help balance spoke tensions from one side of the wheel to the other.

That said, the increased requirements are well understood and all modern wheels are designed to withstand the increased forces at play. Anyone reading this article has likely noticed the increased spoke count in disc brake wheels, which contributes to the increased weight and some level of decreased aerodynamic efficiency required to support the increased braking forces at the hub.

Of course, mistakes do happen and a mis-tensioned spoke could break out on the open road. However, even that seems unlikely in the Kelderman case given Roval’s claim the spoke in question broke on the drive-side of the wheel.

All in all, it seems nigh on impossible that disc brakes could cause an overheating issue for spokes. Perhaps the only question remaining is why Kelderman’s instinctive reaction was to blame disc brakes. Perhaps such a reaction suggests a continued resentment towards disc brakes within the pro peloton? That’s an entirely different discussion, but at least we can skip the overheating spokes section.

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