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Time calculations climbing vs flats

Old 04-09-24, 09:21 PM
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As a native Hoosier living in the PNW, I cut my teeth on the flats and now I ride hills. Even the occasional mountain pass.

Flats are faster, but good grief are they ever boring. The steeper the grades, the slower overall.
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Old 04-10-24, 03:14 AM
  #27  
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Originally Posted by Tomm Willians
I’m about to ask an extremely vague question that I fully acknowledge has near limitless variables but here goes……..
Giving a general scenario of two routes of equal distance one being flat, the other having a good bit of climbing (and descending) would you be faster at one of the routes? I’m just curious if the increased speed of the descending on a climb essentially gives a similar time to riding a flat?
Doing the Death Ride for the first time this summer and doing my best to overthink it.
It’s 103 miles with of course time limits, I know what I can do a flat century in so hoping those numbers have at least some relation to what I’m facing.
Flat is faster. You wont make up as much time going down as you loose going up.

To get a grip whats going on I suggest playing with at speed calculator like Bike Calculator

It lets you play with in all the variables, including negative grades like -5%.

Last edited by Racing Dan; 04-10-24 at 03:18 AM.
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Old 04-10-24, 03:19 AM
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Originally Posted by downtube42
As a native Hoosier living in the PNW, I cut my teeth on the flats and now I ride hills. Even the occasional mountain pass.

Flats are faster, but good grief are they ever boring. The steeper the grades, the slower overall.
I know what you mean but, as someone who lives at the top of a hill, it makes a nice change to do a flat route occasionally. My average speed is substantially faster over a flat route.

A simple thought experiment will give you the answer. As the hill gets steeper and steeper you eventually get to a hill that it's impossible to cycle up, so your time to complete the route will be infinite.
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Old 04-10-24, 09:38 AM
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Originally Posted by jgwilliams
I know what you mean but, as someone who lives at the top of a hill, it makes a nice change to do a flat route occasionally. My average speed is substantially faster over a flat route.

A simple thought experiment will give you the answer. As the hill gets steeper and steeper you eventually get to a hill that it's impossible to cycle up, so your time to complete the route will be infinite.
Indeed, a flat stretch is lovely after a long climby bit. It's the endless miles of straight flat squares of central Indiana that kill with boredom. Climbing out of the rolling Ohio River valley, and hitting some miles of flat corn and soybean land, is nice.
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Old 04-10-24, 10:25 AM
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From tracking my rides, I have worked out my own personal rule of thumb regarding how climbing affects average speed. For every 10 feet/mile of climbing, my average speed drops about 0.5 mph. So, for example, if I can do a route that has 50 feet of climbing per mile at a 16.0 mph average, when I go do a route with 70 feet/mile, I should expect my average speed to be about 15.0 mph.
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Old 04-10-24, 01:26 PM
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Originally Posted by Mtracer
I agree with all, flat will be faster.

Here's my 2 cents and an engineering and physics perspective (a nerds way to look at it),. If you put out the same power for both courses, and they took the same time (they do not), you would expend the same total energy. Energy = Power x Time.

The energy you put into climbing a hill, you get back descending. But you climb much slower, and therefore you lose less energy in aerodynamic losses. Going downhill, you'll be much faster, and aerodynamic losses will be very much higher. Aerodynamic losses are very non-linear and for example, if you descend just 2X faster than you climb, you will expend 8X more power in aerodynamic losses, but since you'll descend the same hill in half the time, the net result is 4X more energy lost to aero drag descending vs climbing.

Therefore, since you will have expended more energy going up and down the hill, but used the same power, it must take more time.

Even without this issue with aerodynamic losses, if the hill is steep enough, you reach a limit where no matter how fast you descend, you can't make up the time. For example, if on the flat, the route took one hour, but the climb is so steep, it takes you 1hour and 10 minutes to climb, you could descend infinitely fast, and can't make up the time.

Finally there is simply the distance. Going up and down a hill is a longer distance to travel.

Thumbs up to the OP for asking the question and generating a discussion, I'll assure you, every technical weenie on BF has asked this question to themselves. I think to most anyone, it's sort of intuitively obvious that flatter would be faster, but if you don't actually think it through, you don't know.

I'm also betting the nerds on BF will find some technical point to argue about for the remainder of the thread. I'll even wager that Special Relativity will get brought up at some point.
Wow. This reminds me of the "The US is only half the size THEY tell you" YT video...
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Old 04-10-24, 01:45 PM
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Gravity is the key difference between riding on the flat and riding in hills. When riding on the flat you require practically no power to overcome gravity at your cruising speed. When climbing, much of your power is used up fighting against gravity and therefore your speed is much lower and it adds a ton of time that you can never recover on the descents at any speed. Wind resistance is higher on the flat, but you can still ride at a much higher speed than you can on climbs.
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