The finding of 37mm marathon's being lowest rolling resistance is an interesting one. However I wonder whether the relatively good performance of the marathon line is a bit of a fluke. The greenguard and also the thicker smart guard is partly latex which has lower impedance than butyl or straight up tire casing. Even the people at BRR suspected that said (partly) latex belt worked in some effect to reduce rolling resistance as it's a piece of flexible material between the tread and the inner casing. It could work as a tiny piece of suspension that showed up in drum tests.

How that strip shows up for a rider however, is a different story. I use marathons, marathon plusses and marathon winter plusses when needs call for them. But in my mind marathons at least are slower than the test numbers would indicate. I'm fairly sure the winter hasn't been tested and I'm not sure about the marathon plus. The super stiff sidewall doesn't flex much at all which means that the rider experiences a lot more chatter and bumps than one would with a suppler tire.

The mondial is a super slow tire on a drum test, but it does have pretty flexible sidewalls. It's in my mind not really a slow tire either.

I can't imagine that they would want to run a studded tire on their testing equipment. I was unaware that they made a Winter Plus version, that would be exceptionally slow.

Marathon green guard has lower rolling and puncture resistance. The Plus is slightly more puncture resistant. The Plus Tour even more. But the more puncture resistant, the more rolling resistance. Choice depends on preferences.

For me, the more interesting bit is the relationship between pressure and rolling resistance. I used to keep mine at 40 psi (too lazy to pump at 50+ . I've ordered an electric pump
​​​​​

Yeah it is not a fast tire. Serves a purpose though.

You might want to rethink that idea. As mentioned before, drum tests only paint you half the picture. On a drum the rolling resistance will continue to reduce as pressure increases. In the real world though once the tire has a bike and rider there is a break point. When you reach high enough of a pressure the rolling resistance will begin increasing rapidly. As in it's better to be severely under pressured rather than even a little bit over pressured.

https://silca.cc/blogs/silca/part-4b...-and-impedance

Interesting data. Not clear how it translates to 50mm@50psi, though. The break points in their data occurs at much higher pressures, where the tire cannot absorb bumps in the road.

I may try to experiment this fall. Long path which is a mix of excellent tarmac and gravel. If I can get my power meter to work again, I'll report.

Thanks for the link. Interesting. But, they were clearly riding rock hard tires to get to the point where increasing pressure increases effective resistance. Riding an unladen bike (not touring weight), I do not think I ever get over 80 psi, I do 80 psi on the rear wheel of my road bike with 28mm tires, wider tires get less.

I did the super hard tires thing decades ago with tubular tires, but I can't remember when the last time was that I rode such tires. I am sure it is over two decades ago.

Keep in mind that the tire used in their test is 25mm. The break point applies to all tires but the pressure at which the break point occurs differs between widths. A 50mm tire at 50 psi is going to be some seriously rough riding. I think I had my 40mm tires at 50psi fully loaded on tarmac and I'm no featherweight. On gravel I went a lot lower.

What I find to be the most interesting data point was the roughened concrete curve. It's clear that with 25mm tires there really isn't a pressure where you'd even get below the break point before you arrive at pinch flat territory.
It would be interesting to see that same test with wider tires etc. Even the lowest rolling resistances they got weren't actually that low. You'd expect a much better result from a GP4000 than 43W.

There are no potholes in Bavaria. Potholes are not a known concept here. I entered Bavaria via Lake Constance and exited today via Füssen, didn't see a single pothole the entire time. Same story in Baden-Württemberg where I was before Bavaria. Forget potholes, there are hardly even cracks on the roads here. Even single lane farm roads in southern Germany are smoother than the road in front of the freaking White House. I don't know what else to say other than that the German government clearly has a much higher road budget than America. But we all already knew that right? They are famous for their country's immaculate driving experience.

I'm fully on board with the idea that wider tires will indeed smooth out bumps. But what bumps? The wide tire has nothing to smooth if there are literally zero bumps in existence.

Adapt you tire width choice to the conditions of your chosen touring route, that's all I'm saying. If you're touring in an area that has bumpy roads, wide tires are a great idea. And don't forget to consider the entire route. I could tour on 28s in Germany, but 28s wouldn't be wide enough when I get to the Balkans next month, so I'm using 35s even if they are pointless in Germany, because I don't want to change my tires every two weeks.

The Germany example is a particularly exceptional one, I've noticed the same in Germany and in Europe generally, even the UK, the road surfaces are tons better than our roads here in my part of Canada.
As you say though, it's all about what you can expect and figuring out a good compromise -- and if you think you will be on gravel roads or trails or whatever sometimes, having wider in the range of 38-40mm is a good compromise for comfort and float with lower pressures , but a very little speed difference compared to a 32 or 35.

I've just put on some 38-40mm slicks on my touring bike and they are particularly light and well rolling tires, and compared to riding my commuter with regular Joe Blow Marathons 35mm, there's really no difference, but 40 compared to 35 does have a nicer ride over the real life paved road conditions I ride all the time.

I am born just at the shores of Lake Constance (Ueberlingen), in total I lived there around 30 years, in Baden-Württemberg and in Bayern. Yes, Germany has great roads. And yes, even on these perfect roads a 40mm tires offers more comfort than a 23mm tire. )