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23 to 25 mm tyres: how much room?

secretsamsecretsam Posts: 4,904
edited November 2015 in Road buying advice
How much clearance do I need if I want to switch out my 23mm to 25mm? My bike's a 2012 Cinelli with pretty tight clearances, so I may be stuck with 23mm!

It's just a hill. Get over it.

Posts

  • 2mm more than you have now.
  • bmxboy10bmxboy10 Posts: 1,917
    I think we have answered this before? I had a Saetta and 25 Conti GPs were too tight on the rear.
  • It depends on the tyre/ rim combination. I would certainly avoid Michelin Pro 4 Endurance as they came up almost to 28mm on my RS500 wheels.

    The Schwalbe Duranos seem much skinnier, but you'll be safest measuring them first. I'm sure your LBS will be happy to help :)
  • singletonsingleton Posts: 2,183
    It depends, some 23mm tyres run close in width to some 25mm tyres.
  • AnonymousAnonymous Posts: 79,667
    The narrower the rim, the closer the tyre will get to the frame. Wider rims will make wider tyres fit better.

    A 25mm tyre on a 23mm rim could have loads of clearance but if it was sat in a 19mm rim it would protrude outward from the rim more making it more likely to brush the frame/mudguard/brake caliper.
  • keezxkeezx Posts: 1,319
    Do not assume that a tyre will build higher on a narrower rim as it is not always true.
    The rim-tyre combination is basically a circle, if the cicumference increases, the diameter can increase too.
    1zce89x.jpg
  • AnonymousAnonymous Posts: 79,667
    Do not assume that a tyre will build higher on a narrower rim as it is not always true.
    The rim-tyre combination is basically a circle, if the cicumference increases, the diameter can increase too.
    1zce89x.jpg

    That diagram is very inaccuracate in the fact that the narrower the rim the tyre appears to shrink in surface area even at a higher suggested tyre pressure. Where a tyre may not necessarily bulge upwards it would bulge outwards. In the diagram the tyre not only does neither it gets smaller
  • keezxkeezx Posts: 1,319
    Well, somebody (from the HED factory) did some work to show what happens with rims&tyres (so not me) and it shows at least that it's not always clear and predictable....
    My message is: don't count on building a tyre lower on a wider rim.
  • AnonymousAnonymous Posts: 79,667
    Well, somebody (from the HED factory) did some work to show what happens with rims&tyres (so not me) and it shows at least that it's not always clear and predictable....
    My message is: don't count on building a tyre lower on a wider rim.

    I didn't suggest you did the diagram but you have to admit that it doesn't make sense in parts. Besides we all know a 25mm conti is not the same as a 25mm Vittoria or Schwalbe etc. Many can vary alot in actual diameter.
  • keezxkeezx Posts: 1,319
    It's not a diagram but a model what shows what can happen with some specified tyres on 3 different rim widths.
    If you want to prove it doesn't make sense you 'll have to do the tests yourself or deliver a good explanation why it doesn't make sense which you did not....
    Tyres differ in stiffness locally and size of coarse , that might explain why they do not all take the same form on the same rim with the same pressure.
  • AnonymousAnonymous Posts: 79,667
    It's not a diagram but a model what shows what can happen with some specified tyres on 3 different rim widths.
    If you want to prove it doesn't make sense you 'll have to do the tests yourself or deliver a good explanation why it doesn't make sense which you did not....
    Tyres differ in stiffness locally and size of coarse , that might explain why they do not all take the same form on the same rim with the same pressure.

    OK, let me explain another way. The tyres are either 23mm or 25mm - both the same brand in all tests

    Look at the white line and the deep red line. They should be exactly the same length. The line should represent the width of the tyre from bead to bead. But the white line is noticeably shorter than the red line. I can understand the 23mm being shorter than the 25mm but the 25mm should be the same length regardless of the rim width. Even if you say its to do with pressure then the pressure is higher in the shorter line so it cant be the rubber expanding.

    Does this make any more sense to you cos to me it just comes across as complete BS.
  • secretsamsecretsam Posts: 4,904
    I think we have answered this before? I had a Saetta and 25 Conti GPs were too tight on the rear.

    Yeah, but I lost the answer! Did you ever get a solution? And I've fitted new wheels as well (still super narrow, though, 15mm rims)

    It's just a hill. Get over it.
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