28c Tyre Pressure
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  1. #1
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    28c Tyre Pressure

    Hello. I have Shimano RS100 wheels that are 17c. 28c GP5000 tyres and I weigh 183lbs. I know this gets asked alot but what would you recommend for psi for the most comfort? I ride on alot of rough roads so comfort is paramount.

    Also what is the lowest psi I could get away with?

    Thanks in advance.

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  2. #2
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    "Also what is the lowest psi I could get away with?"

    The answer to that, and your overall question, is 'trail & error". Or 'it depends'. Some people 'ride heavy' and have a knack for not seeing railroad tracks while others just float over stuff.
    At your weight I'd start at 85 and experiment from there.

  3. #3
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    Quote Originally Posted by Champ340 View Post
    Hello. I have Shimano RS100 wheels that are 17c. 28c GP5000 tyres and I weigh 183lbs. I know this gets asked alot but what would you recommend for psi for the most comfort? I ride on alot of rough roads so comfort is paramount.
    Bicycle tire pressure calculator

    Use that as a starting point. The 2nd calculator. Then adjust till you get it dialed in.

    Quote Originally Posted by Jay Strongbow View Post
    Some people 'ride heavy' and have a knack for not seeing railroad tracks while others just float over stuff.
    ^^^^ This.

    I know a guy who weighs ~220-240. Rides 23/25mm tires. He rarely gets flats. Rides low spoke wheels without destroying them.
    And I know many others who weigh much less who seem to get flats just from looking at their bike.
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  4. #4
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    Quote Originally Posted by tlg View Post

    I know a guy who weighs ~220-240. Rides 23/25mm tires. He rarely gets flats. Rides low spoke wheels without destroying them.

    And I know many others who weigh much less who seem to get flats just from looking at their bike.
    I started my relationship with road bike cycling back in 1983. Back in the eighties the stock or standard everyday tire on bikes got flats just sitting in corner of your room or even if you looked sternly at them.

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    Quote Originally Posted by tlg View Post
    Bicycle tire pressure calculator

    Use that as a starting point. The 2nd calculator. Then adjust till you get it dialed in.

    ^^^^ This.

    I know a guy who weighs ~220-240. Rides 23/25mm tires. He rarely gets flats. Rides low spoke wheels without destroying them.
    And I know many others who weigh much less who seem to get flats just from looking at their bike.
    Thanks very much. Using the calculator what weight distribution do you think I should use?

    Thanks for the replies.

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  6. #6
    tlg
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    Quote Originally Posted by Champ340 View Post
    Thanks very much. Using the calculator what weight distribution do you think I should use?
    Depends on how you sit on the bike. Do you sit more upright or a lower aggressive riding position.

    If you wanted to be really specific, have someone balance you on the bike with a bathroom scale under the front, then rear wheel.
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  7. #7
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    Quote Originally Posted by tlg View Post
    Depends on how you sit on the bike. Do you sit more upright or a lower aggressive riding position.

    If you wanted to be really specific, have someone balance you on the bike with a bathroom scale under the front, then rear wheel.
    My 32 year old back is like a 70 year olds so I sit very upright.

    Cheers again

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  8. #8
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    Haha, according to the first calculation on that site, I should have my tire pressure at 185 psi.
    Lost in translation?
    What Does ‘weight measured at wheel’ mean?

  9. #9
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    Like most topics regarding bikes there is disagreement on what is the best air pressure or formula for coming up with a number. The disagreement extends to certified experts on cycling and those that are accepted as experts based upon their body of work. I am neither. The only thing that seems agreed upon on air pressure is if you lower the PSI within tire recommendations of maximum and minimum the ride will be softer.

    Here is one answer for someone that has achieved a satisfactory air pressure on a 23c and is moving up in size. It explains larger tires mean larger volume so a lower PSI is appropriate as you move up in tire size.

    https://www.bicycling.com/repair/a20...tire-pressure/
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    Last edited by GlobalGuy; 05-16-2019 at 12:30 PM.

  10. #10
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    Quote Originally Posted by rideit View Post
    Haha, according to the first calculation on that site, I should have my tire pressure at 185 psi.
    Lost in translation?
    What Does ‘weight measured at wheel’ mean?
    It means exactly what it sayes, measure your wt at the wheel. Put the scale under the front wheel, sit on the bike, read the wt. Repeat the the procedure with the rear wheel.
    If you want it exact, do the same without u... subtract those wts.
    Is that so complicated?
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  11. #11
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    Thanks for the help guys.

    Another question. In the Beginners Corner it doesn't show any threads. This is the same when using Tapatalk and also the web page, all i can see are the sticky threads. Any ideas?

    Many thanks.

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  12. #12
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    I'm running a similar wheel, Ultegra 6800's with GP4000's in a 28 width. I'm 225 and running 75 psi front and rear. Have about 200 miles on this combo without a pinch flat so far.
    You can't fix stupid.

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  13. #13
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    Quote Originally Posted by Champ340 View Post
    Thanks for the help guys.

    Another question. In the Beginners Corner it doesn't show any threads. This is the same when using Tapatalk and also the web page, all i can see are the sticky threads. Any ideas?

