Road Cycling - Does it matter? Climbing questions

ok, my friend and i were talking tonight about climbing a hill. he told me that there's not much difference to climb a hill with a 23lb bike vs. a 16-17lb bike. he said the 23lbs bike may be slower to climb but u can still get up there pretty quick.

now i know chainrings plays a factor, but it just seems that lighter bikes are much more easier to climb a hill compared to the 23lbs bike, if the chainrings and rear cogs are using the same teething. am i right to think that way or is my friend right that it doesn't matter about the weight of the bike?

Ruirui,

Go to the Analytic Cycling website here (http://www.analyticcycling.com/ForcesLessWeight_Page.html). You put in different numbers to see the effect of weight will be on climbing time.

thanks SteveE! good site!!! but i'm not 100% sure on how to actually read it. can you explain this one for me? here are the data i inputed: 78.42kg (173lbs = 150lbs + 23lbs bike) vs. 76.20kg (168lbs = 150lbs + 18lbs bike).

Benefit From Less Weight
This Much Less Weight 2.26 kg
Over This Distance 2000 meters
On Hill of Slope 0.03 Decimal
Faster by 4.06 s
Ahead by 29.58 m
Frontal Area 0.5 m^2
Coefficient Wind Drag 0.5 Dimensionless
Air Density 1.226 kg/m^3
Weight Rider & Bike 78.47 kg
Rolling Coefficient 0.004 Dimensionless
Power 250 watts

thanks SteveE! good site!!! but i'm not 100% sure on how to actually read it. can you explain this one for me? here are the data i inputed: 78.42kg (173lbs = 150lbs + 23lbs bike) vs. 76.20kg (168lbs = 150lbs + 18lbs bike).

Benefit From Less Weight
This Much Less Weight 2.26 kg
Over This Distance 2000 meters
On Hill of Slope 0.03 Decimal
Faster by 4.06 s
Ahead by 29.58 m
Frontal Area 0.5 m^2
Coefficient Wind Drag 0.5 Dimensionless
Air Density 1.226 kg/m^3
Weight Rider & Bike 78.47 kg
Rolling Coefficient 0.004 Dimensionless
Power 250 watts

He's basically saying that if you raced your identical twin up a 2 kilometer 3% grade that whoever got the 18 pound bike would win by 4.06 seconds, or 29.58 meters. The "identical twin" part is because the calculations make the assumption that both riders are putting out 250 watts.

The graph at the bottom is showing your time difference as either the grade (i.e., the axis marked "slope %") increases or the weight drops. Note that the weight difference produces a linear change in time; that is, a 4kg drop in weight produces double the benefits of a 2kg drop in weight. The grade axis doesn't behave that way. Meaning that a weight drop that doesn't correlate to much benefit on a 3% grade (i.e., not very steep at all) will produce a lot of benefit on say an 18% grade wall -- you save a lot more then (18 / 3) * 4.06 seconds.

Hope that helps

Faster by 4.06 s - this is how many seconds faster the light bike is when the light bike crosses the "finish line"

Ahead by 29.58 m - this is how far back the heavy bike is when the light one crosses the "finish line" in meters

Over this distance 2000 meters - is the length of the test, both bikes are even at the start.

This much less weight - the difference in weight between the two bikes

Power 250 watts - your legs' power 250w is a solid sustained effort by a good enthusiast rider, 600w is Ullrich or Armstrong's max sustained effort. Sustained meaning several minutes.

slope of the hill - is the slope, rise/run, 0.03 = 3%

Air Density - this is how thin the air is from an aerodynamic perspective

Frontal Area -area of your silluet, veiwing you from the front on the bike

Coefficient Wind Drag- this is how slippery your shape is, without regard to size. 1.0 = a flat plate, 1.5 = parachute, 0.5 = you in tight cloths on a bike, 0.3 = waxed c5 corvette

Rolling Coefficient - rolling resistance with the effect of weight taken out of the picture

I'm sure a lot of us see 4.06 meters and 29+ seconds over a 3%, 2K course as fairly substantial, but why do I think that your friend is going to see this more as substantiation for his opinion?

