Tyre width quirks

Discussion in 'General Cycling Discussions' started by Cyclist33, 10 Jul 2012.

  1. Cyclist33

    Cyclist33 Guest

    Just done something that for unknown reasons I never did before... Took a ruler and measure the width of my tyres.

    On my hybrid the conti city contacts, which are rated as 32s, the actual measured width pumped up to a normal pressure, is 25mm. This explains why they look, and feel, similar to the 25s I had on my felt racer last year. They weigh in at 520 grams each, without tubes, so pretty hefty for what turns out to be a road tyre. By contrast my sisters new giant hybrid has giants own 32mm tyres, which actually are 32, and a sight more plush. Still, I can get a decent lick of speed out of my cannondale so maybe if I put on some proper road tyres at 25mm I will not lose comfort compared to the current setup, but might be able to drop half a kilo if I got, say, some 250 gram rubber.

    On my hard tail, the WTB Raijins are rated at 2.1". Actually, measured from outer edge of side knobs, the width is 2.0". Not a big difference. By contrast, I have a spare front tyre which is a Kenda Nevegal 2.1. This is significantly wider than the Raijins. I use the Kenda on the front with a heavy Geax semi slick on the back when I want to spare the Raijins and if ferrying the little un around. Both the Kenda and Geax tyres weigh in at around the 740 gram mark whereas the Raijins are around 520 gms, so quite a different feel when accelerating on climbing.

    How do YOUR tyres measure up against their published specs, and how does this affect your ride?

  2. Ian H

    Ian H Guru

    East Devon
    Tyre measurements are the height, not the width. Having said that, they are mostly nominal.
  3. OP

    Cyclist33 Guest

    Er, the 32 in "700x32" is the nominal width in mm of the tire from bead to bead. Isn't it?

    And if what you say is true, then what units are the "2.1" emblazoned on the sides of my WTBs?

  4. OP

    Cyclist33 Guest

    They do seem to be somewhat arbitrary!

  5. TheDoctor

    TheDoctor Resistance is futile! Moderator

    2.1?? That's inches. 2.1 inches.
    The width of the tyre is an overall width when inflated, not bead to bead (which is obviously constrained by the wheel rim). It'll end up being much the same as the height of the tyre - given half a chance, it'll try and adopt a circular cross-section.
  6. OP

    Cyclist33 Guest

    Er, I do kinda know all this. When I said bead to bead it was just quicker than describing it another way.

    To address the point about whether the rated width is height or breadth, how can one measure an inflated tyre's height, as part of it would always be obscured by the rim?

    But in any event, what I was originally asking was what tyre width quirks do you find on your own bikes?
  7. fatblokish

    fatblokish Veteran

    In bath
    Not found any, but then I've not looked.
  8. ufkacbln

    ufkacbln Guest

    The tyre size is a nightmare.
    There are 5 different 20" tyres with a total difference in diameter of over an inch and a half!

    The best bet is to look at the ETRTO number in the format xx-yyy where the xx is the nominal internal width of the tyre at the maximum (NOT the bead) and the yyy is the bead diameter.

    That way you get a tyre that fits your rim, 406 will fit all my rims.

    Note: these are tyrre measurements. The rim will have a set description and this is constant for the bead width.
  9. GrasB

    GrasB Veteran

    Nr Cambridge
    Measure the bead to be circumference around the outside of a 50-559 kojak & big apple & you'll find they're the same. Mount on a 559-20 rim then inflate to 20psi & the tyre width is the same (x§ but inflate to 40psi & the Kojak is narrower (BA:51mm, K:48mm)! Now mount the same tyres on a 559-33 rim & the Kojak is wider (BA:52mm, K:53mm). Has your brain exploded yet?
  10. tyred

    tyred Legendary Member

    Michelin tyres always appear to be oversized in my experience.
  11. The key word in all of this is 'nominal'.
    gaz likes this.
  12. Boris Bajic

    Boris Bajic Guest

    I measured all the way round the tyres on my several bicycles and then measured the diameter of each wheel with the tyre fitted.

    On every occasion, the distance all the way round seemed to be about three times the diameter. Maybe just a little bit more.

    Later the same day, I asked three men to dig a hole fourteen metres deep in seven hours.

    I also bought three sausage rolls with a single banknote and counted my change carefully.

    In every case the answer was Lithuania.

    Am I onto something here?

    Michael Gove says I should have answered my questions in Latin.
    Cyclist33 likes this.
  13. akb

    akb Über Member

    You lot have far too much time on your hands! ^_^
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