Weight is also a substantial factor in the wheels and tires. I experimented heavily with everything from 26x1.25" tires to 26x2.25" tires, with light tubes all

Weight is also a substantial factor in the wheels and tires. I experimented heavily with everything from 26x1.25" tires to 26x2.25" tires, with light tubes all the way to thorn proof tubes with that green goop in them (Man I was sick of flats...). The difference in the speeds I was able to attain not just from rolling resistance but to the amount of weight I had to spin was huge. I settled eventually on 26x1.75" tires with a solid center tread and kevlar lining. They were amazing on road (commuting) and worked well in other situations too. For context, I was riding 12mi/day commuting to/from work in Reno NV back in the mid 2000's. Rode a steel framed Specialized Rockhopper that was converted to a fixed gear tank- not your average fixie. Featured trekker bars, an MTB sized IRO hub, cliffhanger rims, racks front and back, the works. Best bike I ever had.