55/Rad

Sure a lighter bike is better, I'll agree with that. But it has more to do with what is in the legs and heart - 250watts or is one able to put out more than the other.

Sure, I'm a 250lbs fat guy on a 21lb bike and suck at climbing hills but I bet you if that 2,000 meters was all down hill, I'd get there first. :D

Yep, weight and gravity. The bigger you are and heavier the bike, the slower you are up the hill. But going down the otherside - watch out below! Flying low and fast! :)

Would rotational mass of the wheels skew the result as well? Compare for example, two bikes that weigh the exact same. The first bike has a heavy frame/parts and light wheels while the second bike has heavy wheels and a light frame/parts. I would bet the light wheels win.

-mark

he said the 23lbs bike may be slower to climb but u can still get up there pretty quick.

...am i right to think that way or is my friend right that it doesn't matter about the weight of the bike?

Where you're wrong is thinking your friend said the bike weight doesn't matter. You can't really argue with may be slower to climb but u can still get up there pretty quick.

Would rotational mass of the wheels skew the result as well?

I don't think it's significant. With climbing, unless you're powering out of switchbacks, your speed is relatively constant.

Rotational mass is only really important for speed changes. In fact if anything, I'd say for climbing a slightly heavier wheel might help if there are little undulations in the road. Once that wheel is spinning it'll have more monentum to carry it over the little bumps. I'm just pulling that out of my ass though... 10 times out of 10 I'd pick the lighter wheels :D

Rotational mass is only really important for speed changes. In fact if anything, I'd say for climbing a slightly heavier wheel might help if there are little undulations in the road. Once that wheel is spinning it'll have more monentum to carry it over the little bumps. I'm just pulling that out of my ass though... 10 times out of 10 I'd pick the lighter wheels :D
Saved that post at the last second - good pull!

55/Rad

Would rotational mass of the wheels skew the result as well? Compare for example, two bikes that weigh the exact same. The first bike has a heavy frame/parts and light wheels while the second bike has heavy wheels and a light frame/parts. I would bet the light wheels win.

-mark


You're right. That first site is an example of bad science and interpreting a single conclusion from too many variables. This is too common. It's like saying butane lighters cause lung cancer because people who buy more butane lighters get lung cancer.

For example, two objects over the same height and distance can take differing energy to get there in the same time if the mass is centralized in one object over another, this is especially true for rotating mass and the central design parameter for racing cars and racing bikes. Very important for acceleration.

Take two equal riders, same weight of bikes, but one bike has rear suspension, hard tail will beat out every time uphill because of energy transfer efficiency. Same is true for lighter wheels if starting from a stop.

I think what your friend means is that with weight and bike costs, there are greatly diminishing returns, it often does not make sense to simply make a lighter bike if that bike cannot transfer energy as a heavier bike would. Spending an extra $200 for a carbon fiber part for a weight savings of 0.2 grams is pointless, unless you like the look of the cool part and that will get you to ride more. That's still cool.

I think that a bike working well (comfort, handling, stopping, durability, energy transfer) is more important than just weight. Broken bikes don't go very fast.

If bike weight is the issue in question, 3% grade is not a very good parameter. A cyclist in reasonable shape will be fighting the wind as much as gravity. I'd say bike weight becomes a much more significant issue around 5+% grades.

Wheel weight at the rim is significant only in acceleration, for small ranges of variation in wheel weight (say 500-1000grams). On the level once upto speed the energy
to keep that speed will be independent of wheel weight; with constant power input
the bike with lighter wheels will accelerate faster and thus be farther away from the
start than the bike with heavier wheels. On hills though, going up you are CONSTANTLY accelerating, if you don't accelerate you slow down or stop, even
go backwards. To maintain the same speed you have to accelerate to counter
gravity and heavier wheels will be an additional decrement in speed that is not seen
on the flat. Air resistance is an independent variable directly proportional to the
bicyles speed relative to the air. Steve

On hills though, going up you are CONSTANTLY accelerating, if you don't accelerate you slow down or stop, even go backwards.

