Tire break in and rolling resistance?
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Originally Posted By: 190E26FTW
Mpg will rise with most tires as they wear down but with the Bridgestone RE960's they have a stickier compound underneath that gets exposed as the top layer is worn off so it remains glued to the road. I had these same tires on my Mercedes and I tore it up pretty good on I 280 and US 101 in SF. It stuck to the road. Only issue was that it was very loud for me after you put more miles on it. They wore out before 30,000 miles for me. I have Michelin Primacys back on now and they sure ride better and with less noise. I do notice that the sidewalls are much softer now. So with any tires...its a little give and take depending on what kind of performance you seek.
What pressure are you running your 960s at? I always kept all 4 corners at 35 psi.
I keep them at 35psi. But every time I take the car into Costco they set the tires at 30psi per Toyota spec.
Mpg will rise with most tires as they wear down but with the Bridgestone RE960's they have a stickier compound underneath that gets exposed as the top layer is worn off so it remains glued to the road. I had these same tires on my Mercedes and I tore it up pretty good on I 280 and US 101 in SF. It stuck to the road. Only issue was that it was very loud for me after you put more miles on it. They wore out before 30,000 miles for me. I have Michelin Primacys back on now and they sure ride better and with less noise. I do notice that the sidewalls are much softer now. So with any tires...its a little give and take depending on what kind of performance you seek.
What pressure are you running your 960s at? I always kept all 4 corners at 35 psi.
I keep them at 35psi. But every time I take the car into Costco they set the tires at 30psi per Toyota spec.
Just in case if you did not do this already. Jack the rear of your car up and spin your rear wheels with the tranny in neutral and your Parking Brake off. See if the wheels have heavy resistance or not.
I recently had the same problem and thought it was my tires and it turned out to be a maladjusted parking brake that was always on, on my left rear wheel. Thus giving me bad MPG. It would not spin as freely as the other side. Could be something as simple as that.
I recently had the same problem and thought it was my tires and it turned out to be a maladjusted parking brake that was always on, on my left rear wheel. Thus giving me bad MPG. It would not spin as freely as the other side. Could be something as simple as that.
I though that tire with higher trendwear rating has lower rolling resistance, and harder rubber has lower rolling resistance, and smoother trend pattern has lower rolling resistance. In other word, a tire that makes your car go all over the place, has lower rolling resistance. No?
Originally Posted By: meep
Help me out here: what combo provides Low RR but high treadlife? ... I can't see it...
A thin tread made of hard rubber.
Help me out here: what combo provides Low RR but high treadlife? ... I can't see it...
A thin tread made of hard rubber.
Originally Posted By: meep
Ok, so help me out... I've obviously read your page a cpl times.
The triangle is traction/RR/treadwear.
But I can't see the full triangle. Help me out here: what combo provides Low RR but high treadlife? ... I can't see it...
M
Originally Posted By: PandaBear
I though that tire with higher trendwear rating has lower rolling resistance, and harder rubber has lower rolling resistance, and smoother trend pattern has lower rolling resistance. In other word, a tire that makes your car go all over the place, has lower rolling resistance. No?
Let me try to explain it in a different way:
On a scale of 0 (zero) to 10, rate each: treadwear, traction, rolling resistance.
Add those 3 items together and the total can NOT be larger than 15!
Example:
Treadwear = 5
Traction = 5
RR = 5
- OR -
Treadwear = 10
Traction = 3
RR = 2
- OR -
Treadwear = 2
Traction = 3
RR = 10
Do you see now that there is a compromise being made to 3 items? - so the combination that gives good RR and high treadwear is poor traction!
Ok, so help me out... I've obviously read your page a cpl times.
The triangle is traction/RR/treadwear.
But I can't see the full triangle. Help me out here: what combo provides Low RR but high treadlife? ... I can't see it...
M
Originally Posted By: PandaBear
I though that tire with higher trendwear rating has lower rolling resistance, and harder rubber has lower rolling resistance, and smoother trend pattern has lower rolling resistance. In other word, a tire that makes your car go all over the place, has lower rolling resistance. No?
