Thanks. I see that rolling resistance is pretty insignificant on the charts.
Perhaps the biggest reason I bought a Radrunner was the EBR review, which persuaded me that modern technology would let me ride on fat tires at low pressure without much rolling resistance. The editor said he’d reduced pressure for comfort, but he didn’t say how much. The founder overloaded his bike with the editor on the back. He said he was running 18 psi.
Rolling resistance was terrible. The manual said instead that I must keep the tires inflated to the pressure on the sidewalls, no more, no less. At the time, only one tire would fit the Radrunner, but the manual didn’t state the pressure. Months later I finally found it, obscured by the reflective band: 30 psi.
The ride went from rough to rougher, but the tire was quieter and the rolling resistance was lower. Unfortunately, the tubes were porous. They were supposed to be butyl, which is cheaper than natural rubber, and butyl isn’t porous because it doesn’t contain substances that form bubbles in the mold. Something has changed.
Seepage would sneak up on me, which meant pressure was usually well below 30 psi. I tried to use a stretch of pavement with a drop of about 1% to calculate rolling resistance at different pressures. It didn’t work, largely because most pavement in this town has bumps up to 1.5 inches high. You can’t avoid them because you can’t see them unless you wait until dark and shine a light along the surface to create shadows. Hitting those bumps is like braking sharply.
After a better seat position on my Radrunner allowed me to stabilize myself with pedal pressure, I would sometimes ride with my thumbs and forefingers forming rings around the hand grips but not touching them. When I hit invisible bumps, I noted that the backward jumps of the bars against my thumbs were bigger than the upward jumps toward my fingers. The apparent backward jumps were really me lurching forward against the braking effect of colliding with bumps. Pneumatic tires meant that not all this lost forward energy was converted to upward energy, which is why the upward jumps were smaller.
The rolling resistance of the 26 x 1.95 tires on my Radmission seemed much lower. I decided to compare them on a stretch of a 6.1% grade near my house. I’d approach the starting point at a certain speed, maybe 6 mph, let it coast, and check my speed at a certain point downhill. Both bikes had identical KT speedometers, but the idea seemed flawed because a grade that steep would quickly accelerate a bike to speed where air resistance would count far more than tire resistance. Both bikes were set up for the same riding position, and our gross weights would be the same. I figured air resistance would keep the results very close. Instead, the Radrunner was faster every time.
I imagined why. Hitting the front of a bump compresses air in a pneumatic tire, and, being faster than a suspension, it can restore some of the lost speed by pressing against the back of the bump. The Radrunner tires, with less pressure and more volume, must have been a better at pushing off against bumps this size.
Pavement around here is particularly rough, but I recently read an article saying most road bikers use too much pressure. Those recommendations came from research on very smooth surfaces, but even new asphalt pavement has spaces between pebbles which make it rough enough to resist a rolling tire. It said that’s why pros are using wider tires and lower pressures than before. The pressure for the least rolling resistance depends on the roughness of the surface. It may be that the low rolling resistance in your charts is for an unusually smooth surface.
Speed was the early hype for pneumatic tires. John Boyd Dunlop made pneumatic tires in 1888 for his mother’s wheelchair. When he found that it would roll down a grassy slope faster than one with solid tires, he contacted the local bicycle club. Many bicyclists would pay big bucks for a racer’s edge. The club president put together investors to open a factory in Scotland. They got the world’s attention by winning races in Ireland and England.
Dunlop got a patent, but it was disqualified as prior art because the same thing had been produced for carriage wheels decades earlier. Production was delayed for years, I think due to the realization that they needed improvement. The race victories had come on grassy cricket fields. These tires would not have gone far on roads, and a puncture would have required 24 hours in a shop for replacement.
The Michelins, who had been making rubber products for decades, devised a two-piece system. The carcass was more durable than a Dunlop. It was mounted without glue, so the rider could patch a puncture in 15 minutes.
In 1891, two French newspapers sponsored a 743-mile reliability race from Paris to Brest and back. This was Michelin’s chance to introduce its tire. They and the Humber Bicycle Company sponsored the legendary Charles Terront. They hired another racer as his manager, to arrive by rail in each town ahead of Terront in case he needed anything.
