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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
    
The same reason you can't get a 1.5L or smaller engine anymore (in a non-hybrid): car manufacturers marketing is all about power, not efficiency. Yes small tires are the best, but good luck finding a modern vehicle that works with them. –  R.. Dec 7 '13 at 4:08

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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
    
Not sure cars are getting lighter - i think it depends on the class of car, take a VW golf, in the 80s it weighed ~ 900Kg, now its over 1300kg. –  Mauro Dec 6 '13 at 10:20
    
Mauro - not specific cars, but the trend towards smaller cars, such as city cars etc. The ever impending fuel shortage is pushing manufacturers down this route. –  Rory Alsop Dec 6 '13 at 10:30

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

This is very huge subject.

İn a simple way; wider tire does not necessarily means better contact, handling or braking. It all depends the weight, adjustment of suspension and tire pressure. Wider (from nominal size) the tire tend the brake or accelerate badly. It may just serve for better cornering (if sidewalls are low enough) and easy cooling off.

Wider the tire more mass to move for engine and that means bad fuel economy.

There will be no considerable increase at the contact area with bigger tire size but just the shape of the contact area tend to change. If tire is too wide the contact area will be elongated to the sides more than front and backwards. Because you will need less pressure with wider tires.

I suggest to read more on this subject because it is very interesting and also vital for all drivers.

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Do you have suggestion for a book or good article? TY! –  MeIr Dec 6 '13 at 15:12

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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Small and light cars like the Mazda 3 and Civic are standard with 205-55r/16. these tires are quite wide and prone to aquaplaning on water and slush but they make the car look better. A better tire would be 195-60R/16.

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I think your answer provides a lot of opinion on your part. While the width of the tire has some to do with hydroplaning, tread pattern and wear on the tire has a lot more to do with whether a tire will hydroplane or not. Tire manufacturers are quite aware of this and design treads to pump water and slush away to the sides instead of pushing it in front of the tire. Your example of width difference of 10mm is not going to have a significant difference one way or the other on whether a tire is going to hydroplane. –  Paulster2 Dec 31 '13 at 21:58
    
Paulster, you assume the tires never wear, they do and when a tire is 50% worn, the treads are not able to properly evacuate water. In the case of sluch, it is even worst. The wider the tire on a lighter car like the Mazda 3 and the Civic will be a contributing factor in aquaplaning specially when the tire is 50% worn or more. –  sp Vivier Jan 4 at 20:03
    
I guess you missed the part in my comment which said, "tread pattern and wear on the tires has a lot more to do with ...", neither of which you state in your answer. You really should read before you comment. –  Paulster2 Jan 4 at 22:54

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