The 700C x 25 debate

Betcha didn’t even know there was a debate on this arcane topic, didja? It came up the other day when a club member, who is a pretty good rider and is usually out front on our group rides, said he’d switched to the slightly wider 25 mm tire. He said he was pleased at the better ride, better traction, better cornering — all at no appreciable increase in rolling resistance.

That touched off a firestorm on our club Yahoo board. Why, there must have been eight or nine comments bouncing back and forth about the relative merits of the 25s vs. the skinny 23s that most of us “macho” bikers ride.

And one member pointed out that the size of the contact patch (where the rubber meets the road) is more dependent upon the circumference of the rider’s waist than the width of the tire itself. The wider the waist, the greater the bulk, the higher the weight, the more tire deformation — they all add up to more traction, but with more rolling resistance.

A 23 mm tire on the left, 25 mm on right.  The difference is obvious.

A 23 mm tire on the left, 25 mm on right. The difference is obvious.

Although, if you want to really gauge rolling resistance, the famous wheelbuilder Jobst Brandt has a nifty little interactive page that lets you calculate the rolling resistance of your tires after you enter the effective frontal area of the tire, its drag coefficient, the air density, the combined weight of the rider and bike, the phase of the moon, the odds of your maternal grandmother being born on a Sunday, and multiplying that by the slope of the regression line of the area of adhesion.

I haven’t tried 700 x 25 tires on my bike. It came with 23s, and I’ve been happy with them. But for a smoother ride, it might be worth the switch. Can you enlighten me any further on this burning topic?

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10 thoughts on “The 700C x 25 debate

  1. I generally ride with wider tires than most. I believe if you read Uncle Al at roadbikerider.com he generally encourages wider tires.

    I rode a 200 mile bike race once on 700 x 35 tires. I used to ride my bike regularly on club rides with those tires.

    I think my Roubaix has 25 tires or maybe even wider.

    I also remember seeing a site once that guaged the resistance based on tire size and there seemed to be very little.

    It all goes back to what I have maintained. It’s not about the bike.

  2. I don’t have any science to back this up, but I rode 23s for the first time this past season and while they felt slightly faster, the stability was lacking. I don’t know how two milimeters can make that big of a difference, but I do know that I’m putting 25s on in 2009.

  3. My first inclination is that the difference between 25 and 23s for most of us is psychological. The creme de la creme of the cycling world will likely notice a difference and be able to take advantage of it, but for the rest of us (the bottom 99.5%), it’s most likely an academic (or better yet, a religious) argument… something to feel strongly about for the sake of having something to feel strongly about.

    I can definitely say that I feel a difference between my 23s and my 37s, but that’s a much larger spread.

  4. I like wide tires. My old road bike came with 25s and when I wore them out, I put 28s on there. I felt much more confident with the 28s, especially on rough roads, and they cornered better. I didn’t notice being any slower; if anything they gave me the confidence to ride faster. Then again, I don’t really ride for speed.

    I currently have a touring bike with 37s on it, and I love them. I contemplated keeping the road bike as my “fast” bike, but ultimately sold it. It was only moderately faster, and I can do everything on the touring bike I could on the road bike, and more.

    We have horrible roads around here, so the wider tires are great. And I can ride the same bike on gravel roads, or even trails, as long as they aren’t too technical. The bike also did very well in snow last night — it’s very versatile.

    But, if you only ride on smooth roads in good weather, maybe skinny tires are fine.

  5. 25s are probably just a tiny bit heavier than 23s, but the weight is in the worst place, at the outside of a spinning wheel.

    I ride 23s cause it never rains here. Wait, it’s been raining all week :)

  6. I used to get 18s in the 80s. I don’t know what happened to such slight tires. I just remember I rode them on my all-aluminum (yes, forks too) Cannondale Black Lightning and, being younger then, felt fine.

    • I rode 18’s Continentals on my Fiorelli road bike that I use to have in the late 80’s and I remember the ride being very harsh compared to the 20mms or 23mms that I would normally ride. 23 years later I am planning to switch to 25mm or 28s to get a little more comfort than the 23s offer.

  7. Pingback: Switching to 25s « Bike Noob

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