jwill911

When I got my CS200cad I just entered 2070 in the bike settings for my 700x23c wheels and thought nothing more of it. On New Years day a friend and I did the Delta Century route and since we had lots of time to talk we determined my odometer mileage was off by some factor. His cycle computer agreed with the route map at 99.6 miles and I had a reading of 96.7. So that is roughly 2.91% lower reading on my Polar. I measured one complete revolution of my front wheel and get 2134mm. The book says to subtract 4mm to account for your weight and enter the value. So I would enter 2130? This confuses me, I would think if I was reading low I would want a smaller number not a larger number.

Maybe I'm just over thing this. Can one of yous guys straighten me out on this.

Thanks,
jw

Rowan

Yep, it's hard to get your head around if you are not inclined that way.

But, the wheel roll-out really is the most accurate method... and if measures 2134, then you enter 2130.

If you do the calculation, the difference in your original coding and the wheel rollout is exactly the 2.91% between your computer and your friends.

Don't sweat things you don't have to... just ride with it, preferably the 100-miler again, just to confirm

Anyway, look at the percentage difference as being that you're travelling 29.1 metres short in every kilometre (this is where metrics come in handy because that represents your 2.91%). It means the computer is saying your wheel is covering a distance shorter than it should every revolution. The only way to overcome this is to increase the wheel's circumference in the computer's "mind"

jwill911

Thanks...I guess I was thinking in terms of revolutions not distance/circumference. I just entered the 2130. I'm riding a 60 miler with the same guy this weekend, we'll compare again.

jw

Rowan

Well, the computer *is* counting impulses from the probe, but the constant factor it uses to calculate distance is the circumference.

HillRider

I'm surprised your circumference value is that high for a 700x23 tire. Cat-Eye's calibration table gives 210 cm for their cyclometers with 3-digit calibration numbers or 2095 mm for the ones with 4-digit calibrations. I use 209 (or 2090) with all of my cyclometers and get good agreement with all of the cue sheets I've followed.

Depending on your tire make and model, the circumference can vary a bit. Not all "23's" are really 23.

jaws

I also have the CS200 and am having the same problem with odometer. However in my last 2 rides, I have noticed that the speed readout will go to 0 for a moment and then come back on to give a speed reading so I my problem is different. Does anyone know why the wireless would lose contact occasionally?

HillRider

Wireless cyclometers (and heart rate monitors) can be affected by outside emf sources like electric power substations, radio towers, cell towers, etc. A friend had an early Polar heartrate monitor that would always drop to zero when we rode by a local transformer station. Scarred the sh** out of him the first time it happened.

Some wireless devices are "coded" to reduce outside interference and "crosstalk" between nearby wireless devices but I don't know if this is 100% effective.

europa

I've got the same beastie and for me, it's the cadence meter that's sensitive. I cured that by moving the magnet a whole 2mm Seriously, it went from ultra dodgy to super reliable with that small movement on the magnet. I also find the heart rate strap a wee bit touchy with skin contact, though once I've got it working (and wet, that's part of the secret), it seems to work reliably - it hasn't told me I'm dead yet which the other HRM I use on the beater does with horrifying regularity.

I'm not sure I want to know about the distance travelled being out, but now that you've raised it, I'm going to have to check it aren't I

Richard

jwill911

europa, I have my magnet positioned ~5cm from the peddle spindle. I also have had period where the cadance drops to zero then comes back to life. It is really quite annoying when I doing my spin intervals on the trainer and want to keep at 100 RPMs. Also the fact I have nothing but the non-functioning cadance to stare at. Where did you put your magnet to get the best results?

Thanks,
jw

byte_speed

I'm pretty OC about tire mesurement. I ink a spot on the front tire and actually ride the bike a short distance on light colored pavement, then meaure the distance between the resulting ink spots. I make sure the tire is at my usual riding pressure before taking measurements. I go for a minimum of at least 4 wheel revolutions/ink spots and take an average to get better accuracy. I've found this to be quite accurate, if a bit of a pain.

I wasn't aware of the circumference - 4 mm formula. I'll have to check this method sometime, it sounds a lot easier.

HillRider

I believe the -4mm correction is based on doing a rollout on an unladen bike and it compensates for the rider's weight. If you are measuring rollout while riding the bike, the correction shouldn't be needed.

europa

I just made sure the path the magnet swept was as close as possible to the centre of the sensor - prior to that, it'd been a tad high. The positioning along the crank is about where yours is.

Richard

Rowan

Try new batteries if the computer is playing up, especially after any period on the bike. Also ensure the probe is as close as possible without touching when the wheel flexes (different, obviously for the cadence probe, and I can believe 2mm will make a difference).

If you want medical-quality interface between your HRM strap and your chest, get a bottle of gel from a pharmacy that has not only the "stickiness" but also the ions in it to improve conductivity. But wet and perspiration should provide enough moisture for transfer of the electrical impulses to the sensor in the strap.