The same person on a much lighter bike will go faster. The same heavy person losing 50 pounds using the same bike will go much faster than they did before on the lighter bike. The same heavy person that rewards himself/herself with a new lighter bike for losing the weight will go faster with a bigger smile.

+1

. . . and as we age a bit, we also tend to slow down a bit.
At age 73, am nowhere near as fast as what I was 20 or 30 years ago . . .
If you got the extra coins, get the fancy/lighter bike; if not . . . pedal on!

The Weight vs. Wind resistance Tradeoff (http://www.recumbents.com/wisil/Hein/Hpvpaper.htm)

I would imagine a light rider would also be more aerodynamic, and thus faster, another advantage to losing weight. Or just get a fairing and be as big as you want.

Another thing to consider is rolling resistance of the tires. Will it be higher for a heavier rider or does the heavier rider increase the pressure in the tires to maintain the same contact area on the road as the lighter rider.

Another paper stressing aerodynamics of the bike (http://www.recumbents.com/wisil/Hein/ME599_Report1.pdf)

On the road cycling forum it's been the general concensus that on the flats, the weight of the bike matters little if any. Heavier, but more aerodynamic wheels will give you a speed boost, more evident at higher speeds/faster riders. Magnus Backstedt, the largest UCI rider, also goes for speed records.

When deciding whether to get a lighter bike, don't fall into the trap of thinking that a ligher bike only represents a x% reduction in total bike and body weight.

It takes just as much energy for a 150 pound man to pedal an extra 5 or 10 pounds of bike up a hill as it does a 250 pound man. Simple physics. Its the same weight and the same hill. Each man derives the same benefit from reducing the same bike weight.

Restated, the amount of energy to move an extra five pounds up a hill is independent of the motor pushing it up.

* * *

Don't even think that the extra bike weight will help you go faster on the downhill. It will, but not enough to make up the additional time spent pushing it up. That's why the Tour de France has minumun weight limits for bikes, but no maximum limit.

I weigh 326 lbs
Mooky

In that case, you probably exceed the maximum weight rating for most lightweight bikes anyway.

Go for it!
Get a nice bike that you'll enjoy riding and you'll ride it more.

I love physics!

I read with great interest the reference to a "gravity boost" on the downhill as a result of heavier loads carried on bikes. By extension, the same argument could be made with reference to heavier bikes as well. The reality is this: downhill runs do not become faster as a result of having heavier bikes. This thinking goes against what has been known in the field of physics ever since Da Vinci. If you recall, he dropped similarly shaped and sized weights off the leaning tower of Piza. They were made of different materials and weighed differently. They would hit the ground at the same time in spite of being of differing weights.

This is the case because compared with the size and mass of the planet, (the gravity source) they are for all practical purposes, of the same relative weight and mass.

Da Vinci concluded that where there is a difference in the rate of fall of objects, it is due to confounding variables, wind resistance, for example. A feather, or a parachute will fall more slowly than a steel ball because of air resistance, a counfounding variable in our equasion.

When riding up hill, weight does make a difference as we must work to move the weight against gravity. Therefore, a lighter bike will climb more easily than a heavier one. On the flat, weight makes little difference as inertia plays a role. Once an object is set in motion, it tends to "want" to remain in motion unless acted upon by other factors, rolling resistance (friction), for example. Accelerating a bike to one's desired cruising speed will be affected by weight in much the same manner as climbing hills would.

As an experiment, try coasting downhill (don't pedal) with and without an additional load. The weight and configuration of the bike will make no difference. Just make certain you use the same bike for both runs. Sit on the bike in the same position in both the loaded and unloaded conditions. Use the same line on the same hill in both cases. The independent variable is weight and the dependent variable is speed. All extraneous variables have been controlled. Note the speed on the cyclometer at the conclusion of the run in both the loaded and the unloaded conditions. I predict the null hypothesis, that you will see no significant difference in speed. If you do see a difference, do not pass go, proceed directly to the Nobel prize for physics, and collect that $200.00! :)

Cheers

Charles

Hey, I agree, however, it was Galileo who did that. And Newton later sorted out all the laws of gravity.

Since we're getting into correcting mistakes, the thing that made me laugh most on this thread was Piza, probably as in Pizza. Sure that's how you say it, but it's spelled Pisa!

I was training for a century. A work friend had been a nationally ranked road racer. He also happened to have a Ph.D in exercise physiology and be in charge of the human performance lab at the hospital where I worked. I was asking him about the value of some overpriced aerodynamic parts as an upgrade for my bike. He waited until I had finished presenting my ideas and looking at my abdomen said, "Steve, excuse me." He gently poked a finger into the three inch roll of fat around my waist. "Losing this won't cost a dime. Let's talk again after you do that." I did lose it and my average speed, my endurance, my climbing, and my recovery times were all improved. Usually it's the engine.

Hey, I agree, however, it was Galileo who did that. And Newton later sorted out all the laws of gravity.
Actually its doubtful that Galileo ever dropped anything off the tower of Pisa. If he had, he would have declared that heavier objects *do* fall faster than lighter ones. Light and heavy objects fall at the same rate -- in a vacuum. But, as any biker knows, we don't live in a vacuum -- we're surrounded by air and wind. What the historical Galileo did was much less dramatic but more scientific -- he rolled objects down very shallow planks. By using shallow planks, he was able to accurately time the movements and reduce the effect of air resistance.

So, its quite possible that if a light biker and a heavy biker both roll down the same hill, and both have the same profile to the wind, that the heavier biker will come out ahead since he has more potential energy to expend at the top of the hill against the air resistance pushing back. The wind resistance going up the hill is probably not significant since wind resistance increases per the cube of the speed.

Still, one assumes that the overall effect of additional weight must be negative, since you don't hear of professional racers strapping weights to their frames or bodies. :D

Ah! But what about two identical riders, one with a 20 lb bike, one with a 30 lb bike. What if the rider of the 30 lb bike loses 10 lbs of pure fat off his body?

Who's faster now? Or are we now into the realm of apples v. oranges?

Usually the heavier rider on the 20lb bike. There is some strength tradeoff for the weight loss.

Few years a ago was in Africa. No bike, feeling glum and fat. Bought an indian made bike called a "HERO" heavest thing you can imagine. Rode like cement. Rode it across E.Africa, got dysentery, got a sun tan, got thin. Bike was still crap.

I few when I got home.

Give it a go. Cheaper that Carbon Fiber

You know, I've never ridden a recumbant bike (nice forum by the way :D ), so if any of my observation seems whack, it probably is.

On a mountain bike, the a rider/bike combo will benefit from having more weight (bottles, repairs, etc) moved up onto the rider because that weight will be suspended by the rider's arms and legs. More weight on the bike - "unsprung weight" - hampers the bike's ability to move vertically and bounce over obstacle. For this reason it's beneficial for a fat guy to ride a lighter bike.

On a recumbant bike, at least from what I can observe, the rider is supported by the seat. The rider is unsprung. This would seem to wash some of the difference between rider weight and bike weight.

Just a little input. Again, I don't know much about recmbants so I welcome any corrections here.