I applied a 1.5x factor to try to get a ballpark number for resistance on a smooth road, but I suspect most of us will experience even higher drag. I'm not sure though if an X factor would be more appropriate or an offset. For comparison purposes, 1.5x is probably decent.
I'm planning to do some testing in hot and cold environments, because I'm curious about the temperature effect. Just from these tests I could tell that the tire resistance would drop substantially as the tire warmed up from 65 to ~90F.
After I was done, I thought the Maxxis Radiale might have been been unfairly penalized from being squashed on a single 3 inch diameter roller, so some day I'll try it with two rollers and maybe a higher pressure to see if there is a substantial difference. I know this tire sucks though based on my speed while riding it on the road. I wasn't something I could really "feel" but my speed data after the fact indicated that something weird was going on.
Which brings up another interesting point... you can't really tell what the rolling resistance of a tire is by fondling it, weighing it, or riding it... or judging by price or what the ads say.
Maxxis Radiale 22 Wow. Now I know why my rides were always so slow with these on. They have a smooth ride and corner nice though. Big tread lip transition… probably the least aero tire as well. And the most expensive. Very small casing.
Deda Tre HST 23 I was hoping for this one to do well. It's very light, supple, and smooth. But resistance is very high.
Vittoria Rubino Pro 23 A relatively inexpensive tire that has a nice ride, and would be suitable for training. Small tire though for a 23… might want to opt for the 25.
Schwalbe Ultremo ZX 23 The durability, tread life, and price of a full racing tire… but lacking the speed. Nice large round profile, light, and feels nice, though.
Michelin Pro4 Race SC 23 I was hoping that this tire would be at least as good as the GP4000. But it's slower, as well as being more puncture prone and shorter lived.
Continental GP4000S 23 A little more resistance than the best tires, but represents a big improvement in durability and longevity.
Continental GP Supersonic 20 Good fast TT tire if you are using narrow rims.
Vittoria Evo Corsa CX 23 Probably not very aero with the large round shape, tread pattern, and tread lip, but good Crr as expected.
Vittoria Evo Triathlon 22 If you like "open tubulars" this is a good one to go for. Nice smooth shape except for the lip where the glued-on tread meets the sidewall.
Continental Attack 22 Performed surprisingly well. Might be a better than average sample, since it is lighter than a newer one I have (which I'll test as soon as it's broken in). Construction is similar to the Supersonic, but this tire has an anti-puncture belt.
Continental GP Supersonic 23 Did very well, as expected. Smooth tire; should have good aerodynamics. No anti-puncture belt, and very thin tread, but are not as prone to puncture or damage as you might think.
BTW... any way to get the image to display full size?