Let me try to explain it in a different way:
On a scale of 0 (zero) to 10, rate each: treadwear, traction, rolling resistance.
Add those 3 items together and the total can NOT be larger than 15!
Example:
Treadwear = 5
Traction = 5
RR = 5
- OR -
Treadwear = 10
Traction = 3
RR = 2
- OR -
Treadwear = 2
Traction = 3
RR = 10
Do you see now that there is a compromise being made to 3 items? - so the combination that gives good RR and high treadwear is poor traction!
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Capri,
this is true if you assume no change in materials and construction. I recently reviewed Bridgeston Ecopia 422 tires. Low rolling resistance and rated 640AA. New tread materials (silica) and stronger and lighter sidewall will give great life and great lowing resistance at a very modest decrease in traction as compared to Bridgeston Alenza tires, rated 600AA but with almost twice rolling resistance of Ecopia.
this is true if you assume no change in materials and construction. I recently reviewed Bridgeston Ecopia 422 tires. Low rolling resistance and rated 640AA. New tread materials (silica) and stronger and lighter sidewall will give great life and great lowing resistance at a very modest decrease in traction as compared to Bridgeston Alenza tires, rated 600AA but with almost twice rolling resistance of Ecopia.
Originally Posted By: friendly_jacek
Capri,
This is true if you assume no change in materials and construction. I recently reviewed Bridgeston Ecopia 422 tires. Low rolling resistance and rated 640AA. New tread materials (silica) and stronger and lighter sidewall will give great life and great lowing resistance at a very modest decrease in traction as compared to Bridgeston Alenza tires, rated 600AA but with almost twice rolling resistance of Ecopia.
Your point is well taken, but at some time after there is a shift in the paradigm like the introduction of new materials, then what I have written becomes true again - It's all relative. If I were to compare tires from the 1960's to today's tires - well, today's tires do EVERYTHING better!
Capri,
This is true if you assume no change in materials and construction. I recently reviewed Bridgeston Ecopia 422 tires. Low rolling resistance and rated 640AA. New tread materials (silica) and stronger and lighter sidewall will give great life and great lowing resistance at a very modest decrease in traction as compared to Bridgeston Alenza tires, rated 600AA but with almost twice rolling resistance of Ecopia.
Your point is well taken, but at some time after there is a shift in the paradigm like the introduction of new materials, then what I have written becomes true again - It's all relative. If I were to compare tires from the 1960's to today's tires - well, today's tires do EVERYTHING better!
Originally Posted By: friendly_jacek
Capri,
this is true if you assume no change in materials and construction. I recently reviewed Bridgeston Ecopia 422 tires. Low rolling resistance and rated 640AA. New tread materials (silica) and stronger and lighter sidewall will give great life and great lowing resistance at a very modest decrease in traction as compared to Bridgeston Alenza tires, rated 600AA but with almost twice rolling resistance of Ecopia.
I got a set of Michelin Primacy MXV4s on a Prius, those are marked by Michelin as a LRR tire(Green X) and have a 620/A/A UTQG. The Michelin HydroEdge and Goodyear Assurance Fuel Max are in the stratosphere for treadlife but are also LRR as well.
As for the best tire with LRR, I would say a road bike tire such as a Conti Gatorskin in a 700x25C or above size.
Capri,
this is true if you assume no change in materials and construction. I recently reviewed Bridgeston Ecopia 422 tires. Low rolling resistance and rated 640AA. New tread materials (silica) and stronger and lighter sidewall will give great life and great lowing resistance at a very modest decrease in traction as compared to Bridgeston Alenza tires, rated 600AA but with almost twice rolling resistance of Ecopia.
I got a set of Michelin Primacy MXV4s on a Prius, those are marked by Michelin as a LRR tire(Green X) and have a 620/A/A UTQG. The Michelin HydroEdge and Goodyear Assurance Fuel Max are in the stratosphere for treadlife but are also LRR as well.
As for the best tire with LRR, I would say a road bike tire such as a Conti Gatorskin in a 700x25C or above size.
