I haven't had issues with clouds, but it can be flaky if one is in a steep ravine, between tall buildings, or under heavy tree cover (I mean REALLY heavy--I run in pretty dense forests sometimes and it's still good as long as I'm not in a ravine). Most of the time it's pretty good, though. And on a bike with the cadence/speed sensor it will also track distance from rear wheel revolutions, just like a standard bike computer, so there is always that measurement if the GPS craps out on the bike.