can someone slipstreaming slow the bike in front down?
Discussion
So i was reading an article in MCN, ("ladies and gents, prepare for some turbulence", page 24, 24/08/10, by Kevin Ash) about how riding with a pillion or having a bike slipstreaming you can cause turbulence to your ride. It goes on to say that a slipstreaming bike can actually slow the leading bike down. I couldn't find the article on the net so here are a couple of extracts (verbatim):
Extract 1:
"in energy terms, (by slipstreaming) the rear bike has clearly gained some energy, and as this can only be coming from the front bike, then that must be losing energy. In other words, it will slow down."
Extract 2:
"You often hear slipstreaming explained as the front bike punching a hole in the air. It isn't of course, you can't create a vacuum behind you - which is what a hole in the air would be - by riding fast. You're actually creating a turbulent flow of air behind you which is moving forwards.
The drag for the bike behind is reduced because its air speed is lower, as it's passing through air moving in the same direction, rather than the stationary air which the lead bike is hitting.
That's fairly obvious, but it doesn't explain why the lead bike, or the rider with a pillion, should feel the effect of something close behind. It's because with a secondary bike in the way, the air that would normally flow around the lead bike into the space behind, now has less room to flow into. There's an obstacle - another motorcycle - so the displaced air must push wider to go around it. This creates an extra barrier of air behind the lead bike, so the stream of air which keeps flowing around it no longer has that space to move into. The only place it can go is wider, around the following bike, which takes more effort.
The same happens with a passenger, who fills the space the air flowing around the rider would have gone into, so instead the air must move outwards and create a wider 'wake'. As it does so, the whole pattern of flow changes, usually meaning an increase in turbulence, even for the rider in front.”
I’m interested to hear what others think about this…
Extract 1:
"in energy terms, (by slipstreaming) the rear bike has clearly gained some energy, and as this can only be coming from the front bike, then that must be losing energy. In other words, it will slow down."
Extract 2:
"You often hear slipstreaming explained as the front bike punching a hole in the air. It isn't of course, you can't create a vacuum behind you - which is what a hole in the air would be - by riding fast. You're actually creating a turbulent flow of air behind you which is moving forwards.
The drag for the bike behind is reduced because its air speed is lower, as it's passing through air moving in the same direction, rather than the stationary air which the lead bike is hitting.
That's fairly obvious, but it doesn't explain why the lead bike, or the rider with a pillion, should feel the effect of something close behind. It's because with a secondary bike in the way, the air that would normally flow around the lead bike into the space behind, now has less room to flow into. There's an obstacle - another motorcycle - so the displaced air must push wider to go around it. This creates an extra barrier of air behind the lead bike, so the stream of air which keeps flowing around it no longer has that space to move into. The only place it can go is wider, around the following bike, which takes more effort.
The same happens with a passenger, who fills the space the air flowing around the rider would have gone into, so instead the air must move outwards and create a wider 'wake'. As it does so, the whole pattern of flow changes, usually meaning an increase in turbulence, even for the rider in front.”
I’m interested to hear what others think about this…
Edited by 2seas on Tuesday 31st August 09:51
y2blade said:
MCN you say!
unreliable? it's the first time i've bought the paper. the pseudo physics explanation seemed logical enough to me - except for the "in energy terms, (by slipstreaming) the rear bike has clearly gained some energy, and as this can only be coming from the front bike, then that must be losing energy" line, which doesn't seem right..You'll get a low prssure area behind the bike, and turbulence as the air fills that low pressure area, but thier description of "an extra barrier of air behind the lead bike" would mean an increase in the pressure behind the bike, so less drag and more speed for the top bike.
MCN talking utter b
ks? Surely not?
regards,
A former internal aerodynamacist.
MCN talking utter b
ks? Surely not?regards,
A former internal aerodynamacist.
I struggle to believe that an adult actually wrote the two "captions" above.
In brief, no, the rear bike does not slow down the leading bike, and you go slower with a pillion due to weight, not drag. For a fixed power output, to go faster reduce the weight. For a fixed weight, increase power. So by increasing weight, we can see the speed goes down. fking halfwits.
In brief, no, the rear bike does not slow down the leading bike, and you go slower with a pillion due to weight, not drag. For a fixed power output, to go faster reduce the weight. For a fixed weight, increase power. So by increasing weight, we can see the speed goes down. f
king halfwits.I'm sure the answer is here somewhere http://en.wikipedia.org/wiki/Newton's_laws_of_moti...
I've got a bad feeling this could be the new 'plane on a conveyor belt' thread?
I've got a bad feeling this could be the new 'plane on a conveyor belt' thread?
surely BOTH bikes can go faster, they effectively become, aerodynamically, one long, more efficiently shaped bike
http://en.wikipedia.org/wiki/Drafting_%28aerodynam...
http://en.wikipedia.org/wiki/Drafting_%28aerodynam...
bass gt3 said:
I struggle to believe that an adult actually wrote the two "captions" above.
