Throwing this out there for ST experts. This just came up on a recent email discussion and thought it might may for a good topic.
Copied email thread:
There is a guy, Al Morrison, who has conducted extensive study to the difference in rolling resistance and efficiency of different tire
widths. His general conclusion is that 25mm tires are, indeed, faster than 23mm tires, for myriad reasons.
His latest findings are in this PDF: http://www.biketechreview.com/...ire_testing_rev9.pdf
The thing is, many racing frames have very tight tire tolerances, and running a 25mm tire (at least one that’s true to advertised width, as
many are narrower) can cause clearance issues if a wheel is even slightly out of true.
“Many riders have argued for years that narrower tyres – especially on the road – are faster and more efficient than wider ones when in fact, the opposite is true. According to Wheel Energy, the key to reducing rolling resistance is minimising the energy lost to casing deformation, not minimising how much tread is in contact with the ground.
All other factors being equal, wider casings exhibit less casing ‘bulge’ as a percentage of their cross-section and also have a shorter section of deflected sidewall. How big a difference are we talking about here? For an equivalent make and model of tyre, Wheel Energy claims the 25mm-wide size will measure five percent lower rolling resistance on average – the supposed average limit of human detection – than the more common 23mm-wide one.
Unless you’re a pure climber and solely focused on weight, the takeaway message here is that you’ll go generally faster on wider rubber even if it’s slightly heavier.”
Over the past few years we’ve seen a few examples of this. The aussie track guys, some Garmin guys rear tires, etc…
I think the perfect application would be in a climbing stage where the Crr has a greater component of drag vs. aerodynamics. In a pure TT or even a typical road race it would be difficult to justify a 25mm tire on a bicycle wheel designed for 21-23mm tires - EXCEPT in a crit or when course and weather conditions permit.
-SD
Except that totally ignores aerodynamics. And the aerodynamic differences between a 23 vs 25mm tire can certainly outweigh any Crr differences.
Alan Morrison posts pretty regularly on this forum (AFM is his handle, IIRC).
Further, neither the recumbent blog from almost a year ago or that magazine article actually much of anything specific at all other than a 25 mm pro race 3 rolled “better” than a 23mm one. Considering that no pro race 3 are even on the first page, who cares. As almost none of the tires in the chart are 25 mm it is a pretty big leap of logic. And really, posting a link to a recumbent blog should get you banned
Except that totally ignores aerodynamics. And the aerodynamic differences between a 23 vs 25mm tire can certainly outweigh any Crr differences.
Alan Morrison posts pretty regularly on this forum (AFM is his handle, IIRC).
Further, neither the recumbent blog from almost a year ago or that magazine article actually much of anything specific at all other than a 25 mm pro race 3 rolled “better” than a 23mm one. Considering that no pro race 3 are even on the first page, who cares. As almost none of the tires in the chart are 25 mm it is a pretty big leap of logic. And really, posting a link to a recumbent blog should get you banned
forgot about that new rule. Blog link has been removed - Thanks!
Michael
The bicycle is a mechanical system. The object of our quest is balance of all the factors contributing to overall system performance (Jordan makes this point continuously these days). If you are overly focused on one aspect, rolling resistance in this case, then you miss the overall system view which would have told you that while 25mm tires may roll better, that improvement is completely wiped out, and potentially made worse by the additional aerodynamic drag created.
That said, rolling around on 25mm tires at 85 or 90psi in the offseason is wonderful. All discussion of discomfort or “harshness” just falls away.
www.prto TriBriGuy]The bicycle is a mechanical system. The object of our quest is balance of all the factors contributing to overall system performance (Jordan makes this point continuously these days). If you are overly focused on one aspect, rolling resistance in this case, then you miss the overall system view which would have told you that while 25mm tires may roll better, that improvement is completely wiped out, and potentially made worse by the additional aerodynamic drag created.
That said, rolling around on 25mm tires at 85 or 90psi in the offseason is wonderful. All discussion of discomfort or “harshness” just falls away.
Agree on the comfort part. My regular road tires have been Michelin Pro Race 2’s, when I ran out of those I’ve been running Michelin Krylion Carbons - both 23mm tires. This winter I finally put on my Vittoria Pave Evo’s which I think are still only 24mm tires, but I noticed a HUGE difference in comfort. Those tires just absorb all the road harshness.
Michael
If you are talking about aerodynamics, does 2mm (1 mm on each side of the tire) really make any difference? I mean 1 mm is about as small a measurement that one can realistically imagine with human sight, how much wider is the whole unit (rider and bike) if there is one single wrinkle in a skinsuit? How about a strand of hair peeking out from a helmet? How much overall drag does one single break in form to get a drink create? I mean there are numerous factors which measure way more than two millimeters. Without any thorough testing, how could one determine such minutia? I guess I can kind of understand mating the 23mm tire to the new wider rims. It would seem to solve both the aero (by making a smooth transition to the wheel vs a bulge to a 19mm rim) and take advantage of the lower RR with the lower pressure and wider tire. Even that, may be more marketing than practical.
Except how much aerodynamic difference would there really be with a 25mm be on the rear wheel of a road bike? With the rearward weight distribution on a road bike, that’s where it would make the most difference IMO. I have taken to running 23 mm front and 25 mm rear on my road bike, now that Conti 4000S are available in 25mm.
If you are talking about aerodynamics, does 2mm (1 mm on each side of the tire) really make any difference? I mean 1 mm is about as small a measurement that one can realistically imagine with human sight, how much wider is the whole unit (rider and bike) if there is one single wrinkle in a skinsuit? How about a strand of hair peeking out from a helmet?
Yes, 2mm is pretty small, but 2mm over the diameter of both tires is pretty significant, around 2800mm squared or 4.34 inches squared in increased surface area for 700c wheels.
