Tire mileage

Do you mean is it acceptable to have tires on a vehicle that have different mileages? Yes, that is perfectly normal and common. In fact, it is so normal that there had to be special warnings produced for two models where this is not acceptable. More on that in a moment.

For people who follow service recommendations religiously, the standard practice is to rotate the wheel / tires between front and rear, and to switch two of them side to side, at typically around 10,000 to 15,000 miles. This way every tire will be on one corner of the vehicle at some point. This became even more important for owners of Ford front-wheel-drive cars because to make them ride smoother than those of their competitors, the engineers seriously messed up the alignment causing the front tires to run on just the outer edges, and the rear tires to run on just the inner edges. The lean of the wheels was real easy to see when you passed those cars on the road. They also failed to design in any adjustment for that critical alignment angle, so the only hope of extending the tire life was to rotate the wheels/ tires every 4,000 to 5,000 miles. If that wasn't done, the tires wore out in 15,000 miles. Most tire stores would not give mileage warranties when they put new tires on those cars because they knew the tread was being scrubbed off while driving. Ford had similar tire wear issues with many of their truck models.

For everyone else who drove other brands of cars, rotating the tires was less important. Many people, such as myself, never rotate them, but we keep our vehicles in proper alignment. If you do rotate your tires frequently, they will wear longer, but they'll all wear out at the same time, so you'll be buying four new tires. Since I drive mostly front-wheel-drive minivans, it's the two front tires that do the pulling, so they wear out faster. I only buy two tires at a time, for the front, then I put the old front ones on the rear where I get the last miles out of them. By the time those old rear ones need to be replaced for safety, I'm ready for two new ones on the front, where they are needed to prevent hydroplaning, and there's enough tread left for them to be okay for the rear. I buy only two tires at a time, but I have to do that twice as often.

There are two instances where tire sizes become more critical. One is when the vehicle came from the factory with the optional anti-lock brake system. With those, a computer watches wheel speed very closely so it can tell in an instant when one of the brakes is locking up, or slowing down too quickly. If you were to install a tire significantly different in outer circumference than the others, it would rotate at a different speed. The computer wouldn't accept that, so it would set a diagnostic fault code, turn on the yellow "ABS" warning light, and turn the system off. That would leave you with the standard brake system. You'd never notice any difference in driving until you needed that safety system to avoid a crash or skid. It is also important on these vehicles that the spare tire have the same outer circumference as the regular tires. All anti-lock brake systems are tolerant enough of mismatched tire sizes to overlook some with more wear than the others, but they still have to be the same size.

The one glaring and uncommon exception to this story, for the benefit of those owners researching this topic, pertains to four-wheel drive Chevy Astro vans, and some mid '90s Jeep models. Other brands of minivans are available in an optional "all-wheel-drive" version. That is not the same thing as "four-wheel-drive", as found on some trucks. You have to manually select the four-wheel-drive mode when it is needed. All-wheel-drive is constant. It isn't anything you can shift in or out of manually. The engineers specifically call it that to signify it is not meant for off-roading as one might do with a truck. The Jeeps and Astro vans are different. They are true four-wheel-drive vehicles, but you can't shift out of that mode. The front and rear drive lines are physically locked together through the "transfer case" all the time. That puts a lot of stress on all the components any time except when the vehicle is going perfectly straight. To reduce that stress, there are warnings that you absolutely must buy four identical tires at the same time to insure they all have the exact identical outer circumference. If you buy two new tires this week, and two identical tires next week, they still could be sufficiently different enough to cause serious damage to the transfer case. There have been multiple lawsuits related to this issue.

The two newer tires could have been manufactured in a different plant, at a different time, in a different mold, or by a different person. Any of those variables could lead to enough size variation to cause transfer case problems.

Again, this only applies to those two vehicle models. You didn't list which tires do the driving on your vehicle. For owners of all-wheel-drive vehicles, there is a viscous fluid coupling in the rear drive shaft. That coupling allows some minimal slippage to allow the front and rear wheels to rotate at different speeds, such as when going around a corner. Those viscous couplings cause very little trouble, and while they will eliminate the stress caused by mismatched tire sizes, it is still a good idea to avoid that.

How would you know or care? We never go by mileage when determining if a tire is suitable for use. We look at the amount of tread remaining, whether the sidewalls are dry-rotted, and the wear patterns related to alignment and worn parts. The entire point of my story is as tires wear, they become smaller in diameter and circumference. That is what might cause a problem on some cars. I also pointed out it is common to buy two new tires one time, and two new tires at another time. Those too are going to have more or less mileage. I'm confused on why you're asking this. As a suspension and alignment specialist, it is not a question I've ever run into before. If I still haven't answered your question, please add some history or details so I have an idea of why you're asking. Are you having a problem? Are you looking at buying a used car? Are you suspicious of something a tire salesman told you?

