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It seems to me that with every new model of a car, tires are getting bigger. For example, 17 years ago I had Mitsubishi Mirage and it came with P155/80R13. Today I have a Hyundai Accent, and it came with P175/70R14.

What is the purpose of a bigger tire? Why do newer cars come with bigger tires? Is it related to the increasing weight of cars? Is it for stability, fuel economy, or comfort?

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I say it's all a sham! Tire places know you have to pay more for their 20-inch tires than the standard 14 and 15 inch tires, so they buddy up with the auto makers to ensure they stick oddball sized wheels on new vehicles. Everyone makes money but you. – jp2code Oct 13 '12 at 1:40

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Well, your basic premise isn't actually correct. There are a lot of cars which take a 14 and a lot of tyres which are as narrow as your old ones.

That said, tyre technology has moved on so it is now easier and cheaper to make wide tyres which are structurally able to cope, and in most conditions more rubber touching the ground means more grip (let's exclude deep water or snow where a narrower tyre can get more grip)

A greater footprint actually impacts fuel economy quite badly, as you get more friction with a wider tyre.

We have touched on low profile tyres previously, and the added control they can bring, but that isn't really relevant for this question.

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Can you expand your answer? What is a purpose of a bigger tire? Is it related to the increasing weight of the car & stability, fuel economy, comfort or something else? – MeIr Oct 13 '12 at 17:56
I covered most if these topics in my answer. Cars are getting lighter in general. Large tyres lead to worse fuel economy. Low profile tyres are generally less comfortable. – Rory Alsop Oct 13 '12 at 18:05
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Part of the reason for the larger tires is style,people like the look of the larger wheels. The second is handling,even small cars can now produce more horsepower than some full size cars of yesteryear. The shorter aspect ratio or tire sidewall height reduces tire squirm or the tendency of the tire to roll in turns. The wider tire also brakes better. This results in more predictive and consistant cornering and less torque steer. Torque steer is the tendency for front wheel drive vehicles to pull to the side under acceleration. I am sure some of the reasons are also lawsuit related. If you make a car that can go 100+ mph it better handle well at 100+mph.

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What about weight of a modern car? Does it reflect on a tire size in any way? – MeIr Oct 12 '12 at 16:15
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Actually, it's kind of swinging the other way now, at least partially... While the OEM diameter keeps getting larger (for better & more responsive ride/handling), they're going back to skinnier tires on new cars for better fuel economy. To the point where I have a hard time finding tires that fit my older cars properly. For example, I need 245/45R16 and everything today seems to be 225 and narrower (except for some extreme examples).

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