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Originally Posted By: Carbon
Originally Posted By: FZ1
No,boys. You don't get more mpgs as the "tread wears down". Think about it.
You should adjust your thinking to be compatible with the facts.
While part of the apparent decrease in mileage is an illusion due to the decrease in radius, there is still a real component due to reduced rolling resistance. http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=177
Naw,man. You should "adjust your thinking to be compatible" with common sense. Think about it. There is no significant rolling resistance due to a tire being "new",per se. That's why the OP noticed no difference in the mpg over his first 6,000 miles. There is no measureable "break in" period. Lot's of reasons a new set of tires will get different mpg,but"new" isn't one of them.
Originally Posted By: FZ1
No,boys. You don't get more mpgs as the "tread wears down". Think about it.
You should adjust your thinking to be compatible with the facts.
While part of the apparent decrease in mileage is an illusion due to the decrease in radius, there is still a real component due to reduced rolling resistance. http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=177
Naw,man. You should "adjust your thinking to be compatible" with common sense. Think about it. There is no significant rolling resistance due to a tire being "new",per se. That's why the OP noticed no difference in the mpg over his first 6,000 miles. There is no measureable "break in" period. Lot's of reasons a new set of tires will get different mpg,but"new" isn't one of them.
Originally Posted By: FZ1
Originally Posted By: Carbon
Originally Posted By: FZ1
No,boys. You don't get more mpgs as the "tread wears down". Think about it.
You should adjust your thinking to be compatible with the facts.
While part of the apparent decrease in mileage is an illusion due to the decrease in radius, there is still a real component due to reduced rolling resistance. http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=177
Naw,man. You should "adjust your thinking to be compatible" with common sense. Think about it. There is no significant rolling resistance due to a tire being "new",per se. That's why the OP noticed no difference in the mpg over his first 6,000 miles. There is no measureable "break in" period. Lot's of reasons a new set of tires will get different mpg,but "new" isn't one of them.
OK, the beginning of this post is going to look like a bunch on nested quotes, and it's kind of hard to tell who is taking what position.....
- BUT -
All other things being the same, the more rubber, especially tread rubber, in a tire, the higher the rolling resistance.
That means that new - meaning unworn - tires are going to consume more fuel than old - meaning worn out - tires. That also means that winter tires, all terrain tires, mud tires, are all going to be at a fuel economy disadvantage compared to a regular all season tire.
Please note: This has nothing to do with rolling diameters. This is strictly looking at it from an energy consumption point of view. More material = more energy loss!
Originally Posted By: Carbon
Originally Posted By: FZ1
No,boys. You don't get more mpgs as the "tread wears down". Think about it.
You should adjust your thinking to be compatible with the facts.
While part of the apparent decrease in mileage is an illusion due to the decrease in radius, there is still a real component due to reduced rolling resistance. http://www.tirerack.com/tires/tiretech/techpage.jsp?techid=177
Naw,man. You should "adjust your thinking to be compatible" with common sense. Think about it. There is no significant rolling resistance due to a tire being "new",per se. That's why the OP noticed no difference in the mpg over his first 6,000 miles. There is no measureable "break in" period. Lot's of reasons a new set of tires will get different mpg,but "new" isn't one of them.
OK, the beginning of this post is going to look like a bunch on nested quotes, and it's kind of hard to tell who is taking what position.....
- BUT -
All other things being the same, the more rubber, especially tread rubber, in a tire, the higher the rolling resistance.
That means that new - meaning unworn - tires are going to consume more fuel than old - meaning worn out - tires. That also means that winter tires, all terrain tires, mud tires, are all going to be at a fuel economy disadvantage compared to a regular all season tire.
Please note: This has nothing to do with rolling diameters. This is strictly looking at it from an energy consumption point of view. More material = more energy loss!
CapriRacer:
Does that mean for the same size tire with the same age (new for example), a softer compound tire would have more rolling resistance?
If 2 tires, both about the same UTQG (say 300), same temperature and traction rating, same speed rating, same everything else, but only different in summer vs all season, would still tip the advantage of rolling resistance toward all season in general?
