One for the mathematically gifted.

[Banjo]

On a 13.25 mile ride that I do a lot.(measured off bikehike and with my own and other peoples gps and computers confirming it) Since accidentally resetting my computer it now reads 12.8 .

How many millimeters will I have to increase the circumference input of a 700c wheel in the computer to get it right?

I want it fairly good so on longer rides I will know when to expect the climbs to start. Morning Jimbo :-)

 

[PK99]

On a 13.25 mile ride that I do a lot.(measured off bikehike and with my own and other peoples gps and computers confirming it) Since accidentally resetting my computer it now reads 12.8 .

How many millimeters will I have to increase the circumference input of a 700c wheel in the computer to get it right?

I want it fairly good so on longer rides I will know when to expect the climbs to start. Morning Jimbo :-)

measure the actual circumference!

Start with the valve exactly bottom dead centre, tape measure start at valved running forward along ground. Roll out till valve at bottom, measure distance

 

[Banjo]

Nice one. No maths required. :-) Will be interesting to see the difference.

 

[ColinJ]

Ah, but the effective circumference will be different with you sitting on the bike because the tyres will flatten slightly. If you are sitting on the bike, how do you take the measurement?

 

[RecordAceFromNew]

The tyre size, not the wheel size, will give you an approximate figure. Accuracy will be dependent on road condition, tyre pressure, weather, weight etc.

 

[GrasB]

my favoured method, though it does need an assistant & a surveyors tape, is on a quiet straight road/pavement make a mark on the surface. Get on the bike with the valve in a known position. Get your assistant to push you along & count say 10 revolutions of the wheel, mark that on the ground. Now get your tape & measure the distance between the two marks. Divide the distance you get by the number of wheel rotations.

 

[Garz]

Or refer to the computer manual which usually has a table to go with for certain wheel sizes. Mine was only fractionally off compared to what I actually measured.

Bikehike is fairly accurate but doesn't account for you meandering, short cuts or other factors..

 

[slowmotion]

You have already done a "roll out".....over 13.25 miles.

Divide 13.25 by 12.8 and you get 1.035.

Whatever tyre circumference figure you currently have in your computer, multiply it by 1.035. Enter that value into the computer, and you should be sorted.

E&OE

 

[Banjo]

You have already done a "roll out".....over 13.25 miles.

Divide 13.25 by 12.8 and you get 1.035.

Whatever tyre circumference figure you currently have in your computer, multiply it by 1.035. Enter that value into the computer, and you should be sorted.

E&OE

Just out of curiosity I will do the roll test and multiply the existing figure in the computer by 1.035 be interesting to see if it works out close to the same..

 

[slowmotion]

Just out of curiosity I will do the roll test and multiply the existing figure in the computer by 1.035 be interesting to see if it works out close to the same..

Oh lorks! I'm starting to get nervous. I shall not reveal my maths A level grade...

 

[Beardie]

Maths A level grade? Egghead! It took me three attempts to pass O level. This thread is fascinating to me, but I have only a hazy idea what you're all on about.

 

[andyfromotley]

dont bother with all that, take your computer off and enjoy riding without the slavery of max speeds, averages, temp etc.

And for your longer rides look up, if you see a ruddy big lump of ground in front of you theres a hill coming up

 

[ColinJ]

dont bother with all that, take your computer off and enjoy riding without the slavery of max speeds, averages, temp etc.

And for your longer rides look up, if you see a ruddy big lump of ground in front of you theres a hill coming up

I agree - I was actually quite relieved when my cycle computer broke! I found that riding was more fun once I stopped worrying about speed.

My GPS can be used as a very sophisticated bike computer when I do want to know how fast I am going, but most of the time I'm happy to use it just to tell me where I am.

 

[Garz]

My comp does cadence as well as the other normal features, but these days I just use it to log the mileage so when I get back I update the stats for the teams mileage on mycyclinglog.

I wouldn't ride without it as I like to know how far I have travelled and is far quicker than mapping it on mapmyride et al.

 

[Manonabike]

What about using one of the many tables for size and width?