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Bicycle tire size and fit on frame question

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Bicycle tire size and fit on frame question

Old 10-26-19, 08:36 PM
Charlie Pappa
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Bicycle tire size and fit on frame question

I have a 2007 LeMond Buenos Aires Triomphe frame, and I have just discovered that the rear tire is so close to the frame that it has in the past rubbed up top. Today, I did my first wheel spoke tune-up and I apparently deviated the wheel from the center so that now the tire rubs on one side. I plan to reset the position of the tire but I am considering going to the original tire size (700x23) from the one that is mounted now (700x25). My question: Are 700x23 tires smaller in cross-section than 700x25 tires? Is it unusual that a rear tire spins so close to the frame? or, am is it OK as long as there is any clearance, no matter how small?

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Old 10-27-19, 12:31 AM
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I don't understand why you don't understand that 23 is less than 25.
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Old 10-27-19, 01:58 AM
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Yes, of course, 700x23 is smaller than 700x25.

However, tire sizes vary somewhat from brand to brand, so you should get about 2mm difference in size within one brand, but between two different brands, it may be either a greater size difference, or perhaps less.

Note, that 2mm width difference... if you measure from the centerline, that may well only be about 1mm. So, if your tire is rubbing on the frame, the 23 may not make that great of a difference, but perhaps just enough.

You need to adjust the dishing on your wheel. It isn't that difficult of adjustment. If it is only slight, I'll simply true the wheel by making a bias of only adjusting in one direction.

A dishing gauge can help.

Also note, that since spoke tension is unequal in the rear, your dishing may change slightly when a tire is installed and inflated.

You can also do the dishing with the wheel installed in your bike. So, the wheel matches your bicycle perfectly.
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Old 10-27-19, 05:34 AM
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Sometimes the wheel in the dropouts isn't straight either and you need to make sure you are centered there too. As for the tire, yes a 700x25 may rub where a 700x23 doesn't, this happened to me using the same brand of tire. Wheel was true too. I ended up swapping front and back tires as the front was a 700x23 and rode with the 700x25 in the front, but eventually it blew out on the sidewall where the rubbing had occurred. It doesn't take much to weaken a tire I guess.

But if you trued up your wheel and the dish changed, well you didn't get what you wanted then. You need to use a dishing tool, and it can be homemade. I won't go into making one as my brain isn't capable yet this morning but if you look at one online you should be able to design one yourself.
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Old 10-27-19, 10:05 AM
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To be clear, some of the numbers used in bike stuff is a little non-intuitive, but when you say 700c by "X", "X" is the nominal tire width.

Check what zacster suggests: make sure that the wheel is properly seated in the dropout, and centered between the chainstays when you tighten the QR. Make sure that the wheel is true.

If you are relatively light then the 23 may be a good move. Or, if you've used the 23s and they ride fine for you (although I suspect that you went to a 25 for a reason). If you're a bigger person or 23s don't give you a nice ride you may want to find a bike that can accomodate the bigger tires.

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Old 10-27-19, 10:47 AM
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Yes, it is common for tire clearance to be very tight on road bikes from the 1990s-mid 2000's, and they may only take 23mm tires. That was the fashion then.

Wheel 'tuning' or Truing, as it's known, is fairly straightforward once you know what you're doing. It does require some simple tools and a methodical approach. You don't just 'tighten all the spokes' as it can lead to some unintended results, as you found out.
It's not a difficult thing, but there is some nuance and patience required. The tight clearances of a sporting / racing road bike like your Lemond are not a very forgiving field to learn on, either.
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