why cant I go faster

davehun

Hi all.
I have been riding my road bike for a few years. The bike is a felt z75.
I regularly go out with a friend and although I can go up hills a lot faster than him and cycle along the flats faster.
He is always a lot faster than me descending. I can be on the drops peddling as hard as I can only to see him free wheel off into the distance with his hands on the tops on a cyclo cross with big fat tyres !
What am I doing wrong ?
btw he is ~ 80kg and i am ~ 60kg
Thanks for any tips
and no I dont use the brakes!

Bill-87

The fact he's heavier would have an effect, it's like dropping a feather and a brick off a roof, what's going to hit the ground first?

fat lad in lycra

because he's heavier......im well over 19st and cant climb for toffee, but once im over the top you should see me go scary.

ShutUpLegs

What wheels/ hubs does he have?

damo2576

Bill-87 wrote:

The fact he's heavier would have an effect, it's like dropping a feather and a brick off a roof, what's going to hit the ground first?

Never studied Physics?!

mattward1979

This whole Feather cannonball thing doesnt hold true unless we all cycle in a vacuum...


"Downhill

During descents, the negative slope of the hill in the power equation reflects the addition of gravitational potential energy to the power generated by the cyclist. In a freewheel (passive) descent, the cyclist's speed will be determined by the balance of the air resistance force and the gravitational force. As the cyclist accelerates, sv2 increases. Once kaAsv2 (plus the negligible power term associated with rolling resistance) increases to match giMs, the cyclist will reach terminal velocity. Any further increase in speed must be achieved by adding energy through pedaling. However, on steep hills, terminal velocities may reach 70 km·hr-1. At such high associated values of sv2, even the application of VO2max would result in only a minimal increase in speed.

Terminal velocity can be solved for in the cycling equation above by setting power at 0. If one assumes the rolling resistance term is also 0, and that there is no wind blowing (v = s), then the equation becomes:

kaAs3 = -giMs
or s = (-giM/kaA)1/2

Thus, the terminal velocity is roughly proportional to the square root of the ratio of M/A. Scaling reveals that larger cyclists have a greater ratio of mass to frontal area. They therefore descend hills faster as a consequence of purely physical, not physiological, laws. Since the larger cyclist has a greater mass, gravity acts on him or her with a greater force than it does on a smaller cyclist. (Note: A common misconception is to note the equal acceleration of two different sized objects in free fall in a vacuum, and assume that the force of gravity on both is equal. The force on the more massive object is greater, being exactly proportional to mass, which is why the more massive object is accelerated at the same rate as the less massive one.) While the larger cyclist also has a greater absolute frontal area than the smaller cyclist, the difference is not as great as that for their masses. Thus, the larger cyclist will attain a greater s3 before a balance of forces results in terminal velocity.

With lighter cyclists climbing hills faster due to their greater relative VO2max, and heavier cyclists descending faster due to their greater M/A ratio, one might assume that equal performances would occur in races involving equal up and down segments. However, ascents take longer than descents, so a speed advantage to small cyclists on the acsents produces a greater time advantage than large cyclists obtain on the descents. For this reason, smaller cyclists are generally superior competitors on hilly road races."

mattward1979

^^^^^^^^^^^^^^^^^^^

This is why he is faster.

SCR Pedro

davehun wrote:

What am I doing wrong ?

You're not launching a massive attack before the summit of the climb in order to pull out a gap. By the time you're on the descent, your mate won't even be at the summit.

Job's a good 'un!

TyeBag

Don't worry you will catch him at the next hill 

legin

matward thats exactly what i was about to say lol

P_Tucker

damo2576 wrote:

Bill-87 wrote:

The fact he's heavier would have an effect, it's like dropping a feather and a brick off a roof, what's going to hit the ground first?

Never studied Physics?!

embarrasing

ratsbeyfus

mattward1979 wrote:

This whole Feather cannonball thing doesnt hold true unless we all cycle in a vacuum...


"Downhill

During descents, the negative slope of the hill in the power equation reflects the addition of gravitational potential energy to the power generated by the cyclist. In a freewheel (passive) descent, the cyclist's speed will be determined by the balance of the air resistance force and the gravitational force. As the cyclist accelerates, sv2 increases. Once kaAsv2 (plus the negligible power term associated with rolling resistance) increases to match giMs, the cyclist will reach terminal velocity. Any further increase in speed must be achieved by adding energy through pedaling. However, on steep hills, terminal velocities may reach 70 km·hr-1. At such high associated values of sv2, even the application of VO2max would result in only a minimal increase in speed.

