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Old 05-11-2009, 03:47 PM   #51 (permalink)
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The problem with arguing rubber "hardness" and trying to relate it to rolling resistance is that tread rubber compounds have a three dimensional relationship between rolling resistance, tread wear, and traction - and unfortunately "hardness" is only 2 dimensions.

So you can have a "hard" compound that has high rolling resistance, poor traction, but good treadwear and a "soft" compound that has high rolling resistance, good traction, and poor treadwear.

In other words, you can't relate hardness to rolling resistance.

(And BTW, you can't relate rolling resistance to traction or grip either)

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Old 05-11-2009, 07:31 PM   #52 (permalink)
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Quote:
Originally Posted by CapriRacer View Post
The problem with arguing rubber "hardness" and trying to relate it to rolling resistance is that tread rubber compounds have a three dimensional relationship between rolling resistance, tread wear, and traction - and unfortunately "hardness" is only 2 dimensions.

So you can have a "hard" compound that has high rolling resistance, poor traction, but good treadwear and a "soft" compound that has high rolling resistance, good traction, and poor treadwear.

In other words, you can't relate hardness to rolling resistance.

(And BTW, you can't relate rolling resistance to traction or grip either)
Apparently you haven't been following the discussion.

more info based on solid tires

http://www.rehab.research.va.gov/jou...kauzlarich.pdf
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Old 05-12-2009, 08:43 AM   #53 (permalink)
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Quote:
Originally Posted by ConnClark View Post
Apparently you haven't been following the discussion.

...........

Unfortunately, I have been and I wanted to make sure eveyone avoided the trap of 2 dimensional thinking - especially the misconception that hardness and rolling resistance were somehow related, similar to the way it is commonly misunderstood that hardness and traction are also related.

This technology triangle is one of the design compromises that tire engineers have to face, especially when designing tires for the OE market. Vehicle manufacturers are keenly aware that tires have rolling resistance and that using low RR tires can not only improve a vehicle's EPA fuel economy ratings (a selling point), but also provide some relief in the development of a vehicle when the vehicle engineers have difficulty meeting their objectives, such as weight, energy consumption, etc.

The problem is that extremely low RR tires tires also don't have great traction and / or wear life. This is one of the reasons one hears lots of complaints about these properties on tires supplied to new vehicles. It is commonly thought the cost is what is driving this, but that is not the case. It's this technology triangle.

But tires designed for the replacement market are less subject to pressure of fuel economy. Most consumers feel that tires are supposed to deliver good wear characteristics - with traction and rolling resistance being very far down the list of desireables. As a result, most replacement market tires do not have good RR properties - and if there is a compromise to be made, it is between wear and traction - which fuels the misconception of hardness vs traction.

So just a word of caution.
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Old 05-12-2009, 12:03 PM   #54 (permalink)
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Originally Posted by Ernie Rogers View Post
"Changing the profile from 55% to 60%, to tire size 205/60R16, increased my tire diameter by 0.8 inches, a 3.2% increase in diameter. This small change has given about a 5% increase in fuel economy for my car."
So... if I drive 30,000 miles a year, the odometer would register 3.2% less, 960 miles less? So the car would technically depreciate less? Someone call MSN Money and let them know about this "money saving tip"!

This may be my next mod... Although the car height would be raised by 0.4 inches which may negate improvement from slower rotating wheels.
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Old 05-12-2009, 12:47 PM   #55 (permalink)
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Hi Ernie,

Have you checked the calibration of your odometer? You may be getting even more than a 5% increase -- more like 8+%!
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Old 05-13-2009, 02:12 AM   #56 (permalink)
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Speed correction too

Quote:
Originally Posted by NeilBlanchard View Post
Hi Ernie,

Have you checked the calibration of your odometer? You may be getting even more than a 5% increase -- more like 8+%!
Hello, Neil,

Yes, I include a correction for odometer error. But equally important if more subtle is the need to adjust speedometer reading to keep the same speed as before.

Ernie Rogers
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Old 05-27-2009, 10:04 AM   #57 (permalink)
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Quote:
Originally Posted by CapriRacer View Post
Unfortunately, I have been and I wanted to make sure eveyone avoided the trap of 2 dimensional thinking - especially the misconception that hardness and rolling resistance were somehow related, similar to the way it is commonly misunderstood that hardness and traction are also related.

This technology triangle is one of the design compromises that tire engineers have to face, especially when designing tires for the OE market. Vehicle manufacturers are keenly aware that tires have rolling resistance and that using low RR tires can not only improve a vehicle's EPA fuel economy ratings (a selling point), but also provide some relief in the development of a vehicle when the vehicle engineers have difficulty meeting their objectives, such as weight, energy consumption, etc.

The problem is that extremely low RR tires tires also don't have great traction and / or wear life. This is one of the reasons one hears lots of complaints about these properties on tires supplied to new vehicles. It is commonly thought the cost is what is driving this, but that is not the case. It's this technology triangle.

But tires designed for the replacement market are less subject to pressure of fuel economy. Most consumers feel that tires are supposed to deliver good wear characteristics - with traction and rolling resistance being very far down the list of desireables. As a result, most replacement market tires do not have good RR properties - and if there is a compromise to be made, it is between wear and traction - which fuels the misconception of hardness vs traction.

So just a word of caution.
First of all, thanks for the great posts! You and Ernie Rogers have gone above and beyond!

You keep bringing up this point and it is a very important one. When thinking about tires it is very easy, and convenient, to think in two dimensions. But tire engineers and rubber chemists must work with at least three dimensions. The hardness of the tread rubber compound, for example, is usually not taken into consideration when thinking about wear, traction and rolling resistance. Hardness is but one parameter that taken by itself has little relevance to this discussion. More relevant are the tread rubber composition and the tire construction.
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Old 05-27-2009, 04:54 PM   #58 (permalink)
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Quote:
Originally Posted by CapriRacer View Post
Unfortunately, I have been and I wanted to make sure eveyone avoided the trap of 2 dimensional thinking - especially the misconception that hardness and rolling resistance were somehow related,
<SNIP>
The problem is that extremely low RR tires tires also don't have great traction and / or wear life. This is one of the reasons one hears lots of complaints about these properties on tires supplied to new vehicles. It is commonly thought the cost is what is driving this, but that is not the case. It's this technology triangle.
Hello, Racer,

I think I will try logic, and you point out the errors--

1. Low rolling resistance tires never wear well.
2. Tires with hard tread material always wear well.
3. Therefore low rolling resistance tires never have hard tread material.

What do you think?
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Old 05-27-2009, 04:58 PM   #59 (permalink)
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Quote:
Originally Posted by NeilBlanchard View Post
Hi Ernie,

Have you checked the calibration of your odometer? You may be getting even more than a 5% increase -- more like 8+%!
The error has been measured with GPS and is actually a +4.5% correction of the odometer. The increased fuel economy is an educated guess. Speedometer accuracy is very good, reading a little high still.

Ernie
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Old 05-27-2009, 07:00 PM   #60 (permalink)
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Hi Ernie,

The upcoming Michelin HydroEdge "Green-X" tires are LRR and they are rated 800 on the treadwear estimate.

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