Author Topic: tire size  (Read 2050 times)

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Offline Sailor John

tire size
« on: May 21, 2009, 09:51:54 pm »
Is the rolling resistance between a 700 x 28 and a 700 x 32 significant?  Which would you reccommend for pulling a BOB ? I'm using 36 spoke wheel set.

Offline whittierider

Re: tire size
« Reply #1 on: May 22, 2009, 12:30:50 am »
Quote
Is the rolling resistance between a 700 x 28 and a 700 x 32 significant?
Should that say, "Is the rolling resistance difference between a 700 x 28 and a 700 x 32 significant?"?  The difference would be pretty minor, but what a lot of people don't realize is that if they tires are the same model, it will be the wider one that has the lower rolling resistance.  That's because the wider tire doesn't have to bend as sharply at the edge of the contact patch, and less bending means less energy loss.  The numerical results from rolling resistance tests back this up.  Unfortunately, none of the best tires are made in such wide widths.  I guess the manufacturers figure that if you're going that wide, you don't care if the tire makes a couple miles' (or more) reduction in how far you can tour in a day.  I would base the choice of width on the quality of the surfaces you plan to ride.  I've been on parts of Hwy 66 near the CA-AZ border that would make me want a 100mm tire.  It was terrible, but I think bikes would probably be allowed on the nearby freeway shoulder there anyway.  But for most pavement, 25 is fine and affords you some of the best performers.  I've had 28's and 32's on our road tandem and I don't like the too-imprecise feel.

Offline biker_james

Re: tire size
« Reply #2 on: May 22, 2009, 08:00:38 am »
I don't think you would notice the difference in rolling resistance when pulling the trailer. There certainly are different opinions on tires (and wheels, and everything else) as the post above shows. For touring purposes I like wide tires. The wider tires let yu run a little less pressure, softening the ride, they protect the tire from pinch flats, and the rim from damage from potholes and whatever other road hazards you may encounter. The thing to remember when touring is that you seldom know everything that you will encounter-will there be miles of construction, or bridge expansion joints or transistions that hammer the bike when you hit them at speed, or a lot of dirt/sand/whatever on the road surface.
I use panniers on my bike, so the bike itself carries more weight, but I run 700x37's. Are they bigger than needed? Maybe, but I'd rather that than find out I was riding on less tire than I needed as it can be a long way between shops with real touring tires available.

Offline aggie

Re: tire size
« Reply #3 on: May 22, 2009, 01:24:08 pm »
I pull a Bob trailer and have had no problems with 28's.  All the riding was on paved surfaces (albeit some felt pretty rough).  The only real problem encountered was the small wire from truck tires creating several flats.

Offline litespeed

Re: tire size
« Reply #4 on: May 22, 2009, 05:39:14 pm »
For a loaded touring cyclist rolling resistance should be the least of your priorities. I got custom touring wheels made and went from 28mm to 37mm tires. I gained a lot more comfortable ride, the ability to go in much softer and rougher dirt and they last longer. Also the wider rims (Rhyno Lite Sunrims)are more stable and have never really needed adjusting. In over 25,000 miles of loaded touring I have broken one spoke. Worth every penny.