400bhp
Guru
Hmm, not sure about that.
Is 20 miles in under an hour a realistic goal for a MAMIL?
- Thread starter Jon George
- Start date
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Hmm, not sure about that.
Banjo
Fuelled with Jelly Babies
- Location
- South Wales
I did an out and back ride a few days ago in strong wind, (30 gusting to 45mph) struggled into a headwind for 20 miles then basically came back by a slightly different route but with wind behind me. Really flew on the way back but my average speed for the whole ride was still down on normal by about 2mph.
Ithink a headwind takes more out of you than you get back when its behind you.Have to admit though it was good fun doing over 42 mph on a gentle downhill I normally go down at about 30 mph,
Ithink a headwind takes more out of you than you get back when its behind you.Have to admit though it was good fun doing over 42 mph on a gentle downhill I normally go down at about 30 mph,
I did an out and back ride a few days ago in strong wind, (30 gusting to 45mph) struggled into a headwind for 20 miles then basically came back by a slightly different route but with wind behind me. Really flew on the way back but my average speed for the whole ride was still down on normal by about 2mph.
Ithink a headwind takes more out of you than you get back when its behind you.Have to admit though it was good fun doing over 42 mph on a gentle downhill I normally go down at about 30 mph,
Yep, simple maths - for a 20 mile out and back you may spend the first 10 miles going 15mph, the second 10 miles going 25 mph - the average is not 20mph. This is because you will spend 40 minutes going 15 mph and 24 minutes going 25 mph.
This is why it is more efficient to go harder into headwinds
Banjo
Fuelled with Jelly Babies
- Location
- South Wales
I also think that when your galloping along with a tail wind the temptation is to ease off and let the wind do the work.
numbnuts
Legendary Member
- Location
- Gone over the hill and far away
What's the rush I say........
gavroche
Getting old but not past it
- Location
- North Wales
That's definitively an impossible target for this MAMIL so congratulations to you and keep it going.
400bhp
Guru
Not sure how you've worked that out? Completely dependent upon the cyclist doing 15mph out and 25mph back. The difference being 67%. It could have been 16.67 out and 25 back? (50% difference)
I think it mostly comes down to the drag coefficient and the relative difference between the frontal drag and rearward drag (assuming all other stuff constant)?
nickyboy
Norven Mankey
- Location
- You want hills? We got hills
Err, the maths isn't quite so simple as that. The easiest way to understand this is as follows:
Imagine you have an out and back course, 10 miles out, 20 miles in total. On a completely still day you cycle at 20mph. Therefore you experience 400 units of wind resistance (resistance is proportionate to the square of the speed) for one hour.
Now imagine that it is a windy day. You have a 10mph tailwind out, 10 mph headwind back. To maintain the same 20mph out you will experience 100 units of wind resistance (the effective wind speed will be 10mph headwind) for half an hour. On the way back, if you cycle at 20mph you will experience 900 units of wind resistance for half an hour. So on average, you will experience 500 units of wind resistance for one hour.
So you have to work quite a lot harder to maintain the same average on a windy day. Alternatively, you maintain the same effort and go slower.
400bhp
Guru
How are you working out the relative wind resistances? Linearly? See my post above, I think it depends on your drag coefficient which i think will be different forwards and back.
nickyboy
Norven Mankey
- Location
- You want hills? We got hills
You're absolutely right that it will be different out and back due to the wind direction. All I was doing was showing that if you do an out and back in still conditions v windy conditions, you will suffer more wind resistance in windy conditions if you manage to maintain the same speed as in still conditions.
When I've got a minute I'll do the maths to show what happens to speed in windy v still conditions if you maintain constant effort. Either way, in windy conditions you will either maintain your still conditions speed with extra effort or maintain your still conditions effort resulting in a lower average speed
biggs682
Touch it up and ride it
- Location
- Northamptonshire
couldnt agree more , why not just enjoy the ride
nickyboy
Norven Mankey
- Location
- You want hills? We got hills
OK, here's the maths for constant effort and it's effect on speed.
Firstly, one assumption; there is only wind resistance. No rolling resistance or mechanical inefficiencies etc.
Using my example, 10 miles out, 10 miles back. In still conditions, experiencing 400 units of wind resistance, the cyclist can travel 20mph out and 20 mph back. So a 20mph average.
Now add a 10mph tailwind out. To experience 400 units of wind resistance, you would cycle at 30mph (giving you a net 20mph headwind). On the return journey, you would cycle at 10mph (again giving you a net 20mph headwind). So here you will have to put in exactly the same effort as in still conditions to do this.
But the time spent doing it is different. In still conditions you do it for one hour so that's 20mph average. In the windy conditions your outbound takes 20 minutes and your return leg takes 1 hour. So it is 1 hour 20 minutes in total, giving an average speed of 15mph.
Of course rolling resistaces, mechanical inefficiencies distort this to an extent. But whatever happens, your average speed on a windy day reduces due to the above.. So get yer head down and go low
Firstly, one assumption; there is only wind resistance. No rolling resistance or mechanical inefficiencies etc.
Using my example, 10 miles out, 10 miles back. In still conditions, experiencing 400 units of wind resistance, the cyclist can travel 20mph out and 20 mph back. So a 20mph average.
Now add a 10mph tailwind out. To experience 400 units of wind resistance, you would cycle at 30mph (giving you a net 20mph headwind). On the return journey, you would cycle at 10mph (again giving you a net 20mph headwind). So here you will have to put in exactly the same effort as in still conditions to do this.
But the time spent doing it is different. In still conditions you do it for one hour so that's 20mph average. In the windy conditions your outbound takes 20 minutes and your return leg takes 1 hour. So it is 1 hour 20 minutes in total, giving an average speed of 15mph.
Of course rolling resistaces, mechanical inefficiencies distort this to an extent. But whatever happens, your average speed on a windy day reduces due to the above.. So get yer head down and go low
OP
OP
Jon George
Mamil and couldn't care less
- Location
- Suffolk an' Good
I love this sort of stuff - it reminds me of How-It-Works articles in Look And Learn. Cheers - brought back a bit of childhood!
asterix
Comrade Member
- Location
- Limoges or York
If it were me I'd try tweaking the nose of the saddle down a smidgin. It may feel a little odd but you should find you get used to it.
OP
OP
Jon George
Mamil and couldn't care less
- Location
- Suffolk an' Good
I take it you don't mean that the saddle is pointing down slightly at the front, as I understand that has a detrimental increase on the load on the shoulders? To be honest, I think it's less of an adjustment issue, and more to do with the fact that - up until a fortnight ago - I wasn't doing any core exercise and I haven't spent that much time of the drops. (Though that is being rectified.
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