    Many thanks.

    Sent from my SM-N920I using Tapatalk
    Down towards the bottom you should see "Thread display options". You won't see it now, when in this thread, but when you first enter the branch and see the stickeys lined up.
    This branch doesn't get much traffic so change it to look a year back or whatever. Your default probably doesn't go back far enough to capture a period when there were any questions.

  14. #14
    tlg
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    Quote Originally Posted by rideit View Post
    Haha, according to the first calculation on that site, I should have my tire pressure at 185 psi.
    Lost in translation?
    What Does ‘weight measured at wheel’ mean?
    It's a little vague, but what it means is the total pressure for both your wheels. You need to divide it proportionally by your weight distribution. Which is what the 2nd calculator does.
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  15. #15
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    Quote Originally Posted by Champ340 View Post
    Thanks very much. Using the calculator what weight distribution do you think I should use?
    The 45%/55% distribution is pretty realistic. 40/60 gives you a large disparity between front and rear. I like running less in the front than rear, but not as wide a difference as the 40/60 gives me.
    "With bicycles in particular, you need to separate between what's merely true and what's important."-- DCGriz, RBR.

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  16. #16
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    The beginner's corner is all but dead. Best to ask your questions in "Wheels & Tires", "Components & Wrenching", "Bikes, Frames & Forks" or "General" if it doesn't fit the previous three. The manufacturer forums are also next to dead.
    "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



  17. #17
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    Quote Originally Posted by GlobalGuy View Post
    Like most topics regarding bikes there is disagreement on what is the best air pressure or formula for coming up with a number. The disagreement extends to certified experts on cycling and those that are accepted as experts based upon their body of work. I am neither. The only thing that seems agreed upon on air pressure is if you lower the PSI within tire recommendations of maximum and minimum the ride will be softer.

    Here is one answer for someone that has achieved a satisfactory air pressure on a 23c and is moving up in size. It explains larger tires mean larger volume so a lower PSI is appropriate as you move up in tire size.

    https://www.bicycling.com/repair/a20...tire-pressure/
    Looks good to me.
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  18. #18
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    OP - I'm about your weight and run 28s. I think my rims might be slightly wider than yours (Velocity A23s) and routinely run my tires between 50 and 60 psi with no issues at all. I do tend to ride "light", so YMMV.

  19. #19
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    Since this is the Beginner's Corner, and I just feel pedantic this evening....(I do intend this to be helpful, not snarky)

    It isn't a "28c" tire. It is a 28mm tire. The letter C has no meaning when it comes to tire size, only the wheel size. The wheel size has the letter after it, 700c (or 650b, 650c, etc.).

    Unfortunately, some tires are marked "700X28C" when they should be marked "700cX28".

  20. #20
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    Quote Originally Posted by Camilo View Post
    Since this is the Beginner's Corner, and I just feel pedantic this evening....(I do intend this to be helpful, not snarky)

    It isn't a "28c" tire. It is a 28mm tire. The letter C has no meaning when it comes to tire size, only the wheel size. The wheel size has the letter after it, 700c (or 650b, 650c, etc.).

    Unfortunately, some tires are marked "700X28C" when they should be marked "700cX28".
    Actually, if you want to be technical, it really should be marked "622 x 28". See below for the straight poop on bike wheel/tire sizes:

    https://www.sheldonbrown.com/tire-sizing.html
    "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



  21. #21
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    Quote Originally Posted by Lombard View Post
    Actually, if you want to be technical, it really should be marked "622 x 28". See below for the straight poop on bike wheel/tire sizes:

    https://www.sheldonbrown.com/tire-sizing.html
    The Conti Ultra 2000 tires I'm running say, "25 x 622" right beside the "700 x 25C" on the label. The Gatorskins are marked "28 x 622" above the "700 x 28C." On other tires, this 622 figure is embossed on the sidewall.

    I measured bead diameter as 622mm on both rims.

    Also, one maker's 25mm might actually be fatter, "26C", or skinnier, "23C," than another's, so outer tire diameters wouldn't all conform to "700C" if that's supposed to identify outer tire diameter. 700mm is 8mm bigger than 622mm, so bead to outer tire diameter would vary from 4 mm around the rim.

    The "700C" may be nonsensical, but it's there, regardless. We always thought of it as bead diameter slightly smaller than "27 inch."
    Last edited by Fredrico; 06-07-2019 at 02:55 PM.

  22. #22
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    Tire width will always vary depending on rim width. Speaking of nonsensical are rim manufacturers that use the outside rim width.
    "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



  23. #23
    'brifter' is a lame word.
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    Quote Originally Posted by Camilo View Post
    Since this is the Beginner's Corner, and I just feel pedantic this evening....(I do intend this to be helpful, not snarky)

    It isn't a "28c" tire. It is a 28mm tire. The letter C has no meaning when it comes to tire size, only the wheel size. The wheel size has the letter after it, 700c (or 650b, 650c, etc.).

    Unfortunately, some tires are marked "700X28C" when they should be marked "700cX28".
    ^This, thank you!^
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