Tubeless vs. Tubed clincher comparison via CDs

[R Mc]

Howdy everyone.

After reading recently that Campy decided to start building tubeless-compatible clincher wheels after they documented decreases in rolling resistance around 30% AND because I knew that the guys at my LBS had been riding road tubeless set-ups for around a year, I decided it was time to switch.

Matters were helped along when the vittoria evo-cx that would not die fell apart spectacularly in the middle of a ride since that put me in the market for new tires anyway.

Jim, owner of said LBS, made me take his Shimano tubeless wheelset to try them for a couple of rides before I sunk money into the project. I loved 'em. (Gary, the mechanic, has been riding a converted set of Mavic Open Pros for over a year].

So, Gary converted my dt rr1.1 rims to tubeless and, since the set-up changed, I needed to set-up a new profile.

Granted, this is only one set of numbers, but remember, the only change in the profile is the tires: wheels, bike, and rider are exactly the same (and fwiw, tire pressure was between 80-85 psi):

On June 8th, dt wheels with vittoria cx-evo front, conti gp4000 rear) resulted in cda .277 / fric. 7.69
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On July 4: dt wheels w/hutchinson tubeless (@ 80ish psi!!) resulted in cda .253 and fric. 1.74
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[alienator]

There's a lot that needs to be held constant to compare cRR between tires: pressure, temperature, road surface roughness, rim width, and other things. cRR is not an easy thing to pin down in absolute terms. Tests done by manufacturers and magazines typically are done on one kind of surface--usually a drum--so in those tests, the most that can be determined is how one tire does relative to another on that surface, given the other factors held constant. What's not shown in any tests to date, is the relative performance of tires across the spectrum of road surfaces that road tires encounter. It is possible that one tire type performs well on one surface, but then loses out to another on a second surface. One tire may perform better than another in a given temperature range. That there are so many arguments about cRR is some indication of the difficulty of comprehensively testing for cRR.

Also, if you did a series of 10, 20, or whatever coast downs and 4 mile rides, you'd see some variation in cRR and CdA reported by iBike. That's normal for any instrument. Maybe it's been published and I missed it, but it'd be cool to see what sort of uncertainty there is in the coefficients that result from iBike's best fit. With that, you could get a ballpark figure for how much uncertainty there is in a cRR comparo between tires.

[rruff]

On June 8th, dt wheels with vittoria cx-evo front, conti gp4000 rear) resulted in cda .277 / fric. 7.69
>
On July 4: dt wheels w/hutchinson tubeless (@ 80ish psi!!) resulted in cda .253 and fric. 1.74
>

These numbers don't tell us anything about Crr. The Fric constant includes the tilt adjustment as well as Crr... without both we have no idea how big the Crr is. Besides this your CdA went down a lot too (to a number that is hard to believe) even though there was no change to account for it. Usually this indicates that your Crr value will end up high to compensate. Plus, you haven't shown the raw CD and 4mile data so we can see how much the scatter was and take a guess at the error bars that should be put on this.

IME an accurate Crr value is very difficult to get from the CDs. BTW... I wouldn't expect tubeless to have any improvement compared to a comparable tire and latex tube.