Having to push more w/kg just to keep up

I’m hoping someone can shed some light or point me in the right direction regarding an issue I came across recently.

Climbing Alpe du Zwift with a friend, I was having to push roughly 0.8 w/kg more than him just to stay on his wheel.

I have calibrated my Kickr as per wahoo and Zwift and my friend is using the wattbike. He weighs 10kgs more than me but I finished the Alpe with an average power for the climb of 314w and he just 10 seconds slower averaging 288w. The maths simply don’t add up. I changed from the Tron bike half way up to see if that was the issue but the discrepancy continued with me on the Emonda with Lightweight wheels.

I noticed this issue on a different route with the same person a few weeks before but it was a rolling route so the numbers weren’t as constant and therefore I wasn’t 100% sure that it wasn’t just me suffering more than usual to keep a wheel.

Regardless of calibration, I don’t understand how one would have to push up to 1 w/kg more to maintain the same speed.

We discussed it afterwards and know that something is up but there’s no spindown available for the wattbike like the Kickr to remove that possibility from the equation even though it still doesn’t make sense that riders should move at the same speed if they are pushing the same w/kg. When I matched his w/kg my avatar dropped back straight away.

Hi @Iain_Cathmoir, welcome to the forums.

What are your heights? That can also make a difference in speed. Are you sure he has his weight entered correctly? Are you two on the exact same bike?

What about drafting, is he drafting you or the other way around?

I don’t know much about the wattbike but maybe it is not as accurate as the Kickr?

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It is true that for the same w/kg the heavier rider will go faster than the lighter.

It kind of seems counterintuitive but it’s how it works in the real world too apparently (and unless you and your friend both have power meters and ride together up hills at the same w/kg - which I doubt is on any bike computer - you can’t really say it’s not how it works in real life)

I can’t find the original website I read about it on - May have been zwift insider)

Here is an old website mentioning it http://www.olympum.com/sports/impact-of-weight-on-zwift/

Btw the spin down discussion isn’t relevant as zwift sees what is sent to it and uses that.

Thanks for replying Mike,

My data is set at 72kgs and 180cms and my friend’s is at 82kgs and 188cms.

He was on a Madone and I on the Tron bike at first then I switched to the Emonda.

I was sat behind him as the plan was for him to díctate the pace as I’m the stronger rider but even in his “draft” I was having to put around 1w/kg more than him to keep the wheel.

Hi Ben,

Thanks for the link. I understand how it works and I regularly train with power and with other people using power but never have I had to put in 5w/kg to hold the wheel of someone heavier putting in 4w/kg. Not in the real world or on zwift. A small difference is expected but it doesn’t make sense that a substantially heavier rider would have to average 26w less over a climb like that. I always push more power than my lighter friends on climbs to ride together.

It was good for me as I had to push hard and got a PR of 45:20… but something just didn’t add up.


The section on equal power/weight different weights says it is down to air resistance.

This article also backs this up https://www.cyclingweekly.com/fitness/training/the-importance-of-power-to-weight-and-how-to-improve-yours-164589
In the section on “ What affect does power-to-weight ratio have when battling wind and hills?”

Also an interesting video where they ride at the same speed up a climb in real life and compare w/kg figures

heavier riders go faster than lighter riders at the same w/kg.
although you should defo have the advantage going uphill so not sure what’s going on there.
you want spec tarmac pro + mellstein wheels for alpe btw