Quote:
Originally Posted by CapriRacer
Which is why I did a regression analysis based on the 3 "size" numbers for RRC. What was interesting was the r squared value was pretty low - indicating there was something else going on. I actually did quite a few before I settled on that one.
Nevertheless, in every case, the regression said that bigger was better - and I think I understand why that is so. There must be some amount of variability EVEN though the tires are supposed to be "the same". "The Same" is kind of a misnomer in that the construction for each size MUST be different - but they ought to be proportional - and it appears they aren't.
I wish we had more data to work with.
|
Here is my assessment and some conclusions, based on my chart.
1. I think the problem is too complex for simple linear regression, there being five variables involved. Four are shown on my chart (rim diameter, tire width, tire profile, and the dependent variable - rolling force). The fifth variable is the unknown effect of any differing tire construction. A parametric chart lays out the relationships quite clearly.
2. I suspect that two data points were misrecorded during the test or in subsequent data handling. I think the two data points for the blue (14" rim) 195 width line got reversed. If so, correcting that makes that line agree with the others. The blue point for 185 width is also suspiciously low compared to the other two points on that line and the other lines on the chart. But these are all just suspicions. I haven't seen actual data, and took numbers for my chart off of Lambillotte's bar chart (his slide 30).
3. As you said, more data would be better. Nonetheless, there is clear consistency in my chart of the data in Lambillotte's bar chart (when disregarding the above questionable data):
** Rolling force increases with tire width (i.e. within each rim diameter category).
** Rolling force increases with tire profile(i.e. within each rim diameter category).
** With the exception of the two 16" rim tire sizes (different tire construction for these?), rolling force increases with rim diameter.
** Those 155 and 175 tires on 13" rims seem like the gold standard, for applications where they will work. 175-65-14 and 175-70-14 also quite good.
These conclusions are mostly opposite of information/assumptions I have seen posted on this forum and elsewhere. (So maybe this should be a separate topic somewhere in this forum.)