Hello, CapriRacer,
Sorry to give you such a bad time-- you apparently work in the tire industry?
Your story agrees quite well with what I was told five years ago, except the other engineers were a little more frank--but that was five years ago.
It makes sense that the tire makers would want to be cooperative. They would rather set up their own system, rather than a government-imposed one. But, the evidence is TOO plain to miss.
All this time has gone by, but I know of no coefficient published by any tire maker, NOT ONE.
We know that data are being withheld. It's time to get off the dime and be honest with the customers.
Ernie Rogers
An afterthought that may offend you even more-- 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. /Ernie
Quote:
Originally Posted by CapriRacer
Ernie,
I have no idea why you were told this, but it is not true.
The reason tire manufacturers do not give out RR data is:
1) There is no agreed upon test procedure. There are at least 4 methods that I know of and they give different numerical values - although the rank order remains the same.
This is one of the issues troubling the California Energy Commission (CEC) when they try to come up with a regulation. The test results from different sources has to be the same.
2) Different test facilities given different results. This has been looked at and it is apparent that the test facilities can be correlated - however, the "base" facility (the one everyone else has to correlate to) has to be identified and a correlation procedure developed.
It has been suggested by NHTSA (National Highway and Traffic Safety Administration) that the Federal government (NHTSA) be the regulating body rather than have 50 different regulations - and their suggestion is to use a common tire for the correlation, so every tire tested would be a percentage of that - and their preference is the SRTT (Standard Reference Test Tire) Unfortunately, this doesn't address the tire size issue.
3) RR varies by tire size. Very early in the process, the CEC was confronted with the paradox that identical tires gave different results depending on tire size - with large tires giving smaller coefficients.
This might result in "one-off" tires that are used to characterize the entire tire line. However, if it were regulated that EVERY tire size / design combination were to be tested, it would occupy EVERY test facility in the world for over a year. In other words, no new development could take place.
So, NO, the tire manufacturers DO NOT know the RR of every tire they make.
The RMA (Rubber Manufacturers Association) has not only been cooperating with both NHTSA and the CEC to come up with a workable regulation, but they've also encouraging the regulators to understand the issues involved and overcome them. The tire manufacturers - through the RMA wants something that makes sense, is usable, and consumer friendly, and not too expensive. Thus far, it has been difficult to find concensus among the various stakeholders.
Nevertheless, it is just plain wrong to characterize the RMA as "gagging" the tire manufacturers. They ARE the tire manufacturers!! and they are trying to find a way to make it work.
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