# Speed to power calc on a 'basic' magnetic trainer

I'm a dedicated non-MAMIL, and I enjoy riding indoors on a cheap-and-cheerful 14-speed (max tooth ratio 48->14) attached to a \$70 basic trainer while watching the footy or listening to music. No wind, no hills, no roundabouts, no car drivers trying to 'door' me, no public shaming from needing to get off the bike to push when I 'gas out' on a hill - seems all upside to me.

My usual exercise protocol is 'steady state' for ~1hour at an average HR in the high-130s and a total cal burn of ~1000kcal, and twice a week I do an HIIT-style workout -

• ride until I get my HR to the low 140s (which only takes a few minutes at cadence ~85 in top gear with 'wine cask' resistance), then
• 8 x 30-sec maximal effort sprints with 90 sec rest in between.

During my sprints, cadence is 120 (min) to 131 (max) in top gear, and HR always gets to 170 on the second sprint - that's my theoretical max given my age (51) and RHR (58).

After the sprint set, I do another 20-40 minutes at a cadence/gear combination that ensures that my average HR for the entire workout is in the 135-140 range and my average cal burn is 15 kcal/min.

I set my trainer so that it takes a 5-litre cask of wine (which weighs ~5.2kg) to move the pedal from horizontal. (This bit is a key input later, I think).

I'm buying a Wahoo KickR shortly so I will have a fair dinkum speed and power meter and this question will be answered by technology!

Until then I am interested in the performance analytics that can be done with basic mathematics based on what I have now (Wahoo cadence kerjigger in my shoe, Mio Alpha HRM on my wrist, and known-knowns like wheel diameter, crank length, force required to move the pedal, and cog ratio).

By year 10 mathematics it appears that my minimum sprint speed (based on 680mm rear wheel diameter, 120rpm crank cadence and 48:14 ratio) sustainable for 30sec is ~51km/hr, with a peak of ~56km/hr (at 130rpm, only held for seconds - so not relevant).

Those seem inordinately high for a fat old indoor hack - but bear in mind there is no wind resistance, no drag, and to the extent that the 'wine cask' resistance mimics a slope I'm not actually having to move my bodyweight (104kg) or bike (12kg) up the slope.

So here's the question (finally): is there enough information there to estimate power?

We have:

• crank length 175mm;
• rear wheel diameter 680mm;
• gear ratio 48:14;
• mass required to move pedal from horizontal 5.2kg (with empty bike)

I am reasonably certain that my (and the bike's) weight - 104kg and 12 kg respectively - are irrelevant, except to the extent that when I get on the bike the mass required to move the pedal would increase slightly (probably not enough to really make a meaningful difference to the calcs).

Almost all the power formulae that I've found, use the rider+bike weight - which is pointless on a trainer. If I subtract my weight, then the power formulae return garbage (and are way out of whack with the caloric expenditure during the 'effort' sets).

Has anybody got any insight on this?