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  1. #1
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    tire pressure for kids' road bikes?

    I am trying to determine the right tire pressure for a kid's bike (rider + bike = 70lbs).

    To make it more complex, the front tire is a Kenda branded 20"(451mm) x 23c and rear a 20" x 28c (won't get into details on how I ended up with such combo).

    Based on my high school physics knowledge (whatever is left of it), one should basically reduce the normal 110/90psi pressure (assume 200lb adult rider + bike) to 38/33psi, but that feels kinda low.

    For fear of getting snake bites or getting out of manufacturer's recommended range, I pumped these suckers to 55/50-ish. Rider did not complain. He had fun.

    I am wondering if I am doing this right. Is there any reliable formulas for doing this? I know there are a bunch of them for adults but none for kids.
    Last edited by threefire; 4 Weeks Ago at 02:28 AM.

  2. #2
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    Just to clarify, the weight is FULLY CLOTHED rider, bike and whatever is carried on the bike.

    Also keep in mind that most of the formulas out there for calculating tire pressure are with 700c tires. You could possibly do a Google search "20 inch tire pressure formula" or something like that.

    What is the PSI range stated on the sidewalls?

    We aging adults feel every bump. Kids don't really care about this, though it could still be a safety issue if he hits a large enough road hazard.
    "With bicycles in particular, you need to separate between what's merely true and what's important."-- DCGriz, RBR.

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  3. #3
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    My wife weighs 90lbs. She runs 23c's at 50/70psi. Never had a problem. Never a pinch flat.

    She could go less (probably has). My concern is keeping the bead seated at lower pressures with hard cornering.
    Custom Di2 & Garmin/GoPro mounts 2013 SuperSix EVO Hi-MOD Team * 2004 Klein Aura V

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    Yossarian: don't worry. nothing's going to happen to you that won't happen to the rest of us.

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    Quote Originally Posted by blackfrancois View Post
    The 2nd box is a good guideline FOR 700c TIRES. However, the OPs tires are for a kid's bike with 20" tires, so this formula won't work.

    You may in the future want to explain links you post rather than lazily copy and pasting just a link for your message.
    "With bicycles in particular, you need to separate between what's merely true and what's important."-- DCGriz, RBR.

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  6. #6
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    Quote Originally Posted by Lombard View Post
    You may in the future want to explain links you post rather than lazily copy and pasting just a link for your message.
    lofl.
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  7. #7
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    You are certainly not wrong about this. That said, I appreciate anybody's input.

    You do make a good point that smaller wheels have a shorter rubber patch than 700c wheels and probably require higher pressure to compensate.

    Given all the info I have so far, here is the rough math:

    1. Based on blackfrancois' calculator, both wheels should be inflated to about 25-28 psi,

    2. Then suppose those numbers are increased by 40% to account for the shorter rubber patch, so you get 35-40psi.

  8. #8
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    Quote Originally Posted by threefire View Post
    You are certainly not wrong about this. That said, I appreciate anybody's input.

    You do make a good point that smaller wheels have a shorter rubber patch than 700c wheels and probably require higher pressure to compensate.

    Given all the info I have so far, here is the rough math:

    1. Based on blackfrancois' calculator, both wheels should be inflated to about 25-28 psi,

    2. Then suppose those numbers are increased by 40% to account for the shorter rubber patch, so you get 35-40psi.
    My feeling is that 40-45 PSI is probably about where you should be.
    "With bicycles in particular, you need to separate between what's merely true and what's important."-- DCGriz, RBR.

    “Statistics are like bikinis. What they reveal is suggestive, but what they conceal is vital.” -- Aaron Levenstein



  9. #9
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    Quote Originally Posted by threefire View Post
    I am trying to determine the right tire pressure for a kid's bike (rider + bike = 70lbs).

    To make it more complex, the front tire is a Kenda branded 20"(451mm) x 23c and rear a 20" x 28c (won't get into details on how I ended up with such combo).

    Based on my high school physics knowledge (whatever is left of it), one should basically reduce the normal 110/90psi pressure (assume 200lb adult rider + bike) to 38/33psi, but that feels kinda low.

    For fear of getting snake bites or getting out of manufacturer's recommended range, I pumped these suckers to 55/50-ish. Rider did not complain. He had fun.

    I am wondering if I am doing this right. Is there any reliable formulas for doing this? I know there are a bunch of them for adults but none for kids.
    Not real easy to measure, but certainly possible with a little thought: the general guide is tire pressure that results in 15% drop. So if the tire is 28mm, then when the rider is on the bike the rim should be 4 mm closer to the ground than when the bike is unweighted.

  10. #10
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    Quote Originally Posted by threefire View Post
    I am trying to determine the right tire pressure for a kid's bike (rider + bike = 70lbs).

    To make it more complex, the front tire is a Kenda branded 20"(451mm) x 23c and rear a 20" x 28c (won't get into details on how I ended up with such combo).

    Based on my high school physics knowledge (whatever is left of it), one should basically reduce the normal 110/90psi pressure (assume 200lb adult rider + bike) to 38/33psi, but that feels kinda low.

    For fear of getting snake bites or getting out of manufacturer's recommended range, I pumped these suckers to 55/50-ish. Rider did not complain. He had fun.

    I am wondering if I am doing this right. Is there any reliable formulas for doing this? I know there are a bunch of them for adults but none for kids.
    You are over thinking this. Pump up the tires and give them the pinch test. If they feel good let him\her have at it, if pinch flats, patch and pump up 5lbs more and let him\her have at it. Don't drive the fun out till the kid is on 700c wheels.
    Too old to ride plastic

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