FTP W/kg - which weight are we talking about?

[J Wakefield]

I haven't read this whole thread but FTP/Wkg is the following:

 

FTP value i.e. 300W / body weight i.e. 60kg = 5w/kg

 

Use average power not NP.

 

On the last comment here the 50kg rider will go up faster and exert less overall.

[Fat Boab]

I haven't read this whole thread but FTP/Wkg is the following:

 

FTP value i.e. 300W / body weight i.e. 60kg = 5w/kg

 

Use average power not NP.

 

On the last comment here the 50kg rider will go up faster and exert less overall.

 

I'm intrigued - how so?

[bertusras]

From the point of view of 'how fast do you go up a hill' the bike weight does matter. If you have a 50kg rider and a 80kg rider, both on 7kg bikes and both putting out 3w/kg the 80kg rider will go up a hill faster.

 

Why?

Because 80kg x 3w/kg = 240w output that the rider is generating

and 240w / 87kg = 2.75w/kilo (of the kilos that that you're have to carry along with you - gravity doesn't care if it is you or the bike that is heavy)

 

50kg x 3w/kg = 150w

and 150w / 57kg = 2.63w/kg

 

It is only if the bike was weightless (wouldn't that be nice?) that the riders would perform equally. 

 

If the lighter rider had a 5.4kilo bike in the example above then their speed up the hill would be equal. There's also the issue of friction (which would mean the penalty on the lighter rider is less severe), but I've ignored that to keep it simple.

I haven't read this whole thread but FTP/Wkg is the following:

 

FTP value i.e. 300W / body weight i.e. 60kg = 5w/kg

 

Use average power not NP.

 

On the last comment here the 50kg rider will go up faster and exert less overall.

You know. That was going to be my exact answer. Lighter rider wins. But then I went and checked the numbers for a 500m climb in 7.5km at 6.67%, which would be considered a reasonable climb.

 

vs.

 

The lighter rider needs to produce 3.71w/kg vs. 3.41kg for the heavier rider. Does that make sense? I feel confused. However the total power that needs to be produced is much less, and from a fatigue point of view I could understand that the lighter rider will be better. Some help here, John?

[shaper]

 

You know. That was going to be my exact answer. Lighter rider wins. But then I went and checked the numbers for a 500m climb in 7.5km at 6.67%, which would be considered a reasonable climb.

 

vs.

 

The lighter rider needs to produce 3.71w/kg vs. 3.41kg for the heavier rider. Does that make sense? I feel confused. However the total power that needs to be produced is much less, and from a fatigue point of view I could understand that the lighter rider will be better. Some help here, John?

 

The problem with your calculation is that you have based it on both riders doing the hill in 30mins

 

With regard to W/Kg, if both riders put out the same power, then the 50kg cyclist will have a greater W/kg and will climb the hill faster as this needs to be the calculate variable. (Time = speed)

 

Your spreadhseet calculation stipulates the time to climb the hill and what each rider will need to put out as power to ride together and both reach the top in 30mins

 

Whereas if you had the 50kg ride with a power of 273.1W, then calculate his time to climb the hill it will be much less than 30mins

[Fat Boab]

Sometimes web calculators can confuse things. Let me offer a view?

 

1. The power P(W) required to move a mass m(W) against gravity at vertical speed V (m/s) is simply P = m x v x g, where g is acceleration due to gravity (9.81 m/s2). This ignores air resistance and rolling resistance and anything else.

 

1a. Plugging the 57 & 87 kg and 1000 m/hr scenarios into this and you get values of P (W) as 155 W and 237 W. Same as your calculator. So the maths is good.

 

2. Now let's apply this to the 2 rider situation. As we're interested in who's fastest, ie v (m/s), we rearrange the above equation to be v (m/s) = P/(m x g). So,

 

Rider 1, mtotal = 57kg, P=150W, then v(m/s) = 0.27 m/s (965 m/hr).

 

Rider 2, mtotal = 87 kg, P=240W, then v(m/s) = 0.28 m/2 (1012 m/hr).

 

3. The heavier dude wins by this consideration. Other real word retarding forces will be present in practice, but they'll probably be second-order effects and unlikely to significantly effect the outcome.

