Field Testing: on-road rolling resistance

I just got back from a little vacation - it's always nice to catch up with family you haven't seen in a real long time...and that whole vacation thing can sometimes be a bit re-energizing too!

Here's a pretty neat shot I managed to snap of a small cabin in the woods that we were helping to stock up in Northeastern Oregon last week:



Hey, now that I'm all re-energized and whatnot, I decided to take another look (kind of in aggregate) at the data I gathered in this BTR Forum thread:

http://biketechreview.com/forum/viewtopic.php?f=1&t=2552

All in all, thus far, I have managed to do 6 runs at 140 psi and 4 runs at 120 psi on a road that I would characterize as pretty rough. There's a picture of the road surface in the thread linked above, so you can make up your own mind, though.

As it turns out, the 140 psi runs on the road had an average Crr that was ~10% lower than the 120 psi runs.

Interestingly, I also tested the same tires on my smooth aluminum rollers in the garage just after these on-road field tests...and not too surprisingly, the 140 psi run was around 8-10% lower in it's Crr than the 120 psi run.

One might also expect that the on-road Crr values would be higher than the smooth aluminum roller case...and, indeed the on-road values were in the 35% higher ballpark. So, that'd mean that if one was using the Crr values here to estimate things/tradeoffs:

http://www.biketechreview.com/tires/AFM_tire_crr.htm

you might only have to multiply the crr of the tires by 15% or so...more work to be done on this topic, though, eh?

These preliminary results are encouraging to me, in that things seem to be consistent (trend-wise). It's good to pursue multiple, independent, lines of inquiry when exploring a topic, eh? But dang, this field testing stuff is pretty tedious and just about as much fun as watching grass grow! :-)

In Summary:

-140 psi was a wee bit faster on average than 120 psi in this comparison
-rough roads seem to have a higher Crr than smooth rollers
-field testing in order to determine Crr is difficult and boring business

crank it up

The big dawgs are lightin' it up in richmond right now:



that in-car shot of tony stewart's left rear quarter panel isn't too far off the fifty minutes of "rear quarter panels" I got a view of today during the Barrio Logan Grand Prix crit here in socal.

It was this race that put a severe crimp in my season last year... I got taken down late in the race and crashed pretty hard causing some bad things to happen to my rotator cuff. Anyway, I hadn't really planned on racing barrio logan this year, but since they finally added back the M35+ category, I had to support the local racing scene!

Well, I tailgunned it - but I really didn't have much of a choice - I haven't been going so well this year. If I had to put my finger on a single reason for the lack of power I've been seeing this year, I'd put that finger on all those long tempo rides I did last fall in preparation for ironman arizona. Regardless of the cause, though, I am just not pedaling the bike as well as I'd like to at this point. It'll turn around eventually, though, I reckon!

Anyway, it got kinda hard about 10 minutes into the race and that's when the race for 1st ended - six guys went up the road and 3 or 4 of them were sportin' Amgen jerseys. I think anthony galvan finally took it while continuing to sport his ibike power meter on the handlebars. nice!

it was pretty mellow in the back, and I went hard for the last few laps before coasting across the line with my sweet "2nd tier" field sprinting capabilities for a top 10 field finish. Much better than last weeks dana point debacle, where I had to pick myself up off the pavement with six or seven to go before snagging a top twenty.

I'm not sure I'll be doing the Dana Point race next year - too many doodz (master's racers nonetheless) willing to risk contact with steel barriers in pursuit of weekend "glory".

hey, I'm glad I got back on the barrio logan "horse" again, though - it's a cool race that's been around for quite some time. Eventually, the city will repave those roads, and boy that will make things a whole lot safer!

Before I left to go racing in old barrio logan this morning, I re-tested several tires on my rollers in the garage in order to determine their coefficient of rolling resistance. This time around I used my old-skool yellow wired powertap that I purchased used. As it turns out, things were pretty consistent with the SRM that I used last fall for similar testing.