Terminal velocity can be solved for in the cycling equation above by setting power at 0. If one assumes the rolling resistance term is also 0, and that there is no wind blowing (v = s), then the equation becomes:

kaAs3 = -giMs
or s = (-giM/kaA)1/2

Thus, the terminal velocity is roughly proportional to the square root of the ratio of M/A. Scaling reveals that larger cyclists have a greater ratio of mass to frontal area. They therefore descend hills faster as a consequence of purely physical, not physiological, laws. Since the larger cyclist has a greater mass, gravity acts on him or her with a greater force than it does on a smaller cyclist. (Note: A common misconception is to note the equal acceleration of two different sized objects in free fall in a vacuum, and assume that the force of gravity on both is equal. The force on the more massive object is greater, being exactly proportional to mass, which is why the more massive object is accelerated at the same rate as the less massive one.) While the larger cyclist also has a greater absolute frontal area than the smaller cyclist, the difference is not as great as that for their masses. Thus, the larger cyclist will attain a greater s3 before a balance of forces results in terminal velocity.

With lighter cyclists climbing hills faster due to their greater relative VO2max, and heavier cyclists descending faster due to their greater M/A ratio, one might assume that equal performances would occur in races involving equal up and down segments. However, ascents take longer than descents, so a speed advantage to small cyclists on the acsents produces a greater time advantage than large cyclists obtain on the descents. For this reason, smaller cyclists are generally superior competitors on hilly road races."

+ π to that

Cleat Eastwood

I think its more likely that the OP is too scared to let go of the brakes.

Ollieda

Just pick a route with long ascents - beast ahead of him on the way up so you have a headstart on the descent (yes this goes against etiquite of waiting at the top of hills, but sometime you just have to feel like your winning the whole time!)

tom22

the fact that he is heavier will have no effect at all, because:

acceleration is inversely proportional to mass
i.e. as mass goes up; acceleration will go down

people talk about the feather and brick, but that is only because the feather is subject to greater air resistance.

air resistance and resistance in the bike (tyres, BB, hubs, etc.) will be the answer,
as well as he might have sprinted from behind then free-wheeled?!

mattward1979

The question revolved more around why his friend was faster on descents, and the physics explained in the previous post illuminates this perfectly...

If the lighter rider is also being left behind on ascents where he has a natural advantage, again highlighted by the physics, then he is just a "worse" cyclist than the heavier rider..

Nothing much else to it really!!

Im 16.5 stone... But I suck compared to pro cyclists, and I would never expect raw talent, training and pure balls out descending guts to be overshadowed by my gravitational advantage!

oldwelshman

mattward1979 wrote:

This whole Feather cannonball thing doesnt hold true unless we all cycle in a vacuum...


"Downhill

During descents, the negative slope of the hill in the power equation reflects the addition of gravitational potential energy to the power generated by the cyclist. In a freewheel (passive) descent, the cyclist's speed will be determined by the balance of the air resistance force and the gravitational force. As the cyclist accelerates, sv2 increases. Once kaAsv2 (plus the negligible power term associated with rolling resistance) increases to match giMs, the cyclist will reach terminal velocity. Any further increase in speed must be achieved by adding energy through pedaling. However, on steep hills, terminal velocities may reach 70 km·hr-1. At such high associated values of sv2, even the application of VO2max would result in only a minimal increase in speed.

Terminal velocity can be solved for in the cycling equation above by setting power at 0. If one assumes the rolling resistance term is also 0, and that there is no wind blowing (v = s), then the equation becomes:

kaAs3 = -giMs
or s = (-giM/kaA)1/2

Thus, the terminal velocity is roughly proportional to the square root of the ratio of M/A. Scaling reveals that larger cyclists have a greater ratio of mass to frontal area. They therefore descend hills faster as a consequence of purely physical, not physiological, laws. Since the larger cyclist has a greater mass, gravity acts on him or her with a greater force than it does on a smaller cyclist. (Note: A common misconception is to note the equal acceleration of two different sized objects in free fall in a vacuum, and assume that the force of gravity on both is equal. The force on the more massive object is greater, being exactly proportional to mass, which is why the more massive object is accelerated at the same rate as the less massive one.) While the larger cyclist also has a greater absolute frontal area than the smaller cyclist, the difference is not as great as that for their masses. Thus, the larger cyclist will attain a greater s3 before a balance of forces results in terminal velocity.

