[Gnarly 928]

Ok, I must have a 'learning dissorder' but I can never "get it" or remember it from bike to bike and computer to computer..The question is: Which way do you change your settings for Wheel Size to influence the readings? Not really very important in the over all scheme of biking, for me (obviously, or I would have found out before this) but I always get confused about how to make my cyclo-computers read correctly. I've had almost every type and have a drawer full of peices/parts from old ones, have different types, etc. but all have a "Wheel Size number" or a "Correction Factor" that you must enter to get a 'real' reading of speed and distance. And, many of them "lose" this setting as you change batteries or 'fumble-finger" through the setting buttons..And, of course, many of the 'owners manuals' are translated direct from a strange language, making their meaning unclear(to me, at least)
So, I have a CycloSport HAC-4 fancy one that I usually use on all my bikes (right now) unless I am traveling and the batteries go dead...Anyhow, It calls for the default wheel size setting to be at 2080 (from memory, I don't have the booklet right in front of me). So, if I find I am not getting the correct distance on the counter with that setting, which way to I change the programming? Bigger number=Bigger mileage? Bigger number=faster speed readings? Or smaller number= more mileage, speed?..which? Any body have a "pneumonic" to help me remember?
Thanks, Don Hanson

 

[C-40]

wheel circumferance...

The number that you put in is the wheel circumference, either in millimeters or centimeters. The computer counts the number of wheel revolutions and mulitplies that number times the circumferance to get total distance. If the computer displays more miles than you've actually ridden on a course of known mileage, then the number is too large. It will also display a speed that is faster than you're actually going.

The best way to get the number right is to roll the bike along a smooth surface for 3-4 revolutions, measure the distance, divide by 3 or 4 as appropriate, then convert to millimeters or centimeters by multiplying by 25.4 or 2.54 as appropriate. Even greater accuracy can be had if you sit on the bike while doing the rollout, since it will slightly reduce the tire diameter.

A common value for a 700 x 23 tire is around 2110 millimeters.

 

[Gnarly 928]

Thanks, exactly what I needed. I was having difficulty getting it straight about..Circumference (Correction factor) as that influenced the number of rotatioanl signals vs. the speed and distance read-out...."Hmmm, more 'blips" with a smaller correction factor= higher speed readings? or not?..." Anyhow, "larger number=higher speeds and bigger odo readings" will work for my purposes.
Thanks again, Don Hanson