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Just got a shiny (literally) new Lezyne floor pump. Best piece of kit I have ever bought (sorry bike.) The screw on chuck means no air escapes no matter how hard you pump. I am embarrassed to say the hard tires I had before might have been as little as 45-50psi with my old hand pump. They are now a diamond like 115psi. Too many punctures on the way to work was worth £45, cheaper than the sack. But I have discovered it has cost me another way. My 18.8km round trip to work now only takes me 18.6km (?!) My tires are so well inflated that the diameter is greater and it takes less rotations to get in and out. This could cost me hundreds of kilometers by the end of the year and some long hours in the saddle rounding up to the nearest thousand kiliometers. Swings/Roundabouts.

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movingtarget [144 posts] 2 years ago
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 21

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Gkam84 [9086 posts] 2 years ago
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I don't know how the distance has changed.

The distance was x between point a and b..you cannot change that.

Your wheels may take less rotations to cover the distance, but the distance simply cannot change. No matter what you do, if you are taking exactly the same route, day in day out.

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movingtarget [144 posts] 2 years ago
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I could be completely wrong but theoretically, if your tires are marginally bigger wouldn't your wheel factor/circumference approximation change? So if your wheel diameter is now slightly bigger but you're using the same wheel factor calculation on your cyclometer then since the number of revolutions is decreased due to a larger wheel traveling the same distance you would get a "shorter" distance traveled because the computer doesn't know that your wheel diameter has changed? I think the last few sentences would make more sense with a glass of wine.

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mrkeith119 [87 posts] 2 years ago
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Gkam84 wrote:

I don't know how the distance has changed.

The distance was x between point a and b..you cannot change that.

Your wheels may take less rotations to cover the distance, but the distance simply cannot change. No matter what you do, if you are taking exactly the same route, day in day out.

I think he means distance on bike computer as opposed to real distance.

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jason.timothy.jones [294 posts] 2 years ago
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I think you will find that the earth is shrinking, so nothing to worry about

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jmaccelari [241 posts] 2 years ago
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Quite possible. If you have a magnet type odometer, you calibrate it by rolling the bike along the ground. If the tyres are flat when you calibrate, you get a shorter distance for each turn of the wheel. So you now ride to work and get 18.8kms.

If you now inflate the tyres and do not recalibrate the odometer, you will now have a larger diameter wheel (the tyre gets 'puffed out'). This will now take fewer revolutions and you will get a shorter distance - say 18.6kms - since the odometer will register fewer clicks of the magnet.

200m is under 1%, so can be explained by an additional 2.5-3mm increase in wheel radius (5-6mm diameter) due to pumping your tyres up.

If you are using a GPS unit, then some sort of space-time continuum warping due to increased speed is a more plausible reason.

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jmaccelari [241 posts] 2 years ago
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Oh - and I forgot to say: I bought a Lezyne floor pump last year (the steel CNCed one) and it is brilliant - an absolute corker.

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notfastenough [3685 posts] 2 years ago
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track pumps rule

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PJ McNally [591 posts] 2 years ago
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sarcasm doesn't always come across that easily online, does it?

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Leviathan [1988 posts] 2 years ago
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jmaccelari wrote:

Quite possible. If you have a magnet type odometer, you calibrate it by rolling the bike along the ground. If the tyres are flat when you calibrate, you get a shorter distance for each turn of the wheel. So you now ride to work and get 18.8kms....

Bingo JMac, I thought the diameter comment was clear, you know as radius, diameter, circumference are all really the same thing, wibbly wobbly circly pi.
I don't think I will remeasure as that might be considered cheating, but I will cut and paste my commute figure and take the bike computer figure for new rides. My tracking isn't GPS, more Excel. Fact: GPS satellites do travel at relativistic velocities and their locations are calculates using general relativity, Newtonian physics would drift out by metres and break the system in a few days.

great stuff:
http://www.wiggle.co.uk/lezyne-classic-floor-drive-abs-track-pump/

The world isn't shrinking, it is expanding according to Neal Adams:
http://www.youtube.com/watch?v=oJfBSc6e7QQ
He is absolutely crackers of course, his comments are even more entertaining than the video.