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New Roadie, which tire size is best for me?(5 posts)

New Roadie, which tire size is best for me?scratch
Jun 12, 2001 8:22 AM
I need help in trying to choose a proper tire size. 650 vs. 700, 20,23, or 25's? I'm 6' and 190#s. I ride aggresively and train alot.
I primarily will do long road races here in AZ. Any thoughts? Should a lighter rider use the 20's? and a heavier rider use 25's? I don't know...Thank you
I'll repeat what I've been told, with as much personalbill
Jun 12, 2001 9:46 AM
experience as I can.
I don't know why 650 wheels exist. They are used by triathlon guys. I guess, being smaller, they're theoretically stiffer and lighter, but, you know, you have to turn them more times to go as fast, and tires are sometimes hard to find, and, I just don't get it.
Now, I'm assuming that you're thinking about what kind of bike to buy with what wheels, because 650 tires cannot be used on 700 wheels (and vice versa), and, as far as I know, the frame is built around the wheel size and wheel sizes are not interchangeable on the same bike. A bike built for 650 wheels stays that way. And vice versa.
Among the different tire sizes that are interchangeable, 20, 23, or 25 (they go up from there), I just had this argument. The main difference is comfort, with larger tires being a more cushy, with the sacrifice being in the aerodynamics of the wheel. I have heard and am persuaded that, among tires with the same psi, the actual contact point with the road is the same for the different sizes (the 20 being longer and thinner, than the others, etc.), so that there is no total tire deflection and therefore no difference in rolling resistance, tire deflection being the main determinant of rolling resistance.
I can tell you that 25's do seem comfier than 23's with no noticeable difference in speed (although the 23's seem to feel faster). I have never tried 20's.
A heavier rider maybe would want to use a larger tire size, mainly for comfort and pinch-flat resistance. Because the deflection is less relative to tire width in the larger tire, I guess you flat less.
Well, almostKerry Irons
Jun 12, 2001 6:44 PM
At the same pressure, smaller cross section tires (20 vs. 23) will have higher rolling resistance, because they have to deform more to create the same size contact patch. However, narrower tires are typically inflated (and rated) to higher pressures, so rolling resistance is about the same, and more dependent on casing quality. Wider tires are a bit less aero, but "not so's you'd notice" unless you are riding TTs at a very competitive level.

For a 190 lb rider, 23s should be fine, inflated to 8 bar or so. If you're getting pinch flats under those conditions, you're not paying enough attention to where you're riding. Most would say that 20s would be too narrow for a 190# rider, and there's nothing wrong with 25s. You'll typically find that 23s are the most available size. Narrower tires tend to "feel" faster because they are pumped to higher pressures and transmit more road feel. That doesn't mean they are faster - measurements suggest not.

I agree with your comments on 650s.
I'll repeat what I've been told, with as much personalSteve Bailey
Jun 12, 2001 8:50 PM
As Bill put it:

"I don't know why 650 wheels exist. They are used by triathlon guys. I guess, being smaller, they're theoretically stiffer and lighter, but, you know, you have to turn them more times to go as fast, and tires are sometimes hard to find, and, I just don't get it".

Ditto it all, and to expand...

Probably the sole reason(s) for 650's would be either a smaller rider on a 51cm or smaller ST bike, or to get the geometry of a Tri bike, which can be harder to engineer with 700's. That's pretty much it, and getting a position on a 700C wheeled bike, for typically sized riders, that's similar to a 650 bike is possible what with forward seat posts, et al.

The limited wheel and tire choices alone would steer me away from 650 even if all I used it for was Tri's. !

My only comment about tire sizes is that a larger tire will weigh a bit more, if that's important, and that larger tires beyond 27 or so can be problematic getting clearance under the brakes on modern road frames. My Klein Quantum will only accept up to a 27 for example, which on that bike is as large as I would go anyway.

Note also that many of the tire manufacturers lie about the actual sizes. Avocet's seem to run 3-5mm smaller then listed, Specialized seems to run a size large, IRC's a size small, etc... Best check if clearance seems an issue.

SB
my $0.02 on the 650c vs. 700c issueBecky
Jun 13, 2001 6:14 AM
I agree- finding wheels and tires for my 650c-wheeled bike requires a little more work- I can't open the latest issue of Colorado Cyclist and find exactly what I want. Having said that, those "little" wheels are a godsend. As a woman with a very short torso compared to my inseam, the 650s allowed for a short-enough top tube to make me comfortable on my bike for longer than 5 miles. For your cyclist of average build, 650s don't make a darn bit of sense. But for those of us who don't fit the industry's idea of average, they're more than worth the effort to find tires and wheelsets!