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Old 08-27-2012, 06:07 PM   #1 (permalink)
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Size of the tire - are smaller (narrower) tires really better?

Hi,

i have an question which i have a long time in my head:

Often ist said that smaller tires (not smaller amount) are better to save gas.

But i read in a forum for racingbikes (cycle) that tires which are very narrow have a higher rolling resistance than wider tires at same inflation. This is because of the friction inside the small tire. A wider tire has less deformation at same pressure as a narrow tire.

In wikipedia i read that a tire of a normal car has a rolling resistance (Cr) of 0,011–0,015, ad a much more bigger tire of a big truck (LKW) has only 0,006–0,010 on same track.

Iīm planning to buy new summer tires with rims for my golf, and canīt decide between 175/80R14 and 195/65R15. With this information the 195/65R15 should have a smaller rolling resistance, because there is more air inside, and with its bigger wide the deformation should be less than in the narrow tire with high rubber.

Has anyone some information about this things? Could it be that the most narrow tire isnīt the best in rolling resistance?

The diameter of my tires has to be the same because of german laws and police...

Kind regards,

Benny

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Old 08-27-2012, 06:16 PM   #2 (permalink)
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For as much as i know ussually the smaller width tire the better FE, one reason why companies throw small width tires on bigger vehicles to help with the mileage.
Ex. my brothers 01 grand cherokees tires are about the same width as my grand ams. Although the cherokees are trail tested it isn't doing much with small tires on it, but save gas
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Old 08-27-2012, 07:17 PM   #3 (permalink)
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You need to define 'smaller'

What you mean is narrower. Smaller means smaller diameter.

Smaller would prove for worse mileage.
Narrower would provide such a small gain that I would not concider the lose of handling and comfort.
Have you aired up the tires to 40-45psi?
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Old 08-27-2012, 07:33 PM   #4 (permalink)
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I cant even find a 175/80/14 on tirerack(largest seller of tires)

you want to look at a tire w/ an LRR rating (low rolling resistance)

you also dont want to go below the weight rating.

Fundamentally, there is relatively no difference in a slightly narrower tire, and you would not want a REALLY narrow tire. Not safe.
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Old 08-27-2012, 08:25 PM   #5 (permalink)
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I would be very slow to use narrower tires than came on the car. The narrower tires compromise braking, cornering and transient handling (accident avoidance). The tires are your connection to the road, the tires are the single biggest factor determining whether the car does what you tell it to. Tires are no place to skimp.
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Old 08-27-2012, 08:30 PM   #6 (permalink)
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I'd run skinnier tires for sure. Has anyone that is scared of skinny tires actually tried it???

That said, CapriRacer says skinnier tires generally don't reduce rolling resistance. I think it's the kind of thing that varies on a case-by-case basis; I can't just say "skinny tires will reduce r.r." or "skinny tires will increase r.r." but in general my opinion is IF you are not loading the vehicle to it's capacity very often or not at all (like I do) a skinnier than stock tire could very likely help.

That size might be commonly available in Europe. I've not searched to confirm but I think Vekke has done some work in this area.
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Old 08-27-2012, 08:57 PM   #7 (permalink)
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Quote:
Originally Posted by Frank Lee View Post
That said, CapriRacer says skinnier tires generally don't reduce rolling resistance.
Link to more information on his site on this subject:

Barry's Tire Tech

and

Barry's Tire Tech
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Old 08-27-2012, 09:58 PM   #8 (permalink)
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I like size appropriate, some cars come with too wide of tire for their wieght IMO. My 3000 lb malibu is better suited for 205 probably 195 in the winter or rain than the factory 215. Cobalt is 400 lbs lighter with 195, escorts and sentra's I've owned about same weight as the Cobalt had 155's and they cut thru the snow great. Barry say's wider are better and I believe it, but it's a compromise between traction and rolling.

If going summer and winter, go wide summer, narrow winter.
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Old 08-27-2012, 10:38 PM   #9 (permalink)
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the most i can say on the matter is to suggest anyone contemplating buying a different than stock size consider what that means about the pressure on the contact patch.

the smaller diameter means you have more pressure on the contact patch, because the contact patch will inherently shrink from front to back (think higher angle of attack). if you go narrower instead, you also increase the pressure on the contact patch, but at a faster rate. if you go smaller and narrower, you get much higher psi on the contact patch.

i wont guess at what this means to traction, handling, etc... BUT, the rubber that tires are made of can only handle a certain pressure before it deforms too much, just something to keep in mind. small tires + heavy car = bad.

never thought about it until my met 245 class when we talked about rolling metals. instinct makes you think they would use a large diameter roller, but they actually use a small diameter roller that is actually in contact with the metal, because it has a smaller contact patch and requires less pressure. also there is a phenomenon where once metal starts to deform it deforms rather easily if done fast enough.
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Old 08-27-2012, 11:07 PM   #10 (permalink)
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The area of the contact patch at the same pressure remains the same, whatever the size of the tire. In other words, traction and handling should be unaffected... all else being equal... of course, sidewall stiffness is a much bigger issue with a narrower tire... and narrow tires don't come with the nice sticky rubber you can buy with wider performance tires, but if you're getting the same exact tire model in different widths, the only thing working against the narrower one is the flex in the sidewalls.

What changes there are are in the shape. Narrow and small are not ideal because the shape is long instead of wide. This means more flexion of the tire and more heat build-up, with less tire to absorb it... which is not ideal.

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