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Originally Posted by roflwaffle
Many people thought the world was flat! ........
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ROFLOL! Thanks for the chuckle.
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Originally Posted by roflwaffle
..........  It's probably true that, all things being equal, a wheel with a larger radius tire will have slightly less rolling resistance due to less bearing drag........... |
RR testing of tires is designed to test only the RR of the tire. In other words, the tests are designed to factor out bearing drag and other extraneous stuff.
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Originally Posted by roflwaffle
............ but there's no restriction that all things be equal in tire construction, so stating bigger = better is too broad a statement to make given the data. The safest thing to say would be that the tire w/ the lowest RRC is the best one in the context of rolling resistance.  ........ |
I'm not sure but I think you just said the best RR is obtained from the tire with the best RR. If true, that isn't really very helpful for the guy trying to figure out if changing tire size is going to have an effect.
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Originally Posted by roflwaffle
........It's a bit too general. It's true that for Goodyear Integrity tires, excluding most 16 inchers and all 17 inch tires, larger sizes tend to have better RRCs, but that's way more restricted than any statement you've made........
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Yes, the data does not include larger 16" and 17" - it would be nice if it did. However, this is all we have to work with. Since we don't have that data - and have no reason to believe that other tires - or tires in other sizes - behave any differently, this is the best guess we can make. Once we have more data, we can add that to the mix and see what we get. But for now - it seems to be true.
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Originally Posted by roflwaffle
......However for a regression analysis the sample needs to be representative of the population for the inference prediction. If a lot of 16" tires and all of the 17" tires are excluded, then you can't include those larger tires in any statement made, and you would be restricted to a statement about most Goodyear Integrity tires less than 16 inches. Science works because the people that draw conclusions also test those conclusions. You drew the conclusion that bigger = better, so in order for it to be scientific you would need to test it rigorously, not just cite data on one tire brand/type that excludes some of the larger sizes. Citing the data is sufficient for a hypothesis, essentially an educated WAG, but the scientific method is more than just a hypothesis.
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I can appreciate the skepticism, but I think you're being a bit harsh.
Let's take the example above: Roman wanted to know if changing from a 185/60R14 to a 155/80R13 was a good move. How can we answer that question? The data doesn't include a 185/60R14 in the data set.
Some would say that narrower is better - based on ???
But having the regression equation gives us a tool to at least attempt a reasonable answer. If you consider that Roman would have to buy wheels to make this changeover, then we can tell him that the differences are small and he would be further ahead - cost wise - to continue to use the 185/60R14 - and perhaps a move to a larger tire might be directionally better - larger meaning wider, higher aspect ratio - all based on real data.