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Old 04-05-2009, 06:25 PM   #21 (permalink)
Ernie Rogers
 
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Two more items I forgot to mention--

1) Best way to lower rolling resistance is cheap--just raise tire pressure. It's perfectly okay to set tire pressure close to the rating on the side of the tire. My tires are rated at 44 psi, and I usually keep them at 40 psi. (But I use 44 psi if I am trying to get spectacular mileage.)

2) If you keep your tire pressure on the high side, you will see that tread wear is greatly reduced. My Michelin Energy tires have a 40,000 mile guarantee (I think) but I can easily get 80,000 miles from a set.

Ernie Rogers

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Old 04-05-2009, 06:41 PM   #22 (permalink)
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The Rubber Manufacturers are hiding data

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Originally Posted by bwilson4web View Post
I have had no luck finding rolling resistance values at Tire Rack and as for other sources, it has been a mixed bag. It is as if rolling resistance is being hidden.
You hit it on the nose, Bob,

I was told by several tire company engineers that the tire makers are forbidden to give out rolling resistance data--the gag order was issued by the Rubber Manufacturers Association. The reasons given weren't convincing so I can't say why.

The car makers do have the data, however. A sure-fire method to find good tires is to check what the car factories are putting on their fuel-efficient cars.

My idea is that we can force publication of rolling resistance data IF we the buyers push the issue. Returning tires that give bad mileage is one way to do that.

I would say that a Cd of 0.01 or greater is totally unacceptable.

Ernie Rogers
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Old 04-06-2009, 09:31 AM   #23 (permalink)
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Hey Ernie,

Welcome to EM. How about you make an intro post? I bet a lot of people will be interested by the spoiler on your beetle.
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Old 04-06-2009, 11:28 PM   #24 (permalink)
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My friend has "the CR book" I'll see what I can come up with for more numbers for you guys.
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Old 04-07-2009, 01:25 AM   #25 (permalink)
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Quote:
Originally Posted by bwilson4web View Post
I'm impressed with getting a rolling resistance value for the one 14" tire. I had tried to find the values for the Consumer Reports top rated tires and failed to find any metrics:
  • Michelin X Radial (Club Tire)
  • Michelin Agility Touring (Sears)
  • Michelin Harmony
  • Toyo 800 Ultra
  • Sumitomo HTR T4
I have had no luck finding rolling resistance values at Tire Rack and as for other sources, it has been a mixed bag. It is as if rolling resistance is being hidden.

Could you point me at where I might find the rolling resistance values for the Consumer Reports tires?

I recently measured my Prius Crr at 0.0102, which includes the transaxle drag. I'm not really happy with having to buy sets of tires to find the lowest rolling resistance tires.

I had been following the California Air Resources effort to measure tire rolling resistance but got the impression that it 'ran out of steam' last summer. I never saw their report much less some evidence of a continuing effort.

Thanks,
Bob Wilson
I have Michelin Harmony tires on my Mazda and Michelin MXV4 tires on my Mercedes. Both of them seem to offer good rolling resistance. I could feel an improvement in terms of coasting when I replaced some cheap-o tires with Harmonies on the Mazda.
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Old 04-07-2009, 08:43 AM   #26 (permalink)
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Apparently this California initiative on tire rolling resistance for after market tires was one of the last laws signed by Gray Davis (sp?) before he was recalled. It looks like they are trying to hold an open hearing on a final program setup:

Notice of Staff Workshop on the Fuel Efficient Tire Program

Some of the associated web sites suggest we may have the California tire rolling resistance by December 2009. Of course there is the new Governor who has recently tried to 'greenwash' himself.

Bob Wilson
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Old 04-07-2009, 12:24 PM   #27 (permalink)
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Quote:
Originally Posted by Ernie Rogers View Post
.........

I was told by several tire company engineers that the tire makers are forbidden to give out rolling resistance data--the gag order was issued by the Rubber Manufacturers Association. The reasons given weren't convincing so I can't say why.

...........
Ernie,

I have no idea why you were told this, but it is not true.

The reason tire manufacturers do not give out RR data is:

1) There is no agreed upon test procedure. There are at least 4 methods that I know of and they give different numerical values - although the rank order remains the same.

This is one of the issues troubling the California Energy Commission (CEC) when they try to come up with a regulation. The test results from different sources has to be the same.

2) Different test facilities given different results. This has been looked at and it is apparent that the test facilities can be correlated - however, the "base" facility (the one everyone else has to correlate to) has to be identified and a correlation procedure developed.

It has been suggested by NHTSA (National Highway and Traffic Safety Administration) that the Federal government (NHTSA) be the regulating body rather than have 50 different regulations - and their suggestion is to use a common tire for the correlation, so every tire tested would be a percentage of that - and their preference is the SRTT (Standard Reference Test Tire) Unfortunately, this doesn't address the tire size issue.

3) RR varies by tire size. Very early in the process, the CEC was confronted with the paradox that identical tires gave different results depending on tire size - with large tires giving smaller coefficients.

