Technics
Measuring Tools

When cycling in the mountains there are 3 questions you may ask yourself: what's the sense of life and what's the current altitude and the steepness. I don't have an answer on the first question but for the other two there are some nice tools. Essential tools in the mountains are a altimeter (extra funtion on a cyclecomputer) and a inclinometer. Nice gadgets for men and boys. I also mention a correcting method for measured profiles. Nice homework in cold winters and rainy periods.

Cyclo computers with an altimeter

Working of a cyclo Computer

There are as far as I know 3 methods for measuring the altitude of a point on earth. The first one is a mathemathical trigonometric (triangular) calculation (used by the old Greeks). The second one is GPS (Global Positioning System) which uses satellites. Maybe this system will be available in the future. The 3rd uses the atmosperic pressure measured by a barometer.
This is a relative method: you need a reference point with a known altitude and a measured pressure. For another point the pressure difference determines the altitude of this point. So for an accurate altitude respons you need to calibrate frequently with a known altitude. This can be an annoyance.

Another thing that's important is the threshold height of an altimeter.
On a flat route (we have a lot in Holland) the altitude gain should be zero, however because of small pressure differences even if the weather is constant, the altimeter will constantly give altitude differences between 0-5m and your altitude gain will normally grow and grow. For example above water the pressure slightly differs from that above land.
The threshold height is the minimum height difference added to your current altitude gain. The problem is that if you set the threshold too low, small changes in air pressure may give a false reading of a climb. And, if you set the threshold too high, you might not get credit for a climb. A study done by Bruce Hildenbrand concluded that a threshold of 2m is acceptable. This is not a big problem when climbing continuously because the altitude only increases.

The measurement of the percent grade is a trigonometric calculation for which you need 2 points. This means that a the start there is a delay and that the current grade ia based upon a point behind you. On longer climbs with a more constant slope, the computer should be able to give a reliable measurement but it will miss the short steep (and flat) parts!

I have experience with a couple of altimeters and they all suffer from the next problem. Assume you have calibrated the altimeter at the start of the climb: in 9 out of 10 times the altimeter shows a lower altitude (20-100m) than the altitude on the sign (assuming this is the right altitude). After calibrating on the top the measured altitude at the end of the descent the altimeter is higher than the real altitude.
I think this has something to do with wrong temperature correction (in ascent/descent) and the speed of the descent: the altimeter can't keep up with the fast difference in altitude.

Altitude Calibration

I have allready mentioned that you need to calibrate your altimeter frequently. After a calibration the data will become more and more unreliable because of weather changes (pressure changes). If you correct your data afterwards 1 or 2 times a day is enough but when you want an continuous accurate alitude you need to calibrate at least at the start, on a top, at the end of a descent and after a stop if you only have continuous altitude mode (altitude changes during stop).
The problem is offcourse how do I know the altitudes. You can use several sources.

1. Topographic maps (with contour lines) which are reliable but expensive.
2. Other maps. The most used maps are: Michelin (Portugal, Spain, France), Kümmerley-Frey (Alps, Italy) and General Karte (Alps, Italy, parts of Spain and France).
   Kümmerley-Frey and General Karte are quite good in mentioning altitudes but the new Michelin maps don't mention altitudes of villages and towns anymore. Can anyone tell me why they do this?
3. Altitude on signs on top or along the road. Spanish top signs are very unreliable!
4. Other sources on internet.
   For Spain a good source is Pueblos-espana. You can find altitudes and small maps of allmost every Spanish village.

Wheel circumference

The wheel circumference influences the measured distance and therefore the speed and the grade (%): 1 rotation of the wheel adds the wheel circumference to the distance. The right circumference depends on the type of wheel, the tyre and the amount of air in the tyre. You can measure this circumference mathematically:
C = d = 2r. (=3.14159..., d= diameter, r= radius)
Another accurate way is to sit on your bike with the valve of the front wheel below. Put a mark on the ground, make one rotation and measure the difference. The influence of the tyre is small compared to the type of wheel and therefore the manufacturers give suggestions for the diameters.
Suggestions for the most common tyre sizes are

.

