You're welcome. You earned it, by expressing your preferences in a way that minimizes the validity of anybody that might have different preferences or requirements.

You might not realize (or intend) it, but the tone of your comment (and many of your comments) reads as if it ends with "and anybody that thinks differently is an idiot" (I say this as somebody who struggles with the same tendency in myself)

[MENTION=252435]RubeRad[/MENTION], a body in motion tends to stay in motion, but air resistance acts against it. To maintain speed, we have to accelerate slightly, constantly. That's why weight matters. It doesn't always matter as much as we expect, but it definitely matters. You can do experiments to verify this.

I'm thin, and I have a hard time keeping up with bigger people on the flats, so I figure my surface area to mass ratio is my problem. Or more likely, it's my surface area to power ratio. Of course, I'm pretty decent at climbing hills. I'm also very good at descending, and I don't know why that is.

Hill and air drag advantages don't really add up on a bike commute, since you have to reverse. Maybe one way is faster than the other, and in that case, 20 mph is very impressive if you can do it both ways. If you can do it only one way, I will guess you have some big downhills on that route.

Yes, just like a bowling ball drops faster than a feather illustrates how aero changes Galileo's observation that mass doesn't affect the speed of falling objects, the momentum of heavier riders will fight through an equal aero resistance better than for a lighter rider.

So additional weight should actually help speed maintenance on the flats, rather than hurt. This is assuming that the distribution of the weight doesn't add a significant enough aero penalty.

A heavier object is harder to accelerate, but given the same resistances, it also decelerates slower. A heavier bike moving along flat ground should require smaller microaccelerations than a lighter bike, all other things being equal.

Flat ground performance is power-to-CdA. Hill performance is power-to-weight.

Descending performance... it depends. Terminal coasting velocity is dominated by weight-to-CdA. The big guys are often the fastest descenders (they tend to have high weight-to-CdA for basically the same reason that they have high power-to-CdA), but if you're willing/able to get more aero in a good tuck, or if you're on a technical descent and you're a more skilled descender, then you might gain an advantage. But even tiny climbers who get blown around easily by the wind can usually keep up on descents just fine, if they're with a group, because drafting is enormously effective on descents. It's very difficult to drop someone who's on your wheel on a downhill, outside of weird cases like if you're on a low recumbent and they're on a road bike.

No in a way that's very useful. On flat ground with all other things being equal, a heavier bike will decelerate slower when power stops getting applied, but it also accelerates slower, and the same amount of power is required to maintain a given speed.

Because, for some, it's not a hobby. If you approach it that way, as a hobby, who is to argue with that and of course sometimes I treat it that way as well. But for some of us (like me) it's just the way I get to work. Mostly every day, twice a day, since 2010 so it's not, to many of us, a question of maybe just drive.

As far as that saving time goes, it will take me 15 minutes to drive to work on a good day without traffic but more typically 20. Driving home, typically 30 minutes (left turns across the highway with 3 extra lights, vs right turns not and not crossing). Riding, 22 to 30 minutes either way depending on riding fast vs trudging along. Therefore, my not futzing around for five or ten minutes at the endpoints saves me MORE time than driving would save over what I do now. And it's not about punching a clock - it's my time, and even small efficiencies add up to big ones. That perspective makes sense, doesn't it?

Ah but you asked, What's the rush, which may be why your case got jumped.

The difference is in the distance. And how hard it is, but mainly distance. I have a short commute, basically 7 miles plus some at the ends, which means that there are only 5 or 6 minutes difference between time trialing and smelling the roses. Do I care about going 6 minutes faster and taking a shower, vs slower and changing a shirt? Of course not - if I go fast it's because I want to, slow if I feel like it, no other reasons than that. I actually dialed that distance in (previously it was 11 miles) specifically because some days, nasty weather for instance, I don't care about the ride and just want to get there in a reasonable time.

Double that, or triple it, and 15 or 20 minutes variability each way is becoming significant and I think the perspective will always change. I'd be all about speed, every ride, and probably pick the days. But I'd still try to max efficiency packing up and at the bike rack

I think a lot of us have figured out how to minimize the time we waste commuting also involves minimizing the stuff we take with us. Less time packing and unpacking, less weight to slow us down, and less time/hassle getting in and out of the buildings leads to faster more enjoyable commutes for me, and I know I'm not the only one in that situation.

[MENTION=252435]RubeRad[/MENTION] isn't the only one who perceives your posts that way.

I'm not disagreeing with you, but the thread has nothing to do with this.

I will say it is much easier to save two minutes having packed your gear before quitting time than it is to try to shave two minutes on the road.

I am not trolling, but I also not going to go digging up old posts. I am simply agreeing with another poster's assessment of the tone of your post(s). But whatever.

