Ernie,
First, you need to understand that the language that ANYONE who makes a product speaks is SALES. Speak to them in that language and they will not only pay attention, but the pressures of competition will COMPEL them to take action. But this pressure has not been brought to bear. Here’s an example:
http://www.greenseal.org/resources/r...resistance.pdf
On page 5, that report highlighted the fact that a Bridgestone B381 has an extremely low RRC – over 20% better than the next best tire. This was in March of 2003. You’d think this tire would sell like umbrellas in a rainstorm – and, of course, that Bridgestone will see this and react accordingly. But even though plenty of time has passed, this information has not translated into a whole line of tires with the same properties.
WHY NOT??
Look up this tire on Tire Rack. The average rating for this tire is 6.06 (out of a possible 10).
If you compare that to the average rating of other all season tires in the survey, this tire would be 15th out of 21 – if it had made the list. A pretty poor showing! (This tire doesn’t actually show up on the survey result – AND – the average rating isn’t published as part of the summary – I had to do the math myself.)
The only conclusion I can come up with is that fuel economy doesn’t sell tires. This is consistent with what I’ve heard about what consumers want in a tire. So there is no competitive reason to publish the results of RRC. In other words, why should a tire manufacturer go to all the effort (and expense) of testing a tire for RR when it doesn’t translate into sales?
But I’m a technical guy – and my expertise is not in marketing and sales.
- AND –
The reason I spend so much time posting on the ‘net is to try to educate people on tires and how they work. You’ve asked a very good question:
Quote:
Originally Posted by Ernie Rogers
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--I get the feeling at times that the tire engineers themselves don't understand rolling resistance. If they get inconsistent results in different tire sizes, it just means they aren't controlling the right variables. If they will publish the results, we can help them with the problem.
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OK, that’s more of a statement.
The problem isn’t consistent results or controlling the right variables. We’ve been at this for over 30 years and we can consistently get repeatable results – except that there is a problem that is best explained by looking at page 31 of this:
http://www.energy.ca.gov/transportat...%20Testing.pdf
Page 31 is the RRC for a range of sizes, but they are all the same tire line. Bruce Lambillotte has paraded different versions of this data around the tire industry and one time he revealed that the tire line is Goodyear Integrity.
This is the problem you alluded to. There is a 30% variance best to worse for the same tire albeit in different sizes. The test is a standard RR test using standard conditions – all tied to the same load table. This is as consistent testing conditions as can be made.
For background, Smithers is a well respected tire testing company. They do work for tire manufacturers, car manufacturers, etc. They know what they are doing and they deliver good results. This data is consistent with what various tire manufacturers have reported with regard to tire size. In other words, an independent lab, contracted by the California Energy Commission (someone who doesn’t have a “dog in the fight”) reports that tire size is a factor in RRC, even though the tires are otherwise the same.
Starting on page 32, Bruce analyzed various factors to see if he could develop some sort of correlation – with the idea that this would lead to an easy way to characterize a tire line. The best correlation was 86% for load carrying capacity. I should point out that statisticians like to see at least a 95% correlation to feel comfortable that they are mathematically describing a phenomenon.
This, in essence, is the problem confronting anyone who tries to deal with RR when comparing tires of different sizes.
Quote:
Originally Posted by tasdrouille
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I mean measuring RRC is not rocket science. I don't see why they can't come up with standardized test equipment giving repeatable results. Every manufacturer gets the same test bench and make their own measurements and publicize the results.
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The problem ISN’T test equipment or repeatable results. The problem is describing the effect tire size has on RR. If this isn’t overcome, then the tire manufacturers are going to have to test every tire they make in every size they make – and they don’t want to do that. Plus, as I said before, there isn’t enough testing capacity to get this done in a reasonable timeframe.
But this brings me back to the first part of my post. Unless there is an easy to use method to compare tires, then the average consumer is just going to ignore it – which is pretty much what he is doing now.
Today
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