New tire rolling resistance test - 23mm, 25mm, 28mm & 32mm GP5000 tires

[El Chaba]

I concluded some time ago that the move to wider tires for the road was largely driven by the search for something...anything...that could mitigate some for the extra stiffness that was characteristic of the uber-oversize tubed frames that have come into fashion. It was convenient that a larger tire could be run at a slightly lower pressure for some comfort gains without a big hit in increased rolling resistance.

[merckx]

Originally Posted by El Chaba

I concluded some time ago that the move to wider tires for the road was largely driven by the search for something...anything...that could mitigate some for the extra stiffness that was characteristic of the uber-oversize tubed frames that have come into fashion. It was convenient that a larger tire could be run at a slightly lower pressure for some comfort gains without a big hit in increased rolling resistance.

I believe this to be dead-on.

[colker]

Originally Posted by El Chaba

I concluded some time ago that the move to wider tires for the road was largely driven by the search for something...anything...that could mitigate some for the extra stiffness that was characteristic of the uber-oversize tubed frames that have come into fashion. It was convenient that a larger tire could be run at a slightly lower pressure for some comfort gains without a big hit in increased rolling resistance.

... but is it faster now?

[Mark McM]

Originally Posted by tylercheung

What about grip and handling - does anyone test the G-force required to induce skid?

Tire traction can be more difficult to test under controlled conditions than many other tire properties (including rolling resistance), which is unfortunate, since traction is probably the most important property of a tire (if the tire doesn't have traction, then you may not get far enough down the road for other things like rolling resistance and puncture resistance to matter).

The only organization I know of that has published the results of bicycle tire traction tests is Tour Magazine, which periodically does wet weather tire traction tests. These tests consist of rolling down a hill and then riding around a corner on pavement that is constantly being wetted with a water sprinkler. The tester rides through the corner at increasing speeds until the tires slip out (and the rider falls). The test rider wears padded clothing, and rides a special bike that allows them easily jump off if the tires slip, but it should be obvious why this kind of testing isn't done very often.

[Mark McM]

Originally Posted by pasadena

Zipp still recommends 23's as the fastest tire size, on the front wheel at least.
It's the combination of aero and rr.

I'd take that recommendation with a grain of salt, particularly if they don't mentions specific tires, based on the work that Flo cycling did on combined tire/aero testing.

When Flo set about designing their carbon clincher rims, they needed to model the shape of both the tire and wheel together. Based on their previous testing, and the tests published by others, they discovered that the Continental 23mm GP4000 tended to test well aerodynamically, so they based their aerodynamic model around that tire.

After Flo produced their new wheel, they tested it in a wind tunnel with a variety of tires, and not surprisingly, it had nearly its best performance with the 23mm GP4000 (that's what they designed it for, after all). But when they combined aero drag with rolling resistance, they found that the wider 25mm GP4000 had a lower total drag - the lower rolling resistance of the wider tire more than made up for the extra aero drag.

I have no reason to doubt Zipp's claim that 23mm tire has the lowest drag on their wheels, if only aero drag is considered. But when you add in rolling resistance, I wouldn't be surprised if an excellent rolling, but slightly wider, tire ended up being better. Particularly if compared to a poorly rolling 23mm tire.

It used to be that riders selected tires based on which gave the best aero performance with their wheels. But in the future, I suspect that it will be the other way around - riders will select wheels, based on which gives the best aero performance with their tires. And we'll see aero wheels getting wider, to better match wider tires (this is already happening).

[Mark McM]

Originally Posted by saab2000

Take my above comments with a grain of salt.

I've loved my 23mm tires on wide (20mm interior width) rims for several years and may start going to 25mm due to my seemingly ever expanding waistline and the fact that the roads are crappy where I live.

I do run lower pressure and have found it to be nice, with no apparent loss of speed. Just increased comfort.

The reason I mention the lower pressure and people saying it decreases rolling resistance is that supposedly a rock hard tire will deform less over the texture of the road surface. Lower pressure will allow the tire to deform more and actually provide lower rolling resistance overall. I don't know the science.

But I run my 23s at about 80 PSI and 25s a bit lower and they ride very nicely. In fact, I've found a cotton clincher on wide rims like I use now to be close enough to the ride of a quality tubular that my tubular usage has gone down dramatically in the past few years.

I'm speaking here only about paved roads and road tires. Tires and pressures for unpaved roads are a whole 'nuther ball of wax.