This might result in "one-off" tires that are used to characterize the entire tire line. However, if it were regulated that EVERY tire size / design combination were to be tested, it would occupy EVERY test facility in the world for over a year. In other words, no new development could take place.

So, NO, the tire manufacturers DO NOT know the RR of every tire they make.

The RMA (Rubber Manufacturers Association) has not only been cooperating with both NHTSA and the CEC to come up with a workable regulation, but they've also encouraging the regulators to understand the issues involved and overcome them. The tire manufacturers - through the RMA wants something that makes sense, is usable, and consumer friendly, and not too expensive. Thus far, it has been difficult to find concensus among the various stakeholders.

Nevertheless, it is just plain wrong to characterize the RMA as "gagging" the tire manufacturers. They ARE the tire manufacturers!! and they are trying to find a way to make it work.

Last edited by CapriRacer; 04-07-2009 at 12:31 PM..
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Old 04-07-2009, 01:18 PM   #28 (permalink)
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Here is some results of european tire test of this year which I have read:

At the moment best tire on the market is Michelin Energy saver, best in RR in every test! And usually orher michelin models are also in good positions in LRR tests. One test shows consumption difference between models in litres in different speeds.
speed 80km/h 120 km/h
1 Michelin energy saver 5,44l/100km 8,09l
2 Michelin Primacy Hp 5,6 8,2
3 Kumho ecsta spt 5,55 8,26

Other low RR tires in the top 3 test are
Continental premiun contact 2
Hankook vetus prime k105
Nokian V

European manufactures usually use in their eco models 175/70/R14 tire size...
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Old 04-07-2009, 03:16 PM   #29 (permalink)
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Ohh, so the tire makers are the villains here

Hello, CapriRacer,

Sorry to give you such a bad time-- you apparently work in the tire industry?

Your story agrees quite well with what I was told five years ago, except the other engineers were a little more frank--but that was five years ago.

It makes sense that the tire makers would want to be cooperative. They would rather set up their own system, rather than a government-imposed one. But, the evidence is TOO plain to miss. All this time has gone by, but I know of no coefficient published by any tire maker, NOT ONE.

We know that data are being withheld. It's time to get off the dime and be honest with the customers.

Ernie Rogers

An afterthought that may offend you even more-- I get the feeling at times that the tire engineers themselves don't understand rolling resistance. If they get inconsistent results in different tire sizes, it just means they aren't controlling the right variables. If they will publish the results, we can help them with the problem. /Ernie

Quote:
Originally Posted by CapriRacer View Post
Ernie,

I have no idea why you were told this, but it is not true.

The reason tire manufacturers do not give out RR data is:

1) There is no agreed upon test procedure. There are at least 4 methods that I know of and they give different numerical values - although the rank order remains the same.

This is one of the issues troubling the California Energy Commission (CEC) when they try to come up with a regulation. The test results from different sources has to be the same.

2) Different test facilities given different results. This has been looked at and it is apparent that the test facilities can be correlated - however, the "base" facility (the one everyone else has to correlate to) has to be identified and a correlation procedure developed.

It has been suggested by NHTSA (National Highway and Traffic Safety Administration) that the Federal government (NHTSA) be the regulating body rather than have 50 different regulations - and their suggestion is to use a common tire for the correlation, so every tire tested would be a percentage of that - and their preference is the SRTT (Standard Reference Test Tire) Unfortunately, this doesn't address the tire size issue.

3) RR varies by tire size. Very early in the process, the CEC was confronted with the paradox that identical tires gave different results depending on tire size - with large tires giving smaller coefficients.

This might result in "one-off" tires that are used to characterize the entire tire line. However, if it were regulated that EVERY tire size / design combination were to be tested, it would occupy EVERY test facility in the world for over a year. In other words, no new development could take place.

So, NO, the tire manufacturers DO NOT know the RR of every tire they make.

The RMA (Rubber Manufacturers Association) has not only been cooperating with both NHTSA and the CEC to come up with a workable regulation, but they've also encouraging the regulators to understand the issues involved and overcome them. The tire manufacturers - through the RMA wants something that makes sense, is usable, and consumer friendly, and not too expensive. Thus far, it has been difficult to find concensus among the various stakeholders.

Nevertheless, it is just plain wrong to characterize the RMA as "gagging" the tire manufacturers. They ARE the tire manufacturers!! and they are trying to find a way to make it work.
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Old 04-07-2009, 03:25 PM   #30 (permalink)
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I can understand that if you want to know the RRC for all tires you have to test every model in every size as it is known RRC will vary with width and profile.

However, I don't see why exactly that is a problem. I mean measuring RRC is not rocket science. I don't see why they can't come up with standardized test equipment giving repeatable results. Every manufacturer gets the same test bench and make their own measurements and publicize the results. The regulating body then randomly pick samples and performs a couple of tests to validate the results, and that would be sufficient.

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