JHRacing

According to a calibrated CompuTrainer, it takes about 200 watts to ride 20 mph on a flat wind-free road.

Can I extrapolate from this that if I can maintain 200 watts at 75% or less of my max heart rate, I have a reasonable chance of doing a five hour century?

This assumes, of course, an out-and-back course (uphills and downhills and headwinds and tailwinds cancel) and I would need to boost the speed a bit to account for stoplights, rest stops, etc.

blue_nose

Don't underestimate the effect of stop signs, lights and intersections. If I ride at 20mph all the way home on my commute, with the effect of slowing and starting from traffic signals , I end up with aprox. 17.5 mph avg on mile 10 mile ride home.

fuzzthebee

I recently did a 2:56.00 solo metric (out-and-back) averaging 260w and 80% max heart rate. I also recently did a 4:30.00 century averaging 173w and 73% max heart rate, while riding in a group.

Unless you are really aero compared to me, I'd bargain for a higher power requirement.

JHRacing

Based on those data points, looks like I should shoot for 225 W or so. I also wonder about HR gradually increasing over time. Might be 80% for the first two hours, but would it stay there for another three?

VosBike

Actualy, I typicaly find my HR goes down for a given effort the longer I ride if I eat and drink properly...but I've never worn the HRM on a ride longer than 4 hours.

JHRacing

Interesting, I wonder what causes that. I doubt I could track it anyway with all the real-world variance in load and no power meter on my bike. I do notice it slowly rising when I'm doing, say, 30 min. indoors at 80-90% max HR. But I can't stand much longer than an hour on the trainer and I shouldn't really be at that high of a HR on a century anyway.

Eddie O

I've seen the ever-decreasing HR during 24 hour mtb races, but without a dramatic change in lap times. Obviously lap time do decrease, but not at the same rate that my HR does. I too am curious about the physiological effects that make this possible.

I'm about to start training with a power meter, so maybe that data will shed some light.

Eddie O

Richard Cranium

Who knows? Have you maintained 75% MHR for five hours?

I'm somewhat of experienced at 100 mile TTs, and conditions usually dictate variable efforts. If you rode 5hours at identical effort [75%MHR]-- it probably wouldn't be your best performance.

terrymorse 

I can speak to the decreasing HR on a long ride. That's usually explained as depletion of muscle glycogen, when fuel supply to the working muscles is reduced. I notice it as the inability to get my HR above about 77%, no matter how much I concentrate on the effort.

I get slower when this happens, but not substantially slower. No explanation that I can think of for that.

emosspot

I guess this is off topic, but the nerd in me just can't help himself. Hills and wind always make you slower, even on an out and back course. The amount of time that they slow you down is more than the time they help you, so your average speed is always worse on a hilly or windy out and back than a flat, windless one.

supcom

It would take you about five hours to have a definitive answer to the question.

Summit

As long as this is an academic exercise, you could use a calculator like this to get an estimate... https://www.kreuzotter.de/english/espeed.htm

For me (6'1", 160lbs, 20lbs of bike and water/food)... I need 230W to maintain 20mph with no wind on a flat road, assuming I'm riding on the hoods.

Brian Sorrell

How accurate is this calculator for sprints? I was curious about my power output yesterday when I surprised myself in really heavy traffic -- at a few intersections on a really busy road I was trying to beat the right-turn lane to merge straight. This required cranking up to 28.5 mph in a few instances. I did the math on that site with the specs for me and my bike and holy crap! Could I really have pumped out 775W for 30-60 seconds at a time? If so, that explains how I beat I felt later.

So the question: are those calculators reliable for figuring out what your maximum power output is? (Because I was totally tapped out yesterday, so I figure that's all I'm getting out of these legs.)