| **Empirical data on wheel rollout for cyclometer** | woo hoo
*Feb 13, 2002 12:46 PM* | | Has anybody done some tests to determine accurate circumference on 700c x 20, 700c x 23, and 700c x 25?
What about variances due to inflation?
In Centimeters?! |
| **re: Empirical data on wheel rollout for cyclometer** | guido
*Feb 13, 2002 1:01 PM* | | is found in the chart in the instruction book included with the cyclometer. The simplest and most accurate way to determine roll-out is pump up the tire to the pressure you ride it, get on the bike and move it forward exactly one wheel revolution, then measure the distance. The chart in the instruction book is usually accurate enough. |
| **Close only counts in Horseshoes!** | woo hoo
*Feb 13, 2002 1:39 PM* | | Thanks, but I already know this about the charts and stuff. I can do the rollout myself, just curious what others have come up with.
So, how about the numbers from some real experimentation? |
| **re: Empirical data on wheel rollout for cyclometer** | wsexson
*Feb 13, 2002 1:52 PM* | | My tire rolled out to 2 mm less then the value built in to the Flight Deck for 700x23. The circumference adjustment for the Flight Deck is in 5 mm increments anyway. I am not going to worry about the velocity and distance being off by about 0.1%. |
| **re: Empirical data on wheel rollout for cyclometer** | Chen2
*Feb 13, 2002 3:50 PM* | | Best way I've found is to ride flat section line roads with intersections that are exactly 1 mile apart. I use some roads that I checked on a topo map that are exactly square miles. I dial in my circumference number until I can ride intersection to intersection consistently to within .o1 miles. My Cateye Astrale computers have millimeter circumference calibrations. Tire sizes vary with manufacturer. The rider's weight is another variable.
-Al |
| **Ya know what?** | look271
*Feb 13, 2002 5:45 PM* | | It really doesn't matter much. When I 1st got my Mavic Mektronic shifters with it's computer, I was APPALLLED to find out that Mavic gives you a weird-ass numerical value for assigned tire sizes. What, no dialing in the exact number of centimeters!? I really had my tush all puckered up over this, being the how far-how fast kind of guy that I am. I sadly dialed in the correct setting and hoped for the best. 1st organized ride that I did with it was a metric century @ 63 miles. My mileage? 63.1. BFD. Now I don't worry about such trivial things! |
| **Must ride accurate distance** | cyclaholic
*Feb 13, 2002 9:31 PM* | | I am a real stickler for accurate distance measuring. I have tried that rollout measuring with good metric tape and it has never been accurate for me.
The absolutely best way I have found to calibrate my computers is to go to a nearby high school track and ride 1/4 mile laps. As your accuracy gets more precise, ride longer intervals. If you can ride 8 laps and show at 2.0 miles, you've got it. |
| **Its all in the mind.** | Ozzie
*Feb 14, 2002 3:52 AM* | | There were a number of speed and distance records around here locally.
I put two magnets into my wheels and broke them all. Got over 190 kmph down one hill with a tail wind!
Im untouchable in all the local TTs too.
Try it. |
| **Imagine what 3 or 4 magnets could do to your speed! ;o) -NM** | Tig
*Feb 14, 2002 7:18 AM* | | |
| **700c x 23= 208.91cm @ 130psi** | woo hoo
*Feb 14, 2002 9:31 AM* | | Entering 209cm into your cyclometer means that when wheel revolves 770 times you will roll 5280.11 feet
If you use 208cm, the wheel revolves 774 times and rolls out to 5282.14 feet. giving you a 21 foot error over ten miles.
If you use 210cm in your cyclometer, after revolving 767 times the wheel has gone 5284.7 feet, an error of almost 48 feet over a distance of ten miles.
At least mathematically! |
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