Comparison of functions

There are a couple of older computers that are no longer available:
- Avocet 50: the first cyclo computer with an altimeter
- Huger SPY 300H (Huger is now Oregon Scientific)
- Ciclomaster CM 414 (M)
The latest Ciclomaster Altimeter is the CM 215A. This has become available in May 2004.
Specialized has also a Pro cyclo computer with heart rate monitor and memory/download function: the Speed Zone P.Brain Computer
Review Altitude Function 4 computers
http://www.ultracycling.com/equipment/altimeters_update.html

Manufacturer Functions	Cateye	Ciclosport	Specialized	Vetta	Cycle Parts - VDO
Type / Product Info	CC AT 100	Ciclomaster CM 414 Alti (M) 434 Alti/ 436 Alti M Ciclomaster - Computers Bikediscount - info Raddiscount.de	Speed Zone Pro Classic	V100A	MC 1.0 Cycleparts - see products / bikecomputer with altimeter Raddiscount
Reviews / Forums	MTBreview Roadbike review	414 Alti: MTBreview Forum Specialized.de 436 Alti MTBreview Ultracycling	MTBreview Roadbike review1 Roadbike review2 Ultracycling	Roadbike review	Wiggle
Computer
Mount diameter	±26 mm	±26 mm	25.8 or 31.8 mm	25.8-31.8 mm	All (Twist click)
Fat fork compatible	Yes	Yes	?	?	?
Magnet - spoke type (1)	Round	Round	Round or Flat	?	?
Wheel diameter	0-255 cm (±1cm)	0-999.9 cm (±0.1 cm)
Batteries (2)	1x C2032	2x C2032 1x 23A (Sender)	1x C2032	1x C2032 1x 23A (Sender)	1x C2032 1x 23A (Sender)
Wireless	No	Yes	Yes	Yes	Yes
Water resistant	No	No	Yes	?	?
Backlight	Yes	No	Yes	?	?
Temperature Correction	Yes
Basic Functions
Speed	Act./Max./Avg. (0-106,±0.5 km/hr)	Act./Max./Avg. (0-160, ±0.1 km/hr)	Act./Max./Avg. (0-100/200,± 0.1 km/hr)	Act./Max./Avg. (0-130,±0.1 km/hr)	Act./Max./Avg. (0-200,±0.5 km/hr)
Distance	Trip (0-2683 ,±0.01km) Total (0-42949 km)	Trip (0-1000,±0.01 km) Total (0-99999 km)	Trip (0-?,±0.01 km) Total (0-99999 km)	Trip (0-1000,±0.1 km) Total (0-99999 km)	Trip (0-1000,±0.01 km) Total (0-99999 km)
Elapsed Time	Trip (0-10 hr)	Trip (0-1000 hr) Total ( 0-1000 hr)	Trip (0-10 hr) Total (0-? hr)	Trip (0-10 hr) Total (0-10 hr)	Trip (0-20 hr) Total (0-? hr)
Auto start/stop (time)	Yes	Yes	?	Yes	Yes
Clock	Yes (12 hr)	Yes (12/24 hr)	Yes (?)	Yes (24/24 hr)	Yes (24/24 hr)
Stopwatch	No	No	Yes (0-10 hr)	Yes (0-10 hr)	Yes (0-20 hr)
Cadence (Pedal rate)	No	Yes (optional) (30-400 rpm)	Yes	Yes (opt., wired) (15-255 rpm)	?
Sleep mode	Yes (clock)	No	Yes No auto wakeup	Yes No auto wakeup	Yes (clock)
Altimeter functions
Altitude	Act. (-350 - 5800, ±1m)	Act./Max. (-200 - 8200, ±1m)	Act. ?	Act./Max. (-9999-99999, ±?m)	Act./Max./Max. Total (?, ±?m)
Altitude diff. since start	Yes	No	No	No	No
Altitude Gain	Trip (0-±2400m) Total (0-16777 x1000m) Threshold 1m?	Trip (0-65535m) Total (0-65535m) Threshold 5m	Trip Total? Threshold 2m	Trip / Intermediate / Total? Threshold ?	Trip / Total? Threshold 2m
Altitude Loss	Trip (0-±2400m) Total (0-16777 x1000m)	Trip (0-65535m) Total (0-65535m)	No	No	?
Altitude mode (3)	Bike / Continuous	Continuous,also in bike mode! (own experience)	?	?	Continuous
Steepness (Grade)	No	Act. Max./Avg. Up/down (0-99%, after 50-100m)	Act. Max. (last 20 sec)	Act. Max. Up/down	Act. Max./Avg.
Extra Functions
Temperature	Act. (0-50 °C, ± 0.5 °C)	Act./Min./Max. (-19-60 °C, ± 1°C)	Act. (4-40 °C, ± 1°C)	Act./Min./Max. (-19-49 °C, ± 1°C)	Act.
Memory (+software)	No	Yes (optional) (64 hr)	No	No	No
2nd bike option (5)	No	Yes	Yes	Yes	Yes
Special functions		Preset trip start distance Climbing Speed (Act./Avg.)   (0-99900 m/hr) Power (Act./Avg./Max.) (4) (0-9980 W)	Interval timer   (5 s-10 hr) Auto time mode   (0-10 hr)	Speed Comparator Intermediate distance Service Time indicator   (1-1999 hr) Low battery indicator	Preset trip start distance Speed Comparator Service Time indicator

