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  1. #1
    Sswitzky
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    Tire Width and Proper Inflation

    Let’s say I have two tires, a 23mm with actual width around 25mm and a 25mm tire that measures true to stated size.

    Would you inflate both tires to the same psi? (assume both on front or both on rear).

  2. #2
    Cleavage Of The Tetons
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    What is the weight of a laden swallow?

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    Quote Originally Posted by sswitzky View Post
    Let’s say I have two tires, a 23mm with actual width around 25mm and a 25mm tire that measures true to stated size.

    Would you inflate both tires to the same psi? (assume both on front or both on rear).

    My answer is: "Probably"

    There is quite a bit of info missing before I can give a more specific answer

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    Quote Originally Posted by rideit View Post
    What is the weight of a laden swallow?
    Is it an African swallow?

  5. #5
    Russian Troll Farmer
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    I have a non-scientific way of determining how hard to inflate your tires: On my bike, I found that with the classic 23mm wide tires, it worked best for me at 100 psi rear, 90 psi front, which was exactly 13 strokes of my floor pump on the rear, and 12 strokes of the pump on the front.

    Inflating my 42mm wide tires on my gravel/touring bike, I used the exact same number of strokes, and it was perfect, filling them at about 40 psi rear, 35 front. From that, I assume that the having same AMOUNT of compressed air is the key, which corresponds linearly with tire pressure.

    So, If you know how many strokes of the pump from completely flat works for you, use that on every tire width, then check your final pressure.
    Last edited by No Time Toulouse; 3 Weeks Ago at 12:19 PM.
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  6. #6
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    Have you communicated with the tire manufacturer yet? If they haven't put their, or their lawyers, recommendations on the side of the tires, they may be able to respond to an e-mail with the proper inflation guidelines.
    Too old to ride plastic

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    No I wouldn't, I use about 10 PSI less for every 2mm I go up in tire size.

    While not a big deal when moving 2mm in either direction, try using 40mm tires with the same PSI you use on 23mm tires to get any idea if less psi for more mm's makes sense. If you don't blow the 40mm of the rim you'll see quickly that less PSI as tires get bigger makes a lot of sense.

  8. #8
    Sswitzky
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    Quote Originally Posted by Jay Strongbow View Post
    No I wouldn't, I use about 10 PSI less for every 2mm I go up in tire size.

    While not a big deal when moving 2mm in either direction, try using 40mm tires with the same PSI you use on 23mm tires to get any idea if less psi for more mm's makes sense. If you don't blow the 40mm of the rim you'll see quickly that less PSI as tires get bigger makes a lot of sense.
    That’s why I am asking the question. Let me rephrase. If my tires labeled 23mm are really 25mm, should I inflate them as if they were really 25mm? In other words, a lower PSI?

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    Quote Originally Posted by sswitzky View Post
    That’s why I am asking the question. Let me rephrase. If my tires labeled 23mm are really 25mm, should I inflate them as if they were really 25mm? In other words, a lower PSI?
    Experiment, the worse that can happen is a pinch flat.
    Too old to ride plastic

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  11. #11
    Sswitzky
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    Quote Originally Posted by mfdemicco View Post
    Thanks for the interesting article. My only follow up is what tires are considered “supple”? Are Vittoria Rubinos supple? Conti 5000’s?

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    Quote Originally Posted by sswitzky View Post
    Thanks for the interesting article. My only follow up is what tires are considered “supple”? Are Vittoria Rubinos supple? Conti 5000’s?
    Yes, I would think so.

  13. #13
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    Quote Originally Posted by velodog View Post
    Have you communicated with the tire manufacturer yet? If they haven't put their, or their lawyers, recommendations on the side of the tires, they may be able to respond to an e-mail with the proper inflation guidelines.
    How many tires put recommended pressures on them? This varies quite a bit due to rider weight, and even the type of layout. All I've ever seen is MAXIMUM pressure listed on the tire.
    "L'enfer, c'est les autres"

  14. #14
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    Quote Originally Posted by No Time Toulouse View Post
    How many tires put recommended pressures on them? This varies quite a bit due to rider weight, and even the type of layout. All I've ever seen is MAXIMUM pressure listed on the tire.
    You're not looking very hard then. I have three different brands (Vittoria, Challenge and Donnely) and they all have a range printed on the side. So a min and max.

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    Quote Originally Posted by No Time Toulouse View Post
    How many tires put recommended pressures on them? This varies quite a bit due to rider weight, and even the type of layout. All I've ever seen is MAXIMUM pressure listed on the tire.
    Hence lawyers.

    They also put a tire diameter on the side of the tire that isn't always grounded in reality. Like I said in another post, experiment. A cyclists weight, how\where ridden, tire type all come into play, and all of these things have as much to do, maybe more, in tire pressure as tire size.