 

Make sense? Any counter views?

[Fat Boab]

The problem with your calculation is that you have based it on both riders doing the hill in 30mins

 

With regard to W/Kg, if both riders put out the same power, then the 50kg cyclist will have a greater W/kg and will climb the hill faster as this needs to be the calculate variable. (Time = speed)

 

Your spreadhseet calculation stipulates the time to climb the hill and what each rider will need to put out as power to ride together and both reach the top in 30mins

 

Whereas if you had the 50kg ride with a power of 273.1W, then calculate his time to climb the hill it will be much less than 30mins

 

Saw you comment after I hit send. Agreed!

[shaper]

Sometimes web calculators can confuse things. Let me offer a view?

 

1. The power P(W) required to move a mass m(W) against gravity at vertical speed V (m/s) is simply P = m x v x g, where g is acceleration due to gravity (9.81 m/s2). This ignores air resistance and rolling resistance and anything else.

 

1a. Plugging the 57 & 87 kg and 1000 m/hr scenarios into this and you get values of P (W) as 155 W and 237 W. Same as your calculator. So the maths is good.

 

2. Now let's apply this to the 2 rider situation. As we're interested in who's fastest, ie v (m/s), we rearrange the above equation to be v (m/s) = P/(m x g). So,

 

Rider 1, mtotal = 57kg, P=150W, then v(m/s) = 0.27 m/s (965 m/hr).

 

Rider 2, mtotal = 87 kg, P=240W, then v(m/s) = 0.28 m/2 (1012 m/hr).

 

3. The heavier dude wins by this consideration. Other real word retarding forces will be present in practice, but they'll probably be second-order effects and unlikely to significantly effect the outcome.

 

Make sense? Any counter views?

You also missing the point in the calculations, try redoing the calc with rider 1 P=240, same as rider 2... and see who wins?

 

Your scenario is:

 

Rider 1 on a coffee ride P=150w

Rider 2 Bleeding eyes P=240w

 

Both getting to the top of the hill roughly the same time... same as the previous web calculation.

 

You need to compare both riders pushing out the same power and then calculate speed and time

 

Rider 1 240w/57kg = 4.21w/kg

Rider 2 240w/87kg = 2.75w/kg

 

Result lighter rider, same power output will go faster up the hill as w/kg greater..... and is why hill climbing riders weigh next to nothing!

[Fat Boab]

You also missing the point in the calculations, try redoing the calc with rider 1 P=240, same as rider 2... and see who wins?

 

Your scenario is:

 

Rider 1 on a coffee ride P=150w

Rider 2 Bleeding eyes P=240w

 

Both getting to the top of the hill roughly the same time... same as the previous web calculation.

 

You need to compare both riders pushing out the same power and then calculate speed and time

 

Rider 1 240w/57kg = 4.21w/kg

Rider 2 240w/87kg = 2.75w/kg

 

Result lighter rider, same power output will go faster up the hill as w/kg greater..... and is why hill climbing riders weigh next to nothing!

 

I think you're missing the situation 100Tours painted...."From the point of view of 'how fast do you go up a hill' the bike weight does matter. If you have a 50kg rider and a 80kg rider, both on 7kg bikes and both putting out 3w/kg the 80kg rider will go up a hill faster."

 

ie same W/rider kg. Arguably both riders at their respective FTP perhaps? But that's conjecture.

[bertusras]

Well no not quite, as the question originally posed was based on w/kg. If both riders have the same power output the w/kg of the lighter rider increases dramatically. And that's where this came in:

 

However the total power that needs to be produced is much less, and from a fatigue point of view I could understand that the lighter rider will be better.

 

Edit: Fat Boab beat me to it.

 

In the real world I believe it comes down to peak power sustainable, with the disparity between a heavier and a lighter rider not being that big. Asking a 80kg rider to do 6w/kg up a climb for 30 mins would require them putting out 480w for that time, which is just unlikely. Whereas someone with a weight of 67kg would be at 400w. Someone at 50kg would need 300w, but might not actually have the muscle to do so. That's where math and the real world gets blurred.

