calories burned while cycling

Question
I recenty got a trainer for my road bike to hopefully maintain some level of fitness during the long winters. Last night, I decided to do a mostly sprint training session, staying on lower resistance and on the big chainring. I ended up riding 15 miles in 31 minutes.

Unfortunately, none of the online calories burned calculators (nor the one used by the cycling/training site I use) can tell me how many calories I burned since they all go up to 20 mph at the highest end. So it says I burned the same by going 15 miles as I would have if it went just 10 miles, which is obviously not true.

Is there site that you know of that continues it out a bit more? I doublt I will do the 29 mph pace all that often, but I have been getting in the 22 mph range quite a bit, so even those cauclations are off by a little.

If you don't know of any solution, do you know if extrapolating the values would be accurate? I plotted the values for 31 minutes at 0.5 mph intervals up to 20 and tried extrapolating to 29, but I don't know if that is accurate becuase as the speeds approached 20, the increase in calories burned per minute seemed to accelerate quite a bit. By this, I mean, from 14 to 18 mph, it seemed to go increase by about 4 calories per minute (about 10 to 14 calories per minute) But from 18-20, it increase twice as fast...adding another 4 calories per minute to the average. So I don't know if the rate continues to increase or if maybe the body reaches a plateau of sorts.

For the record, I weigh about 175 and the bike weighs about 25 and the trainer is a megnetic trainer that uses the weight of hte rider and bike to create the contact with the resistance unit so I don't know if the full weight of bike and rider comes into play. I'm just really looking for some estimate of calories burned per minute. My guess from extrapolation is anwhere from 1200-1500 for the 31 minute session.

Answer
Hi Tom,

First allow me to apologize for taking so long to answer this. I was at The Park Yool Bicycle Summit for the past 2 days in Washington DC.

I have checked probably the same sites and such as you have and found pretty much the same exact thing you have, once you pass a certain point there really is no formula that allows you to calculate the calories burned. I would say though that as long as you are consistent in the way you figure the calorie burn it should be acceptable.

One other place you might try is you local University if they have a physical education program or if they have any sort of cycling program. For the record though I think most of the formulas and such we deal with on this subject are more of a guess than and accurate reflection.

Hope this helps, sorry I could not find a more accurate way to measure the calorie burned.

Have a great day

Jerry