Compact Cycling Gradiometer

Note: On this page, when I say "grade", I'm referring to the tangent of the angle (dy / dx). Thus a 100% grade would be a hill with an inclination of 45 degrees.



I was pretty happy with the test results, so I decided to start measuring some of the climbs in the area. These numbers should be accurate within about a 2% grade or so. Remember that these measurements were taken over a distance of only a meter, and so do not necessarily represent sustained climbs of these grades. However, I tried to avoid steep sections that were less than 20 meters long, such as the inside turn of a switchback.

Street Max. Grade Avg. Grade City Address Altimeter Grade
Alameda de las Pulgas 20% 8% San Mateo 3704
Ascension Dr. & Anacapa Dr. 17% 10% Los Altos Hills 26390 Anacapa
Bohlman & On Orbit 22% 9% Saratoga 15555 On Orbit
Bunker Hill Drive 16% 9% San Mateo 2248
Club Drive 17% 9% San Carlos 296
Crestview Drive 16% 8% San Carlos 1237
Golden Oak Drive (east side) 19% 10% Portola Valley 430
Golden Oak Drive (west side) 15% 8% Portola Valley -
Joaquin Road 20% 15% Portola Valley 60
Kings Mountain Road 14% 7% Woodside -
La Barranca Road 16% 7% Los Altos Hills -
Los Trancos Road 19% 4% Portola Valley -
Melendy Drive 17% 9% San Carlos 2770
Montebello Road 16% 7% Cupertino -
MoUnt Diablo (South Gate) 16% 5.3% Contra Costa County -
Old La Honda Road 15% 7.3% Portola Valley -
Patrol Road 18% 10% Woodside 725
Quinnhill 19% 16% Los Altos 317
Ramona Road 17% 11% Portola Valley -
Redwood Gulch Road 18% 10% Saratoga -
Summit Springs 23% 13% Woodside 555
Sweeney Ridge 17% 7% Pacifica -
Tollgate Road 17% 10% Saratoga 21196
Viscaino Road (east side) 18% 11% Los Altos Hills 12831
Viscaino Road (west side) 20% 12% Los Altos Hills -
Vista Verde Way 17% 11% Portola Valley -

Other Profiles (altimeter readings only):

Mega Monster Pinnacles Enduro (90.8 mi)
Palo Alto to San Luis Obispo (215 mi)
Stanford to Belmont (16.4 mi)


My first gradiometer, sitting on a stack of 7 pennies. The base is 67mm long, and the stack is 10mm high, giving a grade of 15%, which matches fairly closely to the reading on the gradiometer.

Inspired by the Low-Key Hillclimbs and Western Wheelers' list of southern peninsula climbs, I wanted to see if I could make a cheap, reasonably accurate gradiometer that would be small enough to be easily carried on a bike ride. This is what I came up with. It consists of an audio tape case (with the two "prongs" inside broken off). Inside is a paper card, with the scale drawn on it. A penny hangs by a thread. The top of the thread goes through a pinhole in the card to the backside, where it is secured with tape. The card is glued to the inside of the case, so that it won't move.

Before I glued the card in place, I calibrated it so that, when the case is sitting on the top tube of my road bike on flat ground, it reads 0% grade. (My top tube slopes downward at about a 0.5% grade, so I had to rotate the card inside the case slightly). Thus, the gradiometer uses the bike as a base. It measures the grade over a distance of 98cm (my wheelbase), instead of the 6.7cm base of the case. This helps avoid errors due to bumpy asphalt.

Build Your Own Gradiometer

My most recent gradiometers used a CD case instead of a cassette case. You can just remove (or cut short) the black plastic piece inside the case. It's easy to make your own... just print out this postscript file (or this acrobat (.pdf) file ). Then all you need is a scissors, coin, needle, thread, CD case, tape, and glue (I prefer hot glue, but anything that sticks to plastic should work).

Tape the coin to one end of the thread. You'll want to completely encase the coin in tape, so it doesn't make so much noise when it rattles around in your back pocket. Then use the needle to poke the thread through the upper left corner of the scale. If your paper is light, you can reinforce it with a layer of tape first, and stick the needle through both the paper and the tape. Then tape the end of the thread to the back of the paper. Make sure the thread is long enough that the coin hangs below the scale, but short enough that the coin doesn't hit the bottom of the CD case.

Glue the paper scale inside the CD case. To calibrate it, you can either figure out the exact placement before you glue it, or you can add layers of tape to one end of the base of the gradiometer until it reads 0% on level ground.

Calibration Tests

I ran some tests to see how accurately the gradiometer could measure a known grade. So after calibrating the gradiometer for level ground, I started stacking books under the front wheel. I recorded the readings from my gradiometer. When I was done taking readings, I measured the wheelbase of my bike, and the thickness of each of the books. From this, I computed the actual grade, for comparison. Here's the results:

Wheelbase Rise Gradiometer Reading Calculated Grade
97.8cm 3.6cm 4% 3.7%
97.8cm 8.2cm 8% 8.4%
97.8cm 14.5cm 15% 14.9%
97.8cm 19.9cm 21% 20.5%

Note on Altitude

All of the altitudes (and "feet climbed") on this page are from my much-abused Avocet 50 altimeter. The altitudes are intended to give a rough idea of elevation gained. I haven't done any formal tests, but I think that the altitude readings are within about 10% (accuracy), +/- 100 feet (due to weather).

Links to Other Bay Area Grade Pages

Back to Lucas' cycling page.