Quote:
Originally Posted by Old Tele man
...that's interesting because the Goodyear "eco" tire weighs less, yet has the higher sidewall pressure:
205/55R16 Eagle RS-A: 21 lbs, 44 PSI
205/55R16 Assurance Fuel Max: 18 lbs, 51 PSI
..............
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I hope you realize that most of the weight in a tire is in the amount of tread rubber. To see their LRR tire with less weight makes perfect sense.
And that the pressure written on the sidewall is somewhat nebulous as this may or may not be a function of the strength of a tire.
Quote:
Originally Posted by Old Tele man
...wish they'd publish some standardized (SAE!) LRR numbers for the tires.
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There is a rule in process by NHTSA to add rolling resistance to the UTQG rating - along with the removal of the "Temperature" rating, as the Temperature rating was more or less analogous to speed rating.
The rule was supposed to finalized in February of 2010, but because there was some serious - and justified - objections, it is currently in limbo.
The rule as proposed was to publish the 3 ratings (RR, Treadwear, Traction) in a label to be applied to the tire (and removed from the sidewall). Treadwear and traction tests would remain unchanged.
They successfully resolved the issues concerning the RR test (by mandating a particular SAE test - there were several!). The problem was that different tests resulted in different numbers - and while the test sorted out tires effectively, unless everyone used the same test and the same test facility, the numbers published would be different.
But they got hung up on how to express that number. NHTSA was in favor of reporting the number as a "force" - meaning that larger tires (by load carrying capacity) would look worse that smaller tires. However, if the number was reported as a coefficient (the RR force result divided by the test load), smaller tires (by load carrying capacity) look worse.
Many folks, (the tire manufacturers, vehicle manufacturers, and others) wanted to have the number reported as a coefficient (RRC), arguing that this has more meaning consumers when it comes to buying tires. (the load on a tire is the same for a given vehicle regardless of the tire size applied to that vehicle.), while NHTSA wanted to publish the number as a force value (RRF), arguing that larger vehicles would look less efficient (which they already do in the regular EPA fuel economy test) and that would encourage folks not to buy large, fuel inefficient vehicles.
The counter arguement - and the one that seemed to hit hardest - was that reporting RRF would tend to encourage consumers to buy smaller load carrying capacity tires - which is the wrong direction for safety!
The GAO forced NHTSA to reconsider the rule - and that is where it stands.
One of the problems created by the rule - which was basically unresolvable - was the EVERY tire would need to be tested. That meant that a tire manufacturer had to run a tire 3 times for every size and model so they could be sure they were getting an accurate reading. Since tire lines have many, many different sizes - and there are many, many different models - this testing would take up to 3 years to complete - and that assumes no other testing takes place - meaning no testing of new tread compounds or new constructions. Needless to say, this was unacceptable.
But the issue of test facilities getting the same (or similar) results has been resolved by mandating testing comparisons to a "standard" tire. It's called the SRTT - Standard Reference Test Tire - and it is currently used for treadwear and traction testing. The SRTT would be assigned a value and all other tires would be referenced off of that - and that means the SRTT would need to be tested regularly to track the machine drift (the drag of the bearings of a testing machine change over time, but that can be compensated for if you can figure out what it is.) This, of course, would further delay the actual testing.
I assume that many tire manufacturers are conducting tests while the rule is in limbo. If I were doing the testing, I would test the smallest and the largest tires (by load carrying capacity) and a few in between for every model they make, then interpolate the results for those tire sizes not yet tested, with the idea that they could "correct" the results as they go forward. Even that would take some time.
And that pretty much sums it up!
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