In brief, no, the rear bike does not slow down the leading bike, and you go slower with a pillion due to weight, not drag. For a fixed power output, to go faster reduce the weight. For a fixed weight, increase power. So by increasing weight, we can see the speed goes down. fking halfwits.
but do you agree that a slipstreaming bike would alter the aerodynamics of the lead bike and could cause buffeting for the lead bike? i don't believe a slipstreaming bike could cause the lead bike to slow down, but it does seam possible that it could cause turbulence to it...In brief, no, the rear bike does not slow down the leading bike, and you go slower with a pillion due to weight, not drag. For a fixed power output, to go faster reduce the weight. For a fixed weight, increase power. So by increasing weight, we can see the speed goes down. f
king halfwits.Hugo a Gogo said:
surely BOTH bikes can go faster, they effectively become, aerodynamically, one long, more efficiently shaped bike
http://en.wikipedia.org/wiki/Drafting_%28aerodynam...
For cars I'd guess it's possible, but bikes aerodynamics are so bad you'd have no chance. Bear in mind that on cars the gaps between body pannels can produce enough drag to effect the top speed and you'll get an idea how bad bike aerodynamics are, typically about double the drag of a car per unit frontal area.http://en.wikipedia.org/wiki/Drafting_%28aerodynam...
2seas said:
bass gt3 said:
I struggle to believe that an adult actually wrote the two "captions" above.
In brief, no, the rear bike does not slow down the leading bike, and you go slower with a pillion due to weight, not drag. For a fixed power output, to go faster reduce the weight. For a fixed weight, increase power. So by increasing weight, we can see the speed goes down. fking halfwits.
but do you agree that a slipstreaming bike would alter the aerodynamics of the lead bike and could cause buffeting for the lead bike? i don't believe a slipstreaming bike could cause the lead bike to slow down, but it does seam possible that it could cause turbulence to it...In brief, no, the rear bike does not slow down the leading bike, and you go slower with a pillion due to weight, not drag. For a fixed power output, to go faster reduce the weight. For a fixed weight, increase power. So by increasing weight, we can see the speed goes down. f
king halfwits.If however, the rear bike was so close, and actually interrupted or reduced the drag experienced by the lead bike, it could actually improve the front bikes performance. But only at high speeds and neutral wind conditions.
As for causing turbulence, it would be so negligable as to be irrelevant. The primary forces at work on the lead bike are the air resitance encountered as it punches through the air in front. This will cause a 'bow wave effect' behind. For the rear bike to effect this bow wave sufficiently for it to be noticed by the lead bike would be hard to imagine.
Look at race cars slipstreaming each other, especially in the American NASCAR series. These cars sit right under eachothers rear bumper, as it's the point of least effect and maximum benefit. They then floor the gas, use the reduced air resistance to slingshot past at the finish line. The rear car is effectively driving in a tail wind, even if the wind conditions are still. It's this reduction in drag and resistance that is of benefit, and at no point do you see the front car being slowed down. It is expending the energy required to punch throught he air, and the rear car has no effect on this.
As i said, MCN. f
kwitsHugo a Gogo said:
surely BOTH bikes can go faster, they effectively become, aerodynamically, one long, more efficiently shaped bike
http://en.wikipedia.org/wiki/Drafting_%28aerodynam...
This sounds right to me. A long boat is faster than a short boat.http://en.wikipedia.org/wiki/Drafting_%28aerodynam...
Hugo a Gogo said:
surely BOTH bikes can go faster, they effectively become, aerodynamically, one long, more efficiently shaped bike
http://en.wikipedia.org/wiki/Drafting_%28aerodynam...
Just look at road cyclists - tour de France etc. The slipstream of two bikes togethor make BOTH bikes go faster. It's a tried and tested technique even at 30-50mph. The lead bike has reduced drag as a result of of the rider behind partially filling the low pressure area created behind, so speeds up a bit. The following bike has a lower pressure at the front, along with the turbulent air already moving slightly in the direction your are going (like a tail wind) - so goes a bit faster.http://en.wikipedia.org/wiki/Drafting_%28aerodynam...
redstu said:
Is there a table of effective slip stream distances vs speed?
I noticed a substantial effect a few weeks ago following a car, not too close but it reduced the buffeting considerably. It was slightly faster than I normally ride at so I dropped back and was back into clean air again.
I wouldn't imagine so - it's going to be dependent on so many factors, from air pressure, speed, drag coefficients, frontal areas, differences in the lead and following vehicles etc etc etc.I noticed a substantial effect a few weeks ago following a car, not too close but it reduced the buffeting considerably. It was slightly faster than I normally ride at so I dropped back and was back into clean air again.
MCN are, as ever, talking bks. One of their muppets wrote a book on Moto GP bikes which was good until the half-wit started talking about aerodynamics...
The half-wit claimed that the teardrop is the most aerodynamic shape
That theory was dis-prooved back in the 1930's which is a fair indication of the level of their technical knowledge.
ks. One of their muppets wrote a book on Moto GP bikes which was good until the half-wit started talking about aerodynamics... The half-wit claimed that the teardrop is the most aerodynamic shape
That theory was dis-prooved back in the 1930's which is a fair indication of the level of their technical knowledge.
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