Acceleration = change in velocity/time. If you’re riding a steady speed up a steady incline, you are not accelerating since you are not changing speed or direction. You are fighting the force of gravity that is trying to accelerate you downward, though. Rotational mass on the wheels won’t have much more effect than other mass on the bike or rider.

OTOH, when you stand, wheel weight is very noticeable due to the change in gyroscopic effect from the wheels; lighter wheels will allow the bike to rock back & forth much easier. This makes the bike “feel” much lighter. I’m not sure if this translates into speed or not.

-murray

If bike weight is the issue in question, 3% grade is not a very good parameter. A cyclist in reasonable shape will be fighting the wind as much as gravity. I'd say bike weight becomes a much more significant issue around 5+% grades.

I was thinking the same thing...bike weight is a serious issue at over 10% grade...of course, you can't start griping about the bike if you weigh a gazillion pounds...but if you don't, then having a lighter bike DOES make a difference

How hard is it to loose a few pounds as a cyclist? come on now.

I went from 147lbs to 130lbs on my 5'5" body this spring. Yeah, I could probably lose a few more pounds, but I could also drop a few lbs off my bike. Once the weight is off the bike, it doesn't come back over the winter or after a vacation; it stays off for good! You don't feel hungry trying to keep your bike at a lower weight.

I see no problem with riding a lighter bike so long as you can afford it.

-murray

Rotational weight loss to me is a great bang for the buck. Good light wheels are expensive but it directly effects the efficiency of the ridder's watts. Other than rotational, I feel that the frame/component weight loss is a waste and the real issue should be the cyclist. How hard is it to loose a few pounds as a cyclist? come on now. Light and strong gets to the top first every time.

I went from 147lbs to 130lbs on my 5'5" body this spring. Yeah, I could probably lose a few more pounds, but I could also drop a few lbs off my bike. Once the weight is off the bike, it doesn't come back over the winter or after a vacation; it stays off for good! You don't feel hungry trying to keep your bike at a lower weight.

I see no problem with riding a lighter bike so long as you can afford it.

-murray
Hey Murray, you sound to be in good shape! But I try to remind myself that when my body wieght goes down my heart and lungs do more for me and dont work as hard. right? dropping just the bike weight dosen't do that, it's not attached to my veins.

Hey Murray, you sound to be in good shape!

Thanks! I was never “overweight”, but it’s kind of shocking when none of your shorts fit you in the spring :eek:


But I try to remind myself that when my body wieght goes down my heart and lungs do more for me and dont work as hard. right? dropping just the bike weight dosen't do that, it's not attached to my veins.

Yeah, you’re probably right. I just hear the argument from non bikers that it’s silly to spend money to drop weight on the bike when your XXlbs overweight.

Bottom line, a new, lighter bike just makes you feel better/ride faster just like a new pair of sneakers used to make me run faster and jump higher :)

-murray

Thanks! I was never “overweight”, but it’s kind of shocking when none of your shorts fit you in the spring :eek:



Yeah, you’re probably right. I just hear the argument from non bikers that it’s silly to spend money to drop weight on the bike when your XXlbs overweight.

Bottom line, a new, lighter bike just makes you feel better/ride faster just like a new pair of sneakers used to make me run faster and jump higher :)

-murray

murray.. ur lucky.. i use to be 110lbs from age 18-22 and couldn't gain any weight.. then all of the sudden.. a computer desk job lands me at 150lbs with a pot belly. :( worse part is... all that weight is in the belly! i guess that's what happens when you eat only a 30 min lunch and have a stressful work. time to do the situps!!!

Murray: just because the speed going up hill is constant does not mean the acceleration is zero. Consider going down hill, if the hill continues the speed will
gradually increase until air resistance overcomes acceleration and speed levels out.
The inverse is also true, going up hill you must accelerate to overcome gravitional
pull. If the acceleration is zero you are going to stop and fall over or roll backwards.
If your acceleration exceeds a certain level you will increase your speed up the hill,
if your accleration equals the component of gravity in the direction you are moving
then you will maintain whatever speed you have. Steve

Murray: just because the speed going up hill is constant does not mean the acceleration is zero.

