Cateye Computer Setup

paulmgreen
paulmgreen Posts: 158
edited November 2011 in MTB workshop & tech
It's been a long day and my brains puddled..... Mathematical guru needed!!

I have setup my Cateye Strada Wireless computer by measuring the tyre circumference but against a GPS device the Cateye is reading slightly out - 1.0 mile on the GPS is 1.07 miles on the Cateye.

the tyre circumference I have measured again to make sure it's correct and it is.... The number used was 2090 (as in 2090mm ).

so........ To make the measurement more accurate in what it actually ends up recording...... Does this number want to be larger or smaller???????

Comments

  • nicklouse
    nicklouse Posts: 50,675
    One uses horizontal distance while the other uses distance covered.

    Also how did you measure the tyre circumference? Or did you measure distance rolled with you on the bike? As a squashed tyre can roll less distance.
    "Do not follow where the path may lead, Go instead where there is no path, and Leave a Trail."
    Parktools :?:SheldonBrown
  • paulmgreen
    paulmgreen Posts: 158
    I measured the circumference rolling along......

    The difference between the GPS and the Cateye remained exactly constant for every mile measured (5 miles), there were some slight gradients but nothing great
  • bails87
    bails87 Posts: 12,998
    If you wanted to do this, you'll be making the computer think that each revolution covers a shorter distance, since currently the computer is travelling further than the GPS (well, that's what it thinks anyway!).

    So you'll need to lower the 2090 number by 7%.

    Remeber that the GPS can occasionally cut corners and miss very small turns. More of a problem with MTBs than road bikes. And as nick says, a tyre with weight on it will be squashed and cover a shorter distance than an 'unweighted' tyre. So sit on the bike and one revolution doesn't take you as far as it would it you stood next to the bike and rolled it along. This becomes more obvious with bigger and softer tyres.
    MTB/CX

    "As I said last time, it won't happen again."
  • allen.coulson
    allen.coulson Posts: 424
    So you'll need to lower the 2090 number by 7%.

    No - divide by 1.07 - would be more accurate.
  • bails87
    bails87 Posts: 12,998
    allen.coulson wrote:
    bails87 wrote:
    So you'll need to lower the 2090 number by 7%.[.quote]

    No - divide by 1.07 - would be more accurate.

    Damn, nearly! :lol:
    MTB/CX

    "As I said last time, it won't happen again."
  • paulmgreen
    paulmgreen Posts: 158
    I have changed the number down and now it's reading 1.02 good enough for me !

    Thanks for the inPut fellas
  • jsync
    jsync Posts: 120
    gps can be a bit rubbish at measuring altitude changes so maybe some variance there? I use endomondo and get small changes in distance for exactly the same route, the altitude graphs are a bit random sometimes.

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