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Old 01-05-2011, 11:30 PM   #67 (permalink)
roflwaffle
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Quote:
Originally Posted by CapriRacer View Post
I don't have a specific link - and I know there are different techniques. I would suggest you look up the SAE procedures. I'm reasonably sure those procedures outline factoring out the bearing loss. Just be aware that they may not specifically delineate what part of the procedure is correction factors and which parts are actual testing.



Actually I do. The important factors in rolling resistance are deflection, the amount of material being deflected, and the properties of the material being deflected.

The load tables are based on the same amount of deflection, so regardless of the tire size, I have a pretty good handle on the deflection.

When it comes to the 2 materials questions - amount and properties - there wouldn't be any fundamental differences that would depend on size. While it is true that as the tire size increases the amount of ply cord increases, those increases also occur within the data range. Plus, there is nothing peculiar that happens in the design of a tire that would distinguish one tire from another that would cause a break in the logic.

The only one that comes to mind is the change from a single ply to a 2 ply - and that change is also included within the data range.

In the end, it becomes extremely important to use the same make and model to assure that the construction is consistent with the tires selected for testing. That is probably where the data set is the weakest. I know there are OE tires in that mix - and I think that accounts for low r[sup]2[/sup] value.



I disagree



Actually the author didn't highlight ANY conclusions regarding the affect tire size has on RR - and that makes sense given the context. He was contracted by the CEC to get data to help write regulations. As I explained before the tid bit we are discussing was not important for writing regulations. What was important was that there was a difference - and that would complicate writing a regulation.



Again, I disagree



We have traversed this territory before. I understand your reservations about drawing conclusions on a limited amount of data. I have pointed this out in other situations where I have been on your side of the fence, so I appreciate your sentiment.

Perhaps the best way to say this is: Based on the Smithers data, Bigger is Better.

And unless there are new thoughts, I'm going to discontinue commenting on this as we seem to rehashing the same points.

Arg, the quote sniping! *No!!!!!!11!!!1!

Um, lesse, starting from the back and going forward, saying it's based on the Smithers data isn't inaccurate, but it would be better IMO to describe what the Smithers data entailed so that someone could get a good idea what exactly the data set was restricted to.

The author didn't come to any conclusions, while you did, which is different AFAIK. I mean, if I say some data set points to some trend, and someone else says the data set doesn't point to any trends, then those are differing conclusions given the same data.

You can disagree with the author about whether the data indicates anything or me about whether or not the sample size is too small to draw any conclusions about all the different tire sizes/models from different manufacturers made over different years, but in order to do so in a logical fashion you need to support your case with evidence by saying that all tires are made with so and so manufacturing process and all use a type of construction and compound where whatever values are going to be restricted such that the variation between them is not going to be large enough to throw off your assumption that larger tires = less Crr or whatever. For instance you mentioned the important factors, so provide data on the materials used indicating how that doesn't change a whole lot, how deflection is quantified, and so on. At least if you want to provide a logical/scientific statement. If you qualify your statement by saying it's your opinion then you really don't need anything else to satisfy most statements.



*It's considered kind of a pain because breaking something up into little chunks can loose context, and especially on boards that don't nest quotes because then the person responding has to go back and forth between the reply and the thread to figure out what they were quoted on as opposed to just discussing the different things in one big chunk.
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