Polar has never really been a top-of-mind brand for mountain bikers. But the Grit X, a robust GPS smart watch, launched a few months ago, is helping the Finnish brand gain traction in its quest to meaningfully enhance the lives of adventure-based athletes, including mountain bikers. Our review here:

Although we have used Polar’s cycling-specific devices without any kind of drama on and off since 2016, we were quite chuffed to see the arrival of the Grit X, essentially taking the brand into the hardcore cyclist/mountain biker smart watch category.

It’s very difficult not to compare the Grit X to the Fenix, which Garmin has used to largely dominate this category and which has become the sports smart watch category benchmark.

We need to state upfront that we are not tech experts, so this review lacks hard tech analysis, which can be found with a simple Google search. We are mountain biking experts though and that’s how we spent the past few weeks reviewing the Grit X, on our mountain bikes. And also off them…

For newcomers to endurance sport, Polar is the sports heart-rate monitor pioneer brand. It was THE only genuine training and racing companion until Garmin’s sport/cycling segment arrival around 2004/2005. Despite the changing landscape, Polar has continued to build a very strong foundation primarily in the general fitness and triathlon markets with a committed dig into the cycling and mountain bike markets with these models.

The Grit X looks the part! It has a 30.5mm colour touchscreen with a rugged, rubbery-feel strap and five textured buttons around a stainless steel, military-standards bezel. At 64 grams it’s lighter than it looks (the Fenix 5s is 87 grams). It’s surprisingly light actually.


We did most of our rides with the Grit X on our wrist, because, well, it’s primarily a wearable device and a few rides with it on the bar mount (an optional extra). The large digits with appropriate contrast to the background are easy for most to see while riding, which is more important than you might think!

It does read heart rate via your wrist (Optical Heart Rate) and it also pairs with a dedicated Polar Heart Rate chest-mounted (Electro Carido Graph) strap (optional extra). We tried both and also compared both when on Zwift sessions to – not surprisingly – discover that the chest-strap-based measurement is consistently more accurate than wrist-based measurement. This is not a Polar thing, it’s the same for all smart watches with chest-strap pairing options.

So, if absolute heart rate measurement is critical to you, ensure you use the chest-strap when training and racing. If it’s not super essential, then the wrist-based reading will be just fine. It is rather liberating to be able to have heart rate measurement happening without the reluctant discomfort of a chest strap.

All the expected cycling smart GPS information is recorded, including speed (current, max and average), distance, duration, ascent, descent, heart rate (current, average and max), altitude and calories burned. It also features Strava Live Segments, a must for the competitive riders. It also gives the time (duh), alarm, weather and more. You can see the full, extensive features list here.

After the ride, a scroll through your performance measurements on the Polar Flow app is insightful. Polar Flow is highly informative, but not the most intuitive in terms of navigation, you can also see measurement of your cardio load, perceived load and your estimated RPE (Rate of Perceived Exertion).

There’s also a graph for heart rate and a graph for speed, with duration measured of your time broken into in the five ‘effort’ zones: 1 – Very light/50-60% of Max HR; 2 – Light/60-70% of Max HR; 3 – Moderate/70-80% of Max HR; 4 – Hard/89-90% of Max HR and 5 – Maximum 90-100% of Max HR.

The calorie-burn is also broken down into percentages of what fuel source you most likely burned. For example, on a steady three hour-ride around Northern Farm, it said that of the 1629 calories burned, 43% used carbs, 2% used protein and 55% used fat as the fuel sources. There’s also a graph showing these, which is interesting. We should all understand that this isn’t necessarily absolute, but it is based on your profile as a Polar device user and your level of conditioning as tracked by the device over time, so it’s consistent with you and your performance.

There’s also a post-ride GPS map of your ride that numbers all the uphills and downhills with a feature called Hill Splitter. Hill Splitter is always on and measures uphills and downhills with distance, rise or fall in altitude and time taken to complete them; with a detailed breakdown of each. This is a great feature if you are a gravity focussed rider, allowing you to compare performances on the same descent.

We didn’t use one, but you can add a cadence sensor (optional extra). There is route guidance but not via onboard maps, it’s via the route-planning Komoot app (used by about 1.8 million mountain bikers globally). Pre-loaded routes were never something we needed during the review period, but you can find out more about Komoot here.

Another unique feature of the Grit X is FuelWise. It’s a notification that reminds you when to eat/drink and is based on your age, weight, height, gender, max HR, resting HR, Vo2 Max, and aerobic/anaerobic HR threshold. Not something we really found compelling as our longest ride was just under six hours in duration. But if you are an ultra-marathon or ultra-endurance mountain biker, this could be very useful.


Unlike a regular cycling GPS device, the Grit X doesn’t stop tracking you when you stop your ride. As long as it’s on your wrist, it continues to monitor your activity and sleep when you’re off the bike and over a few weeks starts to build a profile of your habits/routine and lets you know when you are slacking or over extending yourself.

Nightly Recharge is a feature that guides you in terms of whether your body is ready for training or needs to take a break from training. It’s certainly useful for over eager mountain bikers that don’t take enough rest days or incorporate easy rides. It’s pretty clever and we liked it. It’s based on more complex stuff that we can’t really explain, so if you are interested, you can read more here.

While the sleep tracker offers great insight, it did seem to misjudge exactly when we fell asleep on a couple of occasions. But it was only twice in more than 60 nights of measurement, so not worth losing sleep over (couldn’t resist).

The battery has a 40-hour charge, which is quite significant and ample for an ultra-endurance race like Trans Bavians or The 36ONE. A three-day stage race or longer ultra-endurance event, may require a charge, but it does charge from single-digit % to 100% within about two hours. There is also a portable battery pack (optional extra) that allows you to recharge the battery while riding for uninterrupted measurement – ideal for events like The Munga or The Freedom Challenge.

While we only used Mountain Bike and Indoor Cycling modes, there are also the following: Road cycling, Cycling, Downhill Skiing, Hiking, Walking, Body & Mind (Pilates/Yoga), Strength Training, Swimming, Trail running, Running, Multisport and Other Indoor.


The Polar Grit X is a smart watch with rugged good looks that’s packed with features for both on- and off-the-bike user tracking and guidance. At R8999-95, the Grit X is very well priced for this category and offers some unique features that will resonate with performance-driven, conscientious mountain bikers.

PRICE: R8999-95

INFO: https://www.polar.com/za/grit-x