It seems like rolling resistance is one of those values that is very hard to find and it is almost impossible to get.
Does that mean for the same size tire with the same age (new for example), a softer compound tire would have more rolling resistance?
If 2 tires, both about the same UTQG (say 300), same temperature and traction rating, same speed rating, same everything else, but only different in summer vs all season, would still tip the advantage of rolling resistance toward all season in general?
It seems like rolling resistance is one of those values that is very hard to find and it is almost impossible to get.
Originally Posted By: PandaBear
CapriRacer:
Does that mean for the same size tire with the same age (new for example), a softer compound tire would have more rolling resistance?
If 2 tires, both about the same UTQG (say 300), same temperature and traction rating, same speed rating, same everything else, but only different in summer vs all season, would still tip the advantage of rolling resistance toward all season in general?
It seems like rolling resistance is one of those values that is very hard to find and it is almost impossible to get.
A tire's rolling resistance is the conbination of 3 things: The amount of material being deflected (think of it as tread volume, since the tread rubber is the largest volume of material being deflected), the amount of deflecion (basically controlled by inflation pressure), and the properties of the material being deflected (mostly tread rubber).
Tread rubber is subject to a technology triangle where, treadwear, traction, and rolling resistance are tradeoffs. Taking your example, tires with the same UTQG ratings will have similar RR values.
- EXCEPT -
There are things that can be done to the tread rubber that will improve the RR values with only minor losses to treadwear and traction - the use of silica in partial replacemnt of carbon black. This, then bcomes the new set of conditions for the Treadwear/Traction/RR triangle.
But within the UTQG ratings there can be pretty large variances. For example, a tire might have a very high A traction level, or a very low A traction level - and that, of course, is going to have affects that aren't accounted for in the ratings. That means the "softness" - a 2 dimensional property - doesn't explain a 3 way relationship.
Also, the UTQG treadwear rating is such that a tire manufacturer can not exaggerate a rating, but is allowed to understate it.
So comparing UTQG rating is full of vagarity.
But here's the reason why it is hard to find RR values.
1) The tests have to be the same. There are about 6 different RR tests, and you get different values out of each test.
2) The test has to be performed at the same facility - or at least, different facilities have to be correlated.
3) The way of expressing RR has to be the same. For example, RR can be expressed as a force or as a coefficient.
NHTSA has done the first 2 items and the tire manufacturers are in agreement there.
But it is the third item that has caused a problem.
NHTSA wants to express RR as a force - and they proposed a rule in Oct of 2009 with the idea that the rule would go into effect in Feb 2010. The tire manufacturers objected, pointing out that this method made it seem that smaller tires got better RR and that had safety implications. The reason NHTSA wanted to use force was that large SUV tires would have very high values and the management at NHTSA wanted folks to move away from large vehicles and into smaller, more fuel efficient vehicles.
The tire manufacturers want to use coefficient, which makes larger tires look like they get better RR - and that is true if the load on the tire is the same, which it would be if installed on a given vehicle - and that would be better for safety. They felt that consumers would never look at RR values on new vehicles - they would look at the EPA fuel economy sticker for guidance.
The GAO stepped in and agreed with the tire manufacturers and ordered NHTSA to go back and determine how consumers would read the propsed rule - and come back when they could demonstrate that any proposed rule would not compromise safety, and would give the consumer information that would be useful.
In the meantime, NHTSA has had to deal with the "Toyota" issue and that has taken up a lot of resources. It is not known when NHTSA will get back to this issue.
But the tire manufacurers have not been idele. Prior to NHTSA's Oct 2009 proposed rule, the tire manufacturers warned NHTSA that if EVERY testing facility in the world were used 24/7/365, it would still take 3 years before all tires were tested. While this tesing was taking place, NO R&D could take place - and that was a terrible idea. So they proposed a methon where the RR would be tested for samples within a line of tires and estimates provided for the remaining sizes - with the idea that tests would be run at a later date to verfiy the estimates - and that normal R&D would not be interrupted I forget what they proposed as a phase-in period, but it was on the order to 6 to 8 years.
