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CapriRacer · 03-20-2018, 12:31 AM

So let me talk about the charts on my web site.

First, the charts are from a presentation made in Dec 2007 by Bruce Lambilotte of Smithers to the California Energy Commission as a result of the CEC commissioning the study. They were trying to write a regulation and needed the data to do so. I just happen to stumble on the presentation.

Unfortunately the data said the CEC wasn't going to be able to write a regulation based on that data.

(And just an FYI, shortly after that time frame, NHTSA came forward and said they would write a regulation for the entire country, so the CEC decided to wait and see. There's a long story here, but the short version is that NHTSA is due to publish one in Aug 2018.)

OK, back to the charts.

If you'll read the whole web page carefully, you will notice that I thought there might be OE tires in the mix - and for those who don't know, OE tires are designed to the specs published by the vehicle manufacturer, and typically, those tires are designed for better RR than replacement market tires. I couldn't detect any obvious ones, but that doesn't mean they aren't there.

So if you see a tire that seems to have a lower RRC value, it just might be an OE tire.

The other source of anomalous data is that not every tire is in exact proportion to one in a different size. It wasn't stated in the presentation that any effort was made to pick a tire line that was as free as possible from production compromises. If I were doing the study, I would have worked very closely with a tire manufacturer to select a tire line that didn't have unusual design and production compromises that would affect RR. Let me give you an example of such:

Tramlining - aka groove wander - is where a tire tries to follow the grooves cut into pavement to drain water off the road surface and prevent hydroplaning. So the grooves in a tire must NOT line up with grooves in the pavement.

That's a problem because there is no standard for the spacing of the pavement grooves - so by trial and error, every tire manufacturer has a list of what spacing does not work, and then designs the grooves in their tires to NOT be those.

That means that what would work for - say - a 175mm cross section, might not work for a 185mm cross section, and the overall amount of tread rubber might not be proportional and, therefore, the RRC would not line up where it is supposed to.

There are other things that could cause the data not to exactly match up where it should, but I think you get the idea. Just for reference, when I did the regression I got an R squared value of 0.66 - which is not very good. There seems to be a lot going on in this study and it would be great if we could find more data from another source with a better R squared value.

03-20-2018, 12:31 AM	#50 (permalink)
CapriRacer Tire Geek Join Date: May 2008 Location: Let's just say I'm in the US Posts: 796 Thanks: 4 Thanked 393 Times in 240 Posts	So let me talk about the charts on my web site. First, the charts are from a presentation made in Dec 2007 by Bruce Lambilotte of Smithers to the California Energy Commission as a result of the CEC commissioning the study. They were trying to write a regulation and needed the data to do so. I just happen to stumble on the presentation. Unfortunately the data said the CEC wasn't going to be able to write a regulation based on that data. (And just an FYI, shortly after that time frame, NHTSA came forward and said they would write a regulation for the entire country, so the CEC decided to wait and see. There's a long story here, but the short version is that NHTSA is due to publish one in Aug 2018.) OK, back to the charts. If you'll read the whole web page carefully, you will notice that I thought there might be OE tires in the mix - and for those who don't know, OE tires are designed to the specs published by the vehicle manufacturer, and typically, those tires are designed for better RR than replacement market tires. I couldn't detect any obvious ones, but that doesn't mean they aren't there. So if you see a tire that seems to have a lower RRC value, it just might be an OE tire. The other source of anomalous data is that not every tire is in exact proportion to one in a different size. It wasn't stated in the presentation that any effort was made to pick a tire line that was as free as possible from production compromises. If I were doing the study, I would have worked very closely with a tire manufacturer to select a tire line that didn't have unusual design and production compromises that would affect RR. Let me give you an example of such: Tramlining - aka groove wander - is where a tire tries to follow the grooves cut into pavement to drain water off the road surface and prevent hydroplaning. So the grooves in a tire must NOT line up with grooves in the pavement. That's a problem because there is no standard for the spacing of the pavement grooves - so by trial and error, every tire manufacturer has a list of what spacing does not work, and then designs the grooves in their tires to NOT be those. That means that what would work for - say - a 175mm cross section, might not work for a 185mm cross section, and the overall amount of tread rubber might not be proportional and, therefore, the RRC would not line up where it is supposed to. There are other things that could cause the data not to exactly match up where it should, but I think you get the idea. Just for reference, when I did the regression I got an R squared value of 0.66 - which is not very good. There seems to be a lot going on in this study and it would be great if we could find more data from another source with a better R squared value. __________________ CapriRacer Visit my website: www.BarrysTireTech.com New Content every month!