Technical FAQ: Tire size and rolling resistance

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Dear Lennard,
I don’t know that I’ve ever heard of the 23mm-tire/22mm-rim risk. I’ve got in excess of 15,000 miles on this setup though and have never had an issue that I am aware of. Where can I read more? It is a significant question — the 23s on the 22mm inner-width Boyd Rims measure out to 26mm — Bill Mould showed me that. That’s as much as the Cervélo 2016 R5 will tolerate at the chainstay. Something expensive would have to be replaced.
— Don

Dear Don,
While some companies have specific charts of what width tire can safely be used on which width rim, the only way to get the ETRTO specs on that (which are updated every year), is to buy the big book ETRTO publishes annually. Mavic had a chart like this on its site that I used to refer to, and after the reorganization of the site, it is no longer there. Here is an updated table from Mavic that includes the rim-tire combinations from the latest version of ETRTO and ISO. The tire pressures are Mavic’s recommendations, based on tubeless use. When used with an inner tube, the max pressure can be 15 percent greater.

A general guideline is to take the inner rim width and multiply by 1.25 for the minimum tire size and by 2.5 for the maximum tire width. So, a 22mm inner rim width should not have less than a 27mm-width tire on it, and no bigger than a 55mm tire.

While I am aware that people violate these guidelines all of the time and most of the time get away with it, you are playing a bit of Russian roulette, especially with tubeless tires at high pressure. If the inner rim width is about the same as the width of the tire, there is not much preventing it from blowing straight up off of the rim. This is even more important with hookless rims.
― Lennard

Dear Lennard,
I’m reading many articles about tire pressure and width, rolling resistance and watts, and they’ve brought to mind a related question: Does a wider tire with lower pressure wear more slowly than a narrow, higher-pressure tire?

I’m inclined to think that the wider contact patch of modern tires would spread wear over a wider area and slow it, but I’d be interested to know your or even the tire industry’s thoughts.
— Matthew

Dear Matthew,
My experience has been that wider tires wear longer than narrower ones of similar construction with similar riding. And much wider tires wear much longer. Here’s my take on it:

At the same pressure, there is little doubt that the narrower tire will wear faster. By definition, at the same PSI, the same amount of area of the tire tread must contact the road to support the same amount of mass. The narrower tire must compress more deeply to accomplish this.

The casing will certainly wear out and get shredded more quickly because it is flexing so much more on the narrower tire. Look at the sidewalls of cyclocross tires run at low pressure to see this astounding rapidity of casing wear. Casings on cyclocross tubulars tend to give out long before the tread wears out.

A higher percentage of the circumference of the narrower tire will be on the road at any given time than on the wider tire. That will obviously wear the narrower tread faster, and down a narrower strip down the center. The wider tire will distribute that wear over a wider area of the tread, and it will thus last longer.

When the pressure is adjusted to the tire width to keep the hoop stress constant between the two tires, it is a bit less clear. This will even out the casing wear. However, the lower pressure in the fat tire means that much more surface area of its tread will be on the road at a given time than the skinny tire, thus distributing the wear over a larger area and lengthening the tread life.
― Lennard

Dear Lennard,
I’ve been riding bikes and changing tires for many years. I’ve been reading your recent comments and suggestions. While I agree with all of them, I also believe that there is a major problem in the industry with regard to rim and tire standards. This has always been a problem, especially with carbon rims. However, with the emergence tubeless compatible road and gravel tires, the problem has become much more prevalent — even when using tubes. It just shouldn’t be this hard! IMHO, until the tire and rim manufacturers get together and establish consistent and workable standards, otherwise we the consumers will continue to suffer.
— Bob

Dear Bob,
This is actually happening more now than at any other time in bicycle-regulation history. There is more participation by tire and rim companies now at the annual ETRTO standards committee review and update meetings. While some tire and rim companies go rogue and make rims and tires that don’t adhere to the standards, there is less of this going on than there was five or ten years ago.
― Lennard

Dear Lennard,
It was nice to see others mention soapy water too. Another comment is that with tire liners (I use the Vittoria AirLiners on my gravel bike), it can be hard to remove a tire as you can’t compress the sidewall for an initial bead break because it is supported by the insert. I have found that the pinching tool you pictured is the answer to that problem, I bought mine from Vittoria, but it would appear that they are being sold by numerous brands.
— Scott

Dear Scott,
Yeah, that tool is a must with tubeless inserts.
― Lennard

Dear Lennard,
In this week’s column, Oliver Kiesel from Specialized is quoted as saying:

“Also, a tubeless or latex tube setup, as you pointed out, loses around 0.5 – 1.0 bar within a day.” I hadn’t heard that road(?) tubeless was prone to such drastic pressure losses — is this correct? If so, it seems to me to be a good reason to stick with tubes for longer brevets or multi-day events. Back when I had Clement Paris-Roubaix Setas this pressure loss (more like 1.5 bar/day, or so) drove me mad, and if I commuted on them I had to inflate the tires twice a day.
— Stephen

Dear Stephen,
That came as a surprise to me, too. I’m familiar with that kind of air loss with latex tubes (tubular or clincher), but not with tubeless tires. Mine seem to stay at the same pressure for weeks on end.

On the other hand, the tubeless interior of a Challenge tubeless tubular is latex. I have one on my rear wheel (a 40mm Team Edition Strada Bianca tubeless tubular, with sealant), and it does lose air at pretty much the same rate as the 40mm Strada Bianca tubular on the front, which has a latex inner tube.
― Lennard

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Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (www.zinncycles.com) and purveyor of non-custom huge bikes (bikeclydesdale.com), a former U.S. national team rider, co-author of “The Haywire Heart,” and author of many bicycle books including “Zinn and the Art of Road Bike Maintenance,” “DVD, as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.” He holds a bachelor’s in physics from Colorado College.

Follow @lennardzinn on Twitter.