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Rim Size and Tyre Size - Doesn't Make Sense

Discussion in 'Technical Know How' started by MacB, 13 Nov 2009.

  1. MacB

    MacB Lover of things that come in 3's

    Going on modern measurements I think I understand as follows:-

    rims - shown as xxx-xx where xxx equals rim diameter and xx equals interior rim width. ie 622-15 is a 700c mavic open pro road rim and 559-19 is a mavic XM719 mountain bike rim. All these measurements are in mm.

    tyres - shown as xx-xxx where xx is the tyre width and xxx the rim diameter it will fit on to. So 50-622 is a Schwalbe Big Apple for a road rim and 50-559 is the same for a MTB rim, again all in mm.

    But what works with what? I get that you need the diameters to match, so tyre and rim should both be 622 or 559 etc. But what about what tyre width fits on what rim width? to date I've gone by Sheldons little table but am getting confused by what is on manufacturers sites:-

    Mavic A719 722-19 rim accepts 28 to 47mm tyres, Mavic 559-19 rim accepts 1.5 to 2.3 inch tyres. Why they switch to inches from mm I don't know and why one 19mm wide rim takes 28 to 47 and another 38 to 60mm I don't know. There are even bigger discrepancies with other rims, I've seen a 559-17 quoted as taking tyres 1 to 2.1 inches or 26 to 53mm tyres.

    Can anyone make this clearer for me? specifically I'm thinking of running some big tyres/29ers and am trying to understand what I can put on what 700c rim.
  2. hubgearfreak

    hubgearfreak New Member

    Advert
    i've used these for a couple of years with 56-622 tyres, no problems. spa list them as suitable for up to 51mm, but rigida state that up to 62mm is fine. they're cheap enough, very strong, available in black or silver and they lace up lovely:biggrin:
    perhaps not the best choice if your an athletic 10stone weight obsessive, but that's not us, is it:laugh:
  3. TheDoctor

    TheDoctor Man-Machine

    Location:
    Hertfordshire
    I wonder if it's something as simple as 700C being a European size, hence traditionally shown in mm, whereas the MTB 26 inch is American, hence usually shown in inches?
    I've no idea, I'm just guessing really.
  4. MacB

    MacB Lover of things that come in 3's

    Ta HGF that's the sort of thing I was thinking, and a very attractive price as well:biggrin: Strange the discrepancy between Spa and Rigida there, 11mm is quite a difference between limits.

    Still curious as to why MTB tyres are described in inches and road in mm, when the standards are all in mm?
  5. hubgearfreak

    hubgearfreak New Member

    on this occasion, ignore spa, and always ignore imperial measures.
  6. Cunobelin

    Cunobelin Guru

    Location:
    Gosport
    Seconded two 20 " tyres can be up to 2 inches difference in diameter
  7. MacB

    MacB Lover of things that come in 3's

    Agreed, would rather trust the manufacturer which is what puzzles me with Rigida v Mavic. They both do a 19mm internal width rim in 559 and 622 diameters. Both rims are double walled and double eyeletted, though the Mavic rim is a bit lighter. But:-

    For 559 Rigida state 28mm to 62mm and Mavic 28mm to 60mm(though Mavic do the measurements in inches for this)

    For 622 Rigida state 28mm to 62mm, so nice and consistent but Mavic state 28mm to 47mm - this time Mavic use metric rather than imperial. That's a 15mm difference in maximum tyre size for what is an almost identical rim.

    Searching on the web brings up a variety of opinion on what size of tyres you can safely run on which width of rim. However there's no consensus of opinion, the phrase 'but many people run tyres outside these parameters successfully' seems often used. A lot of them also say that, if in doubt, refer to the rim manufacturers website.

    So am I to believe that the, far more expensive, Mavic rim has a 19mm tolerance range yet the, cheap and cheerful, Rigida a 34mm range for tolerable tyre sizes? Yet reduce the diameter of each rim from 622 to 559 and suddenly they have identical tolerances?

    I think Doc may be onto something with the Americans and use of imperial measurements. Only today have I realised that a 29er, 28.xx(28 inch) and 700c all refer to the same diameter of rim, none of which give you a clue about internal rim width, ie where the tyre sits. Whereas the, supposed, standard of 622-19 gives you the two key measurements. Same with tyres, 50-622 tells you exactly what to expect, though tyre chunkiness/puncture protection will impact the overall wheel size re frame fitting. But there's an element of common sense in the last bit and most of us check frame clearances before tyre purchase.

    Another one - my first bike came with 622-14 rims and 32x622 tyres fitted to it, I then swapped out the tyres to 35x622. Yet perceived wisdom on the net indicates that max tyre size for a 14mm wide rim should be about 28mm.

    I'll keep looking:biggrin:
  8. cyberknight

    cyberknight Veteran

    Location:
    South Derbyshire
  9. MacB

    MacB Lover of things that come in 3's

    yep, read all that, also found an article from Chris Juden at CTC which maybe explains my puzzle a bit better. He indicates that the bigger/wider the tyre the more pressure put on the sidewalls of the rim. Apparently MTB tyres are all run on rims that are too narrow but they make the rims stronger to cope. So the comparison I made of Mavic and Rigida above, the difference would be in weight/strength of rims. The Mavic is lighter and so they won't rate it to take the pressure of an oversize tyre at 700c. Whereas the Rigida is nearly 50% heavier/stronger and they rate the rim to cope with the increased sidewall pressures.
  10. TheDoctor

    TheDoctor Man-Machine

    Location:
    Hertfordshire
    It's just not worth thinking too much about some things IMHO.
    That way lies madness...
  11. hubgearfreak

    hubgearfreak New Member

    you're right, but i suspect it may be too late for macb:tongue: