New Swift Dzire: Wheel Related Queries


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Hello Friends,

This is my first communication with you. I think, this forum will be the best place where I can find the answers to all my queries related to car.

I have decided to go for buying a Swift Dzire, and my present query is related to the sizes of wheels and tyres.

Dzire has two specifications:

(a) 14 inch steel wheel + tyre size 165/80R14
(b) 15 inch alloy wheel + tyre size 185/65R15

My questions are:

(a) What are the differences between these two?
(b) What are the advantages and disadvantages?
(c) I understand wheel diameter is related to number of revolutions per km of distance, but how is it going to influence fuel efficiency?
(d) How is the tyre width is related with fuel efficiency? (any quantitative concept?)

As you can understand from my questions, that I have not much of knowledge in this area. So I am looking for your valuable answers.

Thank you.
 
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(a) What are the differences between these two?
Well, the difference is in the size; (a) has a thinner (width) tyre with a higher sidewall mounted on a smaller wheel and (b) has a wider tyre with a lower sidewall mounted on a larger wheel. Understand the meaning of the numbers 165 is the width of the tire in millimeters, 80 is the 'profile ratio' i.e. the height o the sidewall in millimeters, expressed as a percentage of the width of the tire (in this case, 80% of 165mm = 132mm), R = radial tire, and 14 is the diameter of the wheel rim (in inches) on which the tire is mounted.

(b) What are the advantages and disadvantages?
A thinner tire will give better fuel efficiency but poorer grip. Higher sidewall will give a more cushioned ride but poorer handling. Wider tire will give more grip but lesser fuel efficiency. Lower sidewall will provide better handling but a harsher ride. Got it?

(c) I understand wheel diameter is related to number of revolutions per km of distance, but how is it going to influence fuel efficiency?
(d) How is the tyre width is related with fuel efficiency? (any quantitative concept?)
Wheel diameter may or may not affect fuel efficiency, but tire width does affect it. If you make a child wear his father's boots, will the child be able to run fast for a long distance or will he get tired soon? A wider tire is less fuel efficient because it weighs more (= more unsprung weight) and creates more drag. Then there is the question of tread pattern and rolling resistance.

As you can understand from my questions, that I have not much of knowledge in this area. So I am looking for your valuable answers.

Thank you.
No problems. Nobody is born wise. We all gain knowledge by sharing it.
 
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Hi Sam,

The info you gave above is extremely valuable and I had never thopught of it before. I have a Dzire ZDI with wheel rating of 185/65R15. I agree with all the points that you have mentioned above however have confusion around one point:

"Wheel diameter may or may not affect fuel efficiency, but tire width does affect it. If you make a child wear his father's boots, will the child be able to run fast for a long distance or will he get tired soon? A wider tire is less fuel efficient because it weighs more (= more unsprung weight) and creates more drag. Then there is the question of tread pattern and rolling resistance. "

Now the width of my tyres is 185 basically this is what makes contact with the Ground and since I have more surface area I feel that the drive is much more controlled. The height of the tyre is 65 which makes it less than the 165/80R14 rating so Infact the tyre hight has drastically reduced in case of 185/65R15. Again the Diameter of the tyre is 15 instead of 14 so again reduction in tyre area.

So would it be fair to say that basically there might not be much difference in mileage however there are lot of advantages of using a 185/65R15 tyre
 
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Dear sunbaj,

There is hardly any mathematical difference (0.3%) in the speedo/odo readings with the 185/65R15 tire.

You are correct. You only stand to gain in terms of safety (handling and grip) with the upsized tires. The drop in fuel efficiency shall be negligible, but it shall be there nevertheless.

Regards,
Sam
 
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There is hardly any mathematical difference (0.3%) in the speedo/odo readings with the 185/65R15 tire

Thanks for the response and clarifying my doubts. But how did you come to the above figure and could you please help me understand the same.

Thanks
Sunil
 
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Dear Sunil,

The 185/65R15 tire would have a diameter of 24.5 inches and a circumference of 76.9 inches. This would mean that it would do 515 revolutions every km. Similarly, the 165/80R14 tire would have a diameter of 24.4 inches and a circumference of 76.6 inches and this would mean that it would do 516.875 revolutions every km.

(516.875-515)100/516.875 = 0.36%

Regards,
Sam
 

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