Contour Enthusiasts Group Archives Forums General Common Interests Bicycle computer question

Hopefully someone will know this. I have a Trek computer for my M.B. and I can't find the manual as usual. My battery died and I can't remember the calculation for figuring out the number for my tire circumference. I know you measure the total cir. in cm and then times it by a certain number. I need to know that certain number.

Your best bet is the actually measure the outside surface of the tire with a string, and then lay out the string and measure it with a tape measure.
If you want to do it the other way (not as precise) is to measure the diameter of the wheel/tire combo and then multiply by 3.1416. This number is called pi.

Here you go todras, just in case you feel like being really precise, here is Pi carried out to 1000 places:
3.1415926535897932384626433832795028841971693993751058209749445923078164062862089986280348253421170679821480865132823066470938446095505822317253594081284811174502841027019385211055 596446229489549303819644288109756659334461284756482337867831652712019091456485669234603486104543266482133936072602491412737245870066063155881748815209209628292540917153643678925903 600113305305488204665213841469519415116094330572703657595919530921861173819326117931051185480744623799627495673518857527248912279381830119491298336733624406566430860213949463952247 371907021798609437027705392171762931767523846748184676694051320005681271452635608277857713427577896091736371787214684409012249534301465495853710507922796892589235420199561121290219 608640344181598136297747713099605187072113499999983729780499510597317328160963185950244594553469083026425223082533446850352619311881710100031378387528865875332083814206171776691473 03598253490428755468731159562863882353787593751957781857780532171226806613001927876611195909216420198

No that's not what I'm saying. Yes I have measured the circumference Ok I'm not 3 years old here). I just need to know what number to times the circ. by. And no it's not pie. :rolleyes:

Pi aren't circle... PiR^2.

Sorry... :rolleyes:

I LIKE PIE

LOL seriously, laying out the string is the best way.

on mine u just punched in the radius of the wheel....

I have the exact same problem! Finally replaced the battery after a year of sitting dead, and it wants to get configured.
I feel like it's asking for PC load letter.
My best guess so far is rolling circumference in cm, times 10.
And I'm sure you know it's best to do the measuring with chalk lines on asphalt with you on the bike, tires inflated to your normal pressure, etc...

Ya know I'm glad for people like Dan that can read. :rolleyes: Yea Steve it's not x 10 I know. The number should come out to be like 1700 something. That's not it but I know it's close. I guess I'll call the local bike shop.

Err, Pir^2 is AREA of Circle. :rolleyes:

Circumference is Pi x Diameter or Pi x Radius x 2

Another shortcut is to put some paint on the tread of the tire, Sit on bike and roll forward, putting 2 paint marks on ground. Measure distance between marks. This gives you Rolling Radius of tire, which will make your computer that much more accurate.