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I met a guy who mixed 23 and 25 mm for his front and rear tyre respectively.

Now thinking about it, I believe it's a pretty good idea since the rear wheel bear a higher proportion of the rider's weight. Wider rear tyres would support more weight with the same pressure as the front. It also helps reduce the wear and tear on the tyre itself.

So why don't bicycle (especially racing) run a slightly wider tyre in the rear, as the rear wheel mostly bear the weight of rider? It makes the ride more comfortable, and not aerodynamically terrible as the front is still 23 mm.

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    Why would a racer care about comfort in the first place? Or wear and tear? – Batman Aug 15 '15 at 0:02
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    Hi Batman, competitive cyclist care about comfort. Riding 25 mm for 8 hours is a night and day different from 23 mm. Agree that it's not so much for wear and tear, but for training it's a good idea – Nhân Lê Aug 15 '15 at 0:04
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    Does the rear wheel on racing road bikes really bear that much more weight? As long as the road surface is good there is no reason to use wider tires. For cobblestones they do use wider tires. – Michael Aug 15 '15 at 10:05
  • I believe so, as rear tyre requires replacement much more often than the front. – Nhân Lê Oct 7 '15 at 9:40
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I would be genuinely surprised if it made any real-world difference. Some racers commit all sorts of voodoo... err... questionable practices on the off chance it might give them an advantage. In terms of 23 vs 25 mm tires, both sizes are frequently used by pro tour teams, if one had a distinct advantage over the other you wouldn't see both sizes being used at the same events. It terms of aerodynamics, even for sizes up to 32 mm there doesn't seem to be much difference in aerodynamics drag.

In terms of comfort getting the right tire pressure for your body weight will likely have a bigger effect than 2mm gain in the tire width.

Other disadvantages include complications introduced into the assembly and supply chain for the manufacturer, which would eat into profits.

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The bigger question is, what would be the benefits of this setup? If you are willing to sacrifice the few grams of weight and square centimeters of cross section that come with wider tires, why wouldn't you use a wider tire in the front too? The benefits at comfort, grip and possibly rolling resistance apply to front, too.

In my opinion, the bike also looks nicer if both tires are similar. And if you keep spares, the same one goes for both.

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  • From this sheldonbrown.com/tires.html#width, lower rolling resistance would only be possible if the tyre is over inflated. – Kim Ryan Aug 16 '15 at 23:53
  • Could you point out the exact words? I see only that wider tires should have lower pressure, which is related but does not alone lead to your conclusion. – ojs Aug 17 '15 at 16:31
  • The rear wheel runs in dirty air, so size is less of an issue than for the front tyre which is in clean air. That's why you want the front as skinny as possible. – Móż Aug 20 '15 at 8:14
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I've seen time trail racers do the opposite and run a 22mm or 23mm tire in back and a 25mm up front.

One reason not to have a larger tire in back is because it's comparatively heavier and all the extra weight is around the circumference of the wheel. When you are putting power through the crank and trying to spin up the rear wheel, that extra weight is felt and you need more power compared to the effort required when riding a lighter, possibly smaller tire.

One other reason I can think of is that it might actually be more aero to have a larger tire up front when paired with a wide rim, which is the current industry trend. Every wheel manufacturer seems to find evidence that whatever they are doing is the best.

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Racing is all about speed. 25mm tyres have a larger contact area so there is more rolling resistance than a 23mm. It doesn't make a huge difference but it is significant. You wouldn't be competitive on 25s with everyone else runnings 23s.

But for some very tough terrain, such as going over cobblestones, most teams will often run 25s front and back. They also deflate slightly from the maximum pressure to avoid some of the ride harshness.

I started on 28mm tyres on a commuter and soon went down to 23mm. Didn't notice any difference in tyre wear or comfort. Bike was less effort to ride. Only downside is is that it is more likely to catch a rut in the road, but you ride with a bit more caution.

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    How does reducing the pressure avoid punch flats? – andy256 Aug 15 '15 at 2:57
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    The rolling resistance is still part wrong. For otherwise similar tires at similar pressure, wider has less rolling resistance. Now, 28mm tires typically have thicker rubber and coarser casing than 23/25mm ones, but not everyone realizes that. And yes, the part about reducing pressure to avoid pinch flats is completely wrong. – ojs Aug 15 '15 at 8:55
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    Don't let it bother you - it happens, but not frequently on this site. Whoever it was probably wanted to indicate that they thought this answer was wrong, and didn't have time or inclination to explain. With any luck they'll come by and remove their vote later. On some other SE sites downvotes are much more frequent. Just try to make sure that what you write is correct, even if it takes longer to check it's right :-) – andy256 Aug 15 '15 at 9:56
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    @ojs IMO the jury it still out on the rolling resistance angle. Looks like a nice question to ask, so people can put their arguments. – andy256 Aug 15 '15 at 10:00
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    OK, I'm downvoting you too. – ojs Aug 15 '15 at 11:11

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