Originally Posted by maydog
My point was that, all else being equal, changing the width of a tire will not result in huge gains. The data in the article Froze linked shows the differences being a few watts - not nearly enough to increase speed by 5mph.
Exactly why I posted that site. If someone was riding heavy 20 x 2.75 knobby tires with heavy thorn proof or slime filled tubes then switches over to a bike with 700 x 23 or 25 tires than I could buy a 5 mph increase due to weight, width, friction from knobbies, and air resistance against a fatter tire profile, but typically going from a 23 to a 28 won't be anywhere near that, maybe, I say maybe, you might see a gain of 1/2 a second in a 100 mile race, but a 1/2 a second could be the difference between winning and losing!
One of the reasons I bought a Lynskey vs the Motobecane (though this was a minor issue) was the fact that the Lynskey could use a 28 tire on it while the Moto only a 25, not a big deal thus a minor issue as I said, but if time goes by and people start to realize that a 28 could roll a tiny bit better than a 23 or a 25 my bike would be good to go.
Read that site I gave and read the letters, you'll discover that as the tire width increases there becomes a breakeven point and then after that the resistance goes up because of the additional weight a wider tire weighs due to more rubber and casing material, and the less aerodynamic it becomes due the width.
Also pay attention to the discussion on tire PSI, you don't want to run the same PSI in a 25 as you would with a 23, you have to run less which is why the Michelin tire pressure calculator is an important tool; see: http://www.dorkypantsr.us/bike-tire-pressure-calculator.html If you've never used this before use the middle, or 2nd calculator, enter your total body weight fully dressed for cycling and add to that your total bike weight fully ready to cycle, next enter the F/R weight distrubution factors (I personally like the second choice of 45/55) and finally enter your tire sizes. This calculator is based on a formula that has been around for many years, however you can alter the ratings to suit your needs but I wouldn't exceed 5 psi over or under the recommendation, some want a firmer ride and some want a softer ride so those ranges are there to suit that. Also pay attention to your tire's packaging or sidewall information, a few brands have their own recommended PSI range that won't match up to the Michelin calculator, and in those cases it's best to heed to the manufacturer's recommendations. I know my Vittorias came with a chart but that chart matched the Michelin recommendations.