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How much more work in the rain?
So as I'm riding in the rain with my son today, trying to avoid the
spray off his rear wheel (no fender), and then noticing how much water is coming off my front fender, I start thinking about the obvious. All that water, being transported *up* from the ground. That takes work. The question is, how much water is being moved up, and how high? I can't envision any sort of manner in which that effort is negated by an opposing force. My guess is that somebody has already done the math. Anyone here who's already done the work? Thanks- --Mike-- Chain Reaction Bicycles www.ChainReactionBicycles.com |
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#2
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How much more work in the rain?
On Sun, 17 Jan 2010 22:35:25 -0800, "Mike Jacoubowsky"
wrote: So as I'm riding in the rain with my son today, trying to avoid the spray off his rear wheel (no fender), and then noticing how much water is coming off my front fender, I start thinking about the obvious. All that water, being transported *up* from the ground. That takes work. The question is, how much water is being moved up, and how high? I can't envision any sort of manner in which that effort is negated by an opposing force. My guess is that somebody has already done the math. Anyone here who's already done the work? Thanks- --Mike-- Chain Reaction Bicycles www.ChainReactionBicycles.com Dear Mike, The spray is no more than the thin film of water that clings to a smooth rubber tire and is then flung off as the tire accelerates. When you're going 20 mph forward, the contact patch is doing roughly 0 mph at all times, down in the water. After the wetted contact patch rotates a quarter turn (the back of the tire, level with the axle), it has accelerated to 20 mph straight up. When the water-covered contact patch reaches the top of the tire (right over the axle), it's doing 40 mph forward, right into the wind). At 20 mph, a ~2100 mm circumference 700c tire spins at about 255 RPM. Accelerating from 0 mph at the contact patch to 40 mph at the top of the tire in about 1/500th of a second is why the thin film of water is flung off the tire and blown back into your face as spray. But a little spray goes a long way when it's in your face, so things seem much worse than they really are. Very little water is actually raised, no more than wets a tire. Think about the effort required by a spray bottle, which is worked with one finger, as opposed to two legs. That's why you won't notice much of a speed loss on a wet road. Another way to put it in perspective is to ask how much the rain itself slows you down--all those drops of water hitting your whole body and bicycle literally don't have much of an impact. Of course, when the tire has to push significant amounts of water out of the way to the sides (standing water, as opposed to a wet road), then things do indeed become noticeable. Cheers, Carl Fogel |
#4
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How much more work in the rain?
On Sun, 17 Jan 2010 22:35:25 -0800, Mike Jacoubowsky wrote:
So as I'm riding in the rain with my son today, trying to avoid the spray off his rear wheel (no fender), and then noticing how much water is coming off my front fender, I start thinking about the obvious. All that water, being transported *up* from the ground. That takes work. The question is, how much water is being moved up, and how high? I can't envision any sort of manner in which that effort is negated by an opposing force. Humid air is less dense, so you may gain on the swing what you loose on the roundabout. |
#5
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How much more work in the rain?
On Jan 18, 6:35 am, "Mike Jacoubowsky"
wrote: So as I'm riding in the rain with my son today, trying to avoid the spray off his rear wheel (no fender), and then noticing how much water is coming off my front fender, I start thinking about the obvious. All that water, being transported *up* from the ground. That takes work. The question is, how much water is being moved up, and how high? I can't envision any sort of manner in which that effort is negated by an opposing force. My guess is that somebody has already done the math. Anyone here who's already done the work? Thanks- --Mike-- Chain Reaction Bicycleswww.ChainReactionBicycles.com Not much work, actually. Assuming the absence of confuddling factors like knobbly tires with large-scooplike undercuts: That's a *very* thin film of water turned into spray. Compare riding on a wet road, with an apparent large amount of spray, to riding through standing water at least rim-deep, where the displacement slows you and a bunch of much heavier drops are not propelled nearly as far or high. In the latter case, appreciable work is being done; in the wet road case i'd hate to have to quantify a number to a critical audience. In general, water is merely a thicker gas, and aerodynamic principles can be applied. I'm not so sure that there would be any advantage even in competitive circumstances to redesigning any bicycle component to meet a wet road better. If there is anything to be gained, it would, aero and naval architechture principles be along the lines of keeping the thin layer of water attached longer rather than casting it off; if this sounds counter-intutive, consider that clinging water prevents more water being picked up and cast off, which is where the work is performed, so that on average a very thin film of water clinging to the tire for as long as possible is the less power-consuming option. As I say, this is genuinely hairsplitting stuff. Andre Jute "The brain of an engineer is a delicate instrument which must be protected against the unevenness of the ground." -- Wifredo-Pelayo Ricart Medina |
#6
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How much more work in the rain?
