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Old 05-22-02, 12:53 PM   #1
Aerow
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All things being equal...

How much more advantage would a 170 pound (77.1kg) rider have over a 180 pound rider (81.6kg?)

Over a 40k (24.8 miles) course, what kind of a time difference would we be looking at?

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Old 05-22-02, 01:41 PM   #2
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why would anyone care?
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Old 05-22-02, 02:09 PM   #3
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why would anyone care?
probably he is one of the person and he is probably thinking of challenging his boss for raise on a winner take all bet, he wins he get a rasie he, loses, he gets fired, so he must be really sure mathematically that he can beat his boss on a race
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Old 05-22-02, 02:17 PM   #4
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buzzzzzzzzzzzz! Both wrong!

I'm actually trying to decide if it worth losing that extra 10 pounds. I'd really have to hate giving up those pop-tarts! But if it gives me another 1mph on my average speed, I may need to suffer.

Otherwise, it's pizza again for dinner!

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Old 05-22-02, 02:21 PM   #5
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Eat the pizza...and ride like hell tomorrow!
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Old 05-22-02, 02:24 PM   #6
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exactly the answer i was looking for!
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Old 05-22-02, 02:26 PM   #7
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The bigger guy could probably take the smaller guy in a fight, other than that...
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Old 05-22-02, 02:30 PM   #8
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Ahhh .. one of the great things about laying down the miles ... you can eat whatever the heck you want! Well, maybe on Sunday.
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Old 05-22-02, 02:30 PM   #9
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Well, momentum is mass times velocity, so I'm guessing that if the two ran into eachother, the heavier rider would do more damage to the smaller rider. So keep that weight up.

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Old 05-22-02, 02:44 PM   #10
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Well, momentum is mass times velocity, so I'm guessing that if the two ran into eachother, the heavier rider would do more damage to the smaller rider. So keep that weight up.

andy
Guys guys, guys,
your'e not helping the kid,see first he must tell us were he buys his Pizza, then we tell him what to do and how to train with a weight of 170 or 180 :angel: :angel:
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Old 05-22-02, 02:50 PM   #11
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Mother Bear's - Bloomington, IN

Now 'fess up!
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Old 05-22-02, 06:27 PM   #12
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Mother Bear"s???
Has the food there gotten any better than when my sis went to IU? It stunk back then.
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Old 05-22-02, 08:02 PM   #13
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don't know when your sis went to IU, but when I was there (circa 1988) the pizza was the best around.

:thumbup:
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Old 05-22-02, 08:23 PM   #14
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Pete's uh...

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Old 05-22-02, 09:47 PM   #15
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Quote:
Originally posted by Aerow
How much more advantage would a 170 pound (77.1kg) rider have over a 180 pound rider (81.6kg?)
10 pounds.

Quote:
Originally posted by Aerow
Over a 40k (24.8 miles) course, what kind of a time difference would we be looking at?

12.32 seconds
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Old 05-22-02, 11:03 PM   #16
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I don't know about time trials, but if you drop 10 pounds you will almost certainly be a better climber.
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Old 05-23-02, 01:11 AM   #17
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I have 3 time trial courses that I use to gauge my fitness. 2 of them are very hilly and since I dropped some weight, my times have improved dramatically.

I've dropped 15 pounds since Jan 3 and my climbing is really coming on.

It's also easier on my old knees.

Lose the weight. Tear up the road.
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Old 05-23-02, 03:03 AM   #18
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There are way too many factors to calculate it correctly. As many have already suggested, weight only matters on hills and in accelerating. You need to know the grade of the course, your frontal area, the wattage you can pump out, etc.

But, let’s make some assumptions and see what we come up with. I shall use the formula given at http://www.sportsci.org/encyc/cyclin...ngupdown.html. (Please don’t anyone get on my case about my assumptions. They seem reasonable, and I am just using Swain’s equations supplemented by information I found elsewhere. Also, I am not accounting for gear selection and so forth. In short, your mileage may vary.)

Let’s pretend your course is 30 km of flats plus 5 km uphill at a grade of 4% and 5km downhill at 4%. Let’s also pretend you can pump out 250 Watts, and that you do pump out these 250 W over the entire course. We’ll call your frontal area .48 meters squared (which is an average of many numbers I have seen posted). And we’ll assume that your bike weighs 10 kg (making the two “rider + bike” weights: 87.1 and 91.6). Finally, let’s discount acceleration, since that would be almost impossible to model (although it plays a clear role, especially if the course requires a lot of deceleration and acceleration).

At both weights, you will cover the 30 km on the flats at a speed of 32.7 km/h, which makes a time of 0:55:03.

At 87.1 kg, you’ll go 19.5 km/h on the uphill part of the course and 47 km/h on the downhill. The uphill would take 15:23, the downhill 6:23. That makes a total time of 1:16:49.

At 91.6 kg, you’ll go 18.9 km/h uphill and 47.6 km/h on the downhill. The uphill would take 15:52, the downhill 6:18. That makes a total time of 1:17:13.

So, by dropping the 4.5 kgs, you’ll be able to do the course 24 seconds faster. Note that at the heavier weight you get a “downhill bonus” of 5 seconds. But, at the lighter weight you get an “uphill bonus” of 29 seconds. This is why climbing matters in bicycle racing.

