Are wider tires really faster in real life? (25c vs 28c)

ENVE doesn’t recommend running 25’s on the 3.4AR’s. These wheels are ripe with compatibility issues, which has been my only experience with them so far. They’re in the shop getting set up tubeless because I was having such a difficult time. Can’t wait to ride them though, I presume they will be amazing like other Enves.

SES AR wheelsets feature a straight sidewall/hookless bead design and are qualified for use with “Tubeless, Tubeless Ready (TLR)” tires, with a labeled width of 28c or greater ONLY. One may safely run inner-tubes as long as the tire itself is of a tubeless or tubeless ready construction. SES AR aerodynamics and stability are optimized when the wheelset is paired with a tire that is labeled as being 28c. Below is a list of approved/recommended tires as well as tires that have been proven incompatible and cannot be recommended at this time.

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Here’s my thread on the topic.

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Late to this topic, but it is important to recognise a few fundamental points of principle.

  1. Wider tyres do NOT provide more grip than narrower tyres. this is simple physics. For a given weight and a given tyre pressure, the contact surface of the tyre on the road, (regardless of the size of the tyre). is identical in size, but it is shaped differently. The narrower tyre (per physics) will have a longer and narrower contact patch than a wider tyre which will have a shorter and wider contact patch - but the overall size stays the same. Thus, in principle, a wider tyre vs a narrower tyre (equalised for tyre pressure and rider weight) will provide more cornering performance (due to a wider contact patch), but poorer braking performance (shorter contact patch).

  2. The only way to change your contact patch size (not the shape as above) is using tyre pressures. Lower the pressures and you increase the size of your contact patch with a net benefit to both cornering and braking. This is where a larger volume tyre provides you a win as it is able to support lower pressures than a narrower tyre.

HTH.

Sorry, physicist here, but this is only true in a static environment (which cycling isn‘t): wider tires have more grip, because equivalent pressures (in terms of the size of the contact patch) are lower. At lower pressures, you have more compliance, and it is the increase in compliance that increases grip since you have more and more consistent contact between tire and surface. To put it simply, a narrower tire needs to be run at higher pressures, which means it bounces around more. When it “bounces” the contact patch decreases in size, perhaps to 0 (when it no longer makes contact to the ground). That‘s why in practice wider tires do have more grip.

I would also reckon improved compliance due to lower pressures and the larger deformation at those lower pressures with wider tires is also the main factor when it comes to cornering, not the wider contact patch at rest. Again, you need to look at it dynamically, not statically.

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We are in agreement, but your description of a “static” environment is a red-herring. The fact is that the only way to change the contact patch size is with pressures (or weight obviously) PSI is all that is supporting the weight. All tyre width does, at the same PSI is change the contact patch shape. You can’t change those physics. Carcass/sidewall compliance is a factor but much more of a concern in car tyre performance). A bigger road bike tire (eg. Continental GP 4000 and GP 5000) provides a lower rolling resistance at the same air pressure due to it’s shorter/wider contact patch - hence it is more comfortable at a 15% tyre drop air pressure. But when you equalise pressures for the same tyre drop, rolling resistance is basically equivalent. Which is not normally understood in the “wider is better” debate.

When you talk about compliance, you are simply stating that lower tyre pressures produce more grip and more compliance, which is obvious. Your wider tyres support more compliance only due to 2 factors, a wider and shorter contact patch, and their ability, within limits, to run at lower pressures.

Yeah, even at the same pressure though, the shorter/wider contact patch allows for a higher slip angle and therefore more lateral force. I would argue that the higher slip angle range also gives you more feedback and time to react at the limits of traction. That can’t be discounted when we’re talking about cornering

Sort of. Tyres with greater flex in the side wall can operate at higher (max) slip angles, but tyres with less flex in the side wall build grip more quickly i.e. they are more responsive, but also “less forgiving” than tyres with greater flex. From my days playing with cars, the practical implication of this “wider tyres = more grip” reality (note only true in cornering), means that they heat better when cornering but they also cool faster so if you are not heating them enough in the corners performance (lap time) suffers because they are too cold (outside of their optimum temperature).