With lighter cyclists climbing hills faster due to their greater relative VO2max, and heavier cyclists descending faster due to their greater M/A ratio, one might assume that equal performances would occur in races involving equal up and down segments. However, ascents take longer than descents, so a speed advantage to small cyclists on the acsents produces a greater time advantage than large cyclists obtain on the descents. For this reason, smaller cyclists are generally superior competitors on hilly road races."

Good answer but does not explain how many riders hit speeds in excess of the quoted terminal speed of 70km/hr with no additional power input, i.e free wheeling ?

MountainMonster

Leaving all physics aside, maybe he is just a better descender/ doesn't get scared of the corners and grip the brakes alot.

That would be my guess.

meanredspider

oldwelshman wrote:

the quoted terminal speed of 70km/hr

I couldn't find this.....

The terminal velocity of a falling human is something in excess of 100mph IIRC. Short of that, the angle of the slope, quality of tuck (frontal area and drag coeff), weight of the rider + bike, air density, road surface etc will determine the velocity. The whole question is just one of balance of forces.

jgsi

Everyone says it is all downhill after a certain age.... perssonally I feel more uphill bits than ever before, so worry less.

P_Tucker

oldwelshman wrote:

Good answer but does not explain how many riders hit speeds in excess of the quoted terminal speed of 70km/hr with no additional power input, i.e free wheeling ?

That 70kmh was an exmaple terminal velocity for a given steepness of hill. Find a long straight 20%er (if such a thing exists) and I suspect you'd hit well over 100. SOMEONE DO THE MATHS!

dodgerdog

Terminal velocity in freefall is circa 127mph.

The effect of mass in the OP though is overcoming the resistive force and the component of momentum. The forward momentum of the heavier rider is greater (mv.) The resistive component of air resistance, road resistance, bearing resistances and the inertia of the wheels is more easily overcome my the work gravity is doing on pulling said body(+bike) down the slope (ke=1/2mv^2)

Zachariah

Could someone plug the numbers into Matt's equation and work out the actual difference in speed for an 80kg rider vs a 60kg one (all other variables being equal)? I suspect the answer will be quite small.

davehun

I guess the drag will be related to a riders area which will also be related to their height as well as girth!
he is shorter than me as well as being heavier!
I was hoping that I might be able to go quicker down hill with new wheels (at the moment they are 32/26 spoked) and that there might be a few other tricks to reduce my drag oh well pies it is!
His wheels are fulcrum 7's
We are going to try swapping bikes to see what effect that has.

davehun

I guess the drag will be related to a riders area which will also be related to their height as well as girth!
he is shorter than me as well as being heavier!
I was hoping that I might be able to go quicker down hill with new wheels (at the moment they are 32/26 spoked) and that there might be a few other tricks to reduce my drag oh well pies it is!
His wheels are fulcrum 7's
We are going to try swapping bikes to see what effect that has.

secretsam

Tuck arms and legs in, pedals horizontal, chin on stem...and away you go :shock:

Zachariah

^^After pedalling like a loon to get to max speed, mind. Then copy this guy.

procyclist

Just sit 6 inches from his back wheel on descents - wheel slightly to the right so you've got some emergency escape space if he hits the anchors - tuck down low and sit in his slipstream - guaranteed he won't pull away

meanredspider

procyclist wrote:

Just sit 6 inches from his back wheel on descents - wheel slightly to the right so you've got some emergency escape space if he hits the anchors - tuck down low and sit in his slipstream - guaranteed he won't pull away

In fact, you'll be on the anchors to stop running into the back of him....

colsoop

If your much faster than him on hills and the flat then you must be slowing down to wait for him at points on your ride.

On the descending sections can't you just tuck in behind him and get a tow ?

meanredspider

Yup - I have this issue with the guy I occasionally ride with - he shoots up hill, I shoot down them. Instead of him waiting for me at the top, he should wait for me at the bottom of the following decent - else I have to go slower down the hill or wait for him at the bottom.