Boulder Bikes, Bad Data: Wearables' Altitude Problem
By Franklin Everett ShawEver felt like your Garmin was lying to you about that epic climb up Flagstaff Mountain? You’re not alone. Many Colorado cyclists, especially those around Boulder, are battling inaccurate altitude data from their wearables.
It’s time to ditch the guesswork and get real about your elevation gains.
Altitude data from devices like Garmins and Apple Watches is often flawed. This is due to barometric drift and GPS inaccuracies, especially problematic in mountainous terrain. These errors can significantly skew your ride metrics, leading to frustration and a distorted view of your performance.
Let’s dive into how to fix this.
The primary culprit is barometric drift. Your watch estimates altitude based on air pressure. Changes in weather can cause air pressure fluctuations, leading to inaccurate altitude readings even when you haven’t moved an inch.
GPS inaccuracies also play a role. GPS signals can bounce off mountains and buildings, creating errors in your location and altitude estimates. This is especially true in areas with dense tree cover, common in the foothills around Boulder.
So, how do you combat these issues?
First, calibrate your device regularly. Most devices allow manual calibration using a known elevation. Before your ride, find a benchmark elevation point. A USGS benchmark is ideal, but even a trailhead sign with a listed elevation will work.
Set your device’s altitude to match the known elevation. This provides a baseline for your ride and helps minimize barometric drift errors.
Next, compare your data against known benchmarks. Boulder is blessed with iconic climbs like Flagstaff Mountain and Super James. These climbs have well-documented elevation profiles.
After your ride, compare your device’s recorded elevation gain to the known elevation gain for the climb. If there’s a significant discrepancy, you know your data is suspect.
For example, Flagstaff Mountain’s paved road climbs roughly 2,000 feet from the base to the summit. If your Garmin reports only 1,500 feet of climbing, you’ve likely experienced significant barometric drift or GPS inaccuracies.
Consider using alternative tools for verification. The USGS National Map is a fantastic resource for accurate elevation data. You can use it to create elevation profiles for your rides and compare them to your device’s data.
Websites like Ride with GPS also offer elevation correction tools. These tools use map data to adjust your ride’s elevation profile, providing a more accurate representation of your climbing.
Another challenge is the “smoothing” algorithms used by some devices. These algorithms attempt to filter out noise in the data, but they can also smooth out legitimate changes in elevation, underreporting your climbing.
Disable smoothing if possible. This will give you a more raw, albeit potentially noisier, data stream. You can then use post-ride analysis tools to filter out the noise yourself.
Common mistakes developers face when building altitude tracking features include relying solely on GPS data for elevation. This is a recipe for inaccuracy, especially in mountainous regions.
Another mistake is failing to account for barometric drift. Implementing a calibration feature is crucial for mitigating this issue.
Consider using a Kalman filter to smooth out the data while preserving legitimate changes in elevation. A Kalman filter is an algorithm that estimates the state of a system based on noisy measurements. It can be used to filter out noise in altitude data while still accurately tracking changes in elevation.
Here’s a step-by-step guide to calibrating your Garmin:
- Find a known elevation point.
- On your Garmin, go to Settings > Sensors & Accessories > [Your Barometric Altimeter Sensor] > Calibrate.
- Select “Use Current Location” if you are at the known elevation point. If not, select “Enter Manually” and enter the known elevation.
- Save the calibration.
For Apple Watch, the process is less direct. Apple Watch relies heavily on GPS and doesn’t offer manual calibration. The best approach is to ensure your watch has a clear view of the sky during your ride and to compare your data against known benchmarks afterward.
Let’s talk about real-world applications. Imagine you’re training for the Bob Cook Memorial Mount Evans Hill Climb, a grueling race to the summit of Mount Evans. Accurate altitude data is crucial for pacing yourself and tracking your progress.
If your device is underreporting your elevation gain, you might push yourself too hard early in the race, leading to fatigue later on. Conversely, if your device is overreporting your elevation gain, you might not push yourself hard enough.
By calibrating your device, comparing your data against known benchmarks, and using alternative tools for verification, you can get a more accurate picture of your performance and optimize your training.
Another scenario: you’re exploring new trails in the Indian Peaks Wilderness. Accurate altitude data can help you navigate and avoid getting lost.
If your device is providing inaccurate altitude readings, you might misjudge the steepness of a climb or the depth of a valley, leading to navigational errors.
By using the techniques described above, you can improve the accuracy of your altitude data and make your adventures safer and more enjoyable.
Don’t blindly trust your wearable. Take control of your data and get a more accurate picture of your cycling performance in the Colorado mountains. Your legs (and your Strava kudos) will thank you.