4iiii Ultegra 8100 Precision 3 Road Bike Power Meter

The 4iiii Ultegra 8100 Precision 3 is the successor to the Ultegra Precision power meter. In the Precision 3, the sensor is smaller than before to make the power meter fit even more bike frames! Another improvement is that the battery lasts eight times longer than in the previous model.

High accuracy
The Precision 3 power meter measures with high accuracy; its deviation is only 1%. When you put power through your pedals or crank, it doesn't just bend the crank, it turns and flexes in all three dimensions. 4iiii's 3D power measurement system measures this multidimensional load, so you can be confident that your unique pedal stroke is measured accurately regardless of your riding conditions.

Single-sided power meter
The 4iiii 8100 Precision 3 power meter measures your power on the left crank and doubles it to give you total power of both legs. For most riders without limitations, the power on the left and right leg is almost the same for equal efforts. Your cadence is also measured as standard.

Low weight
Due to its super lightweight design, the sensor only adds 9 grams to a standard Shimano crank. This makes it the lightest power meter on the market!

Battery life
The 4iiii has no internal battery but uses button cell batteries, which need to be changed every now and then. Fortunately, the battery lasts more than 800 hours, which is a lot longer than most internal batteries in power meters and in the previous model. If the battery status gets below 15%, you get a notification in the 4iiii Device Configuration app, giving you plenty of time to change the battery before it dies.

Connectivity
Calibration goes via the 4iiii Device Configuration app, which is available for Android and iOS. Through this app you can also see the status of the CR2032 button cell battery. This power meter sends both an ANT+ and a Bluetooth signal, making it compatible with most cycle computers. If you are not sure if your bike computer or sports watch is compatible, take the device's user manual to see if it is compatible with ANT+ or Bluetooth and with power measurement.

• Weight: 9 grams
• Connection: ANT+, Bluetooth
• Accuracy: +/-1%
• Power supply: CR2032 (up to 800 hours)
• 3-year warranty
• Water resistance degree: IPX7
• Active temperature compensation
• Power range: 0-4000W
• Cadence range: 30-150RPM

This crank arm fits an Ultegra R8100 crankset, of course, but also fits other Hollowtech II road bike cranksets.

Caution: The 4iiii Precision power meter is, due to the power meter unit, slightly wider than a Shimano left crank arm. This can cause problems with some bike frames. To find out if your bike frame is compatible, you can perform a test, which involves moving an 8 mm Allen (hex) key vertically between your crank arm and the chainstay. This is illustrated in the last product photo at the top of this page. Or go to 4iiii's own web site, print the handy little document you can find there and stick it on your crank to know exactly between which points the 8mm Allen key must be able to move. If there is enough space for the Allen key, it is very likely that the 4iiii power meter is compatible with your bike frame.

• 1x 4iiii Precision 3 Ultegra R8100 power meter
• 1x CR2032 button cell battery

To be able to install this 4iiii power meter on your bike, you must first remove your current left crank arm. Mount the 4iiii power meter in the exact same way as you would a Shimano left crank arm.

1. Remove the pedal on the left-hand side.
2. Loosen the two crank bolts at the top of the crank arm and remove the safety pin from the slot.
3. Then remove the crank bolt with this crank tool.
4. Now the crank arm is loose. Remove it from the axle; this may require a lot of force; be careful not to damage the crank arm!
5. Next, install the power meter crank arm by following the above steps in reverse order.
6. When your pedal is on the new crankarm you're good to go!

You can also have a look at this blog on how to replace a crankset. Of course, you only have to follow the steps concerning the left crank arm then.

How do I know if my bike is compatible with this power meter?
Firstly, you must have a Shimano road bike crankset. If you don't, you cannot use this power meter. If you have a Cannondale bike, you cannot use this power meter. Other cranksets which are not compatible include FSA, SRAM, Praxis and Hollowgram. You cannot use this power meter on Shimano MTB cranksets either because they have a different design.

That being said, this power meter can be used with older generation cranksets, provided that the mounting method of the crank arm is the same as for the current Hollowtech II crank arms - with two bolts holding the crank arm in place. You may notice a difference in looks though.
Here we list some cranksets that should fit if your bike frame meets the space requirements:
105 R7000, Ultegra R8000, Dura-Ace R9100

Furthermore, it is important that there is enough clearance at the swingarm. If this is not the case, this power meter will not fit, and cannot be made to fit either, unfortunately. The best way to check this is to use the 4iiii model.

How do I know which crank length I need?
Crank length refers to the length of the crank arm and is measured from the centre of the bottom bracket to the centre of the pedal axle. Most bikes come with the correct crank arm length for the corresponding rider body size. In most cases, the length is indicated on the inside of the crank arm. If it is not printed there, you can measure it yourself. It is important that the crank arm power meter you purchase is the same length as your current crank arms.

With what software and/or hardware is this power meter compatible?
This power meter sends both an ANT+ and a Bluetooth signal and is, therefore, compatible with most modern bike computers. However, not all cycle computers are compatible with power meters, so please read the specifications of your own cycle computer.
The majority of Garmin's and Wahoo's contemporary models* can be connected, but the Garmin Edge Explore cannot be paired with a power meter.

* These compatible contemporary devices include:
Garmin Edge 130, 520, 530, 820, 830, 1020, 1030 and 1040
Wahoo ELEMNT and ELEMNT ROAM

If you don't have a cycling computer, you can also use the 4iiii app to track your workout power data.

How do I calibrate this power meter?
Calibrating your power meter is very important for the accuracy of the power reading. Make sure there is no weight on the pedals and that your right crank is up and your left crank is down (positioned vertically). Rotate the power meter a few times so that it turns on. Then you can easily calibrate your power meter via the 4iiii app. Another possibility is to calibrate your power meter via your cycling computer. Most bike computers include this option, so check the user manual to find out how to do this.