Tire psi during winter months...
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  1. #1

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    Tire psi during winter months...

    What is recommended regarding psi in your tires when not riding during the winter. Do you keep them at riding psi and check every week or so, or deflate them a little and let it go at that? I have 700 x 23c.

    By the way, while 700 I know is for tire diameter, what does the "c" stand for in 23c? Is there any difference between 700 x 23 and 700 x 23c?

    Thanks.

  2. #2
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    I don't know of any reason to do anything different seasonally with psi. I ride very little in Dec or Jan and let my tires lose pressure naturally. But the weights of the bikes are not on the tires. I hang all of my bikes from their wheels.

    The c designation is the standard for road rims. This standard assures compatability between various tire brands.

    ~Al

  3. #3
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    It Is A Metric Measurement

    c as in cm or centimeter. But more accurately 23c= 23 milimeters or 2.3 centimeters.

    Perhaps it should have been an 'M' & not a 'c' for the US market.
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  4. #4
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    700c

    The "c" is just a designator. Sheldon Brown has a nice explanation of tire sizes. The Rivendell Reader has discussed it too, in a historical context, but I don't know if that's online.

  5. #5

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    Quote Originally Posted by HAL9000
    c as in cm or centimeter. But more accurately 23c= 23 milimeters or 2.3 centimeters.

    Perhaps it should have been an 'M' & not a 'c' for the US market.
    So if they leave out the "c", does it mean anything? Does it change the tire size? Does it mean it's not for a road bike?

  6. #6
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    Quote Originally Posted by CoachRob
    So if they leave out the "c", does it mean anything? Does it change the tire size? Does it mean it's not for a road bike?
    It's an assumed standard and is often left off. And it does not stand for cm or metric.

    ~Al

  7. #7
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    Just plain wrong

    the "c" does not stand for cm. French sizes come in A, B, C, D and 700, 650, 600, 550, 500, 450, and 400 diameters (not all diameters have all widths). The letters originally designated width, with A as narrow and D as wide, though this is no longer meaningful. The diameters are nominal with a tire mounted, but are not that meaningful (a 700x23 mounted tire is 667mm in actual diameter). Sheldon Brown covers this: http://www.sheldonbrown.com/tire-sizing.html

    The letters (c) applies to the rim size (700) not the tire diameter (23). Any tire/rim designated 700 today is a standard road rim with a 622mm bead diameter per ETRTO (now ISO).

  8. #8

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    If you want to run a lower tire pressure during the winter, then get a wider tire. Running a lower pressure in the same tires doesn't make much sense (unless they were overinflated during the summer).

  9. #9

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    Quote Originally Posted by Kerry Irons
    the "c" does not stand for cm. French sizes come in A, B, C, D and 700, 650, 600, 550, 500, 450, and 400 diameters (not all diameters have all widths). The letters originally designated width, with A as narrow and D as wide, though this is no longer meaningful. The diameters are nominal with a tire mounted, but are not that meaningful (a 700x23 mounted tire is 667mm in actual diameter). Sheldon Brown covers this: http://www.sheldonbrown.com/tire-sizing.html

    The letters (c) applies to the rim size (700) not the tire diameter (23). Any tire/rim designated 700 today is a standard road rim with a 622mm bead diameter per ETRTO (now ISO).
    Read the article x 3 and still am not sure I understand it. Why would a 700 actually be 667 in diameter? I really don't follow Sheldon's explanation on this topic.

    He says, For example, a 700 x 20 C road tire would be [an ISO] 20-622. Why??? If the first # is tire width and the 2nd is the diameter of the bead seat of the rim, in mm, why would the bead diameter be SMALLER (622) than the 700 mm rim it is designed to fit onto? It does at least explain how a 622 bead diameter ends up giving a diameter of 667 when the tire is mounted:

    total diameter = rim diameter + tire (x 2 since it is on both sides of the rim) = 622 + 46 = 668 mm

    But I still don't get the 700. Shouldn't the ISO just call the darned thing a 23 x 622??

