How about on pretty good roads?

Won't the aero advantage of narrower tires (which is quite significant) also factor in?

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I think good roads and average size rider should stick with 22-23 on the front at least for TT.

If you want to get really optimized you need wind tunnel for the tire on your rim, and Crr data. Then guess what your yaw will be, and the pavement roughness, and run the numbers.

I err on the side of aero on the front, and since my frame won't accept anything bigger than a 22mm rear tire, I run narrow tires. I don't think I'm giving up much. Except for the time I used CO2 to pump up my SS20s and I was probably racing on ~60psi. They were smooth!

One thing that needs to be said over and over... when a pro runs a 25mm tubular on his wide rims, those tires are actually 25mm wide. That isn't the same as a 25mm clincher which will usually measure 28mm or so depending on what it is.

Yes, I would say that's generally correct. The important factor to keep in mind though is making sure that the road surface conditions (along with rider mass and speed) don't put the rider into a situation where one can't lower the pressure enough to be below the "breakpoint" pressure for the conditions AND avoid pinch flats.

In other words: 'Tis far better to err on the side of too little pressure, than too much...until you risk bottoming/pinch flatting! ;-)

Here's how I look at it now...Josh's (and previously Damon's) data basically shows that for flat surface, 8cm, and 8mm "bumps", compliance is really mostly driven by tire pressure. https://silca.cc/...r-is-stiffer-harsher

So, if conditions require lower pressures for both comfort, and for avoiding "breakpoint" losses, then the use of a wider measured tire width is valuable, since as a byproduct, it's also taller, which helps to avoid bottoming. This widening can be done by using a wider inner bead width rim on a given tire, or a larger tire...or both.

Once you've arrived at the preferred pressure, then for timed racing on paved roads, you're going to want to run the narrowest width combination that allows that pressure without undue chance of pinch flatting and/or rim bottoming. That will give the best combination of Crr and aero drag.

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http://bikeblather.blogspot.com/

Actually...Josh's data implies that small and large bump compliance is mostly driven by air pressure and not tire width. https://silca.cc/...r-is-stiffer-harsher

What a wider (and taller) tire gives you for rougher surfaces is the ability to run lower pressures without danger of bottoming/pinch flatting.

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Fwiw, a new old 20mm Supersonic came up on eBay 'saved search' of mine today. Someone jump on it so TJ doesn't pick it up ;)

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Thanks for the excellent summary Tom!

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Damon Rinard
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But also the ability to run a lower pressure which gives a better ride but with a lower rolling resistance.
There is middle ground here between running the same pressure and running one that gives equal softness.
This is the wider tyre sweet spot where aero losses can be made up, or total losses lessened by less impedance losses.

Off particular interest is this:

Please see the post-script to this paper about why we believe this to be true, but keeping it simple based on the data we’ve seen here, it certainly seems that wider tires every bit as good or better at absorbing small bumps and imperfections than narrower tires at the same pressure.


Taken directly from Joshes blog linked.

So the larger tyre has a better ability to absorb surface imperfections even at the same pressure and is enhanced when at a lower pressure.

I'm not speaking for Josh, but his own data shows that's not the case...the smaller the imperfection, the less width matters in compliance and the more it's driven by tire pressure alone.

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See earlier in the thread...those theoretical Crr "gains" appear to be not realized once you reasonably drop the pressure for more compliance. And, no matter the pressure chosen, the Aero drag is worse. There's no free lunch if you're talking about pure speed.

The data also shows that it's not a good idea to be flirting too close to impedance losses, since they come on pretty quickly. Like I said above, it's better to err low...

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If those are from 2009, then they may be the "slower" SS, right? Tom A.'s spreadsheet shows .0034 for the 20 mm SS in 2012, but .0030 in 2016.

It will definitely vary from tire to tire but yes these will probably roll marginally slower. Regardless, they came out with a new 20mm SS that is wider and has slightly different construction. Off top of my head I can't remember which one Tom tested in 2016 but if it is the wider one then you would have to assume that much of the RR improvement comes from that.

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The measured widths are in the table...

The 2012 model was pre-"Black Chili", and the 2016 model was nominally the same, but with the Black Chili compound. The measured widths on a narrow Mavic Open Pro were 20.5mm for the 2012 and 20.8mm for the 2016...nearly the same. So, it's safe to say that the improvement was mostly from the compound change.

The 2016 model is from before the latest unannounced model change, or "widening". I haven't rolled one of the newest ones yet.

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Good to know again, thanks!!

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