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interesting stuff in RR27(11 posts)

interesting stuff in RR27Steve_0
Sep 23, 2002 5:14 AM
Mike Barnes used the Whitt & Wilson power model to prove a 170 lb rider/bike combo climbing a 6 percent grade (at ~10.5 mph) will lose ~1.6 seconds per mile per extra pound of weight given a fixed output of 250wts.

Empirically, we all know bike weight to be largely irrelevent on flat and descending terrain; however this data can lead one to conclude the 'advantage' of a light climber can sometimes be more mental than actual.

Interesting.
matches Analytic Cycling calcsDougSloan
Sep 23, 2002 6:23 AM
That finding matches the calculations at Analytic Cycling. http://www.analyticcycling.com/ForcesLessWeight_Page.html

However, I don't think that is "more mental than actual." If you are talking about a 20 gram change, sure, that's not much. But if you are talking about 10 pounds over a 6 mile hill, that's huge.

Benefit From Less Weight
This Much Less Weight 0.453 kg
Over This Distance 1609.3 meters
On Hill of Slope 0.06 Decimal
Faster by 1.61 s
Ahead by 7.74 m
Frontal Area 0.5 m^2
Coefficient Wind Drag 0.5 Dimensionless
Air Density 1.226 kg/m^3
Weight Rider & Bike 77.1 kg
Rolling Coefficient 0.004 Dimensionless
Power 250 watts

Doug
yes and noSteve_0
Sep 23, 2002 7:50 AM
10 #s, 6 miles ~96 seconds.
Huge in a TT? certainly.
Huge for your saturday rides? probably not.
butDougSloan
Sep 23, 2002 8:27 AM
I assumed that if we are discussing time differences, then we were doing so in a context of something that matters. If you're just out tooling around on a Saturday morning, then it doesn't matter a bit, as long as you have enough strength to get up the hill and get home. If you are competing, then every second matters. I don't know of any racer would give up 96 seconds up one hill if they could avoid it. Multiply that by lots of hills, or losing the group (and draft) for the balance of an event, and it becomes critical.

Doug
butSteve_0
Sep 23, 2002 8:50 AM
actually, I was speaking entirely within the context of something that DOESNT matter.

Theres no denying weight shavig helps in a very competitive environment over rolling terrain; however I see plenty of non-competitive cyclists who are (overly) obsessed with bike (or worse, component) weight.

Just wanted to share some numbers for those who ~think~ they need to shave weight (as opposed to the few who KNOW they do).
ohDougSloan
Sep 23, 2002 9:34 AM
So, you are informing all those misguided souls who thought that weight mattered, even though they are not competing, that they should be fat and happy and forget about weight? I'm sure they will be relieved.

However, some people can appreciate a light bike regardless of competition, much the same as it's a joy to drive a 2200 pound sports car even if you are not on a race track. Light is not only faster, it can be fun, too.

As I said, too, there is a hobbiest aspect to light stuff. Even if you can't "justify" light parts from a competition perspective, some people enjoy the process of building a light bike. There must be hundreds of analogies, from engraved shotguns to aftermarket allow wheels for street cars we drive. Those people may well obsess about their hobby, and I see nothing wrong with that, either.

Finally, I don't believe anyone needs to be ashamed of having a expensive, good quality, light bike despite not being a racer or even if they are carrying a few extra pounds. They don't need to justify it to anyone, and I, frankly, get really tired of seeing people scoff at others or impliedly requiring them to justify what they do or ride (or drive, for that matter). There is entirely too much judgment and intolerance going on. If someone prefers a heavier bike, prefers not to spend the money for a light bike, they need not be defensive or question others who are different. If a guy 100 pounds over weight wants to ride an $8,000 bike and obsess about titanium parts, I say "have at it!." The more the merrier.

Sorry for the quasi-rant, and this isn't directly solely at this post. It just seemed to me that there is an implication that light must be justified.

Doug
regarding your last sentence...Steve_0
Sep 23, 2002 11:13 AM
The only (intended) implication was that there is (undeniably) pressure to obtain and/or sell lighter components as 'better'.

Walk into many a bikeshop (heck, peak on this board now and then) and people are espousing the 'benefits' of a light bike.

As I agreed in my other posts, there ARE quantifiable benefits in racing, but this is the 'general' discussion board, which includes many non-racers and novice/young riders which, as you acknowledged, will realize a de minimus of return (but anticipate dramatic return).

My post was directed towards those people, not those as 'guided' and defensive as yourself.

Peace,

Steve.
Still way easier and cheaper to take 10 lbs. off the rider....Silverback
Sep 23, 2002 7:45 AM
...than 10 ounces off the bike, in most cases. I see people all the time agonizing over a 30-gram difference in derailleur or bottle-cage weight, but carrying a 10-pound roll under their jerseys.
easier?DougSloan
Sep 23, 2002 8:35 AM
Your point is good that if someone is concerned about speed and weight, they should lose everything they reasonably can off their bodies and their bikes.

However, I disagree that it is "easier" to lose weight off the body. I can buy some parts and slap them on the bike in 10 minutes and drop several pounds off a bike. If you do this from the beginning, and not replacing decent parts, it's not all that expensive, either.

I don't buy into the argument that you can't be concerned about bike weight if you have any excess body fat. They are two separate issues. While you should be conscious of both if you compete, it is perfectly legitimate to reduce bike weight even if you are carrying a few extra fat pounds. Weight is weight, and lower generally gets you up the hills faster.

If you don't compete, then dropping weight off a bike is more of a hobbiest concern than performance. At that point, you're pretty much doing it for fun.

Everyone should ride a 15.0 pound bike and have 4% body fat, right? :-)

Doug
Big Fat 170 pounder weighing in....funknuggets
Sep 23, 2002 2:30 PM
96 seconds huh.... who needs math? Plus... races never finish at the top of a hill, right? Just wait for the race with the long downhill finish. With the same bike, I have 10 pounds more potential energy just waiting to come down like an avalanche. I just know that my fat ass is rolling down the hill faster than those string beans ahead of me, so get out of the way before I run over your butt and cross the finish line and make a bee line for my cooler of ice cold slim fast.
responding to yourself, is that fred?funknuggets
Sep 24, 2002 6:49 AM
I got it wrong, not potential energy... the fat guy would get to the bottom faster than the skinny guy due to coefficient of friction and likely some aerodynamic principles. I talked to my brother in law who is a astrophysicist for John Hopkins and he said the fat guy wins a downhill race...