There is a technological triangle for tread compound that involves treadwear, traction (especially wet traction), and Rolling Resistance. In order to get an improvement in one area, one or both of the others has to be sacrificed. That means that you can NOT get great results in all 3 areas. At best you will get good results - and frequently to get "good" results, some other way of changing the triangle is employed, like reduced tread depth (something Michelin is using). Note: There are other ways of doing this.
- BUT - .
The term "LRR" is a bit of a misnomer as it means better RR compared to other tires with similar treadwear and traction characteristics. In other words it is not an absolute term. Many tires labeled LRR may have HIGHER RR values than some tires not so labeled.
For a vehicle manufacturer, tires can be an area where fuel economy can be enhanced (resulting in a larger value on the EPA fuel economy tests).. As a result pretty much all OE tires are better than any aftermarket tire for RR - even those labeled LRR - but treadwear and traction are sacrificed - which is why OE tires have such a bad reputation.
The problem is that folks buying tires in the replacement market want tires with good treadwear (unless they are going for grip!), so you won't find many tires with moderate RR values. There is a pretty wide gap between OE tires (with low RR values) and replacement market tires (with good treadwear or traction).
Wouldn't it be nice if RR values were published somewhere, similar to treadwear and traction values? What about a government regulation?
Well, back in 2010, a proposal was put forward, but it was withdrawn. There were 3 problems:
1) What test to perform. There are several different tests, but it turns out that tires can be compared using a single point test - quick and easy.
2) How to correlate different testing facilities. They decided on assigning a value to the SRTT (Standard Reference Test Tire), then adjusting the results based on those values. The SRTT is a commonly used reference where tests can vary by - say - temperature or testing surface. It's an old Uniroyal tire that Michelin makes using certified materials and they test to assure the tire hasn't changed from batch to batch (and if it has, how to adjust the results.)
3) How to express the result so that it is easy for the average consumer to understand. This is where the technical issues got in the way.
First, rolling resistance varies by tire size. So a way needed to be developed to deal with that. NHTSA (National Highway Traffic and Safety Administration) wanted EVERY size to be tested in EVERY tire line for EVERY tire manufacturer. USTMA (US Tire Manufacturers Association) pointed out that it would take 3 years of 24/7 testing to achieve that result - and during those 3 years no research could be done - and that just wasn't going to fly.
Second, NHTSA wanted to use RRF (Rolling Resistance - Force) in order to push consumers to buy smaller cars. The USTMA pointed out that consumers wouldn't buy cars based on the tire's rolling resistance even if they had that information. They would use the fuel economy values published by the vehicle manufacturers - AND that consumers would be better served if RRC (Rolling Resistance Coefficient = RRF divided by the test load) was what was published.
Then there was the issue of how to display this information - which kind of got lost in the 2 points above. One proposal was a traffic light (Red/Yellow/Green) kind of indicator without the actual values being published. Another was a bar graph showing where a particular tire was compared to the best and worst tire - but that meant that any new max or min values would result in obsoleting the previous published graphs.
In the end the proposed rule was withdrawn to work out the 2 issues mentioned above - the size issue and the RRF vs RRC. This was in 2010. In the meantime, there was this HUGE airbag recall that occupied most of the technical resources of NHTSA, so the Rolling Resistance regulations weren't worked on - until recently.
The publication date has been pushed back repeatedly - and just got pushed back again to March 2020. I am not optimistic.
And just for reference, here are my 2 webpages on the subject:
Barry's Tire Tech: Rolling Resistance and Fuel Economy
Barry's Tire Tech: Rolling Resistance and Fuel Economy (Continued)
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