# Touring - Weight on body versus on bike?

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View Full Version : Weight on body versus on bike?

deepakvrao
10-25-09, 09:43 PM
Just curious - I am currently 78kg [down from 88kg]. Now assuming the same fitness level, if I lose another 10kg of body weight, and ride with 10kg of weight as in panniers, will my effort versus speed be about the same?

What I am asking is 68 body weight plus 10 extra weight, is it sort of equal to 78 body weight?

benajah
10-25-09, 10:41 PM
Where the weight is makes a big difference. Weight in the wheels is the worst, on the body not so much. Panniers not so much either. Most likely it won't make that much of a difference.

staehpj1
10-26-09, 07:11 AM
Weight of the wheels is a much bigger deal than weight carried elsewhere, at least when climbing or accelerating.

No claim of scientific fact on this one, but my impression is that body weight seems to matter a lot less than gear weight. I have ridden at a fairly wide range of body weights and didn't notice nearly as much difference as when gear weight changed by a substantially smaller amount. It could just be that my body weight changed more gradually and gear weight changed in jumps and was therefore more noticeable though.

So my guess is that the answer is probably no. As I said that is just my impression though.

Cyclesafe
10-26-09, 09:11 AM
Mass is mass whereever it is on your bike or body. The more mass the more loss from friction and the more work necesssary to "lift" the bike over hills.

Rotational inertia is another matter, however. Along with mass, it also has to be overcome to ride a bike. Rotational inertia increases linearly with mass but with the square of its radius. So the distribution of mass is important.

The most obvious rotational inertia on a bike is from the mass of rims / tube / tire / nipples acting along the radius of the wheel, but there are many others. For example, low mount panniers exhibit less rotational inertia than high mount ones because distance between their center of mass and the ground (the radius) is lower. Other examples include whether or not you have a handlebar bag, whether you have a helmet, or even the distribution of your body weight.

From purely a physics perspective a pear shaped fat person has a mechanical advantage over a gym rat: both have unutilized mass, but the former is penalized the least.

LeeG
10-26-09, 11:45 AM
without a/b lab testing it's mostly anecdotal whether it matters if the weight is in body fat or the bike. It's easy no matter what weight you are to feel the difference when you put the weight on or off the bike, you can't do that with your body fat. My \$.02 of totally WAG opinion is that if you are starting with the lowest body fat ratio for a particular level of fitness you are starting with the highest power to weight ratio possible and any increase you put on the bike decreased that ratio, makes you slower to accelerate and slower up mtns. Not sure at which point high body fat interferes with total power output but I would guess there isn't a linear relation between removing fat and adding on the bike or putting on fat and taking it off the bike with regards to climbing mtns.
I am guessing the lean 175lb rider will climb a hill carrying 50lbs on the bike faster than the SAME rider weighing 225lbs carrying himself up the hill because the body fat is a load on the cardiovascular system. That 175lb rider carrying 30lbs up the hill will definately be faster than the same rider weighing 25lbs more AND carrying 30lbs.

Cyclesafe must be kidding regarding the rotational intertia of panniers.

Dan The Man
10-26-09, 12:00 PM
I would put my money on weight not being as significant a factor as density. 10 lbs of fat on your body is going be a pretty dense and compact package. You aren't adding significant frontal area by gaining 10 lbs. But 10 lbs in your bags will take up more volume and increase your coefficent of drag. I don't have any numbers on it, but I would bet that any power loss due to rolling resistance or hills for an extra 10 lbs will be smaller compared to the power loss from wind resistance for an extra 10 lbs of gear.

If you hit the right size and frequency of rolling hills, having a higher weight will actually make you more efficient because it carries more momentum over from the downhill to the next uphill, keeping your average speed steadier. Since power consumption increases with the square of speed, your energy consumption actually scales with the root mean square of your speed rather than the straight average of your speed. So that means that a lot of variation in speed (slow uphill and fast downhill) will take more work than a constant speed (high mass holds more momentum) even if you average the same speed overall.

