Originally Posted by
tallbikeman
Jan Hein of the Bicycle Quarterly is the guy who has changed everyone's perception of tire sizes and pressures needed. It is interesting to read his scientific experiments that led to the bigger tires and less pressure. His evidence is so strong that the Tour de France riders are now riding bigger and bigger tires with less and less pressure. Jan's evidence shows that it is sidewall flex that determines how efficient a tire is to pedal and bigger is better in all cases. Pressure has a big role in this. He has experimented up to 50mm tires that role easier than 25mm tires at over 100psi. I have changed my tire pressure habits and now experiment with pressure to find the sweet spot for the tires I'm using. My smallest tire on a road bike is 32mm at this time and I'm very happy with them.
I read the same article and it also states that as long as your tires are not wider than you downtube, it will make no difference in speed, which they backed up with a lot of data. I'm 245 and I run 700x40 gravel tires, the rear is 50 psi and the front is 45 psi. I spent an entire afternoon testing. Too much pressure would slow me down over washboard and too little pressure would bottom out on rocks and roots, so I adjusted so neither would happen. The 50 and 45 psi that worked perfectly then gave me pinch flats so I went tubeless. I really didn't want to go tubeless, it was change, and for some reason I resist change on some things. I'm glad I tried it because there is no way I could have used those pressures, and those pressures were the sweet spot that I needed. It's all working now. I love it when a plan comes together. I'll never go back to tubes.