scottfsmith

While that site has lots of data, you need to take it with a big grain of salt. They are all drum tests and it is well-known that drum and road while related are not perfectly correlated. Roads are flat, drums are not. Road surfaces are also different than drum surfaces. Bumpy roads lead to vibration which leads to less efficient cyclist energy transfer and there is no cyclist in the equation at that website.

For example here is their comparison of the GP5000 at all different tire sizes. Their conclusion is there is not much overall difference if you use recommended pressures.

But, in actual on-road studies the wider tires do better. For example, FLO Cycling has the below graph buried in one of their blog posts.



The 32mm tires are clear winners in a test on a road with a bike. Read the post for more details on the test. Note that FLO is a wheel company, not a tire company, they have no skin in this game.

What I would like to see is this kind of data extended out to 35 and 40mm tires, e.g. for the GK slick series.