Measuring a tyre circumference for the computer.

[simongt]

Depending probably on the make / model, cycle computers are for all intents & purposes, accurate enough. Setting them up as we all know, depends on measuring the tyre circumference of your respective steed. So how many of us, rather than rolling the tyre between two points using the valve as the 'marker' measure the overall diameter of said tyre and simply multiply by 3.142 - ?

 

[ianrauk]

I would think that most people now just use their gps machines.

 

[midlife]

I think my Cateye came with a chart?

 

[Vapin' Joe]

Does it matter about pinpoint accuracy? Bearing in mind the data is used for comparison purposes re your previous speeds and distances it hardly matters if it is a tiny percentage out.

 

[Globalti]

The circumference charts on Cateye instructions are accurate. You can confirm this by putting a blob of paint, Tippex or something like mustard on a tyre and rolling it then measuring.

My cycling buddy and I use the chart and on rides we are usually within 0.05 miles in our measurement, which is also usually within 0.05 miles of the measurement on Bikehike.

 

[Tim Hall]

Does it matter about pinpoint accuracy? Bearing in mind the data is used for comparison purposes re your previous speeds and distances it hardly matters if it is a tiny percentage out.

Depends what you're using the data for. Riding an audax and following a printed route sheet you'll have distances between turns, junctions and so on. Having your computer match those bits of information makes for an easier navigational experience.

 

[simongt]

[QUOTE 5000043, member: 9609"]the circumference is a bigger figure so more likely to be accurate.[/QUOTE]
Diameter x 3.142 = circumference; so you still get the right measurement anyway - !

 

[Deleted member 1258]

I would think that most people now just use their gps machines.

There are some of us who don't use GPS and still have a computer on the handlebars. I've got the tyre circumference written down somewhere, But I've changed the make of tyre I'm using so I'll measure again at some point.

 

[Racing roadkill]

No commonly available cycle computer, is accurate enough to negate the simple pi x d calculation, which will almost certainly be more accurate than the rolling wheel method, given the extra variables involved, with the rolling wheel, valve as a datum method.

 

[slowmotion]

I once compared the length of a five and a half mile commute using the Cateye wheel circumference data with the distance using this DaftLogic online tool with an obsessive number of "pins".

https://www.daftlogic.com/projects-google-maps-distance-calculator.htm

They were within fifty metres of each other. It probably only proved that I was really a bit sad.

 

[Nigel-YZ1]

I was once a bit thick and used a tape measure

 

[smutchin]

The circumference charts on Cateye instructions are accurate.

...but the measurements on the sidewalls of tyres rarely are.

 

[Tim Hall]

<off topic>
I saw an excellent demonstration last week, showing how to measure pi using a pie.

 

[presta]

So how many of us, rather than rolling the tyre between two points using the valve as the 'marker' measure the overall diameter of said tyre and simply multiply by 3.142 - ?

Neither, I checked mine using the kilometre posts at the side of the road.

 

[smutchin]

No commonly available cycle computer, is accurate enough to negate the simple pi x d calculation, which will almost certainly be more accurate than the rolling wheel method, given the extra variables involved, with the rolling wheel, valve as a datum method.

The problem I always had with pre-GPS computers was that the tyre circumference settings go up in increments of 2mm or 5mm, or even 10mm in some cases, so regardless of the accuracy of your measurement, you couldn't enter the precise figure into the damn thing anyway.