LRR tires and RRC/4 data

[bobdavisnpf]

Moving discussion of LRR and RRC to techie town...

We're all familiar with the occasional quest for info re: LRR tires, and the lack of coherent info available. I'm trying to figure out just how to make sense of the disparate numbers I'm finding.

So far I've got 3 main sources:
http://onlinepubs.trb.org/onlinepubs/sr/SR...stance_Data.pdf
http://www.greenseal.org/resources/r...resistance.pdf
and Consumer Reports Online's November 2006 tire buying article.

Per Ecos Consulting 2002 tests listed:
Turanza RE92 185/70R14 has a Measured RRC/4 of .01065. Pretty close, but just above Greenseal's chosen cutoff of .0105.
Integrity 185/70R14 has a Measured RRC/4 of .00968
Best tire was B381 P185/70R14 at .00615 -- matches the best reported in Greenseal's report.

The 2002 Ecos Consulting tests were used by Greenseal to create their much-cited, very helpful but rather outdated 2003 report:
http://www.greenseal.org/resources/r...resistance.pdf

Per 2005 manufacturer-reported data list:
Integrity P185/65R14 has a Reported RRC/4 of .01278.
Integrity P225/70R16 has an RRC/4 of .00889. This tire wieghs 25 lb (vs 15 for the P185/65R14). I don't get why it has a lower RRC/4.
Comfortred P195/65R15 has .01139.
Best tires were Michelin Symmetry P225/60R16 at .00650 - a 27-lb tire, and
Michelin Tiger Paw AWP P225/60R16 at .00683 - a 25lb tire. On both these model lines, the smaller/lighter/narrower the tire gets, the higher its RRC/4.
Michelin Rugged Trail T/A P285/70R17, at .00709 is a 44lb monster that beats the RE92 by 33%?

CR's 2006 test involved sending out same-sized tires from different makers to an independent lab, which then ran the same test suite done for the RMA and Ecos Consulting report. This allows for a little more of an apples-to-apples test, but not by much, and as usual they have kept the real data and given us their 5 little dots to reflect the test scores. The full ratings, by the way, include a lot of variables; rolling resistance appears to have almost nothing to do with the overall rankings which include all the usual categories like handling, stopping power, traction, wear, etc.

Comparing the 2 groups, there are very few matches but a couple trends.

195/65R15: 22 tested, 2 match RMA compilation report.
Michelin Pilot XGT H4 - worst
195/60R14 .01238 in RMA
205/60R15 .01231 in RMA
225/60R16 .01079 in RMA
Michelin Energy MXV4 Plus - best
205/60R15 .00949 in RMA
235/65R17 .00855 in RMA
Continental ContiPremierContact was the only other best; no match in RMA data, but it might be a close match to the ContiTouring Contact, which RMA show as best in the 13-member 205/55R16 group (.00825, beating out the Michelin Energy MXV4 Plus's .00903).

205/55R16: 13 tested, 3 match in RMA report.
Michelin Pilot HX MXM4 - better
215/55R16 .00870 in RMA
215/50R17 .00989 in RMA
225/55R17 .00935 in RMA
235/55ZR17 .00942 in RMA
255/55R18 .00947 in RMA
Michelin MX V4 Plus - average
205/60R15 .00949 in RMA
235/65R17 .00855 in RMA
Bridgestone Potenza RE950 - worse
205/65R15 .01070 in RMA
225/60R16 .01050 in RMA
No bests in the V-Rated group.

Sorting the RMA report proved very useful (but tedious: had to massage the data after importing to excel). Among like sizes, the red-dot tires do rank high within each given size description. Just as telling, sorting by profile percentage shows the high-profile tires score better as a trend than the low-profile tires, regardless of make/model.

After a lot more searching, I finally found a doc that explains the test procedure for reporting RRC:
http://books.nap.edu/openbook.php?record_i...20&page=137

The most prevalent is SAE J1269; another one is pretty much the same, SAE J1270. It seems they start by inflating the tire to its max pressure, then weight it to its max load, run it for 30 minutes to warm up, back the load off to 70% of max, then take measurements at 80 kph. They check tire pressure to ensure the tire is running at max +3 psi!! It seems to me, then, that the higher-profile the tire, the more this test will deform it, thus reducing its contact patch. And since the test doesn't start til the tire is at speed, warmed up, and running only straight, any energy penalty we'd normally pay for weight is minimized.