From http://www.m-w.com/cgi-bin/dictionary?book=Dictionary&va=acceleration

Main Entry: ac•cel•er•a•tion
Pronunciation: ik-"se-l&-'rA-sh&n, (")ak-
Function: noun
1 : the act or process of accelerating : the state of being accelerated
2 : the rate of change of velocity with respect to time; broadly : change of velocity

What component of velocity (speed or direction) is changing when you go uphill at a constant speed?!?



Consider going down hill, if the hill continues the speed will gradually increase until air resistance overcomes acceleration and speed levels out.

Yes, if you drop an object, it’s speed increases (accelerates) until it reaches terminal velocity. At that point, it is no longer accelerating since its velocity is constant.



The inverse is also true, going up hill you must accelerate to overcome gravitational pull. If the acceleration is zero you are going to stop and fall over or roll backwards.

This would be negative acceleration. If your acceleration is zero, your velocity (speed) won’t change.



If your acceleration exceeds a certain level you will increase your speed up the hill, if your acceleration equals the component of gravity in the direction you are moving then you will maintain whatever speed you have. Steve

If you are maintaining your speed, you are merely counteracting one force (due to gravity) with another (pedaling force).


Back to the original point, if your speed is constant, your wheels are rotating at a constant RPM. Neglecting air and bearing resistance, it takes no additional effort to maintain the rotation of the wheels regardless of how much the wheels weigh. In fact, the heavier wheel will maintain its rotation longer when subjected to similar bearing loads and air resistance. But, as F!_Fan stated, I’ll take the lighter wheels every time!

-murray

Murray: gravity is a constant downward acceleration to any vehicle going up an
inclined plane, the % of the gravitational acceleration is the cosine of the angle
of the the hill times the gravitational acceleration (9.8m/sec*sec or 32ft/sec*sec).
If your effort in climbing produces an acceleration less than this, you slow down,
if equal your speed is constant, if greater then your velocity up the hill will increase.
On the flat you are moving perpendicular to the gravitational acceleration and the cosine of 90d is 0, hence no contribution. Going downhill gravity accelerates the
rider depending on the length and angle of the hill. Gravity is constant and unremitting acceleration which the bicyclist overcomes every time he goes up a
a hill and glories in going down. Steve

sch-

Please explain to me what component of velocity is changing when you are going uphill at a constant speed in a straight line?!?

There is no acceleration unless there is change in velocity or you have a different definition of acceleration than I've provided. Please provide a reference for your false assumptions.



Murray: gravity is a constant downward acceleration ...

You are confusing acceleration with force. Gravity generates a force between two objects. In the absence of an opposing force (i.e., pedaling), the objects will accelerate towards each other. Since the Earth outweighs us by 10^23 times, we move more than the Earth does.

http://www.cripplefight.com/smileys/deadhorse.gif

-murray

Please listen to Murrays for he is wise and this need not go on forever. :rolleyes: The mighty Buckey Badger has determined the equation for acceleration centuries ago and gravity is not a downward acceleration! It is a force towards the center of mass of an object and all objects generate gravity. ;)

Getting back to the poster's original question, for a typical rider I think the biggest advantage to a light bike is how it feels. You don't have to race a BMW to appreciate the fact that it is lively, handles well, accelerates quickly. Same thing with bikes. A light bike with the right geometry has lively handling that just makes you want to attack hills and sail into turns, IMO.

I have to jump in here. Murray, sch is right on. Gravity is downward acceleration. That's why when you drop something off a building it continues to go faster and faster. Likewise, it's the reason why an airplane can't just fly into space, you need to achieve an escape velocity by accelerating.

Anytime you are moving up at the same speed or for that matter, around a turn at the same speed, you are accelerating. I know you think of accelerating as moving faster and faster which in fact, you are, as it relates to the downward force of gravity being applied to you.

Here's some articles that explain more about the acceleration of gravity:
http://www.glenbrook.k12.il.us/gbssci/phys/Class/1DKin/U1L5b.html
http://www.sportsci.org/encyc/cyclingupdown/cyclingupdown.html

So I think I understand why there is a disconnect here. In fact, when riding uphill, you are not accelerating in relation to the ground. However, you are accelerating in relation to the forces acting on you, if that makes sense. Technically, riding uphill is a constant acceleration.

