The Big Tire Question: 23 or 25?

conti-gp4000sA debate is raging down here in Le Sud, albeit contained to a smallish area directly above my shoulders: should I try out 25 mm tires?

I have not read every article out there on the subject, but once I learned that some pro teams were switching over, I thought it should be given some thought (that is, ask you, so you can tell me what to do). There is talk of LESS rolling resistance on larger tires, a reality I know would make my brain hurt if I tried to think about it, so I will just post this from the internet:

Capture There is also the ‘comfort’ factor, which I can thankfully understand without too much effort.  Disadvantages appear to be ‘weight’ and possibly ‘aerodynamics’.

Anyone out there made the change and feel like enlightening me?


24 thoughts on “The Big Tire Question: 23 or 25?

  1. I debated this subject with my local bike shop over recent months and have made a change. 25mm rims from HED (Ardennes) with 23mm tyres – the tyre takes on a wider profile and is run with lower than normal pressure. Ridden them for a couple of weeks and love them – roll well, great grip and make my Domane even more comfortable. Interesting article on the science on HED web site…. spoke to HED and they told me they are about to stop making 23mm rims as they think 25 RIM (with 23 tyre) is way forward. Bought them with Powertap hub. So… expand your debate from tyres to include rims.
    (Very well done on Etape – sounded tough!)

    • Julian, thanks for that. I will be in the market for some rims sometime in the not-too-far future, I think, so all this is good to know.

      • And to really take advantage of the 25mm tires, running 23mm or 25mm width rims are the key. Most of the new carbon rims are now 23 and 25 wide rather than the old 20mm width. (I run 23mm x 38mm wheels, with 25mm tires)


  2. No, and I can still add to this discussion. A buddy of mine rides a fully enclosed carbon fiber bodied recumbent (yes, it’s awesome and SUPER expensive). He averages between 28 and 30 mph depending on the distance but has completed a century in less than 3-1/2 hours (3:23 I think)… After he doubled the width of his rear tire. With the entire bike encased, including the tires, there are no aerodynamic issues with the fatter tire. His average is up considerably. So yes, there is something to the wider tire dealio… However, one must also consider the fact that you can’t inflate a 25mm tire to the same pressure as a 23 (120 to 125 psi respectively). So the questions are really, how realistic is that diagram? And, does the aerodynamic deficiency cancel out the rolling resistance savings?

    Consider that the important aerodynamic surfaces are leading edges, that which cuts the air first. Considering this, the optimal, it seems to me, would be a tubular 23 on the front, inflated to 140+ psi and a 25 mm clincher on the back, inflated to the max 120… OR we can push a little harder and forget the whole mess.



    • That’s some serious speed from your friend. I remember being shocked at how fast those guys could go when I used to ride the Tamagawa cycling path in Tokyo. It didn’t seem right that some sitting in a Lazy Boy could go faster than me!

      I think I’ll try out 25s after getting through my next set of tires…the ‘pushing harder’ sounds too difficult\

  3. Conclusion to Continentals assumption. Its Jack and the beanstalk marketing at its best.
    I hear Michelin are now working with Garmin’s R+D department to produce a Watt Tyre

  4. Gerry – Yep, 25s are pretty much the way to go on the new rims, most of which are also coming in around 25. And that’s a key point, I know we’ve all ridden around on 23mm tires on 19mm rims for years but you don’t want to go to 25 on anything lest than a 23mm rim and probably not till you get to a 25mm one depending on the wheel rim depth and profile.

    In addition to the contact patch point you make about the wider rims, there’s the aerodynamics at the intersection of the rim and tire bead you need to consider especially in any cross winds. Makes my head hurt to work through all of that but I’m sure one of your readers will be able to explain it better than I can. Cheers, Steve

  5. I use 25 mm in the colder months and 23 mm in the warmer months. Here are some thoughts.

    25 mm is noticeably more comfortable at the same tyre pressure.

    If you compare the weights of 25 mm and 23 mm tyres of the same model, I think that the difference is usually marginal enough that it probably does not really affect the relative rotational weight that you need to push. However, you will always notice a ‘difference’ in rolling resistance because you never ride 25s without knowing that you have 25s installed. The point here is that I don’t know how much of it is reality and how much of it is just psychological because we have been previously conditioned to think that wider tyres have higher rolling resistance.

    Cornering is noticeably better (confident) with 25s.

    One thing that needs to be considered is the tyre / wheel clearance on your bike. If using 25s results in tight clearance against the brake calipers, then riding in bad weather could become an issue as muck can get stuck in-between, slowing you down. On wet rides on the cobbles, I have had occasions where the front wheel was struggling to spin because of all the muck stuck between the tyre and the brake calipers — I had to stop and do a quick cleaning job.

    All that said, I am inclined to run 25s even in summer. Actually, a new model that I’ve been eyeing comes in 26s (in addition to 23s, 28s and in the near future 30s).

    There is also the matter of rider weight. I believe it is well established, but often ignored, that heavier riders should not be rolling on narrower tyres.

    • More to chew over, it seems. I’m genuinely surprised that so many people are riding 25s out there. I just had no idea.

      I like the ‘cornering’ aspect a lot, although I’m sure it won’t save me from we sheep merde. The ‘comfort’ part, I am not too concerned with because I already feel comfortable with my ride. That being said, if it’s more comfortable and not slower, I’m in.

      I’m ordering a pair this week and will try them out in Canada in August.

  6. I’m with Chikashi. Comfort and confidence make a big difference to my rides. I have two bikes. One with 23s and the other with 25s. I reckon if you blind folded me on the same bike with the two different types I’d struggle to tell the difference riding straight on a dry road. Do the same corning a bumpy wet road however… And no, I don’t recommend you take the blindfold test!

  7. I have been running 25 on the back (just to try it and only needed one tire due to a cut) with a 23 on the front. I echo the comfort factor. Here’s a question: I can find a hundred websites that will argue for 25’s over 23’s. Why are there no websites arguing for 23’s over 25’s? Why did we choose 23’s as a standard in the first place???

    • A good question. Until I wrote this post I really thought most everyone was running 23s! By the way, I’m now doing what you are, by mistake. I thought I orders two 25 Contis online last week and realized a little late that it was only one. I’ll do my trip on Canada with the 25 on the back and the 23 on the front.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s