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  1. #1
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    Whats the smallest tire i can put on a 38mm internal rim?

    Hi, im looking for new tires. im currently riding a 3inch on a 38mm internal and want to go smaller. I was super curious on how small I can go.

  2. #2
    Make America Bike Again
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    You can go all the way down to about 1.4x, but I've noticed that people that go down below 2.0x start to have sidewall cut problems and greatly increased treadwear (and no side knobs anymore). Right now you are at exactly 2.0x so maybe you just need a new smaller tire and (smaller rimmed) wheel.
    Gallia est omnis divisa in partes tres: quod Belgiae, quod Celtae, et quod Aquitainae.

  3. #3
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    Maxxis Minion 2.5 WT
    Vermonter - bikes, beers and skis.

  4. #4
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    Quote Originally Posted by VTSession View Post
    Maxxis Minion 2.5 WT
    which is much closer to a 2.3 in reality...


  5. #5
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    About a 2.87.

  6. #6
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    Quote Originally Posted by richj8990 View Post
    You can go all the way down to about 1.4x, but I've noticed that people that go down below 2.0x start to have sidewall cut problems and greatly increased treadwear (and no side knobs anymore). Right now you are at exactly 2.0x so maybe you just need a new smaller tire and (smaller rimmed) wheel.
    I agree with this. I bought a 30.5i set after talking with trek and asking if their 2.3 se5 would work well with that rim width. They told me their 2.3 tire fits a 22-41i width rim. My sidewall hangs out about 1mm past my side nobs and it bugs me bad. But so far so good this season and I’m running a great psi combo. For me I see that the 2x is the number to go with but everyone’s tire choice and riding styles vary.


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  7. #7
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    Quote Originally Posted by .WestCoastHucker. View Post
    which is much closer to a 2.3 in reality...

    BTW for measuring tire height, I simply took 22 inches for the 26" rim or 23 inches for the 27.5" rim, and added twice the diameter of the measurement I took from the casing thickness from the rim to the top knob. Also for calculating theoretical vs. actual tire width, you take your actual internal rim width, compare it with 3.0 for 45mm, 2.8 for 40mm, 2.6 for 35mm, 2.4 for 30mm, 2.2 for 25mm, etc., subtract the difference, and divide by 80.

    Example: current rim is 25mm, tire width is 2.4 inches, in theory this tire should be on 30mm rim, 5mm different / 80 (80 is 3.14 circumference x 25.4 mm/inch). 5/80 = 0.06 inches, so in theory tire should be 24.6 inches wide (0.06 inches wider on 'correct' 30mm rim). Every 8mm rim difference = 0.1 inch tire width difference.

    All of the tires below have between a 2.4x to 3.4x tire to rim ratio. None have fallen off the wheel, unlike what you hear from the doomsayers...


    26 x 1.95 Kenda Aggressive, 18mm rim = 2.0 inches wide (a correct measurement, yay), 25.0 inches high. Yes, a 26" standard tire is 25" high. No one told me this before lol. No wonder I hate it on dirt. I do like it on pavement. 2.8x tire to rim ratio.

    26 x 1.95 Innova (cheap Chinese off brand), 19mm rim = 1.9 inches wide (correct), 25.2 inches high. 2.5x tire to rim ratio.

    26 x 2.40 CST Rock Hawk, 21mm rim = 2.35 inches wide (pretty much right on); 26.2 inches high. 2.8x tire to rim ratio.

    26 x 2.70 Maxxis DHF, on 26mm rim = 2.45 inches wide, 26.4 inches high. On a 35mm rim it should be 2.55 inches wide; 40mm rim should be 2.625 inches wide. This is the only outlier tire for theoretical vs. actual measurement; others have complained about this specific Maxxis tire too (it's discontinued). 2.4x tire to rim ratio.

    26 x 2.80 WTB High Roller, 25mm rim = 2.50 inches wide, 26.4 inches high. Major disappointment. I still like the tire but on this rim it is obviously not a plus tire. If this was mounted on an i40 rim, then 40-25 = 15mm / 3.14 circumference = 5mm or 0.2 inches wider if on a 15mm wider rim. So it would go from 2.5 to 2.7 wide. Height on paper on a 40mm rim would go from 26.4 to 26.7. inches high, still lower than a standard 27.5 tire's height. This makes sense because in theory a 26 x 3.0 on a 45mm rim should be 27.0 inches high. The reason I had to use 25mm for the rim was that I needed to stick with 9x100mm up front for the axle. So basically a half-assed 1/2 plus bike that's really not plus. Again, disappointing. And the flimsy sidewall now has a permanent wobble. 2.5x tire to rim ratio.

    27.5 x 2.35 Kenda Nevegal, 18mm rim = 2.25 inches wide, 27.2 inches high. If in theory you are supposed to put a 2.34 or 2.4 on a 30mm rim, then 12mm extra / 3.14 = 0.15 inches more and you actually get 2.40 inches wide and around 27.5 inches high. Tread is worn so maybe 0.1 inches higher new (27.6 inches high). 3.2x tire to rim ratio.

    27.5 2.50 Maxxis DHF, 18mm rim = 2.375 inches wide, 27.2 inches high as with the Kenda above. Wider tire, stunted height (tire has 1200 miles on it and knobs 1/2 worn). If mounted as in the above example on a 30mm rim, 0.15 inches wider to 2.525; if on a 35mm rim it would be 0.21 inches wider to 2.59. On a wider rim this tire would be WIDER than advertised. So Maxxis, at least in this case, is not 'lying' about its tire widths, people like me are just putting them on skinnier rims than what's recommended. 3.4x tire to rim ratio.


    Bottom line: most tires, if corrected for recommended rim width, have CORRECT tire widths as advertised, within 0.1 inches, and some are actually larger than advertised. It's only when you put them on thinner rims that the actual size shrinks below the advertised size. Going over 3.0x tire to rim ratio is OK if the tire is a standard or voluminous (not a real + tire), AND if voluminous, it has a thick double casing like the Maxxis DHF's do. A plus tire with a thin single wall casing is not recommended for going over 3.0x tire to rim ratio.
    Last edited by richj8990; 08-21-2018 at 01:21 PM.
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  8. #8
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    Quote Originally Posted by evan.c View Post
    Hi, im looking for new tires. im currently riding a 3inch on a 38mm internal and want to go smaller. I was super curious on how small I can go.
    You can try a 2.3 tire with the right design. High volume with a very rounded tread profile. So they won't square off on this rim. Bonty XR2 Team 2.35 can be run on that rim at 14psi or less on the front and 4-5 more on the rear to start. If you get rim hits add a little. If you don't get any bring the pressure down 1 psi at a time.

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