cycling computers

[mtbnewbie]

My first one was a Sigma which just had. Speed, Max. Speed, Distance, Time, Total Time & Odometer (Setable which is a nice feature). It auto starts and stops it's time recording.

My new one is a CatEye Astrale 8. It has both the speed and cadence sensors, has all the same features (except the setable odometer) and also average speed and either an auto start/stop or a manual start/stop.

CatEye Astrale 8

One thing I noticed while I was setting it up was that the manual for the CatEye computer specified a different circumference for my wheel than the Sigma. Not an extremely large variance but still more than I expected.

The old one is a Sigma Sport BC800

Sigma manual says that a 26 X 2.0 wheel should be 2114 mm
The CatEye says that the same wheel should measure 2055 mm
a difference of 59 mm or 5.9 cm, that's nearly two inches!!

I did a roll test and although it wasn't extremely accurate it appears that the Sigma is closer to the mark than the CatEye.

How do you calibrate your computer, based on the printed table or do you do a roll test or tape measure around the wheel?

Anyway I did a test ride last night, very short towing the kids to see the geese in a nearby pond. 2 KM round trip and they both measured the same. Also saw that my comfort zone for cadence is generally in around 70 to 80.

 

[heavy]

I have a line on my driveway made with marking pen and renewed every once in awhile, so I can more accurately calibrate cyclometers. I measure the distance in a full revolution of the wheel by having the rider sit on the bike. I start at one end of the line by using a framing square from the surface through the valve to the axle. Then the bike is rolled along the line until the valve is bottom dead center again. Distance in mm is usually what the meter needs, but some require additional math skills.

Even then, I suppose the tire diameter changes with speed and environmental conditions.

 

[buckybux]

I calibrate mine on a rails to trails trail, which still has the old RR mile markers, and then use a 10 mile stretch. The printed charts have been off by over 10%.

 

[artmichalek]

Even then, I suppose the tire diameter changes with speed and environmental conditions.

As long as you keep your tire pressure consistent it's close enough. As a side note on computer features, a friend and I did a metric century together last fall with different computers (Planet Bike on mine and Cat Eye on his). We had exactly the same ride times and distances which would have worked out to an average speed of 20mph. My computer showed an average of 19.5 and his showed 20.5.

 

[mtbnewbie]

Thanks for the advice. I put a bit of paint on the wheel and road it down the driveway. Then measured from a particular point on the pattern over two revolutions and divided by 2. Got 1980 mm, the Sigma said 2114 and the Cateye said 2055.

Since the recalibration I went on a short 24 km ride. They came out different by about .01 of a km. The Sigma measures of the front wheel and the Cateye other of the rear.

Seems to be close enough, I guess it might could be attributed to slightly different lines and possible rounding that the computers might be doing when I stop at lights. (Have both set to auto) they measured the ride times as 2 sec. different, again could be due to when/how it figures out you have stopped moving.

I am finding my cadence comfort zone is anywere from 80 - 100, depending on terrain and such. I can get up to 100 on the down hills comfortably and without bouncing. Flats generally 85-90, and climbs more 80-90 unless I am really getting tired, then I just don't bother watching and just try to keep going (which is most of the time right now).

Can't wait to get my Heart Rate monitor next weekend, one more toy to add to the mix. I'll remember to watch the road though and not all the little displays. They can be very useful but a bit distracting too, if you are not careful.

I generally just give them a glance once in a while, and review the details after the ride not during.

The Cateye is set to show cadence in big numbers and the average speed in small. The Sigma is set to current speed and riding time.

Going to move the Cateye to the road bike when I have it fixed up.