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Tire mismatch

I just blew a left rear tire on the side of the highway and needed a quick fix. I was planning on putting on the donut and buying the tire from a reputable company when I got back home, but the tire was stuck on the wheel and I needed to go to a (not so reputable) tire shop to have them hammer it off.

When I was there, I asked if he had something in stock to replace it. So he slapped a used tire on it for $30. I knew to check the tire tread with a penny (which surprised him), and that seemed OK, but then when I got home I had a chance to look closer at the numbers.

As a bit of background, I’m driving on steel wheels because the original rims that came with the car are too delicate for New York City highway driving. I previously bent two rims and didn’t want to pay for that again.

So anyway, my other three tires are P205/60/16, and he installed a P205/65/16 tire on the left rear. I believe this means that the left rear tire is about 8/10 of an inch greater in diameter than the others.

My lease is up in four months, at which point I will reinstall the original rims. Can I safely drive for 4 months on tires with this mismatch? How will it affect my speed and odometer readings?



Since this car is FWD, rather than AWD, the mis-matched tire should not lead to any mechanical problems. While having mismatched tires is far from ideal in terms of handling qualities, I think that this is an okay risk to take for 4 months. Also, since the Vehicle Speed Sensor is attached to the transmission of this FWD car, there should not be any disparity in speedometer/odometer readings.

However, you are unclear regarding reinstallation of the original rims. Do those rims have a different set of tires on them? If not, then you are going to have to provide the car with 4 matched tires (both size and brand) when you turn it in at the end of the lease. Leasing companies can impose some really onerous penalties for various and sundry “violations” at the end of the lease, and you should try to avoid that situation.

Leasing is the most expensive way to possess a car, and end-of-lease penalties can really add to the high cost of leasing.

Thanks for your quick reply.

Yeah, I know the pitfalls of leasing and plan on buying outright in the future. I should have known better than to even MENTION leasing on a public forum, as I’ve seen the ire it draws.

I actually have three functional rims and tires sitting in my garage, and I will determine if the fourth can be repaired or needs to be replaced. I plan on returning the car to its original setup in August using my own mechanics, not Mazda’s (although it was a Mazda service tech who suggested switching to steelies in the first place).

Yes, you can. It’s a Front Wheel Drive vehicle and as long as you keep the mismatch on the rear it won’t hurt the car. Your handling, emergency braking, braking, and traction will be unbalanced, and you may trip repeated ABS warning lights, but it won’t hurt the car.

Before making any decisions, try actually measuring the rolling circumference or diameter to find the actual difference. I’ve found that the dimensions stated on tires are not absolutely consistant between makes, and you do have enough wear on the new used one that it made you want to check the tread. Your calculations are correct, but I’ve had 215mm section widths that came out beyond my rims and others that did not, definite differences in section width.

The question you asked: “Is it safe?” is a black and white question, to a shade of gray type of situation. I prefer to think in terms of “risk” - and there is a risk.

Vehicles with odd tires tend to pivot around the odd tire in emergency situations - and the more different the tire, the stronger this tendency. You probably have the worst possible scenario.

So your situation is: You have a pretty bad condition which you only have to endure for a short time. Just hope you don’t have to make an emergency manuever.

It as stated, will not affect car mechanically. But tires we assume have different tread and you don’t know under which conditions, the tires on the rear have less traction which is a safety hazard. You are not safe with the tread mismatch, regardless of the size mismatch. With the size difference alone, there is definitely a traction difference given the contact area is different on each.

We don’t know also how abs, traction control if you have it, will be affected with this small difference. It isn’t like they are all different together in this respect. I’d leave that part to others more knowing comments.

The risk involved is when it gets really slippery out. The mismatch tire will throw the car out of balance and this of course get pronounced when slippery(winter conditions) or heavy rain and typically when you starting to spin.

Is that going to happen through Feb. at this point in NYC, maybe.