  10. #10

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    Quote Originally Posted by CoachRob
    Read the article x 3 and still am not sure I understand it. Why would a 700 actually be 667 in diameter? I really don't follow Sheldon's explanation on this topic.

    He says, For example, a 700 x 20 C road tire would be [an ISO] 20-622. Why??? If the first # is tire width and the 2nd is the diameter of the bead seat of the rim, in mm, why would the bead diameter be SMALLER (622) than the 700 mm rim it is designed to fit onto? It does at least explain how a 622 bead diameter ends up giving a diameter of 667 when the tire is mounted:

    total diameter = rim diameter + tire (x 2 since it is on both sides of the rim) = 622 + 46 = 668 mm

    But I still don't get the 700. Shouldn't the ISO just call the darned thing a 23 x 622??
    700c does not translate into 700mm. I am very likely to be wrong, but I think 700c is just the nomenclature a 622mm wheel, and has no useful mathematical meaning.

  11. #11
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    The 700 is the mm diameter wheel with tire fully inflated. But, as I see it, the 700 size is a rough approximation and accounts for tires a lot bigger than the 23's we're use to now. It's similar to car engines, a 3 liter engine may actually be 2.813, or 2.91, or whatever. If you compare 23mm tires from three different manufacturers they will be three different widths. Likewise, 700c rims are not all exactly alike, but close enough.

    ~Al

  12. #12
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    Tire vs. rim

    If you look at old (and I mean OLD) pictures of racing bikes, you'll see the tires were much, much larger than they are now - probably 40 mm diameter rather than today's numbers in the low 20s. Even though those tires were tubulars, the total diameter was the basis for the rim size designation. The 700 number comes from a NOMINAL diameter of a tire mounted on the rim (vs. the 667 mm diameter of today's 23 mm tire). The desire to match rim sizes with a clincher tire resulted (eventually) in today's 622mm bead diameter rim. Lots of things can vary in a clincher rim, but to mount a tire, the bead diameter must be at the standard.

    And, as is often the case, CoachRob cracks me up: "But I still don't get the 700. Shouldn't the ISO just call the darned thing a 23 x 622??" Need to work on the comprehension thing, Rob. ISO (or ETRTO) DOES call it a 23-622. Look on the sidewall of your tire! It's right there!

  13. #13

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    You're right as usual Kerry

    Quote Originally Posted by Kerry Irons
    And, as is often the case, CoachRob cracks me up: "But I still don't get the 700. Shouldn't the ISO just call the darned thing a 23 x 622??" Need to work on the comprehension thing, Rob. ISO (or ETRTO) DOES call it a 23-622. Look on the sidewall of your tire! It's right there!
    I'm glad I bring a LITTLE joy into your life, Kerry. Thanks for clearing that up. I just checked my tires and they do indeed have 23-622 stamped right on their pretty vulcanized (any relation to Mr. Spock, my FAVORITE Vulcan?) rubber sides!

    That's why I always read your responses first (you should have received my email thanking you for your past advice)! ;)

  14. #14
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    Quote Originally Posted by CoachRob
    Read the article x 3 and still am not sure I understand it. Why would a 700 actually be 667 in diameter? I really don't follow Sheldon's explanation on this topic.

    He says, For example, a 700 x 20 C road tire would be [an ISO] 20-622. Why??? If the first # is tire width and the 2nd is the diameter of the bead seat of the rim, in mm, why would the bead diameter be SMALLER (622) than the 700 mm rim it is designed to fit onto? It does at least explain how a 622 bead diameter ends up giving a diameter of 667 when the tire is mounted:

    total diameter = rim diameter + tire (x 2 since it is on both sides of the rim) = 622 + 46 = 668 mm

    But I still don't get the 700. Shouldn't the ISO just call the darned thing a 23 x 622??
    If you look at an old picture of a racing bike (pre 1930's), notice the size of the tires. Those are the old standard road-bike tubulars, and they were about the equivalent of a 700-38 tire today. These were almost exactly 700 mm in diameter. They have been obsolete for 60 years.
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