If you look at the Josh Poertner blog article referenced earlier, you'll see that there is a inflation pressure "sweet spot" to minimize rolling resistance. Decreasing the pressure further will increase rolling resistance due to casing losses, and increasing pressure will increase rolling resistance due to suspension losses. This sweet spot will vary with tire width, surface roughness, rider size, and other factors.

Since you're an aviator, maybe you'll appreciate the analogy between the pressure sweet spot, and the speed/power curve for air drag:


Tire Air Pressure vs. Rolling Resistance:





Aircraft Speed vs. Power

[Mark McM]

Originally Posted by El Chaba

I concluded some time ago that the move to wider tires for the road was largely driven by the search for something...anything...that could mitigate some for the extra stiffness that was characteristic of the uber-oversize tubed frames that have come into fashion. It was convenient that a larger tire could be run at a slightly lower pressure for some comfort gains without a big hit in increased rolling resistance.

My observations have led to a different conclusion. Decades ago, most people rode wider tires than often seen today - 1" (25mm) tires were uncommonly narrow, and most people rode tires between 1 1/8" (28mm) and 1 3/8" (35mm) wide (these were the days before Kevlar bead tires and hooked rims). Pressures were typically in the 70 - 90 psi range.

Then, starting in the early '80s, people started believing that narrow, high pressure tires must be faster, and tires and rims capable of handling high pressures started being made. During the time that frame tubes started growing in size/diameter, typical tire widths started shrinking and tire pressures increasing - 23mm tires became common, and many were even riding 20mm tires, at pressures up to 120 psi or more.

The move toward wider tires today isn't to mitigate the extra stiffness of modern frames (even the old frames from yesteryear had too much vertical stiffness to provide much shock absorption) - its to mitigate the ridiculously high pressures that people been using during the last few decades.

[saab2000]

Originally Posted by Mark McM

If you look at the Josh Poertner blog article referenced earlier, you'll see that there is a inflation pressure "sweet spot" to minimize rolling resistance. Decreasing the pressure further will increase rolling resistance due to casing losses, and increasing pressure will increase rolling resistance due to suspension losses. This sweet spot will vary with tire width, surface roughness, rider size, and other factors.

Since you're an aviator, maybe you'll appreciate the analogy between the pressure sweet spot, and the speed/power curve for air drag:


Tire Air Pressure vs. Rolling Resistance:





Aircraft Speed vs. Power

It is an interesting graph, to be sure. Mostly it's one for the student pilots who learn about this stuff but in what I do today it's a bit of a different game. Of course, the same principles apply. Our speed and altitude selection is based on a lot of factors and this graph isn't something we would consider but it is, of course, an accurate depiction.

As to rolling resistance, you are correct that there are many different variables.

I've got a bike incoming that is designed as an "All Road" road bike and I'm wondering where I'll end up with the tires. I'm thinking probably 35mm. They'll still probably be ridable on the roads but not too narrow for my liking on unpaved roads. The 38s I'm running now are almost a tad too big for me and sometimes feel a bit sluggish.

I'm not yet ready for the 650x50s that some folks enjoy!

[robertbb]

Originally Posted by joshatsilca

OK, so just looked at the Schwalbe chart and can tell you that chart is what happens when marketing guys make charts... I love how each optimal pressure is exactly a round number in bar!! Amazing!

As the guy who develops and has developed tire pressure strategies for 10+ years for guys like Cancellara, Wiggins, Sagan, and so many others, I can tell you that this chart is straight up wrong from a performance point of view. Now for most people, doing most things, it's probably fine, but if you are after optimizing for performance this isn't it.

Optimal pressure will be different for different surfaces, but if you have a number a safe rule of thumb is that equivalent small bump stiffness of the tire can be achieved at ~2% per millimeter of width change.. so every mm larger in measured casing size you need 2% lower pressure, but again, for the same surface.. as surfaces increase or decrease in roughness, your baseline pressure changes

Part 1 of our episode on Asymmetry starts to get into this topic and brings some context from racing: https://marginalgainspodcast.cc/asymmetry-part-1/

I really appreciate this response Josh!

It's great to get insight from someone who legitimately knows what they are talking about and is willing to take the time to help the average punter who most certainly is not Cancellara, Wiggins or Sagan

Curious as to your thoughts on that margin of error though. With such small changes to pressure required in moving from 23-25 or even 25-28, one wonders if the average floor pump/pressure gauge is up to the task!

I choose butyl tubes simply because the pressure I start a ride with is likely to be the pressure I finish it with. While I enjoyed running latex tubes for a while, if I went out on a century and had a stop for lunch/coffee, I'd find my pressure had dropped so much that any RR gains of the latex tube were probably negated and even inversed towards the end...

