What's not obvious to me, however, is what the results mean for real world riding. Does a stiffer stem make you measurably faster?
No in this case stiffer is not necessarily faster. However stiffer results in better feedback and tracking of the bike and generally a better handling bike. To be totally honest I doubt that the stem alone makes that much difference as well. However when you add up deflection from a stem, handlebar, steerer tube, frame etc... the differences can be quite dramatic.
Is there any reason why your tests don't include a single "knock-off" Chinese carbon stem? Of course, there is no inherent anti-bias against them on the tester's part! And there's certainly no conflict of interest in regard to any undisclosed relationship between an authorized dealer and the makers of some of the name-brand stems on test! Perish the thought! Right?
Yes there are plenty of reasons we didn't include any. Mainly because we don't support the counterfeit market, just the same as we don't support buying and selling of stolen bikes. I have no interest in validating what they do by including them in any of our testing.
As for biases, I never claimed to be unbiased in our reviews/tests, in fact I claim the opposite. Our reviews clearly have a section of "opinions" Obviously opinions are biased since it's based on what I like and dislike about each item. The testing and numbers section though is not biased, as the results are whatever they are.
So what you're really saying is the ultimate aim of these tests is to sell brands of stems (and bars) that the tester's employer stocks in their store!
Again, that's incorrect. Having been in business for over 40 years we have accounts with virtually every manufacturer in the industry. I can't think of a single brand of stem that isn't available to us. So no it's not to promote anyone over the other, as we can sell virtually any stem on the market. In fact we regularly choose to test things that we don't generally stock and when we feel items do well we may add them to our stock. So it does benefit us to test things that aren't our general stock items.