Okay, experiment over. We can now all return to the real world--which means, go out and time yourself, then lose the weight and time yourself again. Let me know if my calculations are even remotely correct!

Cheers,
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Old 05-23-02, 04:57 AM   #19
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ok, i need to read through Jamie's message and his link, but first

Quote:
There are way too many factors to calculate it correctly. As many have already suggested, weight only matters on hills and in accelerating. You need to know the grade of the course, your frontal area, the wattage you can pump out, etc.
jamie
Quote:
At both weights, you will cover the 30 km on the flats at a speed of 32.7 km/h, which makes a time of 0:55:03.
jamie

this idea that weight only makes a difference on hills and accelrating i just don't believe... so on flats extra weight has virtually no penalty i just don't buy... (there was another thread about heavier riders faster downhill and heavy bike vs light bike, etc)

if that were the case, then why on a very flat camping-tour last weekend where i had my BOB trailer packed with tent, sleeping bags, water, food, etc. and it weighed something like 30kg i struggled to go 25kph on flats with good smooth asphalt and relatively high-pressure tires, when i can take the trailer off-road with maybe 5-10kg and ride on rolling gravel trails with knobby tires at a faster pace with less effort???

and the increase in wind resistance is virtually nil b/c the trailer rides low and behind me...

someone mentioned the increased rolling resistance from weight causing the tires to deform more... maybe that's it...

just from the top of my head... the idea that a body in motion stays in motion so a heavier bike/rider requires no more energy to keep at speed i also find wrong... to sustain a speed on a flat, there must be a balance of forces: rolling resistance which is higher with more weight, and wind resistance which is probably about the same must equal the power from the pedals, so the equilibrium speed for 2 bike/riders of different weights but with the same wind profile and power will have different speeds if for nothing else than the increased frictional force from increased tire deformation from the extra weight...

? any way, i don't have a real scientific answer for you about the benefit of loosing 10lbs... but i am pretty sure that it would make a significant difference. and if you ate better and trained more in order to loose the weight you would gain even more of an advantage... i'd say go for it! if you ride a ton and eat a little less junk food super-lightweight sugar/fat foods then it should come off relatively easily in 3-6 months until the end of the season...

from Jamie's example, i would guess you'd gain more like 1 minute or more...

Last edited by nathank; 05-23-02 at 05:00 AM.
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Old 05-23-02, 07:40 AM   #20
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When towing a trailer, even on the flats, both rolling and wind resistance are playing a larger role than is at first obvious, but air resistance still takes the prize.

Rolling resistance is a function of mass * gravity and the frictional coefficient of the tires. Adding weight, does increase the rolling resistance. For cycling, it is often neglected or dismissed because it is so small against air resistance. In the example I posted, it accounts for around 30 Watts of the 250W. And I was using a very low friction coefficient (.004), which I saw often posted as for a racing tire on asphalt. I have seen MTB tire coefficients at .012 or more, meaning they eat up 3 times as much energy. Without having meaningful frictional coefficients for the trailer tires and bike tires, it would be hard to assess their affect in the two situations you mentioned. (BTW, I modified Swain's calculation slightly to include gravity in the friction part--he doesn't mention it, perhaps factoring it into his frictional coefficient, which he only vaguely defines. But since Force = mass*acceleration, you have to have an acceleration (the gravity constant) for the calculation to make sense.)

Also, with respect to the trailer, you have to add its frontal area to that of the rider and the bike. You can, of course, discount part of it, since it is drafting off of you. But, the lower the trailer, the less draft it will get from your upper body (your most significant frontal area). If we suppose that the trailer is 50cm wide and 40 cm tall, that still adds 0.2 meters squared. If we give it a generous 20% drafting deduction, that makes .16 m^2 (and we haven't considered the egg beater effect from the added two wheels). Going from .48 to .64 is a huge difference. If I take the 87kg posted above and add the area into the calculation (not adding any mass), the same 250 Watts will get you 29.8 km/h rather than 32.7 km/h. If we add 30kgs to the trailer, you should be able to go 29.4 km/h.

The frontal area (i.e. “aerodynamicness” of your riding position) really matters. I used the .48 m^2 area because I supposed a mid to large-sized rider in a normal position. If I use .42 (still in the mid range), the same 250 Watts will allow an 87kg rider to go 34.1 (instead of 32.7). If we use a super-aero position (estimated as low as .32 m^2), we could go 37.2 for the same energy output on the flats (although I believe this super-aero position can only be held while not pedaling). On a 6% descent, our imaginary rider in his super-aero position would go 56 km/h without even pedaling. Whereas, sitting normally in the saddle (.48) would slow him to 46 km/h.

Calculating the frontal area seems to be one of the big difficulties in doing these equations. I am just using averages of what I have seen posted, and make no claims about their validity.

I did all these calculations (and the surfing to find the equations) because I had mistakenly believed that less weight would save significant time in a race (on the flats). Having been corrected in this forum, I got curious about how all the different forces effect the cyclist. As was pointed out to me, an object in motion tends to stay in motion unless acted upon by a force. Air resistance is (by far) the most significant force at any speed above 15-20 km/h (on the flats).

Cheers,
Jamie
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Old 05-23-02, 08:46 AM   #21
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too late. i ate the pizza.

so as AlphaGeek pointed out way back when, i will ride like hell today and forget all about my original question.

(i must admit this has been very educational!)

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