If I was riding a time trial travelling at 25mph in an aero tuck but there was a 30 mph tail wind would I go faster if I sat up . This assumes I could still get the same amount of power to the cranks . Flat surface constant wind .
On a conveyor belt?
No
Yes.
For the same reason you should slipstream unless you’ve got a tailwind pushing faster than you’re travelling.
In the 1960s there was a trend for cycling jerseys to have silk fronts and shoulders and wool backs. The idea being the silk would cut through the air but a tailwind would catch on the back and push you along. I know!
GCN are always on the lookout for potential content - ask them to test it out. Sounds right up Ollie's street....
If I was riding a time trial travelling at 25mph in an aero tuck but there was a 30 mph tail wind would I go faster if I sat up .
Yes, of course.
All depends on what tyres you're using and the colour of your bar tape.
You are only doing 25mph because of
1) your pedalling,
2) the aero tuck,
3) and the wind pushing on your back cross section.
As soon as you sit up you increase front resistance, but also increase wind catching at the rear.
I dunno if this means you will go faster or slower, but its not just as simple 25mph minus 30mph.
Surely if you sit up there is no frontal resistance as the wind is travelling faster than you are
As soon as you sit up you increase front resistance
No, if the air is moving faster than you there is no front resistance - only „back resistance“ which is a good thing that you want to maximise.
It is the same situation as a sailing boat being pushed along by the wind from behind. The more area of sail it has the faster it can go, up to a point.
No, if the air is moving faster than you there is no front resistance – only „back resistance“ which is a good thing that you want to maximise.
This would imply zero air pressure on your chest. Hmmmm..
For the same reason you should slipstream unless you’ve got a tailwind pushing faster than you’re travelling.
Eh!
But Shirley if you've got a tailwind it's coming from behind you and so hits your back and it's immaterial that there's someone else in front of you... in fact if the person you're wheelsucking is a competitor, rather than a teammate, it's a double win as you're stopping them getting the benefit.
This would imply zero air pressure on your chest. Hmmmm..
Surely the tailwind is air moving past you so there will be no air pressure on your chest . IANAS
Surely the tailwind is air moving past you so there will be no air pressure on your chest . IANAS
Me neither...
if the air is moving faster than you there is no front resistance
except the way that fluids move around a curved surface (like your back) does create some, but it will be minor compared to the sail type effect
If you've a 30mph tail wind, you must have your brakes applied to only be doing 25mph. Assuming it is a flat level road. Even with no pedalling (on the flat) you should eventually reach nearly 30 (30 minus a bit for rolling resistance).
You should be seeing more like about 50mph ground speed if you're pedalling properly. The speed you'll reach will be when your pedalling effort forward equals the combination of the (approx) 50mph rolling resistance + the 20mph air resistance).
I could have said that I was travelling at 50mph with a 60mph tailwind would that make you happy . You would probably have accused me of trying to make myself look epic then . Thanks for your contribution .
ONLY in a LAB.
Yes, and could be improved upon if you unzip your jacket and tie each side onto each wrist. Viola, instant downwind sail.
But as we all know this is highly unlikely, as winds only come from the front.
There's no point doing a time trial in 30mph winds. That's getting close to gale force and you'll be blown sideways half the time and your time will be awful. And when you're riding with the wind at your back it'll be like being on a turbo with no airflow and you'll overheat.
I dunno if this means you will go faster or slower, but its not just as simple 25mph minus 30mph.
I think it is. It’s you vs the block of air you’re pushing against. At least, in lab conditions where you can imagine the wind has laminar flow.
In the real world, I suspect a ‘25mph tailwind’ is, in fact, complex mixture of vortices and deadspots and I have no idea how that would relate to a force pushing you.
But if the wind was overall moving faster than me (Ie I could feel it on my back) then yes - I’d absolutely sit up. Sometimes I like to pretend my back is a sail and I can direct a cross-tailwind.
"except the way that fluids move around a curved surface (like your back) does create some, but it will be minor compared to the sail type effect"
It might actually create a low pressure area in front, slightly pulling you forward, in addition to the pushing force from behind. this is why, in more normal aero situations, the shape and texture of the rear is so important, to minimise that low pressure area behind, which can cause drag.
I have no doubt however, that sitting up in this (hypothetical) situation would be beneficial. wind from behind would continue to push you forward until your own speed matched the wind. only above that would frontal drag be an issue.
As a paddler, I would like to submit this to the jury for consideration.
If you’ve a 30mph tail wind, you must have your brakes applied to only be doing 25mph. Assuming it is a flat level road. Even with no pedalling (on the flat) you should eventually reach nearly 30 (30 minus a bit for rolling resistance).
You should be seeing more like about 50mph ground speed if you’re pedalling properly. The speed you’ll reach will be when your pedalling effort forward equals the combination of the (approx) 50mph rolling resistance + the 20mph air resistance).
I was going to say something similar to this ^
I could have said that I was travelling at 50mph with a 60mph tailwind would that make you happy . You would probably have accused me of trying to make myself look epic then . Thanks for your contribution .
the majority of work you are doing riding at 25mph (on road tyres) is overcoming air resistance. with a 30mph tailwind there is no air resistance.
TBH with decent tyres and hubs, I'd expect you to get near to windspeed just by sitting up and not pedalling. (assuming you got up to windspeed yourself, becasue acceleration is different kettle of fish)
To go into a bit more bro science, its often quoted that 12-13 mph on a road bike is where aero becomes the dominant force to work against.
Lets assume that means tyre drag = aero resistance at 12.5mph.
air resistnace is also proportional to the square of velocity (relative velocity between bike and air).
therefore at twice the speed air resistnace is quadrupled. and your total resistance to maintain 25mph is 4 parts air resistnace, 1 part rolling resistance.
remove air resistnace with a 25mph tail wind, and you have cut the power required by 80%.
Now that Ive started zwifting and can see some power numbers, I know that 20% of my FTP is barely turning the pedals round. 20% of a comfortable cruise, even less so.
However, from a meterological sense, a constant wind (rather than gust) of this magnitude is rare, and as pointed out, would be miserable and dangerous to ride a tt bike in anything but dead down wind.
I remember one time at a Neilson windsurf and biking centre in Ortakent, Turkey. The winds there were quite predictable; in the morning a cooling breeze came from the sea onto the land and most afternoons it switched and the warm air from the land came hurtling down across the bay. The morning rides always used to finish with a hot slog up the big hill until you got to the top and had a beautiful run down to the centre with that lovely breeze in your face cooling you down. One morning, either we were late or the switch came early so we rode down at the same speed as the hot air. It was like being in an oven. I couldn't help thinking these were exactly the conditions to make great crackling on a piece of moist salty skin.
You should be seeing more like about 50mph ground speed if you’re pedalling properly. The speed you’ll reach will be when your pedalling effort forward equals the combination of the (approx) 50mph rolling resistance + the 20mph air resistance).
except to add your 20mph pedalling effort to the 30mph behind you'll still need to be pedalling at 50mph. That would mean 53/11 at close to 130rpm cadence, and not many can hold that cadence for long. Any less and you'd effectively be 'cavitating'
This would imply zero air pressure on your chest. Hmmmm..
Theres plenty of air pressure on every side of you whatever way the wind's blowing - you're currently balancing a 12 kiliometer column of air weighing several tons on your head. You make it look easy though.