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No, it‘s not just that. I would argue that we need to be clear whether we compare tires at the same pressures or at equivalent pressures (i. e. choosing pressures so that the surface tension in both tires is the same). I would argue you should compare tires at equivalent pressures, because the casing tension determines the size of the contact patch. Wider tires will have a lower equivalent pressure compared to a narrower tire, which improves compliance and therefore grip at the same time. Running a wider tire at the same pressure will decrease the size of the contact patch, but not necessarily decrease the friction.

There is also way more to rolling resistance than your static considerations, precisely, because tires are in motion, not at rest. For example, wider tires run at equivalent pressures deform more, which means they have more friction. But this is more than compensated for by impedance losses, which are a dynamical phenomenon. That is why there is no the optimal tire pressure, the point where you minimize the sum of casing losses and impedance losses depends crucially on the surface you roll over. Plus, the rougher the surface, the more of a premium I would put on compliance, not just to maximize comfort, but also grip and safety.

There are also other factors to consider when e. g. include cornering, because then tire shape, tread pattern, internal rim width and other things become important. Or if we just look at compliance, casing material, thickness, rubber compound, etc. all become factors, too.

That‘s the wrong car tire analogy. The proper analogy would be changing rim size: if you go for smaller rims with taller tires vs. larger rims with shorter tires (keeping tire diameter constant in the process), you will have more compliance and comfort on smaller rims with taller tires.

mmm, that is a very small determinant in reality. Even with very stiff low-profile car tyres. Certainly no material difference at any meaningful tyre pressure. For example, put 1 psi in a bike tyre and you will flatten the sidewall with a single pound of weight. So, simply not material.

Sorry, that’s simply not the case. Contact Area= total weight/tyre pressure. You can discount casing “tension” as above.

Of course there is, but there are plenty of on-line resources, specifically with bicycle tyres, which measure actual rolling resistance in controlled conditions to say that the differences are not material.

Have a look at the link: at the same casing tension, the pressures in 25 mm and 28 mm tires differ by 11 % = 1 - 25 mm/28 mm. A difference of that magnitude is certainly meaningful and can be felt.

It is the casing tension that determines the spring constant. If you look at the article I sent you, the quantity \sigma_H that they compute is a pressure. Have a look at the second-to-last formula:

P is the pressure, D_m the mean diameter and T the wall thickness. If you keep wall thickness constant when comparing tires, then this means if you want to keep \sigma_H constant, you need to keep the product of tire pressure and mean diameter constant. Consequently, you need a lower pressure for wider tires to generate the same casing tension. This casing tension is what resists deformation, i. e. it determines your spring constant.

Of course, this simple equation is a simplification of reality and e. g. assumes that you keep internal rim width constant. So the difference is larger if you compare a narrower tire on a narrower rim vs. a wider tires on a wider rim. My current road bike wheels have an internal width of 25 mm, for example, which is much wider than e. g. 21 mm that is a common internal width for more “traditional” road wheels.

We’re going around in circles. The reality is that “casing tension” as per the article you reference is actually a red herring. As is compound, profile, construction, bias ply, and tread. Not to mention aero… They are all factors, naturally, but avoid the fundamental issue which is that contact patch size, for the same weight, is only determined by tyre pressure. Not by rim width, nor by tyre size. The physics is very simple.

You are confusing the ability to run lower PSI’s in tyres, and in wider tyres particularly, with the fact that you can run them in all types of tyres. That said, the other important point is that, at the same pressures, wider tyres will show less rolling resistance (i.e. 28c<25c<23c) due to the different contact patch shape (shorter/wider, same area), but if you (as your article suggests) reduce the tyre pressures in your 28c or 30c tyres, then you will be increasing rolling resistance to the same of greater than your 23c tyre inflated correctly (i.e. 30c>28c>25c>23c). By decreasing pressure in your wider tyre, you are increasing the contact patch area so inevitably increasing rolling resistance. This may or may not matter depending on the rim profile and your usual speed.

As I stated, there are on-line resources showing this in real, controlled conditions (IIRC with Conti 5000’s).