Red and bold: permanently in Display (1) The common magnets to be placed on a spoke don't fit on flat spokes. There are magnets special made for flat spokes (Cateye,Mavic) (2) All computers use the CR2032 type battery. (Quite expensive). For senders they use type 23A (3) The altitude mode for bikes should be an auto start/stop for altitude meaning that the altitude value doesn't change during a stop. Normally this will happen because of pressure difference when the weather changes. A continuous mode is usefull for walkers. (4) Calculated from weight, grade and speed. (5) You can use bikes with different wheel diameters

Magnet for round spokes Cateye flat spoke magnet (no Mavic Ksyrium) Mavic flat spoke magnet

Type CR2032 Type 23A

Pros & Cons

Inclinometers

In stead of derive the grade (%) from the speed and altitude difference there are also other tools (inclinometers) that measure the grade directly.
The adjustment of these tools is very critical: one mm rotation means a reasonable diffrence. When this is done it's a hell of a job to keep this tool in place: don't touch it and you'd better don't rotate your handlebar anymore.

Sky Mounti	Red X Control King
The Sky Mounti works on same principle as a leveling rod: with an air bubble. The accuracy is about ±1% (if placed correctly) Pros - Nice and simple display - No battery needed Cons - Only fits on 25.8 mm diameter handlebars - Bubble vibrates much on bad roads or roads with stones - Poor construction: plastic breaks when screwed to tight

Links

http://www.campmor.com/webapp/wcs/stores/servlet/CategoryDisplay?categoryId=47917&storeId=226&catalogId=40000000226g

http://www.backcountrystore.com/store/product_group_gallery.html?cat_id=3&subcat_id=23&brand_id=&sort=sku&pg_id=77
http://www.bizrate.com/buy/products__att278328--265335-,cat_id--30020100.html

Correcting measured data

Recording data can be done automatically (with a cyclo computer with memory) or manually (with a voice recorder). Personally I record data with a voice recorder because I can give addional information and can record exact points.
Normally you can trust the data shortly after a calibration but on a cycling trip the data this is not the case unless you calibrate very often. So you need to correct this data. This is my correcting method.

Step 1
Put your data in a spreadsheet. Split your data in smaller parts. You can take out the (longer) climbs but split your data at least at a calibration point, at the begin and the end of a long descent and at a long stop.
Do the next steps for each climb.
Step 2
Find 2 points with a reliable altitudes preferable from one source and as far away from each other as possible.
Step 3
Do a 1st correction for each point with linear translation. This is a simple formula. See below.
Step 4
Do a 2nd correction for each point
- if a point has a known altitude and it's within 10m of the correction take this altitude.
- otherwise round the first correction towards 5m
Step 5
If many known altitudes don't fit on the corrections there is probably something wrong. Check the 2 reference points or split your data set in even smaller parts and do it again.

Assuming your reference altitudes are correct I guess this method is accurate within 10m for each altitude!

Translation formule Suppose for the 2 points: point 1: measured altitude Am1 and correct altitude A1 point 2: measured altitude Am2 and correct altitude A2 For each measured altitude Am the correction A is: A =F(Am) = A1 + (Am - Am1) * (A2 - A1) / (A2m - A1m) See spreadsheet example (Excel 95)