The higher in elevation you go, the more potential energy you have. This is because you can drop in elevation (i.e. come back down a hill) with no energy required on your part, and as a result you lose potential energy.

This is why it's so hard to go up hills, it requires energy - but all that energy is not lost and can be recaptured by dropping back down in elevation. The amount of energy available is based on weight and elevation difference.

It's a physics term http://en.wikipedia.org/wiki/Potential_energy

Not me... the fast group rides in my area range from 18-20 and that is hammering. Pretty much 65-75 ft per mile in all directions.

and yes i realize it was sarcasm :)

Ahh! ... But ofcourse :)

Ok. You have me here. This is true but you were supposed to wait.

Still, this has no relevance to average speed.

We saw the real world answers posted back on page 2. If you ride a bike more than around your suburban neighbourhood it becomes painfully obvious. It ain't rocket surgery.

In the 25+ years I've been racing i've used every bit of techno gadgety devised including the Power Meter I new have latched to my bike. If I ride 3 hours on dead flat road expending Xkcal and compare my ave speed to 3 hours on a hilly course expennding roughly the same kcal my ave speed is MUCH lower.

Gibberish be damned. I'll take my hard data thanks.

Kinetic Energy >>>>> mgdeltah

Again, sir, you are laughing at something which you simply fail to comprehend.
If you would be so kind as to do some research about the subject "potential energy" before mocking me about it.
Funnily, "potential energy" is often taught in highschools by using the example of a bike and a hill ;)

Potential energy and wind resistance isn't the whole story, ofcourse.
Obviously climbs can slow a person down by such a rate that one climb can take longer than the whole course would take when flat.
In that case it is indeed impossible to make it up on the descent regardless of air resistance.
This is dependent on the climb itself and on the maximum aerobic (and especially anaerobic for short steep climbs) power output of the rider.

Sounds like you two are in violent agreement.

That's a climbing speed? I must be fatter than I thought. Wind resistance at 30kph always struck me as quite noticeable.

Anyways, back in teh real world, long extended clmbs teach you alot about the affect of climbing on average speed.

What I learned: On any route where the miles of climbing is equal to the miles descending, your average speed will always be less than twice your average climbing speed.

Bottom line: As noted by others above, going up takes away more from you average speed than going down gives you back, and that to go faster (on average), climb harder.

Physics be damned.

Don't disregard the math OR the physics, both posts are pretty solid. Or my earlier post either ;)

The mathematical observation about average speed is easy to overlook. We tend to think that going up a hill at 5mph and back down at 35mph, that the average would be 20. That would be wrong: the average speed would be only 8.75 mph.

I think this is the formula he was looking for:

Va = (2 x Vup x Vdown)/(Vup + Vdown)

where Vup is average speed going up the hill, Vdown is average speed going down the hill, and Va is overall average speed.

It's kind of important. Even going out against the wind and back with the wind, the average speed is lower than the average of speeds. If we mess around with the formula and plug in some what-if numbers it's enough to quickly convince us that our top speed isn't nearly as significant to an average as is the bottom speed. In terms of energy expended, the physics of air drag reducing that top speed for a given effort increases the distinction even more.

Yep. It took me a while to realize this, but even in a vacuum, or when descending speed is near infinite, the ascending speed is alway the rate limiting factor.

Physics: it's just not a good idea, it's the law.

Potential energy is the last food you ate? No?

I like to consider the laws of physics to be suggestions.

Anyway, a lot more replies than I expected! In case you're wondering, the reason I'm trying to "compare" my average speed is because I'm a college kid without a job who has all summer to train as much as I want each day (nice, right?) and it's really the only method of comparison I have to see how well I'm doing. Racing's not too popular where I live and I won't be able to get into that until I go back to school in the fall, so I can't compare myself against cat-whatever racers. And there's no way I can afford a power meter. So that pretty much leaves average speed.

Although... I just realized there is a perfectly flat 1 mile loop around a local high school. Once the school is empty for summer, I can go and time trial around it and I think that would give me the best basis for comparison.

Anyway, thanks for your all's help! It does seem like the hills can indeed make a good bit of difference. In regards to the climbing, I'll take 10-15 minutes going up a hill on the way out, and it takes me like 5 minutes on the way back in, so I do spend a lot more time at a slower speed.

Get a job. Buy an HRM

Exactly.
Average speed can be handy to get an idea of your abilities and especially to keep track of your fitness level over time.
The best way to measure your average speed is:
-make sure your cyclometer is near perfectly calibrated. (do not use GPS or other devices as they can never be as accurate)
-find a flat course that is round. (to eliminate wind influence as much as possible)
-ride for at least 20 minutes.

Okay, this brings me to the next logical question then...

On flat, wind-less ground, what sort of 40 km time trials (or whatever the most popular distance is) correspond to what categories? I know Pro1/2 is like 27+ mph, but what about Cat 3, 4, and 5? Like maybe 25, 23, 21?

Not quite. You need to add some qualifiers to the bolded sentence. The ride you describe would be the "best basis for comparison to a rider riding the same course under the same weather conditions on the same or similar bike with the same or similar purpose who calculated average speed the same way you did.

If just one factor is different then the comparison could be completely meaningless, or at a minimum not an accurate comparison unless the results are adjusted for the variables. If you compare your results on the described ride against someone who calculates their results by using an adjusted average but you use actual averages then there is no comparison. Or if the other rider wasn't doing a time trial effort but you were then the comparison is also meaningless. Of if it was pouring rain for one rider and not the other. Or it was 110 degrees and no wind for one rider and 72 degrees with a 5mph breeze - etc.

yeah i only drop about 1mph climbing mountain roads vs flat ground. 24mph all the way to the top.

A lower tech way to figure out where you fit in is to just ride with others and see who basically rides your pace.

The average speed of this thread sucks.

I'll agree to everything Bob said.

And the rest of you will too someday.

My experience jibes with cato's. Compared to a flat route, climbing 100 feet/mile including some steep grinders will lower my average by 4 mph or so.

No one's forcing you to endure stupidity on the internet.

Using average speed to measure your improvement will work somewhat, as long as it's long enough to help reduce the effect of the variables. Comparing your time to misc people on the internet is not so useful. So, if you have a 1 mile loop and do 15 laps, and track it over several months, you may get some semi-useful data.

Correct usage alert !! :thumb:

I don't have a clue what your Cat5 and such mean but I know the Belgian champion timetrial did 46km in one hour 45 secs.
He's a pro though.
In the category "elite without contract" the Belgian champion did 47,5km/h over a 23km course.

A little googling will tell you the speeds of champions in your area, I'm sure.