Weight on flat ground
08-15-14 | 07:51 AM
#26
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From: Vancouver, BC
It's all about inertia, air-resistance and friction
The question is not new... Triathlete Magazine 1999
We have two riders competing against each other in our hypothetical time trial.
The first is Mr. Heavybike, whose bike weighs 22 pounds.
Then we have Mr. Lightbike with a 17.6-pound bike.
Both riders are identical, each weighing 165 pounds and able to produce 250 Watts of power in our time trial. Both bikes are also identical except for weight. Both riders have equal aerodynamics. These are typical values for riders who can do a one-hour 40K.
If you look at the physics, the weight has no input into the calculation of drag on a flat course, except in one place: Rolling resistance. This is the drag created by the tires against the pavement, and it is really heat generated by the rubber as it deforms across the contact patch. When we do the math, 250 Watts will propel Mr. Lightbike at 24.99 mph, and Mr. Heavybike at 24.96 mph. That gives Mr. Lightbike about a 3-second advantage in 40 km. When was the last time you lost a race that long by three seconds? How much is that three-second gap worth to you? That’s the consideration when you pay a bunch extra for lighter parts, and only you can assign that value. But remember that we are comparing bikes that are 4.4 pounds different, not 4.4 ounces.
The question is not new... Triathlete Magazine 1999
We have two riders competing against each other in our hypothetical time trial.
The first is Mr. Heavybike, whose bike weighs 22 pounds.
Then we have Mr. Lightbike with a 17.6-pound bike.
Both riders are identical, each weighing 165 pounds and able to produce 250 Watts of power in our time trial. Both bikes are also identical except for weight. Both riders have equal aerodynamics. These are typical values for riders who can do a one-hour 40K.
If you look at the physics, the weight has no input into the calculation of drag on a flat course, except in one place: Rolling resistance. This is the drag created by the tires against the pavement, and it is really heat generated by the rubber as it deforms across the contact patch. When we do the math, 250 Watts will propel Mr. Lightbike at 24.99 mph, and Mr. Heavybike at 24.96 mph. That gives Mr. Lightbike about a 3-second advantage in 40 km. When was the last time you lost a race that long by three seconds? How much is that three-second gap worth to you? That’s the consideration when you pay a bunch extra for lighter parts, and only you can assign that value. But remember that we are comparing bikes that are 4.4 pounds different, not 4.4 ounces.
08-15-14 | 07:58 AM
#28
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Having ridden a 60 pound touring bike, once up to speed the weight isn't as obvious as you might think. Hills, of course, are a different story.
At 20 mph, 50% of your energy is spent to overcome air resistance, at 30 mph, it's closer to 90%.
At 20 mph, 50% of your energy is spent to overcome air resistance, at 30 mph, it's closer to 90%.
08-15-14 | 09:06 AM
#29
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The only relevant component is air resistance on the flats, not the weight. So if the guy lost 50 pounds but had the same aero-profile his speed would be unchanged. And if he gained 50 lbs and had a better aerodynamic profile his speed would increase.
08-15-14 | 09:13 AM
#30
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anyone mention acceleration? weight affects acceleration. cycling is all about speed changes and all those instances of acceleration add up and affect overall avrg speed. I think :-)
08-15-14 | 09:17 AM
#31
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From: Vancouver, BC
That was my point. There is a direct correlation between weight and aero profile. Also between efficiency and bodyfat %. So adding 50 lbs of weight to a rider is different than adding lead weight inside a seat tube.
08-15-14 | 09:21 AM
#32
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From the same article above and of course the weight could just as well be on the rider and not the bike, it's only about the aerodynamics:
What if the reason Mr. Heavybike’s bike is heavier is because it is more aero?
Let’s suppose that Mr. Heavybike is only 1% more aero on his bike. To achieve that, he would only have to reduce his frontal surface area by 1%, from 0.5 square meters to 0.495 square meters. This is pretty easy unless Mr. Heavybike’s position is already very carefully refined. A 1% reduction in aerodynamic drag will increase his flatland speed to 25.03 mph. That’s faster than Mr. Lightbike’s 24.99 mph. But what if Mr. Heavybike borrowed his machine from Mr. Reallyheavybike. How much would his bike have to weigh to soak up a 1% aero advantage? The answer is about 11 pounds more than Mr. Lightbike’s machine. So, Mr. Lightbike is stylin’ at the start line with a 17.6-pound bike, but Mr. Heavybike will match his performance on a 29-pound bike if he’s only 1% more aero.
What if the reason Mr. Heavybike’s bike is heavier is because it is more aero?
Let’s suppose that Mr. Heavybike is only 1% more aero on his bike. To achieve that, he would only have to reduce his frontal surface area by 1%, from 0.5 square meters to 0.495 square meters. This is pretty easy unless Mr. Heavybike’s position is already very carefully refined. A 1% reduction in aerodynamic drag will increase his flatland speed to 25.03 mph. That’s faster than Mr. Lightbike’s 24.99 mph. But what if Mr. Heavybike borrowed his machine from Mr. Reallyheavybike. How much would his bike have to weigh to soak up a 1% aero advantage? The answer is about 11 pounds more than Mr. Lightbike’s machine. So, Mr. Lightbike is stylin’ at the start line with a 17.6-pound bike, but Mr. Heavybike will match his performance on a 29-pound bike if he’s only 1% more aero.
08-15-14 | 09:24 AM
#33
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From: Haunchyville
For a more in depth discussion, read this thread: https://www.bikeforums.net/road-cycli...article-2.html
08-15-14 | 09:31 AM
#34
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I'm sorry there is no direct correlation between weight and aero profile. Maybe for a given individual you could prove that they are less aerodynamic as their weight increases, but it depends where the weight goes. A lot of weight winds on on your stomach and butt and that could even improve your aerodynamics. Look at Zipp wheels, they increased the width and they became even more aerodynamic.