[pasadena]

ZIPP:
The aero improvement of the 23mm tire over a 25mm+ tire outweigh any relative losses in rolling resistance.

When Si on GCN did a KOM hillclimb challenge video, Zipp also recommended 23's as the fastest tire width.

Originally Posted by Mark McM

I have no reason to doubt Zipp's claim that 23mm tire has the lowest drag on their wheels, if only aero drag is considered. But when you add in rolling resistance, I wouldn't be surprised if an excellent rolling, but slightly wider, tire ended up being better.

Pretty good article from Slow Twitch:

The new standard / minimum tire size is 25-26mm. The old standard of 23mm is dead. NOTE: When I say 25mm, I mean the INFLATED size on a modern clincher rim (so the tire label probably says 23mm). Anything under a measured 23mm, on a modern wide rim is DEFINITELY dead, short of some rare special cases.

The ‘What Should I Use’ Cheat Sheet

-If you’re a pro, aspiring pro, or just super-duper fast, use a tire that’s labeled 23mm (inflating to 25-26mm).

-If you’re an average, middle-of-the-pack person, trying to be competitive and have fun, use a tire that’s labeled 25mm (inflating to 28-29mm).

-If you’re a fat-tire-lover like me, and want to feel like you’re riding a magic carpet, use a tire that’s labeled 28mm (inflating to 31-32mm). With any luck, more new wheels will emerge, making this a legitimate aerodynamic choice.

https://www.slowtwitch.com/Tech/What...018__6822.html

[joshatsilca]

Originally Posted by robertbb

I really appreciate this response Josh!

It's great to get insight from someone who legitimately knows what they are talking about and is willing to take the time to help the average punter who most certainly is not Cancellara, Wiggins or Sagan

Curious as to your thoughts on that margin of error though. With such small changes to pressure required in moving from 23-25 or even 25-28, one wonders if the average floor pump/pressure gauge is up to the task!

I choose butyl tubes simply because the pressure I start a ride with is likely to be the pressure I finish it with. While I enjoyed running latex tubes for a while, if I went out on a century and had a stop for lunch/coffee, I'd find my pressure had dropped so much that any RR gains of the latex tube were probably negated and even inversed towards the end...

robertbb, thanks for the comment and thanks for giving me a great opportunity to plug some SILCA pumps with super accurate gauges!! In all seriousness though it was the last 10+ years of doing this that inspired us to make super accurate gauge pumps, and if you read our Road to Roubaix Blog story you'll see that we considered this secret so secret that I travelled around Europe with a $1000 gauge for a few years in a pelican handgun case and we only used it out of site of other teams and the media.. Now we make a handful of pumps with specially tuned digital sensors to achieve 0.5psi accuracy at these types of pressures which are used by more teams than those we 'officially' work with.

As for latex, look at the modern latex, we sell tubes made by Vittoria which have a new formula with graphene in them and leak so much slower than the old ones. When we plotted Cancellara's roubaix run in 2010, we measured his tires to have nearly 1psi per hour loss.. so we tuned pressures so they would be perfect a few hours into the race when he was on the worst cobbles.. The new generation of latex tubes might lose 4-5psi per 24 hours, and will save you 2-5 watts per tire which is a bigger savings than a full ceramic bearing upgrade for about 1/50th the price!!

[sfo1]

Seems that tire size needs (or should be paired with) rim inner - outter measurements?

A GP 4000 25mm on a rim that is 17 id - 25 od vs same tire on a rim that is 20 id - 28 od will perform very different, no?

Maybe we all drink the cool aid and spend more $ to gain one watt?

Originally Posted by pasadena

ZIPP:
The aero improvement of the 23mm tire over a 25mm+ tire outweigh any relative losses in rolling resistance.

When Si on GCN did a KOM hillclimb challenge video, Zipp also recommended 23's as the fastest tire width.



Pretty good article from Slow Twitch:

The new standard / minimum tire size is 25-26mm. The old standard of 23mm is dead. NOTE: When I say 25mm, I mean the INFLATED size on a modern clincher rim (so the tire label probably says 23mm). Anything under a measured 23mm, on a modern wide rim is DEFINITELY dead, short of some rare special cases.

The ‘What Should I Use’ Cheat Sheet

-If you’re a pro, aspiring pro, or just super-duper fast, use a tire that’s labeled 23mm (inflating to 25-26mm).