MOD NOTE TO ALL: Please stay on topic, and avoid personal disagreements.

Tom - I think you misspoke a bit there, and probably meant that to maintain speed you have to have to have some continued input of force.

Back to the original topic, I have a 15 mile commute. Starts out with a nice downhill where I get to about 45 mph that enables me to hammer across a half mile flat maintaining 30 easily if I want. The next few miles are through town with stop signs and lights, traffic, and a few small hills. Then a stretch of about 9 miles (with one light) that are nearly flat but with seven spots with grades where my speed will drop between 12 and 17 mph depending on how I feel that day. On the flat sections between those I'll ramp back up to 20-24 mph (or a bit higher coming down some grades) until I get to our campus where I have a mile gradual climb to the door.

After all that my average speed is usually 17.5 to 18 mph. If I have a day where I feel sluggish it may be slightly lower but still over 17, and if I have a day where I feel great and hit it a bit harder I generally will be at the 18 mark. The defining points aren't my top speed, or the speed I go down the hill leaving home, but what I do up those small grades that might be 1/4 to 3/4 mile long, AND what happens as I go through town.

If I simply looked at my speed on the flats I'd think I'm a 20+ mph commuter for sure. Or I could set my computer to ignore speeds below 10 mph

OK I'm learning about physics. Thanks, folks. My lesson is that heavier object will decelerate more slowly than a lighter object. That makes sense, and I can feel it intuitively. Still, I may be wrong, but I believe it's easier to maintain a faster pace when the bike is light. Am I right or wrong?

[MENTION=152773]noglider[/MENTION] you weren't entirely wrong because there are dead spots and peak pushes during the pedal stroke which does result in a cycle of small accelerations and decelerations. But the extra momentum of greater mass (against an impeding force) cancels the extra effort needed to accelerate it, so it comes out even. In the simple model. The impeding force isn't constant though (with air resistance for example), so the thrusting power stroke needs more power than a smooth one. These are small quantities however.

I think that your opinion that "it's easier maintain a faster pace" on a lighter bike, which I'm pretty sure most people will generally agree with you on that, comes from cumulative fatigue from all the accelerations. And from controlling the bike, and all the up grades of course.

wph probably knows way more about physics than I do but - I believe a heavier object traveling at the same speed as a lighter object has greater momentum. Assuming there were no difference in drag or wind resistance (probably a bad assumption), the heavier object would decelerate more slowly than the lighter object.

wph - agree or no? I know there is a lot more complexity that could be brought into it, but that's as much as I remember from high school physics long ago.

If bike weight doesn't matter, there must be some reason racing is always trying to make bikes lighter. Or at least there was until the minimum weight rule came about. I'm still not convinced weight doesn't matter even though I can't bring enough knowledge of physics to prove it.

Bike weight matters, just not to the degree that some folks would like to believe that it does. It matters when accelerating from a stop, and climbing up a hill. On flat ground, I'm not gonna say it doesn't matter at all, but... it doesn't really matter at all. Up there past 22mph or so, aerodynamic drag is so much more significant than weight as to make weight insignificant. And going downhill, more weight is always better. Mostly.

Hang on. How can more weight help going downhill? I don't get it.

I wonder if there is a factor where a person's physique makes a difference. I'm not a very powerful rider, so is it possible that my bike weight makes a bigger difference than it does to more powerful riders? I average 13 mph on my commute. On days when I take my racing bike, my average goes up 2 mph.

I agree, assuming both are the same size and shape but different weights. Off hand, and I could be mis-remembering from applying the equations, but I keep it simple:
Acceleration is (Weight - Drag)/mass, from the force equation. weight is Mass * g.

So a = g - Drag/Mass. That's simple enough for me, the greater the weight the faster you accelerate (down). When the velocity is high enough that weight equals drag, you have terminal velocity, which is also higher for the heavier one.

Check.

I just want to reiterate I am (fairly recently) noticing and working on my own verbal tone, and saw some of my own problems and thought I'd drop a 'helpful' note.

Alan if you actually want to hear what I'm thinking about tone, PM me and I'll be glad to chat. (That sentence was very difficult to write without sounding antagonistic)

Unless you're riding in the vacuum of space, I'm gonna go with gravity. Math isn't my forte by any means, but

Fnet = mg − fd(v)

where the total force accelerating the object downwards is the difference between the force of gravity and the drag force; in short, heavier things fall faster. The weight is (usually) enough to overcome the relative differential in drag-- that is, a lighter rider on a lighter bike produces more drag relative to the force gravity is exerting on them. In the real world, my rider + bike weight is about 50lbs greater than my wife's; unless she drafts me down a hill, I will just pull away from her the entire way down.