rmur asked me these questions in a PM and I hope he doesn't mind me answering them here so that anyone else with the same questions can see the answers
(1) Why such a high Crr? I was figuring 0.004 for a fellow who pays attention to tires.
Well, the simple answer is, they're not my tires/tubes
I was wondering if someone was going to notice that.
Seriously, I'm running a VF Record front and a Bonty RXLPro23 on the rear on my wheels (latex tubes, of course)...and last month at the Piru TT I had the perfect opportunity on my outbound leg to nail down a Crr of .0038 to go along with a CdA of .228 m^2. My friend's 404s had Vittoria Open Corsa CX 20s with what I had assumed to be latex tubes inside. I hadn't had time to switch out tires yet so I just went with what he had for the testing. When I got done, and started looking at the data, things weren't matching up with the true elevation difference with the slightly higher Crr I had originally assumed...so I quick popped off the front tire and discovered the -gasp!- butyl tubes inside.
Check this out though...so I took a look at AFM's chart. I looked at the percent difference between my tires and the Vittorias and adjusted the .0038 Crr. I then looked at the percent change from latex to butyl and adjusted it again. That gave me an assumed Crr of .0056. When I put that into the spreadsheet, the calculated CdA for the zero yaw condition worked out to be...ta da! .228 m^2, just like the Piru data. Pretty cool, huh? Shows pretty clearly to me the validity of Al's testing.
What I learned is that with the "mini-halfpipe" course I used this time for logistical reasons (closer and shorter, i.e. more laps) is that with the lesser elevation difference as with my original "halfpipe", I don't see as high of max and average speeds...so the testing is much more sensitive to crosswinds since they can have a bigger affect on the apparent wind angle.
Everything as "same" as I could get it. The funny thing is...if I had to choose which one "felt" faster just from perception alone...I would swear the P2K "felt" faster...go figure.
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Now for the reality check: (1) Why such a high Crr? I was figuring 0.004 for a fellow who pays attention to tires.
Well, the simple answer is, they're not my tires/tubes
I was wondering if someone was going to notice that. Seriously, I'm running a VF Record front and a Bonty RXLPro23 on the rear on my wheels (latex tubes, of course)...and last month at the Piru TT I had the perfect opportunity on my outbound leg to nail down a Crr of .0038 to go along with a CdA of .228 m^2. My friend's 404s had Vittoria Open Corsa CX 20s with what I had assumed to be latex tubes inside. I hadn't had time to switch out tires yet so I just went with what he had for the testing. When I got done, and started looking at the data, things weren't matching up with the true elevation difference with the slightly higher Crr I had originally assumed...so I quick popped off the front tire and discovered the -gasp!- butyl tubes inside.
Check this out though...so I took a look at AFM's chart. I looked at the percent difference between my tires and the Vittorias and adjusted the .0038 Crr. I then looked at the percent change from latex to butyl and adjusted it again. That gave me an assumed Crr of .0056. When I put that into the spreadsheet, the calculated CdA for the zero yaw condition worked out to be...ta da! .228 m^2, just like the Piru data. Pretty cool, huh? Shows pretty clearly to me the validity of Al's testing.
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(2) Re the x-winds, I wouldn't get too hyper over those apparent levels - remember the demonstrated dependency of Wind_Chung. What I learned is that with the "mini-halfpipe" course I used this time for logistical reasons (closer and shorter, i.e. more laps) is that with the lesser elevation difference as with my original "halfpipe", I don't see as high of max and average speeds...so the testing is much more sensitive to crosswinds since they can have a bigger affect on the apparent wind angle.
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(3) Everything the same - you didn't tuck any harder etc? I joke about it sometimes but I honestly do believe there could be a small placebo-like effect (in general) Everything as "same" as I could get it. The funny thing is...if I had to choose which one "felt" faster just from perception alone...I would swear the P2K "felt" faster...go figure.
okay seems like you had the ducks nicely aligned. Sometime it'd be interesting to go out on a plain jane road bike and do this sort of thing! I can see you riding a P3C and drop bars in your crits soon!