In essence, then, the SAE J1269 RRC test seems to demonstrate how over-inflation and contact-patch distortion "improves" the RRC and, thus, the likelihood a tire could be called "LRR".

The attached file has the data sorted by 1) wheel diameter, then 2) section width, then 3) aspect ratio, then 4) RRC/4. This was the setup I find most useful for comparisons. Not sure if it will take in the final doc, since I used Excel 2007 for the 4-level sort and then saved as an Excel 2003 file.

Cheers!
Bob

[JimboK]

Great stuff, Bob. Thanks for taking the time to research and compile all this. Timing is good for me; I plan to buy new tires before the winter. I was leaning toward the Michelin Energy MXV4+ before they were discontinued earlier this year.

Now, if only there were more data for various brands for the Prius' 185/65R15.

[treehggr]

Yeah thanks, I appreciate all the research you have done. I just wish it was a little easier to gather the data needed to find the best LRR tire available for our application. I've been looking into this as well. The only issue as stated by Jimbo is that they seem to test tires that are not R15's. I have been looking into the Continental ContiTouring Contact tires and these seem to be the best bet for replacing the stock integrity's.

[bobdavisnpf]

<div class='quotetop'>QUOTE(treehggr @ Jul 6 2007, 05:54 AM) [snapback]473922[/snapback]</div>

Yeah thanks, I appreciate all the research you have done. I just wish it was a little easier to gather the data needed to find the best LRR tire available for our application. I've been looking into this as well. The only issue as stated by Jimbo is that they seem to test tires that are not R15's. I have been looking into the Continental ContiTouring Contact tires and these seem to be the best bet for replacing the stock integrity's.
[/b]

You bet. Now my big limitation is that I don't have time to contact all the makers to ask for updated RRC 4/ data for their current lines.

While the RMA data tends toward higher-performance aftermarket-type tires, there are quite a few 15's in the bunch. The CR article is also well worth the cost of a month's access to their site, since they make a point of testing so many identical 15's.

If you really want to go nuts on MPG, you might be interested in the Bridgestone B381. This tire, with RRC 4/ of .00615 in the 185/70R14, has been the hands-down LRR champ since 2002. It's got about the right size (857 revs per mile) and you can find 14" wheels with a 5x100 bolt pattern - www.1010tires.com has the easiest search since they don't make you search by vehicle only when searching across brands.

[JimboK]

<div class='quotetop'>QUOTE(JimboK @ Jul 6 2007, 08:19 AM) [snapback]473916[/snapback]</div>

I plan to buy new tires before the winter.
[/b]

Turns out, "before the winter" suddenly is now. Awoke to an unrepairable flat this morning, described here.

[ekpolk]

<div class='quotetop'>QUOTE(JimboK @ Jul 7 2007, 10:05 AM) [snapback]474621[/snapback]</div>

Turns out, "before the winter" suddenly is now. Awoke to an unrepairable flat this morning, described here.
[/b]

May be too late for you, but I just discovered that Michelin now has released a new model, the "Primacy MXV4". Per TireRAck info, it appears to have the same tread pattern as the discontinued Energy MXV4+. Unfortunately, the model is brand new and the info at TR says zip about LRR. I love my MXV4+s and they have plenty of life left, but I was beginning to worry about a replacement. Anyway, good luck with the replacements. I'm going to do some research on these new Primacy MXV4s, and will post what I find.

[JimboK]

<div class='quotetop'>QUOTE(ekpolk @ Jul 7 2007, 04:25 PM) [snapback]474744[/snapback]</div>

May be too late for you, but I just discovered that Michelin now has released a new model, the "Primacy MXV4". Per TireRAck info, it appears to have the same tread pattern as the discontinued Energy MXV4+. Unfortunately, the model is brand new and the info at TR says zip about LRR. I love my MXV4+s and they have plenty of life left, but I was beginning to worry about a replacement. Anyway, good luck with the replacements. I'm going to do some research on these new Primacy MXV4s, and will post what I find.
[/b]

Yeah, you're right, it's too late. But thanks anyway.

After the Energy MXV4+ was discontinued, a couple of the Continentals caught my attention, the Conti PremierContact in particular. Though overall it scored in the middle of the pack in the CR review from November, it scored high in both tread life and rolling resistance. Unfortunately, no local tire dealers stocked them. Many offered to order them when I called around yesterday, but I couldn't ride around on the donut spare until they came in. So I went with Hydroedges. Any port in a storm.