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Old 12-09-2009, 06:06 AM   #11 (permalink)
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Quote:
Originally Posted by Old Tele man View Post
...tire "hysteresis" is a function of rubber flexing upon contact with the road, then compressing under weight, then un-flexing upon release from the road.

...that's *why* an older, well worn tire has a lower rr value than does an identical brand new tire.
Hysteresis is the amount of heat generated for a unit volume of rubber doing a unit of flexing. Think of it as internal friction.

And since there is less rubber in a worn tire, that's why worn tires have lower RR than new tires - everything else being equal.

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Old 12-09-2009, 09:00 AM   #12 (permalink)
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Quote:
Originally Posted by CapriRacer View Post
Hysteresis is the amount of heat generated for a unit volume of rubber doing a unit of flexing. Think of it as internal friction.

And since there is less rubber in a worn tire, that's why worn tires have lower RR than new tires - everything else being equal.
...heat is a byproduct of hysteresis, not the other way around, because hysteresis is the "lagging" of stored energy behind its causing force.

...examples of hysteresis are: tires, transformers, magnetic recording, magnetic amplifiers.

...just about anything that deforms but doesn't exactly return to its pre-deformation characteristics, ie: less than 100% energy IN to energy OUT ratio...with some manner of intermediate energy "storage."

Last edited by gone-ot; 12-09-2009 at 09:08 AM..
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Old 12-09-2009, 11:31 AM   #13 (permalink)
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Ok, OK, but we do agree that it's the amount of rubber (and not the hysteresis) that causes the change in RR between new and worn tires, right?
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Old 12-09-2009, 04:03 PM   #14 (permalink)
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Originally Posted by CapriRacer View Post
Sorry, but sidewall stiffness hardly enters the equation when it comes to RR.

RR is pretty much all about the tread compound - how much, what kind, how much deflection (basically inflation pressure). You just can't escape the Wear / Traction / RR triangle.

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Quote:
Originally Posted by Old Tele man View Post
...that's *why* an older, well worn tire has a lower rr value than does an identical brand new tire.
I thought that was because an old tire is smooth, while a new one has a more "knobby" tread, like a mountain bike tire.
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Old 12-09-2009, 05:37 PM   #15 (permalink)
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...when a rubber knobby is bent over, it absorbs energy, but when it's released from being bent over, not all of the energy is returned as "springy-ness" in the rubber, but rather is wasted as heat.

...less rubber to absorbe energy = less energy stored, and thus less energy not being returned and ending up as wasted heat.

...some of the newer "tread" designs incorporate "deflection bumpers" in between the rubber block pieces to lower rubber-on-rubber contact which is purely "heat-generating."

...here's what Consumers Report says: "...As tires wear out, you’ll likely see improved fuel economy since the tires will have less rolling resistance as the tread (mass) is removed from the tire. Installing new tires, identical in brand and model as those removed, and you likely see a reduction in your fuel economy."


Last edited by gone-ot; 12-10-2009 at 10:12 AM..
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