JB.
New member
Been on the forum less, lately, so I thought I'd put this up before I forget about it.
I've mentioned here a few times that I think the CR tests are about the only reliable method of establishing tire performance. I've never, for instance, seen any reason to believe that the Tire Rack surveys have any value beyond enabling people to pull the trigger on a tire purchase (a legitimate function -- just not the one most people think they are getting). I see no way the combination of high rates of error -- measurement error (tire evaluation) and sampling error (self-selected) -- could produce anything valuable from the perspective of establishing a decent approximation of true performance.
Anyway, it wasn't CR, per say, that I supported; just the notion that competent, objective physical testing was the only organized activity that had a chance to be useful, especially compared to the alternatives.
Well, at least as it concerns me, CR shot itself in the foot with the publishing of its latest tire tests. Right off the bat I was annoyed that the old tests went away when the new ones came online, but I had saved the old ones so no worry. I put them side by side and a comparison between the two resulted in enough contradiction that I was eventually moved to seek the counsel of tire engineer Barry Smith. The formatting of my question on the allexperts site got messed up so I put it in green, below, but I want to support the site so you'll have to click here if you want to read the full answer.
Summary of Answer: On-vehicle tire testing is problematic under any circumstances and CR has never done anything to inspire confidence that they have a good handle on it. Same category tires are grouped pretty closely in individual parameters so test variability plays a large role in how tires get ranked.
"Question: I'm wondering how common it is for manufactures to make significant tread compound changes to otherwise identical tires -- that is, same model and what appears on pretty close inspection to be the same tread pattern (including siping amount, shape, etc).
I ask because I'm trying to understand the tire ranking changes in the new Consumer Reports of 6 AT tires (out of 15) that were previously tested 3 years ago and appear to be unchanged. I could understand the entire new list being graded on a curve to avoid the difficulties of trying to precisely duplicate past test conditions, but that wouldn't explain the 6 tires as they have been realigned relative to each other. Among the 6, there were two instances (separate tires) of a 2-notch ranking drop in objective traction categories, so imprecise data that drifted over the edges of ranking assignments wouldn't seem to work as an explanation either. I looked for a trend based on improved rolling resistance but, ironically, that column was the least affected. Two attributes which saw a lot of change - all for the worse - were wet braking and snow traction. None of this seems to follow any pattern including making much sense via the triangle of tire design (thank you). But focusing only on the 6 tire relative realignment, something that would explain it is finding out that tread compound changes are not uncommon in otherwise unchanged tires.
And since we're on the subject, how reliable do you personally consider the CR tire tests to be?"
So - I'm glad I asked. Always enjoy getting a clearer picture of where signal and noise are to be found. When tire shopping, I'll continue to stick with basics as the best way to avoid introducing noise -- even when on-vehicle test results are available. I'm perfectly happy shopping for tires based on obvious and objective parameters that fit my use, while at the same time enjoying the luxury of feeling no anxiety at the prospect of missing out on a tire reputed to be "awesome" or getting stuck with one that's "crap".
I've mentioned here a few times that I think the CR tests are about the only reliable method of establishing tire performance. I've never, for instance, seen any reason to believe that the Tire Rack surveys have any value beyond enabling people to pull the trigger on a tire purchase (a legitimate function -- just not the one most people think they are getting). I see no way the combination of high rates of error -- measurement error (tire evaluation) and sampling error (self-selected) -- could produce anything valuable from the perspective of establishing a decent approximation of true performance.
Anyway, it wasn't CR, per say, that I supported; just the notion that competent, objective physical testing was the only organized activity that had a chance to be useful, especially compared to the alternatives.
Well, at least as it concerns me, CR shot itself in the foot with the publishing of its latest tire tests. Right off the bat I was annoyed that the old tests went away when the new ones came online, but I had saved the old ones so no worry. I put them side by side and a comparison between the two resulted in enough contradiction that I was eventually moved to seek the counsel of tire engineer Barry Smith. The formatting of my question on the allexperts site got messed up so I put it in green, below, but I want to support the site so you'll have to click here if you want to read the full answer.
Summary of Answer: On-vehicle tire testing is problematic under any circumstances and CR has never done anything to inspire confidence that they have a good handle on it. Same category tires are grouped pretty closely in individual parameters so test variability plays a large role in how tires get ranked.
"Question: I'm wondering how common it is for manufactures to make significant tread compound changes to otherwise identical tires -- that is, same model and what appears on pretty close inspection to be the same tread pattern (including siping amount, shape, etc).
I ask because I'm trying to understand the tire ranking changes in the new Consumer Reports of 6 AT tires (out of 15) that were previously tested 3 years ago and appear to be unchanged. I could understand the entire new list being graded on a curve to avoid the difficulties of trying to precisely duplicate past test conditions, but that wouldn't explain the 6 tires as they have been realigned relative to each other. Among the 6, there were two instances (separate tires) of a 2-notch ranking drop in objective traction categories, so imprecise data that drifted over the edges of ranking assignments wouldn't seem to work as an explanation either. I looked for a trend based on improved rolling resistance but, ironically, that column was the least affected. Two attributes which saw a lot of change - all for the worse - were wet braking and snow traction. None of this seems to follow any pattern including making much sense via the triangle of tire design (thank you). But focusing only on the 6 tire relative realignment, something that would explain it is finding out that tread compound changes are not uncommon in otherwise unchanged tires.
And since we're on the subject, how reliable do you personally consider the CR tire tests to be?"
So - I'm glad I asked. Always enjoy getting a clearer picture of where signal and noise are to be found. When tire shopping, I'll continue to stick with basics as the best way to avoid introducing noise -- even when on-vehicle test results are available. I'm perfectly happy shopping for tires based on obvious and objective parameters that fit my use, while at the same time enjoying the luxury of feeling no anxiety at the prospect of missing out on a tire reputed to be "awesome" or getting stuck with one that's "crap".
