# General Cycling Discussion - What's up with AVG. MPH?

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View Full Version : What's up with AVG. MPH?

Eureka
06-09-03, 08:28 AM
Finally got a decent ride in this weekend. This part of New York has had rain for the last 113 weekends and while there was no sun, there was no rain either.

So I head out to do 20 miles, riding with others I meet on the road. At the end of 20, with the help of those new companions I had an average mile per hour of 15.4.

My plan on the return was to meet up with others again and beat that average. Two obstacles: wind and no other riders!

So, to the point. Why is it that on my return it took a very long time, and significant effort for me to get my FINAL average back to 15? I kept hovering at 14.9 - losing speed on the hills, gaining speed back on the downhill - but never breaking through to 15.

I know a watched pot never boils but this was ridiculous. I actually rode past my house to get to the magic number.

Now mind you, I am not a stupid person. It's not like my speed at this time was 11 or something. I was up near 20 for miles.

Is there some law of physics that the longer you ride the more it takes to get your average up a notch? It sure dropped fast on the uphills.

deliriou5
06-09-03, 08:41 AM
yeah... but it's more like a law of math than it is of physics....

a drop in a cup is more significant than a drop in a bucket which is more significant than a drop in the sea.

and it's always easier to drop your avg speed than it is to increase it. the closer your average gets to your max cruising speed, the harder and harder it is to maintain that average.... your average asymptotically approaches your max speed.

that's why it's easier for a 3.3 GPA student to improve to a 3.4 than it is for a 3.8 GPA student to improve to a 3.9.

greg360
06-09-03, 11:57 AM
I have to agree with deliriou5 and believe he explained the principle splendidly.
I've also heard this approach applied to financial endeavors, such as why (after a stock has lost 50% of its value) does a stock price have to increase more than 50% to get back to it's pre-loss price.
It's great to be able to do the math, but being able to see it from a tangible/nonnumerical point of view (a drop in the bucket, etc) is most useful for de-clouding this kind of analytical thinking.

Captain Crunch
06-09-03, 12:09 PM
The simple answer is that you are going slower for longer than you are going faster! Below is a little quiz which relates to this problem very well. Before you look at the answer see if you can figure it out on your own.

Question:

You have a 1 mile loop racing track. Your goal is to average 60 mph for two laps. You do the first lap at 30 mph. How fast must you go on the second lap in order to average 60 mph?
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Here is the correct answer! Good job to those who got it correct.

No, it is *NOT* 90 mph. If you do the first lap at 30 mph, it takes you 2 minutes for one lap. An average of 60 mph is 2 laps in 2 minutes. Thus, it is *IMPOSSIBLE* to average 60 mph if you do the first lap at 30 mph (even if you could travel at the speed of light--which you can't, because you have mass--you'd still be averaging slightly over 60 mph.

The place where people's intuition breaks down is that the basis for finding average speed is time, not distance. So, while it would be true that one minute at 30 mph and one minute at 90 mph *does* give you a 60 mph average, it doesn't work if you do one mile at 30 and one mile at 90. The reason is that you spend two minutes doing 30 mph but only 40 seconds doing 90 mph (which comes out to 45 mph).

cyclezealot
06-09-03, 04:49 PM
On the flats, I have many time average 17-20 mph range for long distances. I still and always will be a bike addict.
Not sure of my priorities. Speed kills? Apply to cycling.?
I had my crash. Think best cause was likely, speed caused me to miss some object in the road. ? Not sure what happened.
Just I know my pending rotor cuff surgery will get me off the road for awhile and I do not like that. Will I be ready for my September tour.....Yes, speed can feel great at times- but I am really in cycling for the touring.
I will be off the bike probably two months. that is going to make me nuts. During those two months, I Will not like to be out and see others out riding. Envious is the word.. Just a thought.

06-09-03, 07:00 PM
Ah yes... Averages are fun!

People have the same difficulty with grade point averages. So easy to go down yet so difficult to get back up!

brent_dube
06-09-03, 11:40 PM
Just try to think of actual time before average MPH.
Its all math.
Remember, average is a number driven from time/distance. Think about your time, rather than speed. Like others explained... going by average MPH can be confusing.

RainmanP
06-11-03, 11:32 AM
Aside from the whole average question. When riding with other cyclists I find I always seem to ride faster with the same perceived effort, even when riding side by side. Naturally when drafting you can go faster, too.

Bokkie
06-11-03, 02:57 PM
Captain Crunch - you just did my 'ead in. Last ride I did t'was abart having fun. Now, I'm a-finking dat I need me kalkyoulator to do the sums. My brain dunnarf 'urt bad, like.

Great explanation though.:beer:

Captain Crunch
06-11-03, 03:31 PM
Bokkie

Thankfully bike riding is brainless. Now let's get out and ride sans calculator.

Bokkie
06-13-03, 01:37 AM
The way my memory has been of late, I'll probably go out riding - sans bike!

Pat
06-14-03, 05:12 AM
Good illustration on the 30 mph loop and then how fast do you have to go to avg 60.

Another thing about averages. Most bike computers shut off when you stop but most run during the approach and take off at a light or stop sign. This can have a pretty large effect on your average speed. I had a 20 mile loop I did. I did it a few times and just let the computer run and took my average speed (cruising at 20+). I then turned off the computer every time I had to slow down for something that was traffic related like a stop sign or traffic light and this loop was out in the country with very few of these. My average speed was 2 mph faster with the interruptions cut out.

Also, hills were mentioned. A reasonably steep hill will slow you down below 10 mph and that will just kill your average speed because, as pointed out, you spend a lot more time climbing at a low speed then you do descending at a fast speed. They don't cancel out.