So there you have it. The tire manufacturers are prepared to publish their values, but are afraid to do so until NHTSA finalizes how the information is going to be presented. NHTSA has not been known for its consistency and has the power to issue sanctions. It's a stalemate!
CapriRacer:
Does that mean for the same size tire with the same age (new for example), a softer compound tire would have more rolling resistance?
If 2 tires, both about the same UTQG (say 300), same temperature and traction rating, same speed rating, same everything else, but only different in summer vs all season, would still tip the advantage of rolling resistance toward all season in general?
It seems like rolling resistance is one of those values that is very hard to find and it is almost impossible to get.
A tire's rolling resistance is the conbination of 3 things: The amount of material being deflected (think of it as tread volume, since the tread rubber is the largest volume of material being deflected), the amount of deflecion (basically controlled by inflation pressure), and the properties of the material being deflected (mostly tread rubber).
Tread rubber is subject to a technology triangle where, treadwear, traction, and rolling resistance are tradeoffs. Taking your example, tires with the same UTQG ratings will have similar RR values.
- EXCEPT -
There are things that can be done to the tread rubber that will improve the RR values with only minor losses to treadwear and traction - the use of silica in partial replacemnt of carbon black. This, then bcomes the new set of conditions for the Treadwear/Traction/RR triangle.
But within the UTQG ratings there can be pretty large variances. For example, a tire might have a very high A traction level, or a very low A traction level - and that, of course, is going to have affects that aren't accounted for in the ratings. That means the "softness" - a 2 dimensional property - doesn't explain a 3 way relationship.
Also, the UTQG treadwear rating is such that a tire manufacturer can not exaggerate a rating, but is allowed to understate it.
So comparing UTQG rating is full of vagarity.
But here's the reason why it is hard to find RR values.
1) The tests have to be the same. There are about 6 different RR tests, and you get different values out of each test.
2) The test has to be performed at the same facility - or at least, different facilities have to be correlated.
3) The way of expressing RR has to be the same. For example, RR can be expressed as a force or as a coefficient.
NHTSA has done the first 2 items and the tire manufacturers are in agreement there.
But it is the third item that has caused a problem.
NHTSA wants to express RR as a force - and they proposed a rule in Oct of 2009 with the idea that the rule would go into effect in Feb 2010. The tire manufacturers objected, pointing out that this method made it seem that smaller tires got better RR and that had safety implications. The reason NHTSA wanted to use force was that large SUV tires would have very high values and the management at NHTSA wanted folks to move away from large vehicles and into smaller, more fuel efficient vehicles.
The tire manufacturers want to use coefficient, which makes larger tires look like they get better RR - and that is true if the load on the tire is the same, which it would be if installed on a given vehicle - and that would be better for safety. They felt that consumers would never look at RR values on new vehicles - they would look at the EPA fuel economy sticker for guidance.
The GAO stepped in and agreed with the tire manufacturers and ordered NHTSA to go back and determine how consumers would read the propsed rule - and come back when they could demonstrate that any proposed rule would not compromise safety, and would give the consumer information that would be useful.
In the meantime, NHTSA has had to deal with the "Toyota" issue and that has taken up a lot of resources. It is not known when NHTSA will get back to this issue.
But the tire manufacurers have not been idele. Prior to NHTSA's Oct 2009 proposed rule, the tire manufacturers warned NHTSA that if EVERY testing facility in the world were used 24/7/365, it would still take 3 years before all tires were tested. While this tesing was taking place, NO R&D could take place - and that was a terrible idea. So they proposed a methon where the RR would be tested for samples within a line of tires and estimates provided for the remaining sizes - with the idea that tests would be run at a later date to verfiy the estimates - and that normal R&D would not be interrupted I forget what they proposed as a phase-in period, but it was on the order to 6 to 8 years.
So there you have it. The tire manufacturers are prepared to publish their values, but are afraid to do so until NHTSA finalizes how the information is going to be presented. NHTSA has not been known for its consistency and has the power to issue sanctions. It's a stalemate!
