I've just bought a tacx turbo trainer and want to get a tacx training tyre for my mountain bike.

Can I fit a tacx 26x1.25" training tyre to my wheel with current tire 26x2.1" ?



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    I would not call 0.85" difference "slight" – Matej Lieskovsky Jan 17 '17 at 0:23
  • @MatejLieskovsky Have you read the duplicate question? Specifically the answer that says: "Even going much smaller would probably be fine." – Móż Jan 17 '17 at 0:50
  • @Móż Yes I did. I also read the similar question linked there AND the page by Sheldon Brown linked from the accepted answer on that question. I am firmly convinced that making the tire 40% narrower is outside of what was meant by "much smaller" and almost certainly would NOT be fine on regular roads (unless the rim was very narrow to begin with). A 26x1.25 is a 32mm wide tire while a 26x2.1 is a 54mm, if you wish to check the chart. – Matej Lieskovsky Jan 17 '17 at 1:17
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    Normally it's because trainers grind tyres down really fast, so you want to run a cheap, hard compound tyre rather than buying new off-trainer tyres every few hundred kilometres. It's as much because of the little cross-ways dent the roller makes in the tyre as the grippy surface, and the solution to that is a bigger roller... on a bigger trainer, with heavier parts and more metal, so it costs more. Sadly the market for "big heavy expensive wind trainer that's slightly easier on tyres" is pretty small. – Móż Jan 17 '17 at 1:38
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    There is also trainer tape - a layer that goes around the outside of your rear tyre to protect it from the trainer. – Criggie Jan 17 '17 at 2:16

I regularly run 50mm and wider tyres on narrow rims which is the opposite of what you want to do, but suggests that your actual rim width might be narrower than you think it is. Viz, you might find that you have 25mm or narrower rims, in which case a 32mm tyre is perfectly reasonable.

I have run tyres narrower than the rim in the past but I don't really recommend that on leaning bikes. In this case, the question is for a trainer where leaning isn't an issue. The problem is that when you have (for example) a 45mm rim with a 25mm tyre extreme leaning can make the rim hit the road, at which point you will lose traction and crash. But this is an extreme problem, you're very unlikely to experience it in normal riding.

The increased pressure shouldn't be an issue unless you have exceptionally lightweight rims, but I'm guessing from the question that this isn't the case. If you do have a high-end carbon fibre mountain bike with ultralight, extra-wide carbon rims they should have the maximum rated tyre pressure printed on them or listed in their specifications. You should respect that. But that's not normally done for aluminium rims because the rim isn't the limiting factor for tyre pressure.

I've blown the sidewall off a rim, and running a narrow rim with wide, high pressure tyres was likely part of the cause for that. The manufacturer replaced the rim without questions, however, suggesting that they agreed that it was a weld fault at the join (where the blowout started). But you're not doing that, you're running a narrow high pressure tyre on a rim that is most likely capable of working with a wide, high pressure tyre. I would not worry about this, especially on a trainer where you're more likely to suffer hearing damage from a blowout than major crash injuries.


Going down by 0.85" without replacing the rim is generally discouraged, but since there are few road hazards on a trainer (those would threaten damage to the rim), this might be doable. Proceed with caution as the narrower tire will require significantly higher pressures and might not seat as well in the rim, heightening the risk of a blowout. If possible, I recommend getting a second rear wheel with a narrower rim and swapping entire wheels, which is significantly faster than replacing a tire.

Frame clearance and other similar constraints should not be a problem.

  • 1
    Totally misread that! haha my brain read 2.25 to 2.1 – Nate W Jan 17 '17 at 0:24
  • @NateWengert: I guessed that might be the case. Errare humanum est. – Matej Lieskovsky Jan 17 '17 at 0:26
  • Can you explain how bead seat diameter is affected by tyre width - are you talking about rim profiles, or the (far-fetched) idea that the diameter depends on tyre width? – Móż Jan 17 '17 at 1:25

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