-If you’re an average, middle-of-the-pack person, trying to be competitive and have fun, use a tire that’s labeled 25mm (inflating to 28-29mm).

-If you’re a fat-tire-lover like me, and want to feel like you’re riding a magic carpet, use a tire that’s labeled 28mm (inflating to 31-32mm). With any luck, more new wheels will emerge, making this a legitimate aerodynamic choice.

https://www.slowtwitch.com/Tech/What...018__6822.html

[pasadena]

Originally Posted by sfo1

Seems that tire size needs (or should be paired with) rim inner - outter measurements?

A GP 4000 25mm on a rim that is 17 id - 25 od vs same tire on a rim that is 20 id - 28 od will perform very different, no?

Maybe we all drink the cool aid and spend more $ to gain one watt?

Yes, you're right about that line of thinking.
My general understanding is, in cross-section, a U shaped tire is more aero than a O shaped tire.

Personally, I just don't sweat it. I like geeking out and webwheeling about it but in reality...

In a race, I just care about conserving energy. Light, aero wheels w/ tires I trust.
Someone said, generally all XXmm depth wheels are about the same aero savings.
So yeah, there are just so many other factors in a race, to me, it just doesn't matter.

For PR's, 'baseline' matters more. I want to keep my equipment consistent.
I note, if I try for a PR, did I use my carbon wheels or alloys. That way, I can just focus on my physical gains.

So, in that regard, it doesn't matter what you own.

In all honesty, the biggest gains I feel are when the tires are new.
New Rubino Pros feel great! New Sworks tires feel awesome!
When they start flat-topping? I'm sure you loose more watts there than anything else.

[joshatsilca]

Originally Posted by pasadena

Yes, you're right about that line of thinking.

In all honesty, the biggest gains I feel are when the tires are new.
New Rubino Pros feel great! New Sworks tires feel awesome!
When they start flat-topping? I'm sure you loose more watts there than anything else.

We have data on this in our Tires and Aero Blog post: https://blog.silca.cc/part-5-tire-pr...d-aerodynamics

You are correct, that next to having the proper size tire for your rims, replacing them as soon as they begin to show wear makes a very big difference!!

[Mark McM]

Originally Posted by pasadena

ZIPP:
The aero improvement of the 23mm tire over a 25mm+ tire outweigh any relative losses in rolling resistance.

When Si on GCN did a KOM hillclimb challenge video, Zipp also recommended 23's as the fastest tire width.



Pretty good article from Slow Twitch:

The new standard / minimum tire size is 25-26mm. The old standard of 23mm is dead. NOTE: When I say 25mm, I mean the INFLATED size on a modern clincher rim (so the tire label probably says 23mm). Anything under a measured 23mm, on a modern wide rim is DEFINITELY dead, short of some rare special cases.

The ‘What Should I Use’ Cheat Sheet

-If you’re a pro, aspiring pro, or just super-duper fast, use a tire that’s labeled 23mm (inflating to 25-26mm).

-If you’re an average, middle-of-the-pack person, trying to be competitive and have fun, use a tire that’s labeled 25mm (inflating to 28-29mm).

-If you’re a fat-tire-lover like me, and want to feel like you’re riding a magic carpet, use a tire that’s labeled 28mm (inflating to 31-32mm). With any luck, more new wheels will emerge, making this a legitimate aerodynamic choice.

https://www.slowtwitch.com/Tech/What...018__6822.html

As discussed in the SlowTwitch article, there is no single tire width that will always be best. Different riding conditions may favor different widths. As mentioned, here's a few factors that may influence the optimal tire widths:

Surface roughness - rough surfaces increase suspension losses, which can be mitigated with wider tires

Speed - rolling resistance is a larger percent of drag at lower speed, so decreases in rolling resistance with wider tires may outweigh losses due to aerodynamics; conversely, aero drag increases with the square of speed, so narrower tires may be best at the highest speeds.

Rider weight - rolling resistance is proportional to rider weight, whereas weight doesn't affect aero losses, so the wider tires may be better for heavy riders, and narrower tires may be better for lighter riders

Crosswinds - wind drag in cross winds is increased when the tire width is greater than rim width, so narrow tires may be best in strong cross winds.


For 135 lb. Caleb Ewan doing a 45 mph final sprint with a crosswind, Zipp's recommendation for a 23mm tire is certainly correct. But for a 210 lb. rider doing a Grand Fondo at 18 mph, a 25mm or 28mm tire is probably more optimum, even on the same wheels.