[J Wakefield]

Well no not quite, as the question originally posed was based on w/kg. If both riders have the same power output the w/kg of the lighter rider increases dramatically. And that's where this came in:

 

 

Edit: Fat Boab beat me to it.

 

In the real world I believe it comes down to peak power sustainable, with the disparity between a heavier and a lighter rider not being that big. Asking a 80kg rider to do 6w/kg up a climb for 30 mins would require them putting out 480w for that time, which is just unlikely. Whereas someone with a weight of 67kg would be at 400w. Someone at 50kg would need 300w, but might not actually have the muscle to do so. That's where math and the real world gets blurred.

 

The counter point would be does the heavier rider have the muscle to sustain that value also and does he have the aerobic capacity to keep the sustained effort? More muscle more oxygen etc. 

 

If both riders in a perfect world were in the same shape the lighter would be up the hill 1st. 

 

There is a reason why climbers are the size they are and there are no 80kg KOM / GT winners. Same as there no 60kg sprinters.

 

Lastly, while those calculation charts are great, they also not, there are so many additional variables that need to be taken into account. A perfect example is all the calculations based on climbing speeds. Yes, a lot are near as damnit but many aren't. Without sounding like a ass smoke blower here but when you speak to some riders who climb in front group at a Tour and they give you some real life data, they say they weren't climbing at that predicted value given. I was once told "I have no idea how guys are doing that if I am with them 15% off"

 

My .32c

[jcza]

The counter point would be does the heavier rider have the muscle to sustain that value also and does he have the aerobic capacity to keep the sustained effort? More muscle more oxygen etc. 

 

If both riders in a perfect world were in the same shape the lighter would be up the hill 1st. 

 

There is a reason why climbers are the size they are and there are no 80kg KOM / GT winners. Same as there no 60kg sprinters.

 

Lastly, while those calculation charts are great, they also not, there are so many additional variables that need to be taken into account. A perfect example is all the calculations based on climbing speeds. Yes, a lot are near as damnit but many aren't. Without sounding like a ass smoke blower here but when you speak to some riders who climb in front group at a Tour and they give you some real life data, they say they weren't climbing at that predicted value given. I was once told "I have no idea how guys are doing that if I am with them 15% off"

 

My .32c

 

Indurain at 80kg and Cocquard at 60kg? 

[Fat Boab]

Despite Einstein's modification, Newton's view of the world is a pretty good starting place to discuss such power, mass, velocity scenarios ie mechanics. Thereafter, sure, layer physiological considerations, but they shouldn't obscure the mechanical consideration, but rather better inform it. Roll on Friday!    

[J Wakefield]

Indurain at 80kg and Cocquard at 60kg? 

 

 

Indurain was 1 in a million - no one has been since. More of an outlier. He was complete as a cyclist. (in a way I wish we had another like him in modern times)

 

Cocquard - 2nd tier sprinter. When the Sprint mafia are there he isnt. Exceptionally quick for size yes. When you look at his results in 2017 his wins have come at lesser known / level races.

 

You cant take 2 riders / athletes in the last 30 yrs as a comparison. 

[Fat Boab]

The counter point would be does the heavier rider have the muscle to sustain that value also and does he have the aerobic capacity to keep the sustained effort? More muscle more oxygen etc. 

 

If both riders in a perfect world were in the same shape the lighter would be up the hill 1st. 

 

There is a reason why climbers are the size they are and there are no 80kg KOM / GT winners. Same as there no 60kg sprinters.

 

Lastly, while those calculation charts are great, they also not, there are so many additional variables that need to be taken into account. A perfect example is all the calculations based on climbing speeds. Yes, a lot are near as damnit but many aren't. Without sounding like a ass smoke blower here but when you speak to some riders who climb in front group at a Tour and they give you some real life data, they say they weren't climbing at that predicted value given. I was once told "I have no idea how guys are doing that if I am with them 15% off"

 

My .32c

 

Yet there's a lot of rider-bashing and finger-pointing based on such climbing data, shamefully so. Nothing like a journo, or a Twitter-scientist to start throwing mud around for the populists! (Rant off. Not at you John.)