Why Measure Power?

There has been an evolution from using only using heart rate measurements for training purposes to measuring the power output of the cyclists. To meet this need training method several approaches have been taken to develop power meters than read out the power in watts, being applied to the pedals.

Two Components

Most power meters are in two components. There is the mechanism to make the reading using something like a strain gauge. This is either built into the crank, the hub or some other part of the bike where power being applied to the pedals can be measured or estimated. Then there is the computer head which is mounted on your bicycle handlebar where you get the reading. The computer heads offer other cyclometer features including speed, distance, heart rate and even GPS on some models. The communication between the two components is either via a wire or wireless.

ANT+Sport^TM is a 2.4 GHz wireless network with standardized communication between devices including bike power sensors, speed sensors, cadence sensors and heart rate straps. This allows separate manufacturers to independently develop sensors and computers, allowing you to pick and choose your favorites to create a system that meets your needs. For example if you have a Garmin Edge 705 GPS based cyclometer, which offers not power measurement sensor, could be coupled with the SRM or Quarq crank to read out power and could be used instead of the computer heads offered by those companies.

Offerings

PowerTap:

This offering is from the Saris Cycling group (makers of the CycleOps cycling trainer). It uses a special hub and handle mounted computer to measure and display the power at the pedals. It requires a rear wheel with the PowerTap hub. There are wireless options. It adds weight to the bike due to the hub and the need to use a wheel that can accommodate the PowerTap hub. It is also expensive, especially for the wireless version. Although there is a 2.4 Mhz wireless option, it does not support ANT+Sport^TM so you are stuck using the PowerTap computer which really looks looks like a prototype built by an engineer for development and not a product ready for the mass market. It can be used on a bike trainer to measure your power output. Moving to another bike will require moving the wheel and the computer head.

Best For : Those looking for a reliable approach to measuring power and are willing spend considerable money and take a weight penalty.

SRM:

This offering is from Schoberer Rad Messtechni. It uses a special crank to measure the power to the pedals. There are a variety of versions to match some of the popular cranks, including DurAce and SRAM. SRM supports ANT+Sport so you can either use it’s computer head (which kind of looks like a prototype) or another device that supports ANT+Sport^TM such as the Garmin 705 Edge or iBike.

Best For: Due to the extreme expense it is geared toward professional cyclists or those who are prepared to spend as much measuring power as they might spend on a good quality road bike.

Polar:

This offering is from Polar, famous for heart rate monitoring. It uses a device to measure chain tension on the bike and transmit that to certain models of their heart rate monitor or cyclometers. It is can be difficult to calibrate and but once it has been it can have a reliable output. You do the power level read out on compatible Polar heart rate montiors (such as the 725i) or Polar Cyclometers. When used with the latest CS600 cyclometer, you can get an efficiency readout on the cyclometer. This efficiency is an estimate of what percentage of the calories being burned by your body go into moving your bike along, a step beyond just measuring power.

Best For: Those who use Polar advanced cyclometers or heart rate monitors and are looking for a lightweight and less expensive approach and are willing to go to the effort get it properly calibrated.

iBike:

This offering from Velocomp is a relatively new approach. It is different in that it does not directly measure your power output as is done with the above products. It measures the parameters of what you work against and then calculates what your power would need to be to achieve the speed you are going. Except for the front wheel pickup it is all contained in a well designed computer head that is about as large as the computer for the PowerTap and weights 100g. You can also easily transfer from bike to bike. It has some negatives. It can not be used to measure power on a bike trainer. It also seems to have a short battery life due to using a non rechargeable watch type battery. It needs to be mounted so it gets a clean air flow since it uses wind speed in it’s calculations so use with aerobars can be difficult. Cost: Moderate to Expensive.

Best For: Those who are looking for a less expensive and very lightweight approach to estimating power. Those with aero bars should look elsewhere.

Quarq:

This offering is from Quarq and uses a special crankset to measure the power, similar to the SRM approach. It offers ANT+Sport^TM compatibility. It’s computer head is one of the more sophisticated cyclometers you can buy and has a GPS option. Cost: Expensive

Comparison Reviews:

• Power Tap vs. SRM vs. Polar at BikeTechReview
• Accuracy of PowerTap and SRM at Medicine & Science in Sports and Exercise
• iBike Power Meter Reviews - paper that gathers references to many different reviews
• Measurement Comparison of Power Tap vs. iBike vs. Quarq
• Active.com review of iBike

Categories: Equipment
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Yesterday my new BR Light arrived by FedEx, just in time to give it 45 minutes on the charger before I jumped on the bike and headed north to Morgan Hill for a ride up Henry Coe with the Nightriders. I waited until dark before I started the ride back home from Morgan Hill so I could test out the new light. I had purchased the C2-H model, which is a handle bar version and the model with the higher lumen (and shorter run time).

The light has three power settings, high, medium and stealth. I had them program my light so the stealth mode was at 5% instead of the normal 2% because when I tested it last Friday during the mountain bike ride, I didn’t feel the 2% would be adequate. I am glad I made that change.

Before I get into how the light performed on the road, in the dark, here are some interesting comparisons between my new light and an older 20/10 watt dual light system I have used in the past.

On the left is the new BR Light, which is all self contained in one unit. That means the mount, the light, the battery, the controller switch are all together. Compare that with my old light with a separate battery, a bag for the battery, cables to connect the battery to the light, a light mount, and a control switch I had to attach to the handle bar.

I weighed both setups (san chargers). The BR light weighed 14.2 oz (408 grams) while my old light came in at 2 lbs, 2.5 oz (992 grams) or more than twice the weight. My old light has two lights, a 10 watt and a 20 watt, for a total of 30 watts, but with both lights I can only get a couple hours of run time, even with that heavy battery.

