The 255 has a new sensor and should give more accurate results. But the 245 has a good enough sensor and can be found for half the price of a 255. But the 255 has other new features. Check out the comparison of the two models on DC Rainmaker and make your choice. ergepard.
Hi there, I have a Forerunner 245 Music. When I start a running activity I can only see Distance, Timer and Pace, but I also want to see my Heart Rate without having to hit any buttons. The HRM-Run should give you all the run Dynamics, so it's the most full featured strap for the 245. The Tri adds swim mode that 2xx can't use anyway. I prefer an optical bicep band myself though (Scosche Rhythm, Polar OH1, Wahoo) dark_77 • 4 yr. ago. "The HRM-Run should give you all the run Dynamics, so it's the most full featured strap for It has a built-in heart rate monitor, which allows you to track your heart rate during workouts and see how your fitness level is improving over time. This will ensure that the monitor is in contact with your skin and can accurately track your heart rate, as well as prevent any interference from your watch or other accessories.

In GPS mode, the Forerunner 245 has a battery life of 24 hours without music, or 6 hours with music, whereas the Forerunner 255 can last 30 hours without music, or 6.5 hours with music.

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forerunner 245 heart rate not working