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It is often stated that wider (performance) tires offer less rolling resistance at the same pressure (or less pressure at the same rolling resistance, which is beneficial for comfort). The well known Bike Rolling Resistance has published some comparatives on that: GP5000 Marathon (for reference, but the question is focused on performance/supple tires)

Given this fact is known, I noticed that bike/tires manufacturers only offer incremental increases in tire clearance on road bikes (gravel went from 40mm to 50mm clearance in a few years for instance, even if they rarely sold with the largest tires). But on the endurance road bike part of the spectrum, new models are sometimes limited to 35mm (the only exception I'm aware of is the Specialized Roubaix SL8, with 40mm clearance but sold 32mm tires).

So what would be the drawbacks of using wider tires on performance (endurance) road bikes, given they provide additional comfort for equivalent rolling resistance? (the focus is mostly on endurance, as for pure performance, the trade-off is often comfort against weight or rolling resistance).

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    It doesn't actually change the question, but on rough roads running wider tyres at the same pressure as narrow ones can increase the rolling resistance as they're too hard to tenis road buzz. At optimal pressure they may be able to reduce rolling resistance and improve comfort - up to a point.
    – Chris H
    Dec 16, 2023 at 12:55
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    @ChrisH Sorry if this is just a problem at my end (if so, I blame Monday), but what does "tenis road buzz" stand for?
    – TooTea
    Dec 18, 2023 at 11:42
  • Note that GCN published a video on that, where they compare 26, 35 and 50mm sections. One nuance to add though: the 50mm tire is a Schwalbe Super Moto, that is a urban reinforced tire (weighting almost 1kg each), so it's not a fair comparison — it's of course hard to find 50mm performance road tires to have a fair comparison. To give another comparison point, the Michelin Power Adventure 30mm and 48mm (performance gravel semi-slick - one of the rare tires available in this size range), that weights respectively 340g and 510g.
    – Rеnаud
    Dec 18, 2023 at 11:46
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    @TooTea road buzz is the continuous vibration you get on some surfaces. Where my phone got "tenis" - not even English (but I have several languages installed) - from, I have no idea. I mean "reduce", so I probably wrote "attenuate"; it has a habit of not picking up the first letter of words
    – Chris H
    Dec 18, 2023 at 11:54
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    It sometimes helps to understand the reason why tires used to be narrower: brake design, not aero or rolling resistance. Moving to disc brakes on road bikes enabled new wheel, tire, and fork designs without limitation of tire width.
    – R. Chung
    Dec 18, 2023 at 20:20

5 Answers 5

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There's no substantive disadvantage in many situations.

Each wheel can accommodate a range of tire sizes to achieve good aerodynamic drag figures. If you run tires too big, this will disrupt the profile the designers were trying to achieve. This is what the Rule of 105 gets at - this rule of thumb says that for optimum aerodynamic drag, the width of the rim at the brake track or the sidewall area should be 105% that of the tire's width (actual width, not nominal width printed on the tire).

I don't know how much the penalty is. From listening to podcasts like Josh Poertner's Marginal Gains, I think that if you slightly exceed the ideal tire width, you might look at less than 10W penalty at high speed (45 km/h or so). That's meaningful to high-performance riders. That's probably OK for most others.

In addition, if your tires are too wide, I think this may make for worse handling in heavy crosswinds. It will probably reduce the stall angle of the rim - that is, at what angle does the drag markedly increase. Think of the graphs of drag vs airflow angle that manufacturers sometimes present. Drag tends to rise gradually as the angle gets steeper, although at some point it rises faster. That's the stall angle. In winds where the airflow angle is changing suddenly, this can make the wheel feel unstable. Within reasonable limits, the magnitude of this effect is probably manageable - e.g. if your rims are designed for 28mm tires but you put 32mm tires on them, and you're not in a super windy place like Kona, Hawaii.

This Slowtwitch.com article by Nathan Barry discusses in general how crosswinds affect the bicycle. Basically, when the wind hits you, its effect can be decomposed into a side force (pushing the bike left or right) and a yaw moment - this is the one that feels like the wind is causing steering input. Now consider that the wind can be intermittent and it can change direction.

enter image description here

Barry didn't discuss tire size. November Bicycles, which builds wheels, has sometimes discussed crosswind stability on their blog, e.g. this 2014 post.

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  • I'm not aware of a combination of (aero) rim and tyre that would allow testing that 105% rule with 35-40mm tyres, and it would need to have a really deep section to taper sensibly. It would be an interesting experiment. But it might eat into the other benefits of a wide tyre, by flattening it out
    – Chris H
    Dec 16, 2023 at 12:59
  • And in heavy crosswinds, the same tyre on similar rim profiles handles quite differently on 2 of my bikes (tourer vs gravel/endurance - worse on the latter) so I reckon bike geometry is a bigger effect than the sort of thing you're king about at the end.
    – Chris H
    Dec 16, 2023 at 13:02
  • @ChrisH Gravel race rims seem to have very wide external width compared to the internal width, to optimise aerodynamic. For example, the Hunt 42 has an external width of 36mm for internal width of 25mm.
    – Rеnаud
    Dec 18, 2023 at 16:26
  • @Renaud OK, I've never seen gravel race rimsin the flesh
    – Chris H
    Dec 18, 2023 at 21:16
  • To be fair, that Hunt design is extremely rare. They and 3T may have been the only firms to attempt some sort of rim optimized for gravel tires,
    – Weiwen Ng
    Dec 18, 2023 at 23:30
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Short and simple it’s a combination of aerodynamics, weight and perception/history.

The wider the tyre (and the frame which fits the tyre) the more aerodynamic drag you are going to have. Weight also increases, not just for the tyre but rims and frames need to be bigger as well (also the spare tube you are carrying). People still perceive narrow, high pressure tyres as fast, even though that’s not necessarily true, so change is slow to happen.

