Looking forward to the results from this one!!
Yes, I do know about the casing tension, yet I am saying that testing at the same casing tension instead of the same pressure is wrong. Casing tension basically acts as a limitation what pressure range given tire can use. Wide tires becomes too hard at high pressures and narrow tires bottoms out at lower pressures. Yet nobody rides at those extremes, simply because in a typical race you have multiple surfaces from hard to very loose and you have to find some compromise thatās acceptable everywhere. So you get lets say 25 to 35 psi usable pressure range. And if at every pressure in this range 50 mm tire has lower rolling resistance than 40 mm tire, it means that this is a faster tire. And comparisons at the same casing tension simply misleads.
You make some valid points, but the main reason to do the testing is to find which tire is absolutely faster. Not which tire is faster at the pressure when they feel the same. And to find faster tire we need to test them at the same pressure, and not at the same casing tension. Testing tires at the same casing tension simply leads to wrong conclusions. Iām attaching the picture with some real life test results of gravel tires at different pressures. It sparked a lot of discussions when it was posted - many people claimed, that the test is wrong, because it should have tested those tires at the same casing tension - 35 psi for 40 mm and 25 psi for 50 mm. But why should we use 35 psi for 40 mm, if it is faster at 25 psi? As we can see, the best result for both tires came at the same pressure, and not at the same casing tension. So this is what we should do in order to get some useful results. And if you have some testing results what proves otherwise - please share them.
That doesnāt make sense because one of the main advantages of running a wider tire is to run lower pressures. So why would you test at 35 psi for both a 40mm and 50mm tire when you would never run the 50mm tire at 35 psi?
This is evidenced by the fact that the greatest time savings is with the 25psi 50mm tire vs. 35psi 40mm tire (which, while closer to reality directionally, is still likely too high in pressure for both widths.)
Maybe this is just meā¦ and while I have done my share of lab work back in the day, I donāt see any evidence from a graph / data like this showing that one tire or pressure is better than the other as it seems to fall within the margin of error.
Funny enough, I have been doing my own UNscientific testing on a 15k-ish gravel loop that I use for tempo stuff. Currently despite swapping between two different gravel bikes, two wheel sets and two different tire widths, there just is such a minimal difference that FOR ME it falls in the āit doesnāt matterā category. Like I said, there is just no way to control the limitless variables but the fact that two bikes, two wheel sets and two different tires all fall within 5 seconds of each other over a 15k loop (over a 3 month period) is interesting in itself. But the data collection continues!
It wasnāt a very good test, just rolldown. Too fast or too slow, take your pick. Maybe not even on the same day(s)?
This is before the potential issues with tire construction. We donāt know.
As pack fodder, Iām not as worried about saving an extra couple watts (though itās nice, or course), but what I find so useful about findings like this is that it mostly winds up meaning we have more flexibility.
Thereās a ton of rough, chunky gravel where I live, so itās good to know I can ride a nice fat tire for better comfort and control without actually sacrificing any speed. Another rider who maybe values something lighter that feels quicker can do that and feel just fine about their choice, too. It seems like a bit of a relief that most of us can just run what we prefer.
Definitely! Thinking about itā¦ I guess what it ultimately shows is thereās no penalty (off road) for going wider. So why not?
I sacrificed 15 minutes of my time so you donāt have to. Donāt bother watching this. You are welcome.
General rule of thumb - any video done by legacy media doing any sort of testing is not worth your time.
Bike Radar, Cycling Weekly, Road.CC, whateverā¦ā¦pretty much all crap.
GCN just did a video podcast arguing that the optimal road tire size is 28 if you want comfort and 25 if you want speed (or something close to this). This, despite the beat road teams in the world currently running tire setups measuring 31-32mmā¦
Thatās what Swisside said, they are quoting them (JP).
They do believe in the optimal size being 25 to 28 mm as they are running the 26 and 29 mm aero 111 tyres on the front of the AG2R team. They have also said there is a 6 watt penalty at wind tunnel speeds going to the 29 mm 111 aero tyre on their wheels from the 26 mm version.
Well thatās interesting
Maybe beat combo is 26 aero tire front and 32 rear?
Those numbers are just the wind tunnel numbersā¦.they donāt factor in Crr.
If you listen to one of Ronanās Performance Process pods, he specifically addresses this issue when they talk about the old Bontrager aero tire. It tested great in the wind tunnel and were clearly āfasterā than any other tire. Problem was that it was a dog of a tire when it came to Crr and was actually very slow.
Soā¦.wait for itā¦ā¦.it depends. 
I know, thatās why I said 6 watt penalty at the wind tunnel. The rolling resistance data is available for both elsewhere (brr have tested both). The faster you are and the smoother the roads, the narrower the tyre can be. Other factors like comfort, grip and rider weight also help decide what size.
I think most recreational riders can use wider tyres with little penalty (aero and weight). If only tyres were cheaper Iād experiment a lot more.
That was not my takeaway from that video. I felt like they said: āit dependsā! 25 mm was for TTs on good road surfaces, which totally makes sense. Current standard in the World Tour is 28-30 mm for road races, which seems appropriate to me. Also, they did not even address rim design and tire combination, which is very important for aero. Best aerodynamics happen with a rim specifically designed for a certain tire width. At World Tour speeds, aero matters more than it does for regular humans as well, a lot more, as the speeds are so much higher than normal humans ride at, and aero penalties add up exponentially as speed goes up. For sure, if one can ride at 30 MPH for four hours, one might want to prioritize aero gains. And then, if you live in the mountains, a nice 30 mm tire sure can descend fast (and safely) considering braking and cornering.
Wait a minuteā¦ this thread is about tires for gravel racingā¦ sure hope my Thunderburt, 2.1, Super Race tires show up someday for testing (on B/O). Anybody know where some might be in stock?
Three new/updated gravel tires from Specialized just postedā¦ including some 50mm optionsā¦
Updated Pathfinder, Terra TLR, and Tracer TLR. Also a relevant 2.2 āAirTrakā MTB tire.
https://www.specialized.com/us/en/shop/cycling-gear/bike-parts/bike-tires
Why do they run the slow 60tpi casing?
The all-new Pathfinder TLR is 19% faster, 25g lighter, and 30% more cut-resistant than its predecessor, making the winningest gravel tire even better. Its fast-rolling tread and high-speed center T2 compound ensure top straight-line velocity, while the grippier T5 compound on the shoulder knobs enhances cornering traction. The strong, fast-rolling TLR casing delivers rapid acceleration and top climbing performance while preventing flats. For sheer speed, Pathfinder is the ultimate choice.
Was hoping for a 50 mm pathfinder. Hopefully the other 50 mm tyres test well.
The new sizeways, on paper, are a disaster for my fleet. Iām running Pathfinder Pros on 3 different bikes and 38/42/47 worked a lot better than 35/40/45/(50mm Tracer) will.
Now the sizes are both too big and too small. Probably there will be enough rim variance to have more crossover with the older sizes WAM but will have to wait and see.
Wish I would have stocked up on 47s, I might be the only guy in the world that had mine actually measure 47mm.