So, what you are saying is we might have published RR values by the time 2020 rolls around?
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Naw,man. It depends on the diameter of the new vs. old tires. What if the new tire is a smaller diameter than the "old" tire. My point spoke to the original post where the OP was told by the tire store personnel that the new tires just need to "break in" for mpg to improve. That's a myth. Break in,due to a tire being "new" vs. "used",is negligible. Just my .02.
It isn't exactly a myth that that tires need to "break in". There are mold release compounds that need to be worn off, but it is a myth that it takes a while for the rubber compounds to stabilize. That length of time is about as long as it takes to wear off the mold release compounds.
But what most folks don't realize is that worn tires gett better RR than new, unworn tires - all other things being equal.
They also don't realize that there can be HUGE differences in RR between tires. The California Energy Commission asked Smithers Scientific Services to get RR data for a large group of tires of the same size - and they found a 60% difference worst to best:
http://www.energy.ca.gov/transportation/...e%20Testing.pdf
What frequently happens is that a guy buys a new car, then when the OE tires wear out (and he discovers how poorly they wear) replaces those tires with something that wears better - and immediately experiences a fuel economy loss! Not only is he taking a hit because of the worn vs unworn thing, but the replacement tires (with the better wear qualities) doesn't give as good of RR (because of the improvement in wear properties). The difference in diameter is a minor player here.
But what most folks don't realize is that worn tires gett better RR than new, unworn tires - all other things being equal.
They also don't realize that there can be HUGE differences in RR between tires. The California Energy Commission asked Smithers Scientific Services to get RR data for a large group of tires of the same size - and they found a 60% difference worst to best:
http://www.energy.ca.gov/transportation/...e%20Testing.pdf
What frequently happens is that a guy buys a new car, then when the OE tires wear out (and he discovers how poorly they wear) replaces those tires with something that wears better - and immediately experiences a fuel economy loss! Not only is he taking a hit because of the worn vs unworn thing, but the replacement tires (with the better wear qualities) doesn't give as good of RR (because of the improvement in wear properties). The difference in diameter is a minor player here.
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Originally Posted By: CapriRacer
It isn't exactly a myth that that tires need to "break in". There are mold release compounds that need to be worn off, but it is a myth that it takes a while for the rubber compounds to stabilize. That length of time is about as long as it takes to wear off the mold release compounds.
But what most folks don't realize is that worn tires gett better RR than new, unworn tires - all other things being equal.
They also don't realize that there can be HUGE differences in RR between tires. The California Energy Commission asked Smithers Scientific Services to get RR data for a large group of tires of the same size - and they found a 60% difference worst to best:
http://www.energy.ca.gov/transportation/...e%20Testing.pdf
What frequently happens is that a guy buys a new car, then when the OE tires wear out (and he discovers how poorly they wear) replaces those tires with something that wears better - and immediately experiences a fuel economy loss! Not only is he taking a hit because of the worn vs unworn thing, but the replacement tires (with the better wear qualities) doesn't give as good of RR (because of the improvement in wear properties). The difference in diameter is a minor player here.
Originally Posted By: CapriRacer
It isn't exactly a myth that that tires need to "break in". There are mold release compounds that need to be worn off, but it is a myth that it takes a while for the rubber compounds to stabilize. That length of time is about as long as it takes to wear off the mold release compounds.
But what most folks don't realize is that worn tires gett better RR than new, unworn tires - all other things being equal.
They also don't realize that there can be HUGE differences in RR between tires. The California Energy Commission asked Smithers Scientific Services to get RR data for a large group of tires of the same size - and they found a 60% difference worst to best:
http://www.energy.ca.gov/transportation/...e%20Testing.pdf
What frequently happens is that a guy buys a new car, then when the OE tires wear out (and he discovers how poorly they wear) replaces those tires with something that wears better - and immediately experiences a fuel economy loss! Not only is he taking a hit because of the worn vs unworn thing, but the replacement tires (with the better wear qualities) doesn't give as good of RR (because of the improvement in wear properties). The difference in diameter is a minor player here.
