Maths question about setting up a Cateye

[The Central Scrutinizer]

Think i'll get my anorak out

 

[confusedcyclist]

Also relevant, our tools for measurements might be accurate but not precise, and vice versa

 

[GuyBoden]

Use a Surveyor's measuring wheel, it's what the Professionals use.............

(Yes, it looks very similar to the old type bike odometer, but with a mechanical cable attached to the wheel.)

 

[raleighnut]

No need to mess about with percentages or witchcraft, it is really simple.

IF you are confident/happy that the Garmin/RWGPS figure of 40km is the 'true' figure then adjust your wheel size setting as follows

New wheel size = 2023x40.00/40.18

Good theory but a smaller wheel size will give even higher readings due to more rotations for a given distance, if you swap the 40.00 and the 40.18 around it might work better.

 

[classic33]

I saw a science program on TV some years ago where they asked the question "how long is a piece of string?" They had a piece of string and investigated all the practical and conceptual problems around making a statement about how long it was. (I think they may have mentioned the coastline problem there)

Answer on that part is "25% of its origional length"

 

[I like Skol]

Good theory but a smaller wheel size will give even higher readings due to more rotations for a given distance, if you swap the 40.00 and the 40.18 around it might work better.

I could explain how wrong you are but I am going to bed after a night shift so it will have to wait. See if you can work it out for yourself in the meantime.....

 

[Ajax Bay]

NB Thread title has 'maths' in it.

the front wheel continually does the little balancing adjustments, meaning it travels further than the bike itself. It simply goes in less of a straight line.

Well if one assumes that the variation in direction of the front wheel AVERAGES (mean) at 2% the difference in measurements (between front and rear wheels/rider) would be 0.06% (ie negligible).

deal with that massive issue of the fact that GPS measures linear distance (I think), whereas a Cateye will measure actual distance your tyres have travelled. All those ups and downs....basic trigonometry innit

Well if one assumes that the climb/descent on a ride AVERAGES (mean) 2% (a @Sea of vapours hilly ride) the difference in distance (between a completely flat ride and the one with climb and descent in) would be 0.06% (ie negligible). "basic trigonometry innit" [cos 2 degrees]

 

[Sea of vapours]

...... the difference in distance (between a completely flat ride and the one with climb and descent in) would be 0.06% (ie negligible). "basic trigonometry innit" [cos 2 degrees]

I recall working that out a couple of years ago, after I'd accidentally missed some probably arbitrary distance goal by a couple of hundred metres, and being, whilst disappointed, distinctly unsurprised.

 

[slowmotion]

You'll need to consider the expansion of air in the inner tubes as temperature and barometric pressure vary. Just apply the Ideal Gas Law

PV=nRT

 

[classic33]

You'll need to consider the expansion of air in the inner tubes as temperature and barometric pressure vary. Just apply the Ideal Gas Law

PV=nRT

Would you be going further at the start(cold tyres) than at the end(warm tyres)?

 

[nickyboy]

NB Thread title has 'maths' in it.

Well if one assumes that the variation in direction of the front wheel AVERAGES (mean) at 2% the difference in measurements (between front and rear wheels/rider) would be 0.06% (ie negligible).

Well if one assumes that the climb/decent on a ride AVERAGES (mean) 2% (a @Sea of vapours hilly ride) the difference in distance (between a completely flat ride and the one with climb and descent in) would be 0.06% (ie negligible). "basic trigonometry innit" [cos 2 degrees]

You do realise I wasn't being entirely serious don't you?