An interesting read about tire width and aerodynamics:
http://www.novemberbicycles.com/blog/2014/8/7/november-in-the-wind-tunnel-is-wider-faster.html
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We just tested this same thing on Monday. I’ll post graphs of production wheels we tested, but can’t post anything yet for our own stuff.
The biggest thing we found with all wheels was that until about 12.5 degrees of yaw angle the graphs mimicked each other, with the exception of the 25mm tire having about 10 grams higher drag.
Once you start getting above 10 degrees of yaw angle that is where the 23mm tire starts doing a lot better. So, calm days or faster riders shouldn’t see much of a difference between a 23mm tire and a 25mm tire in terms of aero drag. If you are doing a lot of riding in crosswinds, that is where the 23’s will have an advantage.
I was actually debating riding a 25 front on my ENVE 8.9’s for Lake Stevens so it is good to hear that it is only a minor penalty. I wonder what the 10gr drag vs lower rolling resistance would equate to over a 56mile ride.
The REALLY interesting thing about all of this is that people now seem to consider 23mm width tires “narrow” :-/
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The chart is confusing. Do we want more “seconds gained” or less?
The REALLY interesting thing about all of this is that people now seem to consider 23mm width tires “narrow” :-/
^^^
THIS!
I was actually debating riding a 25 front on my ENVE 8.9’s for Lake Stevens so it is good to hear that it is only a minor penalty. I wonder what the 10gr drag vs lower rolling resistance would equate to over a 56mile ride.
The rule of thumb is 10 grams drag = .1s/km. About 9 seconds in a 56 mile ride.
Im still in the band where I consider 20mm to be narrow!
I had the chance to grab a set of 20mm Vittoria Evo Corsa CX II clinchers at an amazing price so I’m wondering whether you can guesstimate the aero penalty of using these over Conti GP4000S 23mm?
I dont think you tested the 20mm Vittoria’s from the chart on your blog (Conti SS 20mm yes, but not the Vittoria Evo’s).
FWIW, I’m running them on Zipp 808 alu clinchers (hybrid toroidal profile), which have a narrow rim track…hence my initial thought that they might actually be more aero on these wheels than 23 mm (barring ride quality).
Any thoughts?
Im still in the band where I consider 20mm to be narrow!
I had the chance to grab a set of 20mm Vittoria Evo Corsa CX II clinchers at an amazing price so I’m wondering whether you can guesstimate the aero penalty of using these over Conti GP4000S 23mm?
I dont think you tested the 20mm Vittoria’s from the chart on your blog (Conti SS 20mm yes, but not the Vittoria Evo’s).
FWIW, I’m running them on Zipp 808 alu clinchers (hybrid toroidal profile), which have a narrow rim track…hence my initial thought that they might actually be more aero on these wheels than 23 mm (barring ride quality).
Any thoughts?
Dunno. Don’t have any Crr or aero info on those. Hard to make a judgment without that…
The REALLY interesting thing about all of this is that people now seem to consider 23mm width tires “narrow” :-/
Actually, the really interesting thing is the movement of all these wheel manufacturers to use wind tunnel testing as a marketing tool. Hopefully, it drives innovation towards even more aerodynamic designs but I’m a bit skeptical given the general state of the cycling accessories industry though.
I was actually debating riding a 25 front on my ENVE 8.9’s for Lake Stevens so it is good to hear that it is only a minor penalty. I wonder what the 10gr drag vs lower rolling resistance would equate to over a 56mile ride.
The rule of thumb is 10 grams drag = .1s/km. About 9 seconds in a 56 mile ride.
Any ideas how much lower the rolling resistance would be with the 25’s? 9 seconds doesn’t seem like it would be too difficult to make up.
So wheel only I assume many Tour Riders will have different front back for the TTs 22-23 upfront 23-25 in the back.
Thanks. Our “seconds saved” data is per the Tour Magazine yaw angle weighting for 30mph. We’ll be backfilling with more info on scaled wind speeds in subsequent posts, but for now we’re just trying to elucidate the importance of inflated volume and irrelevance of stated volume. An example being that if you feel like you have to run 110psi on a 404 and this feels to harsh, the same tire on a Rail will inflate to 100 psi with the same volume of air. Your relative buoyancy or suspension stays the same, but you get to use lower tire pressure.