08-15-14 | 09:38 AM
#35
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From: Vancouver, BC
I'm sorry there is no direct correlation between weight and aero profile. Maybe for a given individual you could prove that they are less aerodynamic as their weight increases, but it depends where the weight goes. A lot of weight winds on on your stomach and butt and that could even improve your aerodynamics. Look at Zipp wheels, they increased the width and they became even more aerodynamic.
There's a reason TT champions aren't fat.
08-15-14 | 09:47 AM
#36
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For most people riding in an optimal aero position their legs are close to their chest and stomach adding a couple extra inches to their waist and chest is clearly going to have an impact on how low they go. Maybe if you're riding around on the tops or hoods it won't matter as much but you still won't put out as much power with an extra 50lbs of fat so you'll be slower.
There's a reason TT champions aren't fat.
There's a reason TT champions aren't fat.
What if they lost 50 pounds and had a fused vertebrae, and couldn't get into an aero position? Could we conclude that less weight is less aero? No; only that the proper aero position is the only thing that counts, not the weight.
08-15-14 | 09:57 AM
#37
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Give him another 50 pounds and he's going 18.6 miles per hour.
estimations from an online power calculator (21 pound road bike, on the drops, everything else default values)
.8 miles per hour difference is not nothing!
08-15-14 | 10:06 AM
#38
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If our hypothetical roadie is putting out 160 watts and weighs 150 pounds he'd be going 19.4 mph on the flat road.
Give him another 50 pounds and he's going 18.6 miles per hour.
estimations from an online power calculator (21 pound road bike, on the drops, everything else default values)
.8 miles per hour difference is not nothing!
Give him another 50 pounds and he's going 18.6 miles per hour.
estimations from an online power calculator (21 pound road bike, on the drops, everything else default values)
.8 miles per hour difference is not nothing!
08-15-14 | 10:13 AM
#39
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The calculator isn't that sophisticated. The 50 pounds could be anywhere, even on the bike frame, and it would give the same result. It just illustrates that 50 more pounds at a moderate effort does make a significant difference in speed, even on a perfectly flat road.
08-15-14 | 10:20 AM
#40
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I'd probably agree with you, between those choices.
The calculator isn't that sophisticated. The 50 pounds could be anywhere, even on the bike frame, and it would give the same result. It just illustrates that 50 more pounds at a moderate effort does make a significant difference in speed, even on a perfectly flat road.
The calculator isn't that sophisticated. The 50 pounds could be anywhere, even on the bike frame, and it would give the same result. It just illustrates that 50 more pounds at a moderate effort does make a significant difference in speed, even on a perfectly flat road.
08-15-14 | 10:43 AM
#41
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For most people riding in an optimal aero position their legs are close to their chest and stomach adding a couple extra inches to their waist and chest is clearly going to have an impact on how low they go. Maybe if you're riding around on the tops or hoods it won't matter as much but you still won't put out as much power with an extra 50lbs of fat so you'll be slower.
There's a reason TT champions aren't fat.
There's a reason TT champions aren't fat.
08-15-14 | 02:25 PM
#42
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I do see big heavy guys doing 20+ mph on flats, but they are never fat. Next to impact on aerodynamics, excessive fat must also hurt the ability to produce large amount of power for long time on bicycle. Maybe because it becomes very difficult to remain stable in the saddle while doing 90-100 RPM.
08-15-14 | 02:54 PM
#43
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From: Haunchyville
For most people riding in an optimal aero position their legs are close to their chest and stomach adding a couple extra inches to their waist and chest is clearly going to have an impact on how low they go. Maybe if you're riding around on the tops or hoods it won't matter as much but you still won't put out as much power with an extra 50lbs of fat so you'll be slower.
There's a reason TT champions aren't fat.
There's a reason TT champions aren't fat.
08-15-14 | 02:59 PM
#44
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I do see big heavy guys doing 20+ mph on flats, but they are never fat. Next to impact on aerodynamics, excessive fat must also hurt the ability to produce large amount of power for long time on bicycle. Maybe because it becomes very difficult to remain stable in the saddle while doing 90-100 RPM.
1) Not all riding is done where the terrain is flat and riding up hills is much more difficult with excess weight. That makes bicycling far less enjoyable for those carrying around lots of extra pounds without corresponding muscle strength. As a result, these individuals will be under represented in the cycling population.
2) If you do much riding at 20+ mph, even on flat terrain, you're burning quite a few calories therefore making it less likely that you'll be gaining much weight (and more likely that you'll be losing some if currently overweight).
08-15-14 | 04:28 PM
#45
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I do see big heavy guys doing 20+ mph on flats, but they are never fat. Next to impact on aerodynamics, excessive fat must also hurt the ability to produce large amount of power for long time on bicycle. Maybe because it becomes very difficult to remain stable in the saddle while doing 90-100 RPM.
08-15-14 | 09:25 PM
#47
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I have a friend who is around 265-270 and he races as a cat 3. On flat ground he is an absolute ox. I used to ride with another guy who was at least 250 but he could get aero, his back as flat as a table. That guy would pull for miles on the flats.
08-16-14 | 01:28 AM
#48
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The point is that although weight plays a small role on the flats. If that weight is bodyfat and if it is not only 20 or 30 lbs but 50+ lbs, then it will be very hard for these people to maintain 20+ mph speeds. Another thing that happens with excess body fat is that body overheats much faster and will shut down to protect itself.
08-16-14 | 07:11 AM
#49
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I think he's 6'3" actually. He looks like a football lineman, big all over with a big gut. He broke 5 hours in the Tour fo Tucson once and was very close 2 other times. Yes, that includes a lot of drafting, but it's still 109 miles.