1. Lab tests ≠ absolute truth. Not all tests are created equal. People in these forums have repeatedly made the claim that radial tires roll slower than bias ply tires, but the tests they've shared to back up these claims (example from Schwalbe's lab here) were performed on steel drums in a laboratory. Steel drums have been resoundingly proven to not be a reliable proxy for even smooth asphalt, let alone rough asphalt, gravel, or real world trail conditions.
If you have a link for rolling resistance tests that show radials demonstrating a higher rolling resistance than an equivalent bias ply tire, and these tests were not done on a smooth metal drum in a laboratory, I'm all ears. And please share them here so we can all see.
The Specialized video that @Bananamoon linked is exciting because Specialized tested radials and equivalent bias ply tires on non-smooth surfaces, and (according to the guy from Specialized in the video) their test results showed that bias ply tires were faster than radials on smooth steel drums, but radials were faster than equivalent bias ply tires on every other surface.
2. Bigger contact patch ≠ slower. The Specialized tests are just one data point, and they're coming from a manufacturer with an incentive to convince us customers that their cool new product is better and faster than their boring old product. More testing is still needed. But, if true, their results wouldn't be surprising to me, because Jan Heine from Bicycle Quarterly demonstrated a long time ago (the article quoted below is from 2015) that supple tire casings are faster rolling than stiffer tire casings, despite putting more rubber on the road, because tire friction on the ground isn't the main cause of rolling resistance in the real world: hysteretic losses and suspension losses are.
"To make a tire fast, you need to reduce both types of losses: the hysteretic losses from the deflection of the tire and the suspension losses from the vibrations of rider and bike. The key to this is a supple casing. The supple casing flexes more easily, which reduces the energy it absorbs as the tire rotates (hysteretic losses). By flexing easily, the tire also transmits fewer vibrations, which reduces the suspension losses. Thus, a supple tire reduces both types of losses, making this adjustment an extremely effective way to improve your bike’s performance and comfort at the same time."
3. Feels slower ≠ slower: Big, low pressure, supple tires on road and gravel bikes feel slower, even though they are demonstrably faster, which is part of the reason they were resisted for so long. Grand Tour bikes have seen their tires getting incrementally bigger year after year for the last 15 years, from 23mm up to 35mm in certain cases. Ditto for gravel racing, where the standard issue tire has crept up from a 35mm a decade ago all the way up to a 2.2" MTB tire now. Yes, big, low pressure, supple road and gravel tires put more rubber in contact with the road than a thinner, stiffer, or higher pressure tire, and yes you can hear the rubber on the road more, but that dimension of tire feel is not the largest contributor to rolling resistance. In fact, or highly dubious evolved monkey brains will often tell us that slower tires are in fact faster, because the higher frequency vibrations of a rougher tire on the road, gravel, or trail are associated in our monkey brains with speed. Pair that with the fact that a smoother bike will allow our senses to pick up on more stimuli, like the sound of our tires on the road, gravel, or trail, and the confirmation bias is complete. More vibration and less noise means I must be going faster! Now where else have I heard this argument before?
I'm not saying that radials have higher or lower rolling resistance than equivalent bias ply tires. I don't have a clue which one it is. I'm saying that we don't have access to convincing data at this time, and I'm not convinced by the arguments I've heard in favor of radial = higher rolling resistance.
It's interesting, I don't find the rolling resistance to be wildly different for trail riding. While standard casing tires feel more snappy, I would posit that...
It's interesting, I don't find the rolling resistance to be wildly different for trail riding. While standard casing tires feel more snappy, I would posit that it's really just a "feeling" because my times are similar given similar compounds, tread patterns, etc. Where I really notice it is on jump lines - I have to work quite a bit more to clear things with the radials vs standard casings. Could be a skill issue. 😄
My educated guess is any increased rolling resistance is partially offset by the ability of the tire to not be knocked off line. It's also helpful that you can run a firmer/faster compound and still get good compliance/damping. I think Schwalbe's marketing of the radials for more "natural" trails and the diagonal casing for everything else tracks.
That's interesting and makes perfect sense to me. When I ride machine built jump trails, I typically want to air up from my tire pressure for natural trails, otherwise I roll tires on berms and especially on hips where I'm turning off a lip. This effect is both slow and feels sketchy as hell, and when I pump up my tires I feel like I can pump more efficiently and put weight into the bike in more places.
Radials have less casing stability, which is their selling point but also their weakness, so I can imagine them being less stable on machine built jump trails (or any high G-force jump), worse for pumping, and potentially shedding speed.
That's interesting and makes perfect sense to me. When I ride machine built jump trails, I typically want to air up from my tire pressure for natural trails, otherwise I roll tires on berms and especially on hips where I'm turning off a lip. This effect is both slow and feels sketchy as hell, and when I pump up my tires I feel like I can pump more efficiently and put weight into the bike in more places.
Radials have less casing stability, which is their selling point but also their weakness, so I can imagine them being less stable on machine built jump trails (or any high G-force jump), worse for pumping, and potentially shedding speed.
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