QuestionOk, I too am a tire expert trained by Michelin but I know aircraft tires. During my twenty years of work with aircraft and their tires I remember that if one of two tires on a single axle is changed the vehicle will veer to one side. This is due to the aircraft tires grow in circumference over time. My question is do car tires circumference grow as well?
The reason I am asking is I have an 04 sentra that I put about a thousand miles on a week it runs P215/45 R17H tires and I broke a belt in a tire last week and my tire shop replaced the tire with a new one the other three tires only have about 12k miles on them so they replaced the LH front tire and the car pulled under power to one side I had the alignment checked and it was bad and they put it within specs and it still did this. so i had the tire shop move the new tire to the rear until the tire wears in for a few thousand miles and grows to match the circumference of the others. currently it does not pull at all. Just looking to prove my theory that aircraft tires are not much different than car tires other than the obvious items.
AnswerChris,
Do car tires grow with time? Every tire that is inflated grows with time. And, of course, the more pressure, the more the growth - and conversely, the stronger the casing, the less the growth. This means that aircraft tires, which sometimes use very high pressures, are going to grow more than passenger car tires, which use comparatively low pressure.
Is the grow significant? For passenger car tires, only a little, but it is enough to cause a pull. That's why the general recommendation is to replace tires in pairs. This also helps keep the car handling balanced side to side. Under severe conditions (heavy braking for instance) cars tend to pivot around odd tires.
You should be disturbed that the tire shop you went to didn't insist on putting the odd tire on the non driven axle. That should be SOP.
But just to confuse matters more:
Conicity (root word: cone) is a tire property that can affect pull. Conicity is the sideways force that is generated when a tire rotates - and the direction of the sideways force depend on which way the tire rotates.
And it is the vector sum of the 2 front tires that causes pull - but only the amount that exceeds the threshold amount - and the threshold changes from vehicle to vehicle. Some vehicles are incredibly sensitive to conicity levels - and some are not.
And then there's torque steer. During acceleration, the half shafts in the drivetrain twist - and when these shafts are different lengths (on FWD cars, this is almost a certainty), they twist different amounts. That will cause a pull, too.
So if the car only pulled under acceleration, at least part of it was torque steer. And we won't know if the other part is diameter or conicity until the tire grows some.
Please post back in a couple of months. I'd be interested in the end result.