    Like someone else here asked, "What is the weight of a laden swallow?".
    Too old to ride plastic

  16. #16
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    i would not, but inflation guidelines are done with a range. i tend to go toward the lower end of the band simply because of preference to ride quality

  17. #17
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    I think, maybe, the real question of this thread boils down to...

    Is the tire size what is printed on the sidewall or a true measure of the tire diameter?

    I vote true measure=tire diameter\size.
    Too old to ride plastic

  18. #18
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    Quote Originally Posted by sswitzky View Post
    Let’s say I have two tires, a 23mm with actual width around 25mm and a 25mm tire that measures true to stated size.

    Would you inflate both tires to the same psi? (assume both on front or both on rear).
    It depends...on rim width for one thing. Are the 23 and the 25 on the same wheel? If yes I would go down 10 psi on the 25.
    Quote Originally Posted by No Time Toulouse View Post
    I have a non-scientific way of determining how hard to inflate your tires: On my bike, I found that with the classic 23mm wide tires, it worked best for me at 100 psi rear, 90 psi front, which was exactly 13 strokes of my floor pump on the rear, and 12 strokes of the pump on the front.

    Inflating my 42mm wide tires on my gravel/touring bike, I used the exact same number of strokes, and it was perfect, filling them at about 40 psi rear, 35 front. From that, I assume that the having same AMOUNT of compressed air is the key, which corresponds linearly with tire pressure.

    So, If you know how many strokes of the pump from completely flat works for you, use that on every tire width, then check your final pressure.
    This works.

    Quote Originally Posted by Finx View Post
    My answer is: "Probably"

    There is quite a bit of info missing before I can give a more specific answer
    Exactly.

    Quote Originally Posted by Jay Strongbow View Post
    No I wouldn't, I use about 10 PSI less for every 2mm I go up in tire size.

    While not a big deal when moving 2mm in either direction, try using 40mm tires with the same PSI you use on 23mm tires to get any idea if less psi for more mm's makes sense. If you don't blow the 40mm of the rim you'll see quickly that less PSI as tires get bigger makes a lot of sense.
    And this
    Quote Originally Posted by velodog View Post
    I think, maybe, the real question of this thread boils down to...

    Is the tire size what is printed on the sidewall or a true measure of the tire diameter?

    I vote true measure=tire diameter\size.
    And sometimes this

    ETA: I somehow missed the part about the tires actually being the same physical size despite being labeled differently. If they're the same size I'd use the same pressure.
    Last edited by cxwrench; 3 Weeks Ago at 02:37 PM.
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  19. #19
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    Quote Originally Posted by sswitzky View Post
    Let’s say I have two tires, a 23mm with actual width around 25mm and a 25mm tire that measures true to stated size.

    Would you inflate both tires to the same psi? (assume both on front or both on rear).
    For starters, yes, but I'd do some experiments. What a formula says is only a place to start.

    BTW, I think the tire pressure calc. on the Vittoria web site is just silly. It doesn't even take width into account.

  20. #20
    'brifter' is a lame word.
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    Quote Originally Posted by bobf View Post
    For starters, yes, but I'd do some experiments. What a formula says is only a place to start.

    BTW, I think the tire pressure calc. on the Vittoria web site is just silly. It doesn't even take width into account.
    Someone did a study where they used a device like what you'd use to measure durometer...they determined that to maintain the same surface tension, or 'feel' you'd have to reduce pressure by damn near exactly 10 psi for every tire size increase. I would assume this was using the same size rim.
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  21. #21
    changingleaf
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    I will also say probably.

  22. #22
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    Since your two tires are effectively the same size (they have the same measured width), air them the same way. That's what I do.

    My 25mm GP4000S are 29mm on my very wide HED rims (20.5mm internal width, 25.5mm external width). So at 170 pounds, I use 65psi front, 80 psi rear. It's a fast, comfortable ride.

    I've gotten a few pinch flats at these pressures over the years. Each time, it was a sharp edged small rock that I hit at speed. No problems with bumpy railroad tracks or rounded potholes.

  23. #23
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    Quote Originally Posted by rm -rf View Post
    Since your two tires are effectively the same size (they have the same measured width), air them the same way.
    This ^^^^^^^^^^^^^^^^^

  24. #24
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    Quote Originally Posted by rm -rf View Post
    Since your two tires are effectively the same size (they have the same measured width), air them the same way. That's what I do.
    So you're saying if I wanted to use 35 psi in a 23mm tire and not pinch flat I couldn't just take a sharpie and cross out 23mm printed on the tire and and change it to say 40mm? (sarcasm)

  25. #25
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    Quote Originally Posted by sswitzky View Post
    That’s why I am asking the question. Let me rephrase. If my tires labeled 23mm are really 25mm, should I inflate them as if they were really 25mm? In other words, a lower PSI?
    Yes. Those two tires will have the same contact patch on the road and should therefore be inflated the same. The labeling is irrelevant.
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