When does friction outweigh gravity?

[yoothgeye]

I don't know if my title question is correct, but let's get this ball rolling.

I ride mountain bikes with a friend who is about 50 pounds lighter than me. We ride very similar mountain bikes, tuned up about the same, both with knobby tires, same size, etc. On downhills, on the road or off, if we start side by side coasting, my bike always passes his and leaves him behind.

I have always thought that lighter was better, but I'm guessing my extra weight gets me going faster? I thought that too much weight (I am "overweight") would slow you down by causing more friction on the bearing and more rolling resistance.

At what point would my theory be correct, or am I just wrong?

 

[yoothgeye]

Now I'm back in school, the memories are coming back. The first one says we will get to the bottom of the hill at the same time, I guess the hills around here aren't long enough. haha

 

[KC so-cal]

try switching bikes to narrow it down ?

 

[outskirtscustoms]

Well if you weigh more than gravity would in turn have more pull on you therefore making you faster downhill. Up hill is another story. :lol:

 

[55ColumbiaBuilt]

I think it's like that demonstration that the astronaut did on the moon. In the vacuum of space, a sledgehammer and a feather fall at the same rate. Here on earth, if you were to drop, say, a bowling ball and a basketball from a tall building (assuming the two balls were the same diameter for accuracy) the bowling ball always hits first. Things like mass, density, inertia, weight, momentum, friction (with the atmosphere), and time all come into play. That doesn't answer the "why" of your question, because I'm not smart enough to explain it. But these are all the factors that would be applied to explain it. :roll:

 

[Anonymous]

Now my head hurts.

(heh)

 

[yoothgeye]

I don't like being big, but I do like coming in first.

 

[Anonymous]

Pump up the tires too much,check your wheel bearings and back off the brakes.

Throw caution in the wind and go for it!

 

[g-ratter]

With mountain biking i found mental attitude plays a big part. Some one who is worried about getting hurt might be a little more cautious thus slowing them down some.
Was out with a friend once when we hit a section with a lot of tree roots. I kept the speed up and flew over them but he got worried and slowed down and ended up going down.

 

[Anonymous]

Its only pain...It will go away.

Its not how fast you go,but how fast you stop that hurts.

 

[yoothgeye]

At some point this took a turn, this is not about one of us being timid or anything, I'm just saying, when we coast, I end up ahead. The end.

 

[gcrank1]

Inertia.
This is why the gravity vehicles have weight restrictions on vehicle and total with rider.
On pedal power you want light, to accelerate, and to keep it going, though good muscle on a heavier bike can overcome poor muscle on a lighter one.
On downhill 'coasting racing' you want as little friction as possible,low center of gravity, good areodynamics and max the weight. You may get up to speed just a little slower than your mate, but not necessarily, after you overtake your running mass will prevail and you will also go farther once you hit the flats.
Its physics, and, yes, winning IS fun!
Maybe check out info on 'gravitybikes' and 'soap box derby racing'.
Im building up a 'big guy's gravity bike'; it wont be allowed in sanctioned races, but we dont have any around here (that I know of) and Im too big for reworked 20" BMX bikes anyway. Im going to start a topic on it shortly.

 

[gowjobs]

It's more about your weight (gravity's affect on mass) overcoming the friction of your aerodynamic drag more than overcoming bearing drag, I'm betting. Lighter guy should roll off the line better, but will quickly be overtaken by the heavier guy. If the road flattens out, the heavier guy will carry more momentum for a time, but his increased aero/tire friction may cause the lighter guy to catch up after a given distance. Also, the tires of the heavier guy/bike are working harder in the corners, so on a twisty course, the lighter guy may see some small advantage.

 

[deorman]

Not if the little guy remembers the Italians in "Breaking Away" first. :mrgreen:

 

[yoothgeye]

Not if the little guy remembers the Italians in "Breaking Away" first. :mrgreen:

Frame pump in spokes!

 

[Anonymous]

Take a Diet Pill.

Hey Yoot,Only fuggin' with ya.