cyclometer question
JAS
width. However, I have seen some references to these tires on the
newsgroup that say that they are not the size they claim to be (Avocet
Cross K 700c x 32s), but are in fact 28s. So, how can I tell what size
they are? On a long ride with a friend yesterday my computer said we went
48 miles, hers 50. Something's fishy!
Thanks in advance for any clues.
Jennifer
Jobst Brandt
If that's what they are called than that's what they are, however,
measuring the rollout distance isn't hard. The process is described
on the Avocet web page:
http://www.avocet.com/custserv/calibration.html
Jobst Brandt <jbr...@hpl.hp.com>
Rich Clark
JAS <jsto...@email.unc.edu> wrote in message
news:Pine.A41.3.95L.990907...@login6.isis.unc.edu...
> Ok, just got new tires and reset my little computer for the narrower
> width. However, I have seen some references to these tires on the
> newsgroup that say that they are not the size they claim to be (Avocet
> Cross K 700c x 32s), but are in fact 28s. So, how can I tell what size
> they are? On a long ride with a friend yesterday my computer said we went
> 48 miles, hers 50. Something's fishy!
Can you enter the circumference directly? Just set the bike on a flat
surface with the valve at 6:00, mark that spot, and roll one rev. Mark the
second spot and measure the distance, and there's your circumference. Can't
go wrong that way!
RichC
Edward J. Groth
>
> Ok, just got new tires and reset my little computer for the narrower
> width. However, I have seen some references to these tires on the
> newsgroup that say that they are not the size they claim to be (Avocet
> Cross K 700c x 32s), but are in fact 28s. So, how can I tell what size
> they are? On a long ride with a friend yesterday my computer said we went
> 48 miles, hers 50. Something's fishy!
>
>
> Jennifer
You might want to check out Sheldon Brown's site:
http://www.sheldonbrown.com/cyclecomputer_calibration.html
Of course, this won't tell you what size tires you have, but it does
give you a way to measure them yourself. Note that you and your friend
differ by 4%. The difference in tables for 28 and 32 tires is about 1%.
And the number for 28 is smaller than for 32. So if you change your
calibration, it will go the wrong way: for the same ride you will get
about 47.5 miles!
My suggestion would be to ride a known distance (for example, using mile
markers along the road) and see what your computer says. Then take the
number that's already in your computer, divide by the mileage given by
your computer and multiply by the actual mileage.
For example, yesterday my computer read 8.06 miles while going 8 miles
according to the mile markers. If I wanted to make a correction, I would
take the number that's already there (let's say 2130) multiply by 8.00
and divide by 8.06 to get 2114 which I would put in instead of 2130.
However, I had just changed a front flat and with the mini-pump I can't
get the tire as hard as I do with a floor pump, so I'm going to hold off
making the change until I get a measurement with the tire inflated the
way I like it.
If you believe your friend's computer is accurate - that you actually
went 50 miles, then you want to multiply whatever number is in your
computer by 50/48=1.0417 to get the proper number to put in your
computer. But how do you know your friend's is accurate?
- Ed
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| Physics Dept., Jadwin Hall | URL: http://pupgg.princeton.edu/~groth/ |
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Peter James
"Rich Clark" (rdcla...@TRAPacnatsci.org) writes:
> JAS <jsto...@email.unc.edu> wrote in message
> news:Pine.A41.3.95L.990907...@login6.isis.unc.edu...
>> width. However, I have seen some references to these tires on the
>> newsgroup that say that they are not the size they claim to be (Avocet
>> Cross K 700c x 32s), but are in fact 28s. So, how can I tell what size
>> they are? On a long ride with a friend yesterday my computer said we went
>> 48 miles, hers 50. Something's fishy!
>
> surface with the valve at 6:00, mark that spot, and roll one rev. Mark the
> second spot and measure the distance, and there's your circumference. Can't
> go wrong that way!
>
it out. The effective diameter changes enough to be noticeable, especially
if you are setting in mm.
--
Peter James
Ottawa, Ontario