why not the simple solution and just log the damn hours as they are? people want to compare between years, so you look at the training log and it says, rode on trainer for 2h due to crappy conditions outside, and that's what it is. so the next year at that time it was nicer and you were able to get outside...good for you. these things even themselves out. complicating things by having to extrapolate how many hours that would be if you were on the road compared to indoors only makes it more difficult. i have no problem comparing logs over several years by logging the workout as it is.

however, for you more complicated people i have derived a mathematical formula that precisely converts trainer hours into road hours and vice versa.

T(r)= {T(t) * Abs(E - Ent)} + log[(x + R)\t] or

T(t) = {T(r) - log[(x + R)\t]}\Abs(E - Ent)

T(r): time (road equivalent); T(t): time (trainer equivalent); t: temperature in Kelvin; x: # of turns on trainer resistance unit; R: resistance setting on trainer (for fluid or outdoors use R=1); Abs: absolute value; E: emotional status (motivated 2, neutral 1, unmotivated 0); Ent: entertainment (nothing 0, music only 1, TV 2)

More accurate than the 1.5 x trainer time...

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