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Tyre width

Hello, just wondering about the width of MTB tyres. For example, a 2.35 tyre is almost 6 centimetres. Was at a bike shop recently and looked at a bunch of bikes with 2.35 tyres. However, they were nowhere near 6cm wide. They looked like 10cm from sidewall to sidewall to me! (which is about 4 inches). Is there something I'm missing? Do tyres get wider as you inflate them? Does the measurement only apply to deflated tyres? I'm so confused!

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  • steve_sordysteve_sordy Posts: 2,248
    The tyre width is measured from shoulder to shoulder when inflated. But it wouldn't change much even if deflated and certainly not by the difference between 4" and 2.35". There should be no visual confusion between a 4" tyre and a 2.35" tyre! After all, one is more then 1.6" wider (4cm). Are you sure that the bike spec that said the 4" tyres were 2.35" was correctly applied?

    A 4" tyre is a "fat" tyre, for fat bikes, like those made by Surly.

    For many years, a 2.4" tyre was as wide as you could fit on an mtb, and then only some mtbs. Any wider and the tyre would rub on the frame when cornering, or the tyre would carry stones around and strike the seat stay brace. Then wider tyres became the next big thing and what became known as "mid-fat" tyres were suddenly everywhere. These sizes were 2.6" - 3.0", maybe as big as 3.2" but I have never seen any.
    When you first see a 2.8" tyre you will gasp that a bicycle could (let alone should) have tyres that wide. The bikes have to be purposely designed to allow them to be fitted. Why go so wide? Well, with the correct pressure they provide awesome grip so that cornering and climbing become a different experience. But they are much heavier. To get the best out of mid-fat tyres, you either need to go tubeless or fit them to your emtb, preferably both. Buy a digital pressure gauge so that once you find the correct pressure for you and your trails, you can guarantee to keep that pressure for always. We are talking mid teens of psi here, and I don't know about you, but my thumbs are not calibrated for the required level of accuracy.
  • Then wider tyres became the next big thing and what became known as "mid-fat" tyres were suddenly everywhere. These sizes were 2.6" - 3.0", maybe as big as 3.2" but I have never seen any.
    When you first see a 2.8" tyre you will gasp that a bicycle could (let alone should) have tyres that wide. The bikes have to be purposely designed to allow them to be fitted. Why go so wide? Well, with the correct pressure they provide awesome grip so that cornering and climbing become a different experience. But they are much heavier. To get the best out of mid-fat tyres, you either need to go tubeless or fit them to your emtb, preferably both. Buy a digital pressure gauge so that once you find the correct pressure for you and your trails, you can guarantee to keep that pressure for always. We are talking mid teens of psi here, and I don't know about you, but my thumbs are not calibrated for the required level of accuracy.


    With respect, a lot of that is nonsense.

    They are called plus tyres, and don’t need to run them tubeless, or with an ebike. They are an acquired taste, as they can feel vague and disconnected from the trail, as I found. They are also awful in mud, as they just float over the top, rather than digging in. Most modern 29er bikes will take a 27.5x2.8-3 tire.

    As for what you saw, tyre sizes for a prescribed width vary, as manufactures don’t use the same points to measure, some measure from the outside of the tread, others from the carcass. Rim width will also affect the size of the tyre. Once the tyre is installed properly, the pressure will not affect the size.

    That said, they won’t almost double in size, so id suggest, politely, that what you werent always looking at weren’t 2.35 tyres.
    Santa Cruz 5010C
    Deviate Guide
    Specialized Sequoia Elite
    Pivot Mach 429SL
    Trek Madone 5.2 Di2
    Salsa Mukluk Carbon
    Specialized Turbo Levo Expert 29er
  • steve_sordysteve_sordy Posts: 2,248

    ...............
    With respect, a lot of that is nonsense.

    They are called plus tyres, and don’t need to run them tubeless, or with an ebike. They are an acquired taste, as they can feel vague and disconnected from the trail, as I found. They are also awful in mud, as they just float over the top, rather than digging in.........
    "Mid fat" is an alternative to "plus". Plus sounds better when applied to bikes. I'm happy to use your alternative. :)
    The debate about tubes or tubeless is never ending and there are firm supporters and detractors of both views. It is my opinion that tubeless is better, especially for big tyres, but I cheerfully accept that you disagree. :)
    When I suggested fitting them "to your emtb" I was having a joke at the expense of the heavy tyres. :D One of my criticisms of some emtb riders is that they claim that because they have power assist weight no longer matters. Now that is nonsense!

    The "awful in mud" opinion is also an interesting one. If the tyre was a Maxxis Rekon, a typical 2-6-2.8 tyre fitted to expensive new bikes, then I would agree. On my new bike (Jan'19) I very quickly got rid of the 29x2.6" Rekons fitted to my bike (3C front 1C rear) and replaced them with 29 x 2.5" Maxxis High Roller II 3C (f&r), with which I have been delighted. I would have got 29x2.6" but I couldn't find any (and it's only 0.1" difference). It also depends upon what sort of mud. I don't believe that any tyre can deal with clay mud effectively*, but other than that the HRII's are a superb tyre. I agree that they are not a dedicated mud tyre, but how many trails are ridden that are mostly mud that is bad enough to require a specialist mud tyre that then pings off rocks and roots and generally has a skittery ride on hardpack?

    *Can your mud tyre deal with this?

  • steve_sordysteve_sordy Posts: 2,248
    edited December 2019
    I have tried three times to reply to Tom Howard's post, but for some reason it just won't accept it, not even after logging out and back in again.Trying two sentences.

    Edit: aaaarrrgggghhh infuriating! One more time!
  • steve_sordysteve_sordy Posts: 2,248
    Hmm, not sure what to try next. It all looks fine in Preview, but when I press Post, it just disappears. I'll try it without a photo.
  • steve_sordysteve_sordy Posts: 2,248
    Nope, its not having it. I give up! :'(
  • steve_sordysteve_sordy Posts: 2,248
    And just in came you were wondering, I wasn't being abusive, not one tiny bit.
  • steve_sordysteve_sordy Posts: 2,248
    edited December 2019
    duplicate
  • steve_sordysteve_sordy Posts: 2,248
    edited December 2019
    duplcate
  • steve_sordysteve_sordy Posts: 2,248
    edited December 2019
    duplicate
  • steve_sordysteve_sordy Posts: 2,248
    edited December 2019
    duplicate
  • steve_sordysteve_sordy Posts: 2,248
    edited December 2019
    duplicate

  • steve_sordysteve_sordy Posts: 2,248
    edited December 2019
    duplicate
  • mattyfezmattyfez Posts: 638
    edited December 2019
    Some tyres the same width from different manufacturers can size up slightly differently.

    Also if it's got big tread blocks or small ones can make a difference for rubbing the frame.

    There doesn't seem to be a universal specification for mtb tyre measurements, which is unhelpful.

    For a regular frame with reletivley modern forks you can generally get away with 2.4 front and 2.35 rear.

    A plus frame for plus size tyres maybe up to 2.8 to 3? Anything more than that is fat frame territory really.

    But there's no industry wide consensus on frame clearance from regular, to plus to fat.

    You just have to eyeball your frame and current tyre clearance.
  • Is it possible for a tyre to be slightly wider than stated by the manufacturer? For example my cousin's bike has 2.2 inch tyres but after measuring them, they turned to be closer to 2.3 inch tyres.
  • Very slightly though
  • steve_sordysteve_sordy Posts: 2,248
    I logged in this morning and all my previous attempts had appeared overnight!
    So I deleted them all. Dunno how that happened.
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