Disc brakes and impact drivers: Dissecting a modern Tour de France wheel change
Wheel changes have changed. Disc brakes, thru-axles – the fundamental act remains the same, out with the old wheel and in with the new, but the details are very different today than they were even two years ago.
At 2:51 pm last Wednesday, photographer Jered Gruber was standing on the side of the Tour de France route, “looking at stuff,” he told me, when Dimension Data’s Reinardt Janse van Rensberg pulled to a stop in front of him, straddling his bike. He had a front flat. A team car screeched to a halt, a mechanic jumped out, and a wheel was changed.
We see bits of wheel changes on TV, but rarely do we get a live, up-close look at a race-day wheel change.
Gruber shot the whole thing, which took just about 25 seconds end-to-end. That’s from the rider coming to a stop, to the push at the end. The wheel change itself took less than 20 seconds.
Buried in the metadata of each of Gruber’s photos is a timestamp. That’s how we know Gruber was standing there at 2:51 pm. These time stamps allow us to deconstruct a world-class wheel change in the age of discs, thru-axles, and battery-powered impact drivers, second-by-second.
Here’s how it broke down.
2:51:09 pm
Janse van Rensberg has a flat front tire. Unlike the good old days of quick releases and rim brakes, he can’t take the wheel off himself. His BMC uses a thru-axle with a 6mm allen key head. So he stands, waiting for his team car and mechanic.
2:51:15
It takes six seconds for Dimension Data mechanic Martijn van Schaijk to arrive at the scene. In his right hand, he holds a small, cordless impact driver made by Metabo, fitted with a 6mm allen key bit. In his left hand, a new front wheel.
The impact driver is essentially a very tiny version of the tool used in a Formula 1 wheel change, or by the mechanic at your local auto shop. It’s a high-torque device that quickly unthreads the thru-axle. At the end of the wheel change, it will thread the axle back in, too. The driver stops tightening at a pre-set torque, so the thru-axle isn’t overtightened.
2:51:18
Three seconds after he arrives, van Schaijk has the thru-axle removed and is starting to pull the front wheel out.
“Lawyer tabs” are the small bumps on the bottom of quick release forks, designed to prevent the wheel from ejecting if a quick release opens up. There are no lawyer tabs on the bottom of a thru-axle fork, so as soon as the axle is removed the wheel drops out.
Mechanics used to file lawyer tabs off, but the UCI banned their removal on quick release forks a few years ago, dramatically slowing front wheel changes.
2:51:20
Eleven seconds after Janse van Rensberg stopped on the side of the road and five seconds after van Schaijk arrives, the wheel is out.
2:51:21
One second later, the old wheel lays on the ground. Dimension Data runs 160mm front rotors from sponsor Shimano – every wheel has the same rotor setup, and in theory the new rotor should slot into the disc caliper without rubbing. In practice, it almost always rubs.
2:51:23
Janse van Rensberg may not be able to remove the front wheel before his mechanic arrives, as he could have with a quick release wheel but he can at least help hold the bike while van Schaijk slots in the new wheel.
2:51:26
Six seconds after the old wheel is fully removed, van Schaijk has a new one slotted into the fork and brake caliper. His right hand picks up the thru-axle that landed on the ground after it was pulled out and shoves it into the left fork leg. The right fork leg contains the threads. A quick whack with his palm pushes the axle all the way through the hub, where it can engage with those threads.
The impact driver waits patiently on the ground to his right.
2:51:30
Four seconds later, the axle is in place, and it’s impact driver time.
2:51:32
Janse van Rensberg knows that this wheel change is almost complete, and swings a leg back over his bike, ready to clip in and set off.
The impact driver threads in the thru-axle in less than a second.
2:51:35
And he’s off. Twenty seconds after Van Schaijk first arrived at the scene, he gives his rider a big push and sets him on his way, back to the Tour peloton.
The total time, end to end, is roughly the same as it used to be in the rim brake/quick release days, and in fact, may be a bit quicker than swapping a quick release wheel with lawyer tabs in place.
Is a disc wheel change faster than a rim wheel change?
Janse van Rensberg first pulled to the side of the road nine seconds after 2:51 pm. He was on his way 35 seconds after 2:51, for a total time of 26 seconds. But really, you have to start the timer when the mechanic arrives, which was 15 seconds after 2:51. That puts the wheel change time at exactly 20 seconds.
Twenty seconds from mechanic arrival to rider departure is a few seconds longer than the fastest rim brake wheel changes, particularly if we look back to the days when lawyer tabs were filed off. Back then, a very good mechanic could swap a wheel and push their rider off in less than ten seconds. But with lawyer tabs in place, the gap narrows considerably – in fact, a few mechanics have told me that a disc wheel change with an impact driver can be faster.
Parts of the disc wheel change process are slower than their equivalent with a quick release and rim brake system. Slotting the new wheel in, for example, takes a bit more finesse, as the rotor must be lined up inside a narrow gap in the brake caliper. The fact that the rider can’t remove the wheel on his own slows things slightly as well. But the impact driver steals some time back, as the removal and installation of the axle itself takes less than a second.
In the end, thanks to a bit of mechanization, it’s largely a wash. There’s more time to be gained or lost in the skill of the mechanic than in the type of axle and brake used by the rider.
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