Originally Posted by
FL_Gator
Haha, I hear you.. my much older bike that I now use as a trainer bike is good old 23mm, but I did convince myself to switch to 28mm many years ago which at this point feels old school 😆
I too am 200 lbs on an 18lb bike, I ride the rails to trails all over Florida so the pavement is relatively rough and worn most of the time.
If you want to test whether it's faster, don't do what I did: My Canyon runs Conti GP5Ks in 28, but has lots of room, so I thought I'd try 32s. I didn't want to cough up > $65/tire, so I ordered some 32mm Vittoria Corsa G2.0s from Bike Closet (I think the bought up Vittoria's stocks when the Corsa Pro was introduced last summer). Swapped them for the 28mm Contis, and pumped them up to 70/75 F/R, based on Silca's calculator. When I rode them, they felt slow, my speed was lower than usual for that bike everywhere on the route, and the average speed for that route (which I've done dozens of times) was about 0.4 mph slower than the average of all rides on it.
I was puzzled, till I looked up the rolling resistance on bicyclerollingresistance.com and saw that the Contis have 4w lower rolling resistance than the Corsas. Double that for 2 tires and you've got 8w more resistance. I checked bikecalculator.com and sure enough, 8w would work out to about that much slower average speed.
The moral of this little fable: Get the same make and model of tire, or your results will be meaningless.