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  1. #1
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    Will a wide rim allow me to run 25mm tire without rubbing my frame?

    I have plenty of clearance on the front to run whatever size tire I want but the rear is another story.

    A while back I mounted a 25mm tire to my 19mm rim and it rubbed the frame. I had room on the sides of the tire but the tire contacted the at the middle of the tread.
    I'v been stuck with 23mm tires but I'm getting ready to replace my wheels and am looking at my rim options right now.
    I'm wondering if I mounted a 25mm tire to a wide 23mm rim would this reduce the height of the tire? I figure the side walls are being spread out so it seems like the tires total height would be reduced.

    The 25mm tire that rubbed was a Conti 4000s.

    Thanks.
    Last edited by gruntle; 04-12-14 at 06:05 PM.

  2. #2
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    i'm assuming you're talking clincher tires here.

    in my experience, continental gp4000s tend to run a little tall for the size (which is why some tout there aerodynamics).

    a wider rim will generally make tires sit a bit lower. if you think about it, there is a fix amount of material, and if the beads are stretched further apart (due to the wider rim), then there is less material to extend up above the rim. the difference is likely small, but it may be just what you need.

    if your clearance is that tight, i'd give a minute to think about any debris getting caught and potentially damaging the frame and/or locking the wheel.

    if you're talking tubulars, the design means that the tire's dimensions (which can be different from what is quoted) reflect the diameter of a cross-section -- height or width. the width and height won't really change based on the width of the rim. for a clinker, things are a bit more variable.

  3. #3
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    Quote Originally Posted by tetonrider View Post
    a wider rim will generally make tires sit a bit lower.
    Only once the rim gets *really* wide. Consider starting with a tire that measures 25*pi mm from bead to bead when laid flat. Mount that on a *very* narrow rim with just a few mm between the sides so the tire forms a circular cross-section with a diameter of 25mm above the rim. So it's 25mm wide and also has a high point 25 mm above the rim. Now replace that rim with one that's 50 mm wide. The circumference of the tire is still 25*pi mm, but now the tire forms a semi-circular cross-section with a radius of 25mm, so it's 50 mm wide but still extends 25 mm above the rim (circum. of a semi-circle = pi * r). So going from a rim of almost zero width to one that's 50mm wide hasn't gained you anything in terms of vertical clearance.

    Now if you continue to widen the rim the tire will finally start to have a high point closer to the rim - in the extreme case you end up with a rim that's 25* pi mm wide and a tire that lies completely flat across that rim (good luck getting it to seat properly - and of course you'd be riding more on the rim that on the tire).

  4. #4
    Elite Fred mollusk's Avatar
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    My race wheels are "aero" by being significantly wider than my normal training wheels so that there is no sudden change in profile. I didn't have any problems with frame clearance, but I did need to purchase special low profile pad holders for my brakes. It was either that or trimming off a lot of the brake pads for my race brake pads.
    I'm the world's forgotten boy. The one who's searchin', searchin' to destroy.

  5. #5
    Senior Member shovelhd's Avatar
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  6. #6
    Ninny globecanvas's Avatar
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    Quote Originally Posted by tetonrider View Post
    if your clearance is that tight, i'd give a minute to think about any debris getting caught and potentially damaging the frame and/or locking the wheel.
    This does happen. I run 25s on my rain bike because they are comfy, but clearance under the brake bridge is minimal. A few weeks ago I got a piece of gravel stuck between the rear brake bridge and the tire, which brought me to a skidding halt. Luckily I was climbing a hill and not descending, and no damage was done, although the last thing I wanted to do at that moment was stop and get off the bike.

  7. #7
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    Quote Originally Posted by globecanvas View Post
    This does happen. I run 25s on my rain bike because they are comfy, but clearance under the brake bridge is minimal. A few weeks ago I got a piece of gravel stuck between the rear brake bridge and the tire, which brought me to a skidding halt. Luckily I was climbing a hill and not descending, and no damage was done, although the last thing I wanted to do at that moment was stop and get off the bike.
    Seems like 25s might not work out on this frame. I have ridden a several days on wet mucky roads when my winter bike was not available. The road debris was enough to rub off the paint.
    Yesterday I rode a new route on a paved trail that turned to gravel, while nothing got full on stuck with my 23s the tire brought enough gravel pieces through to wear down to carbon fiber!

    I may go with wider rims for other benefits but it seems 25s are not going to happen on this bike.

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