wireles cycle computer position on spoke

capoz77

probably a stupid question, i've set the wheel circumference using the tyre size method (may redo it again with a tape measure and do the rolling wheel spoke to spoke distance covered method)

my question does it matter how high or low on the spoke and fork I mount the sensor and wireless transmitter? - to get an accurate speed and distance reading.

dunker

does'nt matter, no matter where it's placed the speed and distance is the same as one wheel rotation is all that's happening where ever the magnet is placed along the spoke.

Andy B

no it doesn't matter, so long as the transmitter is within the recommended distance from the receiver & the magnet is the correct distance from the transmitter.

capoz77

spot on thanks guys

didn't want my training rides to be half the real distance due to incorrect set up :oops:

redvee

Some wireless computer give a max distance from transmitter to receiver on the bars. Cateye give a max distance of 70cm or 700mm, never sure which is the smaller.

Raymondavalon

redvee wrote:

Some wireless computer give a max distance from transmitter to receiver on the bars. Cateye give a max distance of 70cm or 700mm, never sure which is the smaller.

Erm, 700mm is the same distance as 70cm

capoz77, I'd also measure the tire circumference by hand too, I used the Cataeye manual's "guesstimate" on my 2.35 Maxxis and found my speeds to be about 10-12% out.
I measured it manually and then did a check against a Garmin GPS and have an accuracy of circa 3%

dunker

and measured how much the tyre shrinks when your weight is squishing it into the ground? 0-10% depending on psi?

the defaults do me fine, 20mph on the readout is the same as the road side speed senser/camera things that tell you how fast you're going.

Northwind

The best way to set the speedo, if you're unhappy with using the defaults, is to ride a measured distance then work it back from that. Even then, different tyre pressures can alter it, and your speed will still change in corners as the rolling radius shrinks, but that's as accurate as is really possible. I don't do this, I use the defaults, but ymmv (literally!)

capoz77

evening, so i went out and measured my pump valve to pump valve full wheel rotation and measured how much distance it covered.

2080mm.

I've just got back from a 20 mile ride BUT my computer has had my wheel set as 2332mm as per my guestimate.

Does this mean i've done more or less than I thought?

If the computer thinks every passing of the magnet is 2332mm then I guess its overestimated my distance?

and from my rough workings out my 10 miles becomes 12?

20 miles = 33 506 542 080 mm divided by 2332 = 8907 wheel rotations

8907 multiplied by correct wheel circumference 2080 = 18 526 560 which in miles is 11.5 miles?

i hope i'm wrong here as I found the ride quite tiring. and ive got 60 mile charity ride in 2 weeks :oops:

benneally

it means you have over estimated the distance you cycled. You actually cycled;

20 x (2080/2332) = 17.84 miles.

capoz77

benneally wrote:

it means you have over estimated the distance you cycled. You actually cycled;

20 x (2080/2332) = 17.84 miles.

I see thats worked out as a percentage of the actual wheel circ. vs the wrongly estimated wheel circ. But its confused me!

Whatever the wheel circ is set to I take it the computer counts how many times the wheel goes round and multiplies this by the wheel circ to give a total distance in MM, which it then converts to miles.

So if I divide total distance in mm by wheel circ I get number of rotations?

If I then multiply number of rotations by new correct wheel circ this gives correct distance? hence 11.5 miles?

:oops:

i'd rather it be the 17 mile result, but I don't understand the logic behind the workings out!

benneally

I think u are just slipping up somewhere in ur calculations.

Okay so you covered 20 miles:
20 x 1.6 x 1000 x 1000 = 32,000,000 mm

32,000,000 / 2332 = 13,722.127 wheel rotations

13,722.127 x 2080 = 28,542,024.014 mm (actual distance covered)

28,542,024.014 / (1000 x 1000 x 1.6) = 17.84 miles again


If you take a step back, its clear from the difference in circumferences that its going to be nearly 20 miles. To be 11.5 miles as suggested, then the actual circumference of your wheel would have to be just over half of ur guesstimate. Its not, nearly 90%.

Hope this helps.

capoz77

fantastic makes all sense now! cheers mate 8) 8)