I disagree,but appreciate the additional info. I think the diameter change can be the MAJOR player of these factors. You have to adjust the computed,apparent,mpg by the difference in diameter,from the old tire,to the new tire,to get a more accurate mpg computation. The new compound break in,etc. differences are so small,in effect, as to be unnoticeable,on a tank by tank basis,to the average motorist.
It isn't exactly a myth that that tires need to "break in". There are mold release compounds that need to be worn off, but it is a myth that it takes a while for the rubber compounds to stabilize. That length of time is about as long as it takes to wear off the mold release compounds.
But what most folks don't realize is that worn tires gett better RR than new, unworn tires - all other things being equal.
They also don't realize that there can be HUGE differences in RR between tires. The California Energy Commission asked Smithers Scientific Services to get RR data for a large group of tires of the same size - and they found a 60% difference worst to best:
http://www.energy.ca.gov/transportation/...e%20Testing.pdf
What frequently happens is that a guy buys a new car, then when the OE tires wear out (and he discovers how poorly they wear) replaces those tires with something that wears better - and immediately experiences a fuel economy loss! Not only is he taking a hit because of the worn vs unworn thing, but the replacement tires (with the better wear qualities) doesn't give as good of RR (because of the improvement in wear properties). The difference in diameter is a minor player here.
Originally Posted By: CapriRacer
It isn't exactly a myth that that tires need to "break in". There are mold release compounds that need to be worn off, but it is a myth that it takes a while for the rubber compounds to stabilize. That length of time is about as long as it takes to wear off the mold release compounds.
But what most folks don't realize is that worn tires gett better RR than new, unworn tires - all other things being equal.
They also don't realize that there can be HUGE differences in RR between tires. The California Energy Commission asked Smithers Scientific Services to get RR data for a large group of tires of the same size - and they found a 60% difference worst to best:
http://www.energy.ca.gov/transportation/...e%20Testing.pdf
What frequently happens is that a guy buys a new car, then when the OE tires wear out (and he discovers how poorly they wear) replaces those tires with something that wears better - and immediately experiences a fuel economy loss! Not only is he taking a hit because of the worn vs unworn thing, but the replacement tires (with the better wear qualities) doesn't give as good of RR (because of the improvement in wear properties). The difference in diameter is a minor player here.
I disagree,but appreciate the additional info. I think the diameter change can be the MAJOR player of these factors. You have to adjust the computed,apparent,mpg by the difference in diameter,from the old tire,to the new tire,to get a more accurate mpg computation. The new compound break in,etc. differences are so small,in effect, as to be unnoticeable,on a tank by tank basis,to the average motorist.
Originally Posted By: FZ1
I disagree,but appreciate the additional info. I think the diameter change can be the MAJOR player of these factors. You have to adjust the computed,apparent,mpg by the difference in diameter,from the old tire,to the new tire,to get a more accurate mpg computation. The new compound break in,etc. differences are so small,in effect, as to be unnoticeable,on a tank by tank basis,to the average motorist.
I'm hoping that you realize that when RR is measured diameter isn't a factor in the measurement - and that 60% difference would be huge compared to the 2% diference - say between a 205/65R15 and a 215/65R15!
I disagree,but appreciate the additional info. I think the diameter change can be the MAJOR player of these factors. You have to adjust the computed,apparent,mpg by the difference in diameter,from the old tire,to the new tire,to get a more accurate mpg computation. The new compound break in,etc. differences are so small,in effect, as to be unnoticeable,on a tank by tank basis,to the average motorist.
I'm hoping that you realize that when RR is measured diameter isn't a factor in the measurement - and that 60% difference would be huge compared to the 2% diference - say between a 205/65R15 and a 215/65R15!
60% of what? It's not 60% of mpg,is it? Look,if Diameter increases,it's implicit that tire mass and,therefore,RR would also increase. Again,my point is than "new tire breakin",per se,is not even measureable tank to tank. Lot's of reasons a new set of tires will get different,apparent,or actual,mpg from the tires taken off,but "new tire break in" isn't one of them.
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