2015 Ford Mustang GT: Source of Mysterious Noise Identified
Jason Kavanagh, Engineering Editor on December 2, 2015
I drove our Mustang shortly after it received its new tires and noticed a muted, grindy rubbing noise from the front end when taking left turns with a modicum of spirit (I thought it was from the driver side, others said the passenger side). It would also elicit the noise with the wheel turned full right lock when in reverse.
I put it up on our Rotary Lift the next day to have a looksee. I discovered two areas of concern.
First was that the Ford Racing stabilizer bar had clearly rubbed the chassis on both sides. The contact points were near the bar's sharp 90-degree bend on either side. This was unexpected, but not terribly alarming.
More puzzling was evidence that the inside edge of the driver's front wheel had rubbed the strut body. It was a light rub, and the clearance between wheel and strut was clearly smaller on the driver side than on the passenger side.
As I type this, it is screamingly obvious what was going on. But at the time the explanation was elusive. I was unaware that the car had recently received new tires and had no reason at all to question things from that perspective. Was the rub related to the new Ford Racing struts? A bent knuckle (extremely unlikely, but all options were on the table)? Something else?
I took the Mustang back to Galpin Auto Sports to have them check things over. The stabilizer bar rub was something they'd never seen before, and they've done more than a dozen of these Ford Racing suspension installations on 2015 Mustangs. The wheel rub was a head-scratcher. After they had a good, long look under there and gave all the bits a clean bill of health, they sent the car off to their alignment guy to see if the wheels were pointed in the correct direction. Maybe that would help narrow things down.
While the car was at the alignment shop, I pondered what could be causing the intermittent wheel rub along with the technician that had done the poke-and-prod. At one point he asked if the wheels had been removed recently. I couldn't be certain (one of the downsides of not driving the same car every day), but shoot, maybe someone did mention something about new tires? I dunno.
Then it clicked. The Mustang has staggered wheel widths.
Of course, what had happened was that when the car got new tires, the tire shop inadvertently put a rear wheel on the driver's front corner and vice versa. Each corner of the car was wearing the correct tire size, but two corners had the wrong wheel in place. Doh!
I felt like a rube, missing something so obvious. Even when I had the wheel off, I never thought to check the size specs cast into the inside of the spoke. I guessed I'm just accustomed to 'square' tire and wheel setups. Stagger just isn't on the brain.
The half-inch difference in wheel widths front to rear, plus the 7.5 mm (0.3 inch) difference in offset was enough to result in a very light and intermittent property dispute up front. There was no issue with the front wheel at the back of the car.
Galpin swapped the tires from the offending wheels and put them on the correct corners of the car. Wheel-to-strut rub solved. The stabilizer bar rub remains a mystery, and a bit disheartening given the factory-blessed nature of the hardware, but it's pretty benign in the grand scheme of things. At some point I'll throw a couple of movement-limiting rubber collars on the bar right near its mounts. That'll probably lick it.
The last issue was that the alignment guy realigned the car back to factory specs rather than the Ford Racing specs I'd requested. Argh. So the car went out again for yet another alignment after this episode.
Now, at least, all is as it should be with this car, and we'll be able to move forward with driving impressions and track testing.
Jason Kavanagh, Engineering Editor