The other big thing is the rolling resistance differences created by the inflated width differences. This came into such stark contrast for us following this trip that we’re now pursuing that measurement aggressively.
We’re super reticent to show the graphs like Boyd posted for some wheels, just because some (not Boyd) have done some super questionable stuff with graphs, and the tests are never really normalized from one guy’s trip to the tunnel versus another. The tunnel forces you to swap the same tire from one wheel to the next because different editions of the same tire can cause differences that look significant when we’re talking about wheels as close as these we’re measuring. Even valve stem length becomes something to control. We just used an 80mm for the deeper wheels, and a 48 for the shallower wheels. We gave the wheels we tested against a free leg up from 6 extra mm of valve stem protruding on the 52 vs the 404, and an extra mm coming out of our 34 versus the 3.4. I’m sure that protocol and generosity is not universal.
Our aero numbers are just fine, no matter how you slice it. But while the wind tunnel is a big big piece of the puzzle, the search is on for the fastest overall setup, which includes parameters beyond just how a wheel does with a tire of a stated size that might have absolutely nothing to do with the tire’s actual size on that wheel.
and still pump them up to 120psi when they weigh 160lbs in kit… on shite chipseal…
We just tested this same thing on Monday.
Very cool to see you guys testing this sort of thing. FWIW, in my experience, “Watts to spin” is a function of tire shape/size as well.
I think the tricky part of the wheel+tire testing thing is generalizing the information to the masses. It might be that one has to test the exact setup (due to sample variation) one is trying to decide between on race day in order to truly know which one is fastest.
Glad to see others moving the needle forward, though! Keep up the good work.
Honestly I don’t know why people would just blindly believe the marketing hype that wider is better (Oh wait…). Whatever tire that creates a smooth transition of airflow from itself to the wheel rim/fairing is the best for that particular wheel. ie get what works for your specific case. Probably GP 4000s.
All of this aside I am very interested to know whether the lower rolling resistance is statistically significant and if so whether it saves more time vs. improved aerodynamics.
God damn Boyd, Kraig does not hand out praise lightly.
You guys should celebrate.
Seriously though, the level of testing and data available to the average joe is getting better and better. Boyd, Flo, November, and Swiss Side have all published interesting results along these lines lately. Thanks to all!
We just tested this same thing on Monday.
Very cool to see you guys testing this sort of thing. FWIW, in my experience, “Watts to spin” is a function of tire shape/size as well.
I think the tricky part of the wheel+tire testing thing is generalizing the information to the masses. It might be that one has to test the exact setup (due to sample variation) one is trying to decide between on race day in order to truly know which one is fastest.
Glad to see others moving the needle forward, though! Keep up the good work.
I think the tricky part of the wheel+tire testing thing is generalizing the information to the masses. It might be that one has to test the exact setup (due to sample variation) one is trying to decide between on race day in order to truly know which one is fastest.
That’s been my experience and is why sometimes a “best wheel choice from the options I have available” test result is sometimes not what you think it likely should be based on published data. It can also uncover other issues with your bike/wheels that may not have been immediately obvious but can cost you some speed.
The REALLY interesting thing about all of this is that people now seem to consider 23mm width tires “narrow” :-/
+1
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Im still in the band where I consider 20mm to be narrow!
I had the chance to grab a set of 20mm Vittoria Evo Corsa CX II clinchers at an amazing price so I’m wondering whether you can guesstimate the aero penalty of using these over Conti GP4000S 23mm?
I dont think you tested the 20mm Vittoria’s from the chart on your blog (Conti SS 20mm yes, but not the Vittoria Evo’s).
FWIW, I’m running them on Zipp 808 alu clinchers (hybrid toroidal profile), which have a narrow rim track…hence my initial thought that they might actually be more aero on these wheels than 23 mm (barring ride quality).
Any thoughts?
Same wheel, but different tires, so don’t know if this will help your decision-making process or not:
http://www.trainingandracingwithapowermeter.com/2010/11/aero-tires-and-wheels-skinny-vs-fat.html