In terms of tyre clearance

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  • In terms of tyre clearance
  • Premier Icon SaxonRider
    Subscriber

    Do you need all around the tyre, or side to side only? I’m just looking at a bike with 33 mm tyres that looks like it would have room for at least 38s in terms of side to side clearance, but there is less room at the top.

    Does a tyre’s whole profile get bigger with bigger widths?

    Pardon the ignorance…

    Premier Icon mikewsmith
    Subscriber

    Road? If you look at TT bikes about a fag paper is normal all around

    joshvegas
    Member

    A tyre will try to be as clise to round it can be.

    Less top than side clearance suggests relatively narrow internal width rims.

    cynic-al
    Member

    Josh has it

    Height will increase by half the width

    philjunior
    Member

    As others, it’ll basically grow up and out at the same time (depending on the tread depth).

    You need a bit more clearance at the side as the frame and wheel will flex a little – no so much of an issue in the plane of the wheel.

    Premier Icon Bez
    Subscriber

    Josh has it Height will increase by half the width

    (Pedantry alert)

    Josh does indeed have it, but it means that height will increase by more than half the width. The inner rim width forms a chord across the circle on which the tyre carcass sits*, and that’s fixed. As you increase the circumference of that circle (ie fit a larger tyre) not only does the circle become wider but its centre also moves away from the chord. So you have the increase in radius (the half-the-width that you mention) plus that additional distance from the centre. The narrower the rim, the more significant that effect (at rim width zero the height increases just the same as the width).

    I realise this could really use a diagram 😉

    Less top than side clearance suggests relatively narrow internal width rims.

    That’s one factor, but the other is simply the shape of the frame. It’s quite common for the positioning of the chainstay bridge to result in less radial than lateral clearance.

    Does a tyre’s whole profile get bigger with bigger widths?

    Put your mountain bike and your road bike on the ground and look at the bottoms of the wheels. Is your mountain bike rim further from the ground than your road bike’s rim? There’s your answer 😉

    * for the purposes of this exercise, assume a tyre is uniformly flexible around its circumference; this isn’t quite true, because the tread is stiffer than the sidewalls, but it’s fine for this discussion and in terms of clearance the tread thickness will counteract the effects on stiffness anyway

    philjunior
    Member

    (Pedantry alert)

    Pedantry appreciated, disappointed I didn’t come up with this!

    cynic-al
    Member

    Quite right Bez.

    amedias
    Member

    ah, technically correct, the best kind of correct.

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