Distances

[marooncat]

Just need to have a moan...

I have just replaced my Halfords bike computer with a Catseye one (which does Cadence etc). Both are set to the same wheel size.

One of the routes I come into work regularly was just over 10 miles on the Halfords one... but according to the Catseye one was 9.87 miles and according to my new GPS thingy on my phone it was 9.46 miles

Whichever is right I fear I have been over with the mileage entered so far this year on cyclogs, ok only by a wee bit but still

 

[Angelfishsolo]

Oh that's a pain. I would be more likely to trust the Catseye mileage than a phones GPS so you are not as far out as you think.

 

[HLaB]

With a gps the thing lays down track points in its memory and draws up the dots this can vary slightly from your actual line; so I would be inclined to believe the cateye more.

 

[Hont]

Had the same problem when I switched from a magnetic computer to a GPS. I'm now going about 0.5 mph slower according to the new one. :-(

If your computer has a manual way to enter the circumference of the tyre, you're probably best to do this as there is some variance in tyres.

 

[betty swollocks]

Have you programmed in your EXACT wheel diameter into the computer.
If not, wheel the bike along and measure the distance for one rotation of the wheel. Start with the valve at the bottom and stop when the valve comes round again.
The size of the tyre and the pressure you run it at will affect your readings slightly and may be why they have varied.

 

[jimboalee]

Have you programmed in your EXACT wheel diameter into the computer.
If not, wheel the bike along and measure the distance for one rotation of the wheel. Start with the valve at the bottom and stop when the valve comes round again.
The size of the tyre and the pressure you run it at will affect your readings slightly and may be why they have varied.

Make sure you are sat on the bike when you do the test.

 

[marooncat]

Both computers had the same dimension put in them (the one from the instruction sheet, might have been 2055 from memory). I will see what it makes of the trip home tonight.

I have now looked at the GPS route online and it has taken quite a "average", including going straight across where I almost go two sides of a triangle (it was through some trees so it might have lost satelites)

 

[Randochap]

Both computers had the same dimension put in them (the one from the instruction sheet, might have been 2055 from memory).

You will not get accurate results from using the "suggested" measurement. Do as advised above -- and with you on the bike is important.

 

[marooncat]

Thanks for the advice... following yet another visit from the p*****re fairy today I have accepted that I am going to have to buy a new set of tyres cause mine are kinda bald in places, so will leave the computer setup as it as at the moment till I have got them.

 

[Mike Rudkin]

OK-I have just done a 'roll out' and found that the actual measurement is 15mm greater than the one I picked from the V3 manual.
So,I haved changed 'wheel size' in comp.from 2005 -2120.

Now,will I go faster/further for the same effort or what :-)

 

[MacB]

I don't worry too much on the small detail as I use my comp to monitor improvement. If I was in serious training or racing then it would be a different matter.

 

[Hont]

I don't worry too much on the small detail as I use my comp to monitor improvement. If I was in serious training or racing then it would be a different matter.

The problem being if you change tyres, especially tyre size, you might be comparing apples with oranges.

 

[MacB]

The problem being if you change tyres, especially tyre size, you might be comparing apples with oranges.

Fair point, I would re calibrate then, but the extent of my calibration was taking a distance via google maps and then cycling it, if close enough then fine.