Cateye Wireless - mileage distance is innacurate

Macster1

Hi all,

I have a Cateye Micro Wireless Cycle Computer which is set-up as per instructions but when I check my mileage against Google maps, it differs, e.g, I rode 9.6 miles on my MTB but when I checked the [exact route] on Googlemaps it showed up as 8, obviously happening on all occasions when I go out.

My tyres are Panaracer Fire XC Pro 2.10 and I set up the Cateye exactly and have the sensor at the top of my forks and the wheel magnet as high on the wheel as possible.

I'm going to drive out later to check the mileage but any ideas?

Thanks in advance

Baz

bartimaeus

Was it up and down hill? Two points 8 miles apart on the map may be 9.6 surface miles apart. I would test your computer on a flat route before you change anything.

Also, did you read the L number off the 'Tire Size' chart? This is not always accurate - it may be worth measuring the actual circumference of your wheel in millimetres (by rolling it with the Tires on) and use that as your L number.

stumpyjon

I get the same, i have three Cateye wireless Stradas, I've measured tyre circumfrance with a tape measure and set them up correctly. They all consistently read higher than my GPS mileage wise. As Bartimaeus says I put it down to software working out a flat distance and the Cateyes taking into account reall world distance. Always use the Cateyes for recording distance.

x-isle

However, the caveat with GPS is.......

Even top end GPS units, such as Garmin and Satmap, plot your position every 1 second.

Therefore, on a long ride, that is fast and twisty through trees for example, it might not pick up the full distance covered, lower end GPS, such as iPhone apps, Nokia apps etc, will probably be even less acurate.

There are pros and cons for both computers and GPS.

With a computer, the sensor is (normally) mounted on the front wheel. Tyre compression, spinning wheel once lifted of the ground etc, all add up to more distance travelled. There is a lot of factors affecting both types.

As already mentioned, if you plot a route on Google maps, I'm not sure it take terrain into account, so there will be an inaccuracy there too. If you plot it with mapping software such as MemoryMap, this will take in the terrain.

Macster1

@ Bartimaeus - ah, didn't think of that! It's not exactly hills [all road] but the journey does elevate somewhat on the journey so that could explain it, and I guess over the distance travelled I could easily have done 9.6 miles with the rise from A to B.

So would I measure the actual Tyre or the rim itself? :?

@ stumpyjon - thanks, I'll stick to the Cateye reading - sounds about right with what Bartimaeus said about elevation, common sense really!

Thinking about it some friends and I did a run that was mostly dirt track and a lot of up and down hill and the comp said we had done 7 miles but I felt like we'd done 27! Obviously A to B will be easy or hard depending on terrain :oops:

bartimaeus

Mark a point on the tyre (point x) and line it up with a reference point on the ground (point A). Now roll your bike forward until the point you marked on the tyre (x) completes one revolution (e.g. it is now back on the ground again). Mark this in the ground (point and then measure back to your start point (from point B back to point A).

Or just run a tape round the outside of the Tyre I guess

stu8975

Easier way of doing it, measure height of your wheel inc tyre (diameter) and multiply it by 3.14 (pi) to get circumference..simples.

chasrock

just got Cateye Micro and setup says 2096 for 700x23c. my old computer says 2114. who's correct?

stubs

I have always found a google maps and the like give a reading at least 10% less than the real world distance. Dont forget you arent riding in a straight line you weave from side to side, you have to go round parked cars and going round a roundabout puts a fair few extra yards on. It all adds up over a ride.

alfablue

chasrock wrote:

just got Cateye Micro and setup says 2096 for 700x23c. my old computer says 2114. who's correct?

Neither or both - not all tyres of the same size are actually of the same size, so the only way is to measure the circumference as described above, whilst sitting on the bike.

chasrock

wish i was sitting on bike now, instead stuck in office

Buckled_Rims

Also, theoretically, on an MTB tyre pressure can make a small difference. As alfablue mentioned, siting on the bike with your usual tyre pressure will give the best results.

stumpyjon

x-isle wrote:

However, the caveat with GPS is.......
Even top end GPS units, such as Garmin and Satmap, plot your position every 1 second.

True, but my GPS and PC based mapping software (Tracklogs) usually agree.

MrChuck

Also wireless computers are susceptible to interference sometimes. For instance if mine is near the doors on the train it often thinks it's been doing 90 mph when I get off, and a friend has reported problems with his when he goes past a set of transformers (or whatever they are) on his commute.

boneyjoe

To the OP - I've also had some odd readings like this where the magnet and sensor aren't propertly aligned. Sounds like yours are ok, but might be worth checking again.

St George

Find an athletics track, find out mile distance and compare riding round it.

Raymondavalon

I went through this with a mate who's a mathematician when I bitched about my Strada's accuracy
I had tried the PI method and even did a calibration ride with the Garmin GPS, but it was always a little bit out.
I used twine to measure the true circumference of the wheels on the two bikes with Stradas fitted.

However when measuring this way, I didn't take "squish" into consideration and that's the amount the tyre compresses under my body weight. This I am reliably informed also varies when you pedal or stand up and pedal due to the inertia on the cranks.

It's now accurate to circa 5% in parenthesis to my eTrex when measuring on a long even road with consistent pedaling and I don't think I'll get it any better. My number crunching mate tells me 5% is damned good and I shouldn't complain about it. It under reads (like most car speedometers do) and I am now content with the accuracy I achieve

Macster1

Thanks folks, for all your advice & suggestions


Baz

RealMan

When I was running a cateye and garmin setup they would sometimes be out by about 1%.

Macster1

I think if it's not really massively out then I'll be happy to live with it.

I'm off out later this afternoon so will get one of my mates to zero out with me and then I'll compare with him when we finish

Thanks again


Baz

toasty

chasrock wrote:

just got Cateye Micro and setup says 2096 for 700x23c. my old computer says 2114. who's correct?

Split the difference, there's less than 1% between those 2 numbers anyway!

stu8975 wrote:

Easier way of doing it, measure height of your wheel inc tyre (diameter) and multiply it by 3.14 (pi) to get circumference..simples.

I like that idea, you could even sit on the bike and get someone to measure the squished radius x 2 x PI.

I was pondering a Strada or Micro wireless this week actually, so I was eagerly watching the outcome of this thread I think 1-5% or so error margin is acceptable.