Low weight is only really important for racers who need lightning quick acceleration to be able to attack on hills. For overall efficiency it is all about aerodynamics.

Wogster
10-26-09, 06:34 PM
Just curious - I am currently 78kg [down from 88kg]. Now assuming the same fitness level, if I lose another 10kg of body weight, and ride with 10kg of weight as in panniers, will my effort versus speed be about the same?

What I am asking is 68 body weight plus 10 extra weight, is it sort of equal to 78 body weight?

I'm looking at 100kg from slightly beyond the other side, and the only place weight really matters is on hills, on up hills the heavier bike + rider is going to be slower then a lighter bike + rider given the same general fitness level. Mind you a heavier rider can often produce amazing amounts of torque. There are 150kg guys who power their bulk up hills in gears that lighter riders get knee pains just thinking about. I know of at least one very heavy rider who bent a crank arm. :eek:

On downhills the heavier bike and rider have a distinct advantage:D On flat ground, once at speed, weight really doesn't make much difference, on rolling hills, it can be a wash.

Two riders one who is 78kg and a 68kg rider with 10kg in panniers and the same fitness level, on identical bikes, hmmm, the 78kg rider probably has a little more leg strength, due to the fact they carry those 10kg at all times, in raw power output it's probably the same.

I don't think for touring it makes much difference though, because power output levels are sustained for long periods of time, and if it takes you 20 minutes longer to get somewhere, it doesn't matter. For racing where the rider who is .001 seconds faster wins, it's a big deal....

sstorkel
10-26-09, 10:31 PM
What I am asking is 68 body weight plus 10 extra weight, is it sort of equal to 78 body weight?

That depends: are you going to lose 10kg of body fat? Or 10kg of muscle?

If you can lose 10kg of body fat and then add back 10kg of luggage, my guess is you won't notice a huge difference. It's when you're losing muscle that you'll start to notice a difference, I'd guess.

efuentes
10-26-09, 10:42 PM
If you can afford to lose 10 Kg of fat without getting too low on your Body Fat Index (Lets say below 10-12%) you body will be more efficient overall, and that will translate into better cycling performance.

BengeBoy
10-26-09, 11:14 PM
Have fun with math:

http://www.analyticcycling.com/

10-26-09, 11:16 PM
Well your front to back and side to side weight ratios are SOOOO important that the only way to properly have it adjust is to ride with your setup and adjust it accordingly. on any slope, you will be able to feel a weight imbalance.

I remember loading up the back the first day out and doing wheelies for the first 5 miles of climbs. Definitely make use of good pannier setup and or a towing trailer.

Rosso Corsa
10-26-09, 11:19 PM
The panniers would have a much bigger aerodynamic effect than weight in your body.

Front Half
10-27-09, 02:02 AM
If the weight is transferred from body to panniers, it should sit lower on the bike. The lower the weight, the more stable the bike. Therefore less effort will be required to stablize the bike, resulting in more effort applied to speed.

JohnyW
10-27-09, 04:02 AM
Hi,

it's different 10 kg body mass you transport every second - you are trained on that. 10 kg more luggage on bike is in beginning additional weight - later you will be trained. But still weight on the bike is always different where you mount it (lowrider, frame, rear rack, handlebar bag)...
On the body is the most economic way to transport 10 kg. Unfortunately you can't camp in your body fat...

Thomas

I don't mention it if I transport 5, 15, 25, 35 or 45 kg on the bike. But my measured speed reduces.

stevage
10-27-09, 06:55 AM
I'd just like to point out that weight (wherever it is) also matters more on rough or muddy surfaces more than on roads, just like it matters more for hills more than flat surfaces. I guess it's because momentum helps you less when you're battling friction.

deepakvrao
10-27-09, 07:02 AM
Thanks guys. Guess I need to lose the weight in the first place ;-)