What is 700X38C in km/h on a cycling computer?

Question

I am setting up my cycling computer and have to enter the km/h for the wheels. However the wheels are 700X38C and the instructions only give 700X35C as 2205 km/h and 700X40C as 2224 km/hr... what does this make 700X38C? Thanks!

Answer 1

different computers have different resets. you'll have to google your manufacturer, and see if there is more info at their website..

Answer 2

Those numbers in the manual are usually junk. Always measure via roll-out to get the correct number.  I align the valve stem with a crack or mark, then roll the bike, with me on it, for 3  revolutions of the wheel. Taking a sampling of 3 gives you more accuracy. Measure and divide by 3 to get the diameter. Convert from inches to mm if necessary, 1 inch = 25.4 mm.

Just as a rough estimate - a 700c rim is 622mm at the bead. If the tire is 38mm wide, it's probably close to 38mm tall, so 38mm at top and bottom means 76mm total on top of the 622 mm rim = 698 mm tall wheel. Circumference = Pi(D) = 2192 mm. This number will vary based on the true vs advertised diameter of the tire, as well as the width of the rim, with a wider rim effectively making the tire 'shorter.'

Answer 3

1st, the numbers are the diameter of the tire not km/hr. Next a simple solution would be to extrapolate the info. You have a size a little larger and a little smaller than your with listed diameters, wouldn't you conclude the diameter you need is about in the middle of the high and low numbers?

Finally, as I have answered about 6 or 8 times, a roll out is the best, most accurate and easy way to get a highly accurate diameter.

EDIT: thanks, blazing... I just couldn't bare writing the roll out thing again.

Answer 4

I'm ROFL imagining M R's thought process......  Type?  Go ride?  Type?  Go ride?  s***w it,  I'm going for a ride.

P.S.  The answer is to measure it as noted by blazing.   Even tires of nominally the same size can vary quite a bit.