Last weekend during the NASCAR Craftsman Truck Series Xpel 225 at Circuit of the Americas, something weird happened.
Weird has a lot of definitions, but in this specific case, it takes on the monaker of something that fans simply just don’t see too much.
In the late stages of the race, Marco Andretti was coming down a straightaway far from the rest of the field when his car went spinning.
After a few degrees past 360, Andretti’s car came to a stop in a peculiar manner; his back wheels were nowhere to be seen.
Unless, of course, fans directed their eyes to about 50 yards away from where the car ultimately wound up.
It was something that many racers, including this former one, have never seen before, and happened with no contact whatsoever. It looked like Andretti’s wheels were under his car one minute and the next they were gone. Mainly because that’s exactly what happened.
After the race, Andretti detailed the feel from inside the car that could give keen-eared fans a window into exactly what occurred.
“(I felt) just big vibrations,” he said. “Really, the brake pedal, throttle, acceleration, brake, just huge vibrations. We were limping around. I didn’t have second gear. I would say I’m done with these character builders. I think my character is built at this point and we’re ready for a straightforward weekend, because I haven’t been able to fight yet this season, and it’s getting a little frustrating.”
Vibrations make sense. What else would cause such a complete collapse of what is otherwise considered to be an integral structure of the racecars?
But why was it vibrating so badly in the first place?
The answer can be found in the welds that hold the entire rear end onto the car itself. There are only a pair of them, and they take a ridiculous amount of abuse during a season, especially on road courses as bumpy as COTA.
When the NASCAR Xfinity Series cars and the trucks experience hard braking from high speeds, they have a tendency to wheel hop. When this happens, the drive shaft and arms of the frame flex and unflex to create and lose contact with the asphalt repeatedly.
That hopping puts stress on the welds that hold the rear end housing underneath the car — and, in Andretti’s case, caused the welds to fail. The harsh vibration Andretti…
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