Thinking of getting 16" 205 tires even on summer...

[Le31504]

Yesterday i changed my Summertires 235 45 17" to my wintertires 205 55 16...
I almost directly lower from my fuelconsumption... i went from 21 miles per gallon to 28 miles per gallon... and my consumpton on the screen in car is usally correct...

Also my comfort got alot better and car dont "track" at all (dont know what its called in english) but when the tires follow unevenness in the road rather then going straigt) 235 can track alot

Im really considering going 16" and narrower tires due to the fact that we in Sweden pay about 8,87$ per gallon

So is there anyone else out there that driving on 16" on summer tires? or should i be ashamed even thinking of going 16"? (last one is more or less an joke)

[old guy]

Your mileage should have increased, but not by the amount indicated on your display. You have decreased your rolling radius by ~2% and consequently the display will be off a little as well as your speedometer. When I went from 235/45/17 to 235/40/18 my mileage dropped by ~ 2 mpg and the wheel/tire combo weighed the same. It's all tied in to the location of the rotational mass. Even with the same OD and same total weight the larger wheel moves the mass further from the mid line. Smaller wheels and skinnier tires will definitely give you better mileage.

[Le31504]

yes i know the display can be a little off, but not that much... i will see in a couple if fíllups how much off it is... but if i can get 6mpg more with 205/55/16 Studded tires I must get even better with 205/55/16" summer tires?!?
And with our gas prize thats alot of money just for the good look...

But the question is how much better mpg will a change from 235/45/17 to 215/45/17 give?

[old guy]

But the question is how much better mpg will a change from 235 45 17 to 215 45 17 give?

Little if any. All you will do is decrease the rolling radius but maintain approximately the same location of the bulk of the rotational mass (wheel).

[Le31504]

hmm ok...
But the width of the tire should have some to do with it... Less road contact should mean less consumption?

[old guy]

hmm ok...
But the width of the tire should have some to do with it... Less road contact should mean less consumption?

The width of the tire does have an effect, but probably not for the reason you think. The size of the contact patch has more to do with the diameter of the tire and the weight of the car. A narrower tire of the same diameter on the same car will have essentially the same road contact area. What changes is the SHAPE of the contact area. what affects the mileage more is the increase in CD or drag that results from the wider tire.

[Le31504]

ok... so if i want to save gas the 16" is the way to go rater then buying 215 inch insted of the 235 i got?

[old guy]

ok... so if i want to save gas the 16" is the way to go rater then buying 215 inch insted of the 235 i got?

You are correct. Reduce the radius of the bulk of the rotational mass and you will reduce the energy required to accelerate/decelerate and consequently your mileage will increase.

[Le31504]

ok thanks!
Well i think that the economy in this case will win over nicer looks...
And i think i will have quite good traction due to quattro even with 205s.. i hope anyway

[old guy]

Well i think that the economy in this case will win over nicer looks...
And i think i will have quite good traction due to quattro even with 205s.. i hope anyway

At $8.87 per gallon I can certainly understand your logic. And unless you are pushing your car to the limits I doubt the performance difference will be all that noticeable.

[Le31504]

yea... its expensive to drive here in sweden... or well the gas itself is not so high... the taxes are... and not just the gas taxes are high... the income tax is at 32%.. so well it sucks :-)

Also to go with 205/55/16 is like 30-40% cheaper then the 235/45/17

I dont usually drive at the tracks, but sure i want to do some highspeed / tight corners sometime and i hope the 205 can keep up with me :-)