Michelin tyre sizes accurate?

Discussion in 'Cycling Equipment' started by kolchek, Jul 12, 2011.

  1. kolchek

    kolchek New Member

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    I'm looking at buying some Michelin Pilot Sport tyres online & I was wondering if anyone knows how accurately Michelin label their tyre sizes. I bought a pair of 32mm Continental Top Contacts a while ago & when mounted they were waaay narrower than the 32mm Bontrager Race-Lites they were supposed to replace.

    The Race-lites measure exactly 32mm mounted. The Pilot Sports come in 28, 32 & 35 apparently.

    Thanks.
     
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  2. vspa

    vspa Active Member

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    its funny, i had the same problem with the 4 seasons Continental, otherwise great tires. Maybe the use another numbering system...
     
  3. tafi

    tafi Member

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    I haven't yet found a manufacturer who always quotes accurate tyre widths so i don't expect Michelin to be any different.

    In any case, it depends as tyre construction varies between manufacturers and models. Should it be measured on the width of the casing or on the total width (which is als affected by the width and thickness of the tread and casing protection coatings)? No-one can agree.
     
  4. digifant

    digifant New Member

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    Kolchek,
    If you do get the Michelin Sport Pilot, please let us know your impressions.
    The thing that kept me from buying them is the low 33 tpi
    I went instead with german made ultra gatorskins
    Thanks
     
  5. kolchek

    kolchek New Member

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    Chain Reaction cycles has them incredibly cheap at the moment so I'll give them a try & let you know.
     
  6. digifant

    digifant New Member

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    Kolchek,
    Thanks for the tip.
    I ordered a set as well.
    At this price, it can't be a big risk ;)
     
  7. kolchek

    kolchek New Member

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    Exactly. No probs.
     
  8. digifant

    digifant New Member

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    I've installed the tires (700x35) this morning & rolled them to work ~2km
    I weigh 95kg, so I have inflated them to 110psi, like the continentals
    Michelin says max 87 psi, but I was wondering, what's the max pressure before a blow out?
    Any experience?
     
  9. tafi

    tafi Member

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    Tyre casings are quite strong and will take plenty of pressure, but i have grave fears for your rims (and your safety) at such high pressures. The pressure (directed outwards) tends to try to peel the rim apart. This stress on the rim is proportional to the tyre pressure and the inside surface area of the tyre (which is proprtional to tyre width). Most rims have recomended maximum pressures of around 110~120psi for 23mm tyres. Your 35s have at least 52% more surface area and therefore put at least 52% more stress on the rims at this pressure. If you haven't exceeded the rim's factor of safety then you are very close to it.

    The tyre maximum of 87psi is there for this reason.

    Furthermore, it is a maximum pressure. That can be very different from the ideal pressure (which is usually lower, not higher).
     
  10. kolchek

    kolchek New Member

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    I haven't received mine yet digifant, do the 35s measure about 35 on your rims?
     
  11. digifant

    digifant New Member

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    Tafi, scary story: I'll play safe and deflate to 90 psi

    Kolchek, I took some photos.
    The rim is 13mm wide (Mavic Ksyrium equipe)
    As you see on the last image, the tire is ~3mm from the chainStays (on kona major jake)
    [​IMG]
    [​IMG]
    [​IMG]
     
  12. kolchek

    kolchek New Member

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    Thanks for the pics.

    That's a tight fit!
     
  13. Eichers

    Eichers New Member

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    Hi digifant, how are your rear gears working ... good, bad, etc :)

    Very tight fit ... how come you went for a 35mm tyre?
    Actually, +1 with tafi's post ... between 80 and 90psi should be more than sufficient :)
     
  14. digifant

    digifant New Member

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    kLabs,
    downshifting 2 gears is not always precise: the chain would return 1 gear up.
    I often have to click the lever to adjust. But upshifting is always right.
    I tried the 35mm for the comfort around town.
    Besides, topography makes it difficult to roll more than 30kmh
     
  15. Eichers

    Eichers New Member

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    Hi digifant, I initially had a similar issue, but I found with the MTB RD (XT/M772) that I could rotate it foward so that the chain from the bottom of the sprocket to the guide pulley wheel is always (or nearly always) horizontal. This made a huge difference, providing nearly always perfect shifting :)

    I could rotate the MTB RD forward because the B screw adjusts with the MTB RD mechanism and not against the Derailleur Hanger. :)

    Unfortunately, you cannot do this with a road RD because the B screw adjusts against the Derailleur Hanger :-(


    The only thing with a 35mm tyre is the rotating weight, but you will get a more comfortable ride :)
     
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