FNRttC Southend Ride Friday 10th March 2017

[srw]

https://www.thenakedscientists.com/articles/questions/fatter-cyclists-faster-downhill

"Strictly speaking that's only true if you're in a vacuum. On a bike you're far from it. The big issue with the bike is the aerodynamic drag.

If there were no aerodynamic drag then the fat person or a thin person would end up accelerating down a hill at the same rate. The point is that with the fat person, assuming that they're not incredible wide, the aerodynamic drag is going to be less significant in terms of their falling down the hill than for the thin person. Ultimately, a thin person's going to end up going slower than a fat person. So if you're in a race then you want to minimise that aerodynamic drag and of course the downside to being fat is that there's always going to be a hill on the other side of the downhill, meaning that you've got to put a lot of work in to get up the other side. There's always a catch!"

...which is why a tandem shoots past everyone on the downs and gets overtaken in return on the ups. And is pretty effective into a headwind.

 

[Sketchley]

...which is why a tandem shoots past everyone on the downs and gets overtaken in return on the ups. And is pretty effective into a headwind.

Indeed it is. Which is also why, as you well know, I've been known to hide behind a tandem into the wind......

 

[ianmac62]

I don't really understand why a fat person slices through the air more efficiently than a thin one. Nor why thin tandemistas would slice through the air more efficiently than a fat soloist.

I may of course be stuck on Ladybird Book 1.

 

[User482]

I don't really understand why a fat person slices through the air more efficiently than a thin one. Nor why thin tandemistas would slice through the air more efficiently than a fat soloist.

I may of course be stuck on Ladybird Book 1.

They don't. The point is that a heavier rider will only have a small increase in drag but a large increase in gravitational force.

 

[RoubaixCube]

As a chubby bloke on an 15kg MTB one time coming down Ally Pally. I still get ptsd and flashbacks from the moment i came off the bike while on a full descent from the top.

 

[hatler]

Think feather and lead weight. Drop them together and the lead weight will hit the floor first. Same principle applies to cyclists of different weights.

 

[Sketchley]

I don't really understand why a fat person slices through the air more efficiently than a thin one. Nor why thin tandemistas would slice through the air more efficiently than a fat soloist.

I may of course be stuck on Ladybird Book 1.

Ok look at it this way. I'd assume you would agree it would take twice the amount breaking power to stop a 100kg rider travelling at 20mph than a 50kg rider travelling the same speed? Now just replace the breaking power with a head wind. The wind would need to be twice as strong to reduce the speed of the 100kg rider by the same amount as the 50kg rider. As the force of the headwind is the same for both when riding side by side then it has to effect the heavier rider less than lighter one. If they both stopped peddling then the lighter rider would stop / be blown over first.

This works on the flat and down hill but not so much up hill as the lighter rider has big advantage of needing a lot less power to maintain the same w/kgs uphill.

 

[Sketchley]

Think feather and lead weight. Drop them together and the lead weight will hit the floor first. Same principle applies to cyclists of different weights.

View: https://www.youtube.com/watch?v=E43-CfukEgs

 

[Sketchley]

This part might not be entirely true.

Agreed. But I was simplifying and that seemed an acceptable simplification in order to make the point.

 

[ianmac62]

Thanks!

 

[mmmmartin]

Also - and I speak from personal experience here - those who tend to benefit from a slightly larger figure may perhaps have done so because they've overdone it on the Full English Breakfasts and the Real Ale (not to mention the cheese and red wine after dinner), and this often points to someone who hasn't been out on the bike getting fit. I know this.

 

[User482]

View: https://www.youtube.com/watch?v=E43-CfukEgs

That's in a vacuum, though, so drag isn't a factor.

 

[Sketchley]

That's in a vacuum, though, so drag isn't a factor.

That was the whole point, video show's both in and out of vacuum.

 

[AKA Bob]

That was the whole point, video show's both in and out of vacuum.

All this talk is really pretty irrelevant as there aren't any hill climbs or decents on this ride of note.......

I just hope he doesn't apply so much force through his bottom bracket causing him to rip it out which was my basis of my first ever conversation with @Sketchley when I met him on the first day of LonJoG....

 

[Sketchley]

All this talk is really pretty irrelevant as there aren't any hill climbs or decents on this ride of note.......

I just hope he doesn't apply so much force through his bottom bracket causing him to rip it out which was my basis of my first ever conversation with @Sketchley when I met him on the first day of LonJoG....

I don't remember that conversation. Who had done that? You?