Anytime you are moving up at the same speed or for that matter, around a turn at the same speed, you are accelerating. I know you think of accelerating as moving faster and faster which in fact, you are, as it relates to the downward force of gravity being applied to you.

How can you be going faster and faster, but your speed is not changing?!?

By your logic, a bike going uphill that’s not accelerating will slow down and eventually reverse direction? How could you not be accelerating if your speed is changing?

Try reading the links you provided. From http://www.glenbrook.k12.il.us/gbssci/phys/Class/1DKin/U1L1e.html


Acceleration is a vector quantity which is defined as "the rate at which an object changes its velocity." An object is accelerating if it is changing its velocity.
...
If an object is not changing its velocity, then the object is not accelerating.

So please enlighten me as to what component of velocity is changing when you’re traveling uphill at a constant speed in a straight line?!?

Velocity is a vector composed of speed and direction. You are right that going around a corner is accelerating (towards the center of the curve) because you are changing direction.

From: http://www.sportsci.org/encyc/cyclingupdown/cyclingupdown.html


Going uphill adds gravity to the forces that must be overcome

Reading this article, the only mention of acceleration when going uphill is using g, the gravitational acceleration constant (the rate at which an object accelerates when dropped) for calculating the forces on the rider.



Please listen to Murrays for he is wise

Thanks! It’s good to know I didn’t spend 5 years in engineering school for nothing :)

-murray

Sorry that is just bunk. It is no different than to say that riding on level ground at constant speed you are always accelerating because you are overcoming the forces exerted on you by rolling and air/wind resistance and the force of gravity which is still acting on you but at a 90 degree angle. You are required to add energy to maintain momentum in all of these cases to achieve constant speed, but as long as you are at constant speed no matter it gravity, friction, or nuclear forces that you overcoming you are not accelerating.
The Gravitational Acceleration Constant is only good in an ideal frictionless system, in real life the countering forces of air friction increase proportionally to speed until the GAC is overcome and acceleration ceases and you fall at a constant velocity with a certain momentum. This is physics 101.

This is physics 101.

Well, we have Fuzzy Logic, Fuzzy Math. Now we have Fuzzy Fysics :lol: :lol:

-murray

I stand humbly corrected. Upon further research and lengthy email exchange with buddies, I think I was just wrong. As long as you're not changing direction or increasing velocity, there is no acceleration.

It does take more force to counteract the force of gravity and this increased use of force is necessary to propel one up a hill but as long as this uphill tromp goes at a constant rate in the same direction, there's no acceleration.

I do stand by my statement however, that going at the same speed around a turn or in a circle requires acceleration.

Cheers Murray!

EDIT: my deepest apologies for the thread hijack

It does take more force to counteract the force of gravity and this increased use of force is necessary to propel one...
If that's true, then there is acceleration since Force = Mass * Accel, correct?

It does take more force to counteract the force of gravity and this increased use of force is necessary to propel one up a hill but as long as this uphill tromp goes at a constant rate in the same direction, there's no acceleration.


The increased work required to climb is called potential energy. Basically you need to put energy into an object to raise it against gravity. You get that energy back as kinetic energy when coming back down. If you shoot a bullet in the air at 1500 ft/s, it'll come back at the same velocity (well a little less due to air resistance)... that's why every now and then you see stories about someone being killed by a bullet shot into the air.



I do stand by my statement however, that going at the same speed around a turn or in a circle requires acceleration.


Oh man... you were doing so good until that last sentence :D It's the same thing as riding up a hill except you're balancing friction, angular velocity and centripetal acceleration. What is changing is the direction of the velocity vector but its magnitude is still constant.

If that's true, then there is acceleration since Force = Mass * Accel, correct?