Joseph Jiel-Laval, a bicycle shop owner who had recently won major races, rode for Dunlop. The two pneumatic guys were faster than the 205 with solid tires. Each repaired several punctures along the road. That would have been impossible with the Dunlop design. Michelin wasn’t in the tire business. They would have distributed prototype rims and tires to certain shops for evaluation. I think Laval told the Dunlop investors that he had Michelin prototypes. If he won a race for Dunlop, the world would beat a path to their door, and they could reverse engineer the prototypes to produce a similar product under their brand.
After 24 hours, Terront was even with Laval. At one point, Terront had had to walk his bike to the next rail station, where his manager was waiting with tools. That put him an hour behind, but he caught up. Laval had a big advantage. The Dunlop investors had hired eight racers so that on every segment, one could be riding alongside with tools.
After 24 hours, Terront fell behind but kept pace. Each manager used telephones to monitor the opponent’s progress. Several hours ahead on the third night, Laval stopped to get some sleep, telling his team to wake him if Terront was spotted. Much sooner than expected, he was awakened and told that Terront had detoured around the town and was two hours ahead.
Having slept, one might have expected Laval to close the gap. Instead it increased. Terront finished in 72 hours and Laval in 80. How did Terront manage to pedal faster in his last 12 hours than in his first 60?
https://en.wikipedia.org/wiki/Charles_Terront
The 1891 photo of his Humber shows how. James Starley had invented the first useful bicycle about 1856. The seat had to be almost over the front axle so that thrust on the pedals wouldn’t cause uncontrollable veering. It wasn’t stable against going end over end. Then, the seat could rotate up over six feet while your head was rotated down, and the handlebars kept you from getting your legs under you.
In the 1880s, drive chains made rear-wheel bikes with modern-size wheels possible, but the first ones failed because the smaller wheels rode rougher. In particular, on a high-wheeler, handlebars, pedals, and seat rose together on bumps, but on a rear-drive bike the handlebars led the way, and that was hard on wrists.
Note Terront’s handlebars, swept way back. Some say they were introduced to let riders sit upright as on high-wheelers, but his bike was not designed for sitting straight up. I believe they were made that way so that the clamped sections would serve as torsion bars, isolating the wrists from jolts. For safer handling, a modern manufacturer probably would have clamped the bars on a forward offset to bring the rider’s hands more nearly in line with the steering axis. With his hands so far back, his arms descend steeply. That puts more weight on his hands than if they were farther forward and perhaps higher. It also means reduced stability against being thrown over the bars.
In 1885, Starley’s nephew John had come out the Rover, the first successful rear-wheel-drive bike. Earlier models had put t he seat almost over the pedals to have a pedaling position like that of a high wheeler. Starley moved the seat back, as did Terront’s Humber. This increased comfort because shifting weight to the pedals moved it well away from the seat.
Another big advantage was that the rider’s knees didn’t flex as far. This allowed the rider to apply more torque higher in the stroke. Both bikes had to be geared to make it up hills, but with more leg torque, Terront could choose a higher gear ratio, in effect riding the course in overdrive.
Besides powering the bike, pedaling requires the energy to cycle massive legs in reciprocating motion. It’s particularly demanding on the return stroke, when relatively weak muscles must not only lift the knee but, as the cadence increases, apply increasing force to accelerate the knee upward. Ghost pedaling happens at a cadence where moving your legs takes all the power you can generate.
With a slower cadence, Terront could cut his overhead by cycling his legs fewer times per mile. What’s more, each pedal rotation would require less energy because his legs would need less acceleration. After 60 hours of pedaling, that energy savings gave him an enormous advantage.
Raleigh also understood why the Rover was a breakthrough. Their Roadster was like the Humber but with fenders and much safer handlebars. One could quickly and comfortably pedal 20 miles on an unpaved road without fatigue. A British bicycle cop who rides the Roadster his grandfather bought 50 years ago is the envy of other bicycle cops.
https://sheldonbrown.com/retroraleighs/roadster.html
Because of that race, pneumatic bicycle tires were soon universal. The race also showed the superiority of John Starley’s seating geometry, but 130 years later, most bikes still have the pedaling geometry that’s as obsolete as the high wheeler. (In fact, museum Rovers sometimes have their cantilever seat posts rotated to bring the seat forward instead of aft of the seat tube. Go figure!)