I managed to take some pics of a couple of the "fancier" aero-featured tires - whoa, those weren't rotated like that originally!:


bontrager tire


zipp tire

the bontrager tire has a little "wing" as they call it that tries to fill in the gap between the tire sidewall and the outboard corner of the clincher rim (a mavic open pro is what my powertap is laced onto in the pics). That wing is claimed to improve aerodynamics, just as the dimples on the zipp tire are claimed to improve aerodynamics. Only the wind tunnel knows if these features are significant enough to rise above the "noise" of marketing wishful thinking, though, eh?

speaking of "noise" - let me tell you, those dimples make a heck of a lot of noise when ridden on 4.5" aluminum kreitler rollers. holy crap, not only were they noisy, but the high frequency vibration that I could feel through my chamois was pretty annoying as well! I wouldn't want to do a long roller session on these suckers.

I wonder how much those dimples cost on the supply side of things in addition to the demand side of things (the crr of the zipp @120 psi was only slightly worse than the veloflex @ 60 psi according to my quick experiment).

Interesting stuff!

Put 'em up!

This here's another wind tunnel shoot-out! ;-)

Tested a couple of fast wheels and a slew of fast tires (which just might make more of a difference than the wheel itself).

Standby for a heads up on how you can gain access to the same kind of results that manufacturers generate.

Power Meter Field Testing - WLB Method

Over the past few months, I've been slowly generating data on a variety of field test venues with my SRM power meter.


Any of the variety of field testing methods out there can produce a number. The thing that has always made me curious about those #'s that are generated is "how reliable are they".


The best I've been able to do with the various field testing I've done is +/- several percent on aero props and Crr props using a tedious regression technique that takes about 45 minutes to generate data on a couple setups.


I spent some time and whipped up a script that incorporated a suggestion (thanks Adam!) - where one uses the work per lap of a loop course to generate estimates for cxa and crr -> more discussion here:


http://forum.biketechreview.com/viewtopic.php?f=1&t=2307



the last step for me was to use these estimates and assume that cxa doesn't change over the laps (reasonable!) and calculate the crr on a per lap basis. If one did 6 laps, they'd have 6 independent estimates of crr assuming a consant cxa generated from Adam's work per lap regression method. Similarly, one can use constant crr values across laps to come up with 6 independent cxa estimates (1 per lap).


We can then bootstrap these data sets to get an idea about how reliable the final estimates for cxa and crr are.


Here's a sample plot that shows the output from one of my field tests:







pretty crafty, I reckon -> Adam is a pretty smart dood to figure that one out!


So, yeah, I reckon I'll call this compilation of data reduction techniques the "WLB" method -> y'know, Work per Lap Bootstrap... d'oh!


Here's the wordle version of the data reduction script:





holy cow, that's pretty nerdy, huh!?

Supple?

A couple of quick shots of three tires hanging from my garage door opener track.

Lots of folks talk about tires being supple, and how this "supple-ness" can be a good indicator of tires with low rolling resistance.

Based on this supple-ness deal, which one of the tires above, would have the _worst_ rolling resistance?

Well, I dorked around in the garage this morning with my new toy (an IR, fixed emissivity non-contact temperature sensor) and measured those tires for rolling resistance and also how much they heated up during the testing.

Turns out that the caveman approach of flexing/bending the tire in your hands is a pretty good indicator of suppleness and rolling resistance - at least at a macro-scale!

Here's a link to some #'s for those inclined:

linky-link

Rolling Resistance

What's the potential rolling resistance of this sucker when executed well on bi-cycle:

http://www.gizmag.com/go/3603/

that's pretty cool, if you ask me - why? cuz it seems to be demonstrating concepts that strike at the core of reducing "rolling resistance" in an outside the box approach.

Then again, y'all must remember that I think decoding SRM binary power meter files is prety cool too, so yeah, YMMV!