Using the Garmin 405 for Cycling

I guess I am a bit of a penny pincher but I just haven't been able to get myself to foot the several hundred dollars to buy a high end Garmin cycle computer like the Edge 500/510 or 800/810. I just cannot justify the cost. Also, I don't train with power either. I train with heart rate only. I like to know the stress I am putting on my body, regardless of the amount of power I am putting into the rear wheel.

I bought the Garmin 405 when it was sold at Costco for $140 back in 2011. Its a wrist-watch kind of device pictured below.

One nice advantage with the wrist-watch design is that I can conveniently use the same device for running too. Even though its nice and small, it does include GPS.

The 405 supports several accessories including the Garmin footpod, the Garmin ANT+ Heart Rate Strap and the Garmin speed/cadence sensor. There is also a nice handlebar mount for it but I don't use that because my bar top real estate is all taken up by some aero bars such as in the picture below.

 

I have been using the 405 every year putting in between 4,000 and 8,000 miles per year. I have never used advance features such as the virtual training partner or downloading a route to it to help guide me on an unfamiliar route.

LCD Display

The display supports 3 data fields simultaneously; one in really large font and two others in much smaller font. You can set the 405 to continuously page through 3 different pages of data for a total of 9 different fields. You can set the amount of time between page switches. The display is easy to read in bright daylight.

In night riding, there is an LCD backlight. You just have to tap the bezel/edge with two fingers to activate it. You can set the amount of time the backlight stays illuminated after activating it. But, having it on continuously will run the battery down too quickly. Since I ride with a helmet light, just looking down at the 405 provides enough light to read it during night riding.

GPS and Battery Duration

With the GPS on, the 405 lasts for about 7.5 hours. That's fine for most of my training rides. But, its not good enough for a double century; the kind of ride I like to do.

If you have a cadence/speed sensor, however, you can turn the GPS off and the battery will last for more than 24 hours. The 405 will compute speed and distance traveled by counting wheel revolutions. It just won't track where you went on a map.

Assuming you are not attempting to use the 405 to give you turn by turn navigation, the only thing you'll really loose is that when you go to upload your data to Garmin Connect, it won't include your route map. But, if you've correctly calibrated your wheel size, all your other data will be good. For example, see my data from the 2014 Eastern Sierra Double

This is the mode I used the 405 in when I did my cross-country tour and whenever I do long training rides and double centuries.

Navigation with a Route/Cue Sheet and GPS off

I have followed many a rider with better cycle computers, like 510 or 810, only to wind up off course or worst lost and having to back track. The lesson? You still need to pay attention to your route sheet even with high end devices.

This might be obvious to most readers but I will include a short description of navigating with the 405 here for novices. With the GPS off to save battery power, the way you navigate with the 405 involves a little more interaction with you, the rider. With the speed/cadence sensor, the 405 computes speed and distance by counting wheel revolutions.

First, be sure your route sheet includes distance deltas (the distance between) for each navigation point. If it includes only cumulative distance traveled, you can always compute the deltas and write them onto the sheet. Next, select one of the data fields you display as Lap Distance (and be sure Auto-Lap is off). With lap distance on the display, the 405 will display the distance you have traveled since last pressing the lap button.

If you have your wheel size properly calibrated, it shouldn't be in error by more than 1-2%. On short segments, say less than 10 miles a 1-2% error will be no more than 0.1 to 0.2 miles plus or minus. On a very long segment, say 100 miles (e.g. 100 miles to the next navigation point on your route), a 1-2% error in wheel size calibration will translate 1 to 2 miles in error plus or minus on your route. However, routes with segments longer than 10 miles are rare.

For most situations, as a good rule of thumb, if you start looking for your navigation point 1/2 mile before your 405 says you will reach it, and continue looking until you are up to 1/2 mile beyond where your 405 says it should be, you should find it. Accommodating for 1-2% error on a very long segment you might have to extend these distances plus or minus up to a mile or two.

Upon reaching your navigation point, be sure to press the lap button again to begin measuring the distance along the next leg of the route.

As you proceed along your route, you will soon find that your 405 is either always overshooting or always undershooting your next navigation point. And, you can use that knowledge to adjust what to expect as you reach the remaining navigation points on your route. 

Running on a Treadmill with the 405

Just as with cycling, you can use the GPS feature of the 405 for running too. Since I run for short periods of time, the battery life with GPS enabled is not an issue for me when running.

However, I have still found it useful to disable the GPS on the 405 when doing treadmill running and just rely upon the foot pod accessory. With my stride properly calibrated, the 405 computes my speed and distance traveled based on counting steps. Since on a treadmill I am basically staying in one place, the GPS is pretty much useless anyways. And, with my stride properly calibrated, I have found that the 405's estimates of my speed and distance are spot on what the treadmill computer displays.

I suppose the same rules would apply for using a bike stand trainer. That is, disable the GPS and make sure your wheel size is properly calibrated. Then, estimates of speed and distance traveled while pedaling on the trainer should be close to the real world not including drag due to wind of course ;)

Heart Rate Monitor

The HR strap for the 405 is an ANT+ based device. It is not bluetooth or wifi based. Higher end devices support bluetooth HRMs. I've had minor issues with the 405's the heart rate strap sometimes giving wonky readings. For example, look at this ride data. At 57 minutes into my ride notice that my speed and cadence are steady but all of the sudden my HR plummets from around 160 to below 100 and then stays there for more than 5 minutes. In fact all the readings from the last 10-15 minutes of my ride are bad. That can be a real pain in the neck if you are using the HR reading for training.

Sometimes bad HR readings are due to a weak battery. I have read that sometimes being near transmission lines can cause this behavior too. Other causes can be a lot of static electricity in your garments or body, poor contact with your chest maybe if you have a lot of chest hair or if it gets really, really wet in a heavy rain. On the other hand, moisture on the skin is kinda important to maintain good electrical contact. So, if you are riding such that your chest area is dry and free from any moisture or if a good wind on a downhill drys out your chest area, the HRM may start to give less reliable readings. There is also a gel-like product you can by much like EKG gel to help improve electrical contact with the skin. I've never used it though and I have no idea how much more likely it is to overcome these issues.

My heart does have an odd beat, something called a Premature Ventricular Contraction (PVC). Its a benign condition. However, I wonder if sometimes causes the HRM to give wonky readings.

CR2032 Battery Life

The heart rate monitor, cadence/speed sensor and foot pod all use CR2032 batteries. I have found that these last me an entire year of riding before I have to replace them.