Hello,

If you're referring to being able to get better mileage out of the same size but different brand tires. Yes. It always depends on the tire compound. A more harder compound will give you more mileage than a softer compound. A softer compound tire is always used as a high speed/better traction tire. Harder compound tires don't have the same speed or traction control rating but will last more higher mileage. All tires have a performance (letter) rating. Hope this answers your question and thanks for using 2CarPros.

Danny-

This is the first you mentioned different brands of tires. By using the term, "type" we're thinking you're referring to traction ratings, wear ratings, and temperature ratings.

Absolutely you can have tires of different brands, but the reason that is okay is all tire manufacturers have to design their tires to meet the requirements dictated by the engineers who designed the car. For 99 percent of the vehicles on the road, the car engineers design their vehicles to use what is already in production and readily available in large quantities from the tire manufacturers that supply them.

It's when you get to the Chevy Corvettes and the Dodge Vipers that front and rear tires will be different, and they usually have to face the specified direction, meaning you can't rotate them side to side without taking them off the wheels. Those are uncommon requirements and the owners of those vehicles will be well aware of it. For the rest of us, you can usually put your trust in the tire salesman to sell you the right tire for your car. There's no point in selling you the wrong tire, and no one wants to risk a potential lawsuit.

The first thing you need to look at is the size rating. That's molded on the sidewalls of every tire. Part of that number includes the percentage of tread width that is the height of the sidewall. To say that a different way, in "P205R70x15", for example, the "P" means it's for a passenger car. The "205" is the width of the tread, in millimeters. "R" means it's a radial tire. The confusing number is the "70". That means the height of the sidewall from the wheel lip to the outer circumference is 70 percent as much as the width of the tread.

What that means to you is if you choose to switch to a wider tire, the salesman would select one with a number lower than "70"; perhaps "65" or "60". Those various different combinations can all still have the same outer circumference. The only concern might be if the tire rubs on the front fenders when cornering. You need the correct circumference for the speedometer to remain accurate, although most cars today are available with optional sizes, and those tire sizes can be easily changed in the Transmission Computer's software when necessary.

Some brands and some models of tires are designed for a specific characteristic. For example, we had one Armstrong model that was advertised as being extremely quiet at highway speed. It lived up to that claim, but being of very soft rubber, they wore out very quickly when driven on gravel roads. These turned out to be very bad choices for mailmen. Some tires use harder rubber compounds so they last a lot longer, but they provide less traction because they can slip and spin easier.

Those are the type of characteristics you get to choose which you value more. Even those can be mixed between front and rear tires, but where you want to draw the line is both front tires should be the same manufacturer and model, and both rear tires should be the same, although it's less important on the rear. All tires have a characteristic road force that causes them to pull to one side. By being matched, those pulls offset each other, then, if the alignment is correct, the car will go straight when you let go of the steering wheel. Mismatched front tires can also result in a loss of "predictability". That is the sense that you know where to expect the car to go when you hit a pot hole, turn a corner at highway speed, or brake suddenly. When the two front tires aren't matched, hitting even small bumps in the road will have you constantly correcting the steering wheel, which can make for a very tiring car to drive.

Another thing to look at is the maximum inflation pressure. That's also molded on the sidewall near the wheel lip, but it's small and hard to see. It wasn't that long ago that replacement tires were still available that had a maximum of 32 psi. Because the car engineers knew there was a possibility you would buy those tires, they had to list their desired pressures on the door sticker no higher than that. Most replacement tires had maximum ratings of 35 psi or 44 psi. I found that every single alignment customer was happy if I inflated their 35 psi tires to 35 psi, or their 44 psi tires to 40 psi. Never had a single complaint of harsh ride, but the door stickers usually listed 28 or 32 psi. Even when the car came new with 44 psi tires, and the engineers knew they'd ride best at 40 psi, they had to put "32" on the door sticker in case you bought those 32 psi tires, so you wouldn't over-inflate them to 35 or 40 psi.

A better way to look at this is to think of the ratings on the door sticker as the very minimum tire pressure, and only for the tires that came originally on the car. With replacement tires, go by what the salesman recommends, and make minor adjustments for comfort, as long as you don't exceed what's printed on the sidewall. Those pressures always refer to a cold tire. Pressures will go up significantly with sustained highway-speed driving.

Remember that whatever tire you put on your car, it has to do what the engineers intended them to do as far as braking, comfort, and steering response. There's dozens of different styles of shoes you can wear, depending on what you want them to do, but ideally your left and right shoes will always match. Different brands of tires have to do the same job, but the two on an axle must match so their personalities are the same. You started out asking about different mileages, which means different amounts of wear. Again, as long as both tires on one axle are close to the same, the difference between those on the front and those on the rear has little significance. You can have Goodyears on front and Michelins on the rear, but always set their pressures for the particular tires, if they call for different maximum pressures.