They're not at all accurate, although they might be ballpark accurate on a long, steep climb.
On flat roads, air drag is the biggest retarding factor and this will vary with height, mass, bike equipment, air density, and position on the bike. The Hac 4 can't calculate these (it might do barometric pressure). Thus, it wouldn't know if you were on a TT bike or road bike with your hands on the tops (and thus your drag would be much higher).
You can get a more accurate estimate at www.analyticcycling.com (site appears to be down at present).
Ric
On flat roads, air drag is the biggest retarding factor and this will vary with height, mass, bike equipment, air density, and position on the bike. The Hac 4 can't calculate these (it might do barometric pressure). Thus, it wouldn't know if you were on a TT bike or road bike with your hands on the tops (and thus your drag would be much higher).
You can get a more accurate estimate at www.analyticcycling.com (site appears to be down at present).
Ric
