So buried on several of HED’s webpages- they make reference to a statistical data about dropping 20% of your Crr by going with their new C2 rims. Some of the top tires tested by tour magazine required 34 watts. So 20% savings would be 14 watts with these rims: 6.8watts x 2 wheels. That is HUGE!!! HED references a ‘white pages’ on this subject- but I can’t seem to located this mysterious white page. Has anyone found it on their website???
http://www.hedcycling.com/wheels/ardennes_c2.asp
from HED’s websited:
All good, but what we’ve described so far could be called “quality of ride” improvements. Very nice, but what else is there? What else is lower rolling resistance. 20% lower. (see our white paper on rolling resistance)
Hed Classics models. Lighter, stiffer, stronger, faster. AND, a pure joy to ride. So good we even surprised ourselves.
Im pretty sure that one of the guys over at BTR.com tried to the measure the difference in RR due to rim width and, from memory found it to be so small that it was not of statistical significance.
That’s true if you use the same tire, but I think Hed’s point is that with the C2s you can run a wider tire with none of the aero penalty usually associated with that. A Vittoria Corsa CX23 is going to have better CRR than a CX21, for instance, but you wouldn’t normally put a 23 on a wheel with a narrow rim. I’d be surprised if it was a 20% difference, though.
Right now the lowest crr clincher as measured by biketechreview is a 20mm tire though
=)
that is on a smooth drum though.
Their bumpy roller data DOES indicate that for the same tire, that wider one does have less CRR when both are at optimum pressure. But its just N=1
That’s true if you use the same tire, but I think Hed’s point is that with the C2s you can run a wider tire with none of the aero penalty usually associated with that. A Vittoria Corsa CX23 is going to have better CRR than a CX21, for instance, but you wouldn’t normally put a 23 on a wheel with a narrow rim. I’d be surprised if it was a 20% difference, though.
I don’t mean to be a negative crybaby or anything ;-), but I feel the need make a few corrections to your post…
Right now the lowest crr clincher as measured by biketechreview is a 20mm tire though
Actually…it recently changed to a 23c model (I know because I sent Al that particular tire)…but, I agree with your point that there are PLENTY of narrow tires with as low of Crr as the best wider tires.
Also, don’t forget that Crr is only part of the story…for example, I’ll “give up” a little Crr to gain some aero drag reductions, such as with the slightly higher Crr Bonty “aerowing” tire at 19C
Oh…and “biketechreview” doesn’t measure anything with the tires for the roller data listed, they only host the data that Al Morrison so graciously gathers on his own time and shares with the rest of us. Minor point, but I believe in giving the proper credit where it’s due
that is on a smooth drum though.
Which still is causing the casing of the tire to flex at the contact patch…the main difference between that and a “bumpy” surface is that the maximum amplitude of that flexing is basically constant vs. the varying maximum amplitude. It’s still a good way to “rank” the hysteresis (or lack thereof) of tires.
Their bumpy roller data DOES indicate that for the same tire, that wider one does have less CRR when both are at optimum pressure. But its just N=1
Ummm…I think even Al would tell you to take that set of data with a pretty hefty “grain of salt”…there are some “issues” with how that particular set of data was gathered. I think it’s great that Al gave it a shot…it’s just that I’m not sure if it’s really telling us anything useful (well, besides how to try to improve the test protocol, that is
Ummm…I think even Al would tell you to take that set of data with a pretty hefty “grain of salt”…there are some “issues” with how that particular set of data was gathered. I think it’s great that Al gave it a shot…it’s just that I’m not sure if it’s really telling us anything useful (well, besides how to try to improve the test protocol, that is
I am just noting that they tested each tire at a variety of pressures
and there was a pressure where CRR was minimized.
I don’t recall a test of “optimum” pressure.
I didn’t find a pressure in my tests where Crr was a minimum - I think you are referring to Tom’s outdoor testing using Dr. Chung’s method where he found a minumum Crr at ~ 125 psig (IIRC) for the particular conditions of road and bike/rider for that test. As Tom mentioned the bumpy roller data set was an attempt but flawed. Compensating for the tire heating was questionable plus I only had “bumps” on one of the rear tire rollers. Since the load distribution one each roller isn’t known (doesn’t matter if both are the same) assumptions have to be made. I still have the bumpy roller which was an adventure in itself to get to work. I may build another someday and repeat some of the tests.
it just clicked for me that your team being sponsorsed by S, and that clincher happening to be an S open tubular (that costs as much as a vittoria EVO CX tub by the way). so what’s your agenda huh?
it just clicked for me that your team being sponsorsed by S, and that clincher happening to be an S open tubular (that costs as much as a vittoria EVO CX tub by the way). so what’s your agenda huh?
None at all. I paid for those tires with my own money and sent them to Al (and paid for the shipping both ways). I also sent him some other brand tires (Bontrager, Kenda, etc.) at the same time.
…I was actually quite surprised by that result since the tire appears to be virtually identical to the Bontrager RXLPro23s…in other words, they’re both made for the different brands by Vittoria. It’s interesting though that both of those tires (the Specialized and the Bontrager) have slightly narrower tread rubber glued on than the similar Vittoria model (the Open Pro KS) and that seems to be why they are faster than the equivalent model Vittoria (just my speculation).
Besides, if you ever take a look at what equipment I run for racing…you’ll see that (much to the chagrin of some on my team) I don’t have a “blind allegiance” to the Big S
So, seriously: what does the eyeball wind tunnel think of that Specialized tire? It seems, at least in pictures, to have a rather odd ‘squared off’ thing going on? Does it really look that way in the flesh?
I could see it being good–or maybe not-so-good. I’m curious if you have any thoughts.
I would love to see that paper.
Stop being such a negative cry-baby, Tom. After all, if HED (or jasonogk) claims it, it must be true.
Who was being negative? I merely stated that I’d love to see the paper…which is TRUE!
Better?
(BTW, I’d also love to see any data supporting HED’s claims…so far, there doesn’t seem to be any, yet people are making a mad dash to wider wheels and tires anyway.)
After all, if HED (or jasonogk) claims it, it must be true.