On Jan 18, 7:18 am, wrote:
On Sun, 17 Jan 2010 22:35:25 -0800, "Mike Jacoubowsky" wrote: So as I'm riding in the rain with my son today, trying to avoid the spray off his rear wheel (no fender), and then noticing how much water is coming off my front fender, I start thinking about the obvious. All that water, being transported *up* from the ground. That takes work. The question is, how much water is being moved up, and how high? I can't envision any sort of manner in which that effort is negated by an opposing force. My guess is that somebody has already done the math. Anyone here who's already done the work? Thanks- --Mike-- Chain Reaction Bicycles www.ChainReactionBicycles.com Dear Mike, The spray is no more than the thin film of water that clings to a smooth rubber tire and is then flung off as the tire accelerates. When you're going 20 mph forward, the contact patch is doing roughly 0 mph at all times, down in the water. After the wetted contact patch rotates a quarter turn (the back of the tire, level with the axle), it has accelerated to 20 mph straight up. When the water-covered contact patch reaches the top of the tire (right over the axle), it's doing 40 mph forward, right into the wind). At 20 mph, a ~2100 mm circumference 700c tire spins at about 255 RPM. Accelerating from 0 mph at the contact patch to 40 mph at the top of the tire in about 1/500th of a second is why the thin film of water is flung off the tire and blown back into your face as spray. But a little spray goes a long way when it's in your face, so things seem much worse than they really are. Very little water is actually raised, no more than wets a tire. Think about the effort required by a spray bottle, which is worked with one finger, as opposed to two legs. That's why you won't notice much of a speed loss on a wet road. Another way to put it in perspective is to ask how much the rain itself slows you down--all those drops of water hitting your whole body and bicycle literally don't have much of an impact. Of course, when the tire has to push significant amounts of water out of the way to the sides (standing water, as opposed to a wet road), then things do indeed become noticeable. Cheers, Carl Fogel Dear Carl: You must be on speed. Your mental arithmetic is out by a multiple of 60. Write it down on paper, dear boy. Andre Jute It takes only a fraction of a second to put your mind in gear |
#7
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How much more work in the rain?
On 18 Jan, 11:52, _
wrote: Humid air is less dense, so you may gain on the swing what you loose on the roundabout. That'll save the plastic surgeon a bit of work. How do I get to the swing after decking on the roundabout? |
#8
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How much more work in the rain?
On 1/18/2010 12:35 AM, Mike Jacoubowsky wrote:
So as I'm riding in the rain with my son today, trying to avoid the spray off his rear wheel (no fender), and then noticing how much water is coming off my front fender, I start thinking about the obvious. All that water, being transported *up* from the ground. That takes work. The question is, how much water is being moved up, and how high? I can't envision any sort of manner in which that effort is negated by an opposing force. My guess is that somebody has already done the math. Anyone here who's already done the work? Thanks- --Mike-- Chain Reaction Bicycles www.ChainReactionBicycles.com Slightly off-topic.... I spoke of my tire-building efforts on a web forum, and one fellow responded that a "better" tire would have a circumferential groove in the center rather than any kind of center rib or tread blocks, because (apparently he has observed that) this type of center-section on a tire prevented water from being thrown up. As an example, he mentioned the "Tioga 1.75/1.95 slicks". Tioga doesn't make a "slick" that I can tell, I guessed he meant the City Slicker tire, which does have a center groove: http://www.amazon.com/Tioga-City-Sli.../dp/B000C15FTI ?????? I mentioned that new-fangled invention--the fender, and he wouldn't have any part of it. I've had all kinds of tires on bikes over the years, don't remember much difference in what water they tossed up except that a slick throws it all up in one central stream, where something like knobbies gives you a gentle shower from below. ~ |
#9
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How much more work in the rain?
On 18 Jan, 14:15, DougC wrote:
On 1/18/2010 12:35 AM, Mike Jacoubowsky wrote: So as I'm riding in the rain with my son today, trying to avoid the spray off his rear wheel (no fender), and then noticing how much water is coming off my front fender, I start thinking about the obvious. All that water, being transported *up* from the ground. That takes work.. The question is, how much water is being moved up, and how high? I can't envision any sort of manner in which that effort is negated by an opposing force. My guess is that somebody has already done the math. Anyone here who's already done the work? Thanks- --Mike-- * * Chain Reaction Bicycles www.ChainReactionBicycles.com Slightly off-topic.... I spoke of my tire-building efforts on a web forum, and one fellow responded that a "better" tire would have a circumferential groove in the center rather than any kind of center rib or tread blocks, because (apparently he has observed that) this type of center-section on a tire prevented water from being thrown up. As an example, he mentioned the "Tioga 1.75/1.95 slicks". Tioga doesn't make a "slick" that I can tell, I guessed he meant the City Slicker tire, which does have a center groove:http://www.amazon.com/Tioga-City-Sli.../dp/B000C15FTI ?????? I mentioned that new-fangled invention--the fender, and he wouldn't have any part of it. I've had all kinds of tires on bikes over the years, don't remember much difference in what water they tossed up except that a slick throws it all up in one central stream, where something like knobbies gives you a gentle shower from below. ~ I did use circumferential grooved 27" tyres as a teenager with shortie guards. Cannot remember specifically being upset by the rain, I got wet and put up with it I suppose. By creating the edge where the water collects as the tyre leaves the road surface there is a reduction in the area of contact for the volume of water and the water will leave quicker as long as the groove is wide enough. |
#10
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How much more work in the rain?
On Jan 17, 10:35*pm, "Mike Jacoubowsky"
wrote: So as I'm riding in the rain with my son today, trying to avoid the spray off his rear wheel (no fender), and then noticing how much water is coming off my front fender, I start thinking about the obvious. All that water, being transported *up* from the ground. That takes work. The question is, how much water is being moved up, and how high? I can't envision any sort of manner in which that effort is negated by an opposing force. My guess is that somebody has already done the math. Anyone here who's already done the work? I would assume that there are also traction losses that have to be thrown in. Also throw in the drag created by fenders, if you use fenders -- both aerodynamic and due to the pumping of water through the fender. Depending on the temperature, your body may also be working harder to heat itself, at least on the downhills. There is also the added losses caused by slowing greatly on corners or areas of questionable traction and then getting back up to speed. Loss of lubrication on your chain (yes, water is a lubricant, but on a long ride, my chain starts to feel like it is made of walnut shells). I raced for many years in the spring not-very-classics in Oregon, most run in the rain, and it was a lot of just coping -- coping with not being able to see anything because of wheel spray, hypothermia down hills, slow corners with jumps, crashes and crash avoidance, gritty water bottles, etc. -- Jay Beattie. |
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