Force is the wrong term here... you want Energy or in particular... Gravitational Potential Energy

Ep = mass * gravity * distance

Opie, I did a lot of research on that particular equation and I don't think it applies here (to be fair though, I'm not 100% certain). In that equation, as it relates to gravity, acceleration is 9.8 m/s/s (the acceleration of gravity), mass is the mass of the earth and force is the pull of the earth, measured in newtons.

Oh man... you were doing so good until that last sentence :D It's the same thing as riding up a hill except you're balancing friction, angular velocity and centripetal acceleration. What is changing is the direction of the velocity vector but its magnitude is still constant.

The magnitude does stay the same, or speed, as I stated. But since you're changing direction, it takes constant input of force to do so. You said it yourself, it's called centripetal acceleration, but acceleration nonetheless.

Oh man, you guys are going way over the top..:)
I was wondering about weight and climbing, as I was losing over 100lb in the past 3 years..
I wanted to know how much better I would do if I had lost 20 more pounds, all other things stay equal.

So I made me a spreadsheet (excel) where I can plug in the route (length and vertical climb) and then compare the amount of work (in terms of "nn pounds, pushed up one foot, in one second")2 rider of different weight would do in order to climb that hill (you can play with weight and target time, to equalize the amount of work)...

Have fun.. (click here to download the spreadsheet (www.litman.com/bikes/grade%20and%20work%20done%20calculations.xls))

as a bonus, this spreadsheet gives you also grade and angle of climb.. Remember, I have done this just for fun, and as a motivation (weight loss) tool, so please do go all out flaming the scientific merit of this thing..

The magnitude does stay the same, or speed, as I stated. But since you're changing direction, it takes constant input of force to do so. You said it yourself, it's called centripetal acceleration, but acceleration nonetheless.

You are correct. This is a change in the vector (direction) part of velocity so it is indeed acceleration

FWIW it takes a bigger man to admit being wrong than continuing a false argument :)



If that's true, then there is acceleration since Force = Mass * Accel, correct?

You can push on a wall and it won't move; there is definitely force, but no acceleration. The other thing to consider here is for every action, there is an equal and opposite reaction. IOW, for every force, there is an equal opposing force. If you push on an object and it moves, that acceleration is the opposing force to your push.

Pedaling up a hill is a force that balances the force created by gravity and your climbing. If there is an imbalance in forces, you will either speed up or slow down according to F=MxA.

Make sense?

-murray

You are correct. This is a change in the vector (direction) part of velocity so it is indeed acceleration

FWIW it takes a bigger man to admit being wrong than continuing a false argument :)




You can push on a wall and it won't move; there is definitely force, but no acceleration. The other thing to consider here is for every action, there is an equal and opposite reaction. IOW, for every force, there is an equal opposing force. If you push on an object and it moves, that acceleration is the opposing force to your push.

Pedaling up a hill is a force that balances the force created by gravity and your climbing. If there is an imbalance in forces, you will either speed up or slow down according to F=MxA.

Make sense?

-murray

Murray.. you the man! Would you happen to be a physic's teacher or something? hehe ;) cuz that sounded like my AP Physics teacher in H.S. talking. so you can see.. i'm the type that didn't pay too much attention and fell asleep most of the time.. hehe :D

rui

Murray.. you the man! Would you happen to be a physic's teacher or something?

No, I'm just an engineer, though I did get into an argument with my HS physics over a test question that he was wrong on http://www.cripplefight.com/smileys/thwap.gif

Thanks for the compliments :D

-murray

Taking the weight factor into account while climbing a hill is critical to performance otherwise pro riders wouldn't need to bother riding 15 lb bikes with ultra light wheels when in the mountains. You can put my theory to the test. Try climbing the longest, steepest hill you can find with and without 6 lbs of extra weight strapped to your bike. I think you'd agree it's much easier to ascent without the extra load.
Some people may point out you can just lose 6 lbs off your belly and all will be rosy in the garden, there's no need to spend unecessary money on a lighter bike i hear them cry ! They'd be right of course up to a point. On the other hand this won't be true for a lot of riders who are already at their ideal weight, are already pretty fit and find it hard to lose much more. Therefore, to improve performance, they need to lose grams in other areas. From their rims and tyres would be the best, most cost effective place to lose it from.