The BR light is small enough and light enough to mount on the handlebar with no need for cords (note I have small hands).

I then did a very unscientific test and shined both lights in a dark room against the wall.

The BR light is on the left, the old light on the right. It should be obvious to even the most casual observer that the BR light is much brighter and the light is whiter, which is easier to use on the road.

The mount for the light is attached to it. It is a clever all metal mounting system that I believe is very solid, even fully adequate for mountain biking. Once mounted, it is easy to move the light left or right as you are riding, to aim the beam. The light does not come off as quick as those lights that have a mount that stays on the bike such as my Cateye HL530, but then those mounts are often flimsy. The BR light is relatively easy to attach and remove and certainly faster and easier than setting up a light that has an external battery that you need to attach to the bike somewhere then wire it to the light on the handlebar.

Now back to my ride in the dark. I rode 13 miles in the dark, part through the city streets and about 10 miles on a road that had no street lights and enough times with no cars to test things out. I found that on high power the BR light has plenty enough light for me to go as fast as I wanted. I took my speed up to 30 mph on a short descent and felt fully comfortable.

On the medium setting the light is adequate for 20 mph, what I would usually do on a flat road. If the route was short enough I would still opt for the higher light setting, but the medium setting was fine, especially if the road has a white line to gauge off and is in reasonably good shape.

I had a short climb where I tested out the stealth mode (my light was set at 5%). I found it adequate, but barely, for climbing at up to 7-8 mph. I am glad I had them change the setting and maybe a slightly higher setting would be useful. In any case it is about as bright in the stealth mode as my Cateye HL530, which has a claim of 1,500 candlepower (a useless measurement in my opinion).

I feel that with this particular light, I could basically go all night on a single charge by using the medium setting for flats, the high power for descents and the stealth mode for climbing. The light has a 6 stage battery indicator. A colored LED goes from green (full power) to blinking green, then to orange, then blinking orange, then red, then blinking red. It is a clever system and very easy to see how much battery life left.

I found using the single control button on the light to work very well. It was very responsive.

If I owned a HID light I would make a direct comparison. When we did the night mountain bike ride last Friday we did an informal comparision with some HID lights on the ride and found the BR Light similar in terms of illumination. The BR light has the big advantage of using the new CRED LEDs which are very reliable and much more shock resistant than a HID light. The LED light turns on immediately and it is no problem to shut it off and back on as you wish.

I have a sophisticated light meter back from the early days of photography that will measure LUX, but I have to find some batteries first. They don’t make the mercury button batteries anymore for this device that is 25 years old. When I get it to work, I can do more testing.

In summary, I am very glad I bought the BR light.

Categories: Equipment
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I ride with a group called the Nightriders, who both road and mountain bike. Tonight I decided to join them for a night time mountain bike ride up Henry Coe, the largest State Park in California. I wanted to join the ride tonight because we were going to have guests from BR Lights come join us and bring some of their new lights for us to test out. I was in the market for a new light, needing something I could use for the Furnace Creek 508 in October and other events I want to do, in addition to the night mountain biking.

They let me try both the handlebar light (C2.1-H model) as well as the helmet mount light (Jen-H model) with the auxilary battery pack. I got the lights setup quickly due to a clever design for both the handle bar light and the helmet light. Unlike my existing lights that required me to first put an a handlebar bracket, attach the battery, attach the light, connect the light to the battery and finally attach the control buttons to the handle bar; this unit is all self contained so the battery and control switches are all in one unit. It makes the design look a bit boxy but I was pleasantly surprised that in the field when I had mounted the unit on the bike it didn’t look as big as I thought it would after looking only at their website.

The helmet light is a nice looking design, again all self contained. The only downside of this is that it is a bit heavy on the head, but not unreasonably so at only 300 grams.

We took off soon after 7 pm, with plenty of light to make the first climb. Kyle and Jeni, from BR Lights, were out in the front and I struggle to keep up with them even though we were on a fire road. I realized they were great mountain bike riders in addition to knowing a lot about LED light technology.

Kyle and Jeni from BR Lights

Franz with BR helmet light

As we reached the first regroup area it was getting dark and we had a chance to finally try out the lights.

After the rest of the group arrived we had a chance to compare the lights. Jim had a triple shot on his handlebar so we pointed it ahead to the right and I pointed the BR handlebar light to the left. You can see the comparison in this photo.

Comparison of BR Light (left) and Triple Shot (right)

The BR light was clearly brighter, not only over the wide area, but much brighter in the spot area.

Jim also had on one of the BR helmet lights while he hammed it up for the camera.

Jim with BR Helmet Light

We made our way to the tricky single track. Not being a real experienced mountain biker, I normally would have been very nervous doing this single track in the dark but I found the combination of the BR handlebar light and the BR helmet mounted light illuminated up things fully. I usually was running the handlebar light on half power and relying more on the helmet light, which seemed to work fine.

Both lights have a stealth mode, that sas some extremely long battery life. I tired that mode but found it too weak for anything other than maybe climbing on a road bike.

Some of the riders in our group were using HID lights. I didn’t see that they were any brighter than what I was using, which is quite a feat considering the BR Lights use CRED LEDs, are all self contained with a total weight much less than the HIDs and much greater durability.

It was well past 11 pm when we finished about a 20 mile ride.

I was so impressed with the BR Lights that I ordered the handlebar version (C2.1-H model) right away. I would like to buy the helmet light also but that would be a bit much for me right now, but I am tempted. I hope I get my new BR light quickly before the our big night mountain bike adventure in September.

Franz Kelsch

See also:
http://www.sports.franzkelsch.com
(my personal endurance sports website)

http://www.actc.org
(primary cycling club where you can contact me at webaster@actc.org)

Categories: Equipment
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