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Re: Rolling resistance of Tires?
On Mon, 11 Dec 2006 06:25:22 -0600, "dh" <dh@stargate.com> wrote:
[color=blue]
>"Ray O" <rokigawaATtristarassociatesDOTcom> wrote in message
>news:9576e$457cf9af$47c2b532$9616@msgid.meganewsservers.com...[color=green]
>>
>> "Bill Tuthill" <ccreekin@yahoo.com> wrote in message
>> news:457c8938@news.meer.net...[color=darkred]
>>> Ray O <rokigawaATtristarassociatesDOTcom> wrote:
>>>>
>>>>>> Here is one source of rolling resistance measurements:
>>>>>> [url]http://onlinepubs.trb.org/onlinepubs/sr/SR286Rolling_Resistance_Data.pdf[/url]
>>>>>
>>>> You're welcome! Yes, lower rolling resistance is better, at least from
>>>> a
>>>> fuel economy perspective.
>>>
>>> Good point. Based on Consumer Reports rankings, low rolling resistance
>>> is a tradeoff for quick dry-pavement braking. Snow and wet-road braking
>>> seem more related to tread design (I don't know for sure).
>>>[/color]
>>
>> For the most part, everything about a tire's design is a compromise.
>> Softer tread give better traction but poorer tread life. Deeper grooves
>> provide better wet and snow traction but cause more heat buildup and tire
>> noise. Skinnier tires provide better traction in wet conditions and cost
>> less but poorer traction in dry conditions. Stiffer sidewalls provide
>> better cornering but a rougher ride. A lower aspect ratio provides better
>> handling but a rougher ride and less ability to withstand damage from
>> potholes and curbs.
>>[color=darkred]
>>> Do you have any idea why larger tires have lower rolling resistance?
>>> Small-radius tires have always been associated with economy cars, so I've
>>> always assumed they are more fuel efficient. Guess not.[/color]
>>
>> "Economy" cars tend to have smaller radius tires because they cost less.
>> The effect of a wheel and tire's diameter is much the same as with gears.
>> A small drive gear had an easier time turning a larger gear or tire than
>> it does turning a smaller gear or tire but the drive gear has to rotate
>> more times to travel the same distance.
>>
>> Although I might know more about tires than the average person on the
>> street, I do not consider myself an expert on tires, but I would imagine
>> that 2 of the biggest factors that affect rolling resistance is sidewall
>> stiffness and tread belt stiffness. If the sidewall and tread are soft
>> and squirm or flex more, then more energy is used to overcome the flex and
>> squirm than with a stiffer tire. If you think about the steel wheels on
>> a train, there is little or no rolling resistance and they have a long
>> life but they have poor traction and no cushioning. A train's traction is
>> provided by the sheer weight of the train and the cushionins is provided
>> by massive springs.
>>
>> I think the reason that larger tires tend to have lower rolling resistance
>> is that people are willing to spend more money on larger tires so the tire
>> makes spend more money on R&D and materials and construction on larger
>> tires than on smaller tires. I can't think of a physical reason why a
>> larger diameter tire would have lower rolling resistance than a smaller
>> tire with the same construction. I'm guessing that a wider tread width
>> tire might have lower rolling resistance because the belts across the
>> tread are stiffer than with a narrower tire, or because the additional
>> traction provided by the wider tread means that the tire grabs with less
>> sidewall flexing.[/color]
>
>I was thinking that a larger tire would deform less at the contact patch and
>that would probably be reflected in reduced rolling resistance.
>
>The other tradeoff is that a larger tire will probably have more mass and
>the inertia of the tire itself will affect your fuel economy and brake
>life - but I'm not sure if that would be a measurable effect or not.[/color]
Speaking of measurable effect, how big of a difference in mpg are we
talking about here between the worst and best rolling resistance tire
? Did they measure that?
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