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  • For endurance biking people are usually biking on asphalt. Thus, the wider tires (which are definitely superior in off-road situations, but are heavier and have more drag) are eschewed in favour of narrower tires with lighter weight and lower wind resistance (at least, that's my opinion based on a lifetime of biking). Dec 19, 2023 at 13:58
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    @JonathanBenn: Yes, this is also a factor. Wide tyres at low-ish pressure are especially beneficial for comfort and rolling resistance on rougher ground.
    – Michael
    Dec 19, 2023 at 16:45
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The two drawbacks have already been mentioned: aerodynamics and weight.

However, there's a third drawback. It's the fact that bicycles have their ground clearance set by tire size. So the frame manufacturer has in mind a certain tire size, let's say 25mm. If you choose 35mm instead, you will obviously have a centimeter of more ground clearance.

This won't usually be a bad thing since road bikes have rather limited ground clearance. When riding a road bike on a forest path with tree roots, you may find it difficult to avoid hitting those roots with your pedals. Also riding over deep water puddles is difficult, unless you have enough ground clearance. For cornering too, ground clearance can be useful since you can pedal in steeper corners.

However, too much ground clearance is not without its drawbacks. It will increase the standover clearance of your frame. If your frame has a horizontal top tube, it may be lacking in standover clearance already, and every tire size increase eats it more. Also stopping at stoplights and starting to ride again is more convenient with low ground clearance. Furthermore, too much ground clearance makes your riding position higher which increases air resistance, but this was already mentioned.

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    Just a clarification that may be useful to improve the answer (If the question wasn't clear, the question is not so much about "fitting the widest possible tire on a bike", but rather about the drawbacks that slows down the use of larger sections on endurance road bikes): why would ground/top tube clearance become an issue with larger tires if the frame is designed for that section?
    – Rеnаud
    Dec 17, 2023 at 10:21
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The main drawback is that their max pressure rating goes down as the tire gets wider. There simply is no such thing as "wider tires […] offer less rolling resistance for the same pressure".

The reason for this is simple: Wider tires have less strongly curved walls, and thus suffer more tension at the same pressure. And while you could give tires stronger and stronger carcasses (which would increase rolling resistance again), a tire must be mounted to a rim, and the max tension that a rim can deliver to a tire is limited. Put too much tension on the tire material, and the rim will fail by having one of its sides bend outwards, releasing the tire bead, which in turn releases the restraining force on the tube, which finally produces a very loud BANG. Very dangerous if it happens while riding with rim brakes as the failed rim may block against the brake.

So, while you may be able to use a few different tire sizes with the same pressure, there is an upper limit to this. And road bike tires are usually already used near their upper pressure limit anyways.

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    I should have added a source, like: bicyclerollingresistance.com/specials/… that clearly shows a relation between section and rolling resistance. Of course the question is not about turning an endurance road bike into a fat bike, but more to explore why reasonably larger sections are not used (and that exist in other categories)
    – Rеnаud
    Dec 16, 2023 at 16:38
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    Provably wrong. Working tire pressure for a Boeing 787 tire, which is wider than any bicycle tire I know, is 230psi, and has a very curved wall. Maximum pressure and tire shape are determined by manufacture, and weight carried. Tire width has nothing to do with it (except perhaps bike tires of same witdhs are designed the same way)
    – mattnz
    Dec 17, 2023 at 0:13
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    @mattnz Sorry, that argument does not hold. The Boeing tire is a much more massive sheet of rubber and steel, and the rim on which it is mounted has been designed to withstand the forces on its edge. You are comparing apples with beans. Please think twice before you call another person's argument "provably wrong". Dec 17, 2023 at 8:54
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    On the other hand, without comparing bicycle tires to B787, yes, there's an upper limit that decreases with the section, but that limit doesn't imply that the pressure becomes quickly unbearably low. If looking at the article I linked, it looks like comparable level of rolling resistance can be achieved with 2 bars less (25mm vs 32mm), but that 32mm cannot indeed reach the rolling resistance of a 25mm. Someone happy with 6.5 bars on a 25mm would be fine on a 32mm with 4.5 bars (or maybe a 42mm semislick gravel tire at 3.5bars), and that is the range that is the subject of the question.
    – Rеnаud
    Dec 17, 2023 at 10:10
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    @Renaud That's comparing with wider tires at lower pressure. My point was about comparing tires of different width at the same pressure. I fully agree that you can get round about the same dampening with wider tires at lower pressure, but that tends to massage more rubber in total, increasing the rolling resistance. I hear that wide tires with very flexible side walls are quite comfortable to ride at their intended pressures, though. Dec 17, 2023 at 10:43
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I've listen to this video from GCN and I think it answers some of your questions and reinforce some of the already given answers above.
Eg. Wider tyres 32mm will be a disadvantage if your speed increases to 40Km/h but not disadvantage as compared to a 28mm if going at 30Km/h.

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    Note that GCN also has another video, where they compare 26mm, 35mm, 50mm: the 26mm is the slowest, and the 35 is the fastest. The 50mm is faster than the 26mm as well, but the comparison is a bit complex, because it's a 1kg urban reinforced/rigid tire, that compared against performance/supple tires (but despite that, it still got a better result than the 26mm).
    – Rеnаud
    Dec 18, 2023 at 12:31
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    Also another point: Weiven's answer suggest that the aero advantage is more linked to the "rule of 105" rather than the frontal area of the tires. In this video, they mention that tires were run with the same rims wheels. But because they don't say what is the rim width. But if the 28mm is respecting the role of 105, the 32mm cannot as it represents a 14% increase in width compared to 28mm.
    – Rеnаud
    Dec 18, 2023 at 16:21

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