I learned a LOT about tires riding a recumbent over the last 10 years.
Rule #1 Narrow tires are not faster than wider tires (don't worry, I'll explain)
Rule #2 Higher pressure tires are generally faster than lower pressure tires, but not always!
Rule #3 Kevlar belted tires are slower than regular belted tires
There was a study performed on 20" tires for recumbents and they used everything from 28mm wide Schwalbe Stelvio and Continental tires at 100+ PSI to a 20x1.75 Tioga Comp Pool freestyle slick tire at 90 PSI. They would roll the recumbent down a hill and see how far it went until it fell over. The farthest roll off won. The tires were run multiple times with pressures from 70 to 130 PSI. The Tioga Comp Pool 20x1.75 won over all the skinny high pressure tires, it beat them at 90 PSI even with the Continentals at 130 PSI. The skinny 20" (406mm) tires were 28mm wide with the comp pool at 44mm wide. I was running a 32mm wide 115 PSI tire on the front of my bent so I bought a Comp Pool to see how it worked. It was faster, stuck through the corners better and gave a better ride at 90 PSI. I was surprised.
Weight has a huge effect on rolling resistance of tires. Run a 1 inch wide tire at 100 PSI with a hundred pounds on it, the contact patch will be round. Run a 3/4 inch wide tire with 100 pounds of pressure with 100 pounds on it and the contact patch becomes oval. That oval is a lot of sidewall flex to hold the weight so rolling resistance jumps way up. This is why those 19mm tires run 130 PSI, they need to hold the weight and not go oval. The Tioga won because it had the best casing being very supple, thin and flexible skinwall. Skinny tires are used for aerodynamics and on track bikes, generally 19mm wide on the front for aero and 23mm on the rear for rolling resistance improvement. The narrow tires are also lighter but for something to ponder, it is not a huge difference when the weight of everything is calculated.
Now take a mountain bike, throw on 50 pounds of batteries, motors etc, the weight of the bike and you have 80 pounds of weight. Throw a 180 pound rider on it, add helmet, clothes, water and parts/tools. Rolling down the road is 270 pounds of weight. If running a X5 hub motor, figure 150 pounds on the back and 120 pounds on the front. The back tire will have to run at least 75 pounds of pressure not to go oval and 60 PSI on the front if running traditional 2" wide tires. The beast I am designing will run 3" wide tires of the 24" flavor so the monster can run 45 PSI without oval for better speed and preventing pinch flats.
The funny part is how something that weighs as much as electric bikes do, no aerodynamics on them why someone would try to run 1.25" or 32mm wide tires on the things. The narrowest I would run with a 26" wheel is a 1.50 wide Schwalbe Marathon as it pumps to 100 PSI and will hold 150 pounds without going oval. My son's recumbent runs those tires and he loves them, says they "drift" well. No flats is what I am concerned with.
One of the conclusions they made why the Tioga won and not at the highest pressure they used (130 PSI) it was best at 100 I think. It had to do with the tire being too hard, the imperfect street surface would hammer the tire that it would'nt flex, but bounce. In real world riding on less than glass smooth surfaces, there was a limit to how high of pressure you could go to decrease rolling resistance. The difference between 90 to 110 PSI was very small but the difference in ride was huge...hard to be high performance with your teeth rattling. The testers preferred to run the Tioga Comp Pool at 70 PSI on the front and 90 PSI on the back as a good compromise but still be high performance.
Alas, Tioga changed the manufacturer of the tire and screwed it up. :O(
