So I guess from reading here and talking to several people, the general consensus is that weight has little to no effect on speed on flat ground.

I don't really understand how this can be true. Regardless of the terrain, you are applying the same amount of power to move a heavier weight...kinda like the importance of horsepower to weight ratios in fast cars. I see in strava, there's a guy I have known since I was a kid that has the KOM for many segments around here and his speeds are commonly in the upper 30 mph range. He is easily 230 or more. If he weighed 30-50 lbs less, wouldn't he be much faster? If not, how is this possible? I just can't get how weight has NO effect on flat ground speed.

Someone explain it to me.

Most of what you're overcoming on flat ground is air resistance. That's influenced by your shape/how low in the drops you can get/etc, but weight has little to do with it (yes, bulk will make you a little bigger in cross-section, but so will an unzipped jersey). His zero-to-thirty would be slower than someone lighter, because he has to get that bulk going, but once it's in motion, air resistance is the key.

Uphill, of course, everything is different. And downhill, in the opposite direction.

it could very well be that at higher speeds, as with cars, aerodynamics/ wind resistance holds you back more then weight. same reason an old Lincoln and a new pickup have similar fuel economy. He very well could be a very powerful guy, but his W/KG don't show it because he's a bigger guy. but since he may just have more raw power, is able to go faster.

I wouldn't say it's right to say that weight has no effect on level ground. If you ride a flat 10km stretch of road with an empty water bottle, and then ride it again with a 5lb steel weight in that water bottle, you'll probably go slower the 2nd time. But the difference will be marginal compared with how much time that 5lb weight would lose you in a 10km climb.

By comparison, if you ride that flat 10km with disc wheels, aero bars and an aero helmet that all add up to an extra 5lbs of weight, you'll find yourself significantly faster than the original, unladen 10km. But if you took all those accessories and rode up the 10km climb, they'd be a hindrance more than a help.

It's not so much that weight doesn't matter on level ground, it's that W/kg on the flat is a much lesser consideration than aerodynamics and total power output.

There is also friction in the wheel bearings, but that is very minor compared to air resistance. In any case the friction probably relates to weight (X the coefficient of friction), but we are talking minor fractions of minor fractions here. Air resistance is the key.

Having said that, it is still quite exhilarating to accelerate a very light bike. It just feels really good.

It's not possible. Any change in the mass or the velocity makes a change in the work done. Period. You can't change that.

People feel things differently. Some riders will feel small changes, some will not. What one feels is not always a good indicator of what has changed.
Some small changes are not never noticed, or are only noticed when climbing.
Different riders will have different priorities about changes too. Many may not care. A racer may care about any small changes, because he knows over a long ride, small difference could be the difference between first place and second. It is also true that other factors may be more important than small weigh changes. Such as air resistance at high speed during a flat-ish TT.

I have different weight priorities for my different bikes. My best road bike I built to be a "weight weenie" bike, no matter the cost.
Some of my beater bikes are built to handle rain, or even flooding with fenders, mud flaps, etc. My best MTB is a mostly "weight weenie" bike, and was built that way.
My studded tire snow and ice bike is built for huge bumps in the ice and deep-ish snow. It takes very wide, slow studded tires. It is probably 32-34 lbs.

Newton's first law - objects in motion remain in motion unless an unbalanced force acts on them. Of all the forces that act to slow a bike down, only rolling resistance is a function of weight. At non-trivial speeds (over 15 MPH), rolling resistance is dwarfed by the effects of aerodynamic drag, so weight doesn't really have much effect on the power required to maintain speed on a perfectly flat road. But "maintain" is key. Accelerating is most definitely affected by mass, so a heavy rider will burn significantly more power getting to 20 MPH quickly than a light rider.

I agree completely on the last statement.

What about rolling resistance? He's squishing the tires at 230 more than I do at 195 or another guy at 150.




I get the acceleration part....completely makes sense and it is a good parallel to climbing, at least in my mind. But even once he is at top speed, it must take more power to stay there than it would if he dropped 30 lbs. Right?

You posted this at the same time as my previous post...so you sorta answered my questions there. But if rolling resistance is not significant over certain speeds, why is it harder to pedal with underinflated tires? Would not underinflated tires be a fair comparison to tires that are being squished more by a heavy load? Therefore making it harder to maintain speed?

For discussion sake, lets say the same guy, with the same endurance, same power etc all of a sudden loses 30 lbs of body weight. AIR RESISTANCE NOT CONSIDERED, what happens to his top speed?

Look at it this way (using your comparison):

If you have a super light car that has reasonable power (let's say the Ariel Atom - one of the fastest cars in the Top Gear airfield lap thing). It has 500 hp, it weighs 1290 lbs, so each hp has to move 2.58 lbs. It's not very aero and not super powerful overall so its top speed is probably in the 170 mph range (based on the 350 hp version going 155 mph).

Get a bigger, more powerful car, let's say the Bugatti Veyron. It's a tank compared to the Atom, weighing in at about 4100 lbs. However it has 1000-1200 hp. If you take the 1000 hp number then each hp has to move 4.1 lbs. It still gets to 60 mph within a few tenths of the Atom. However it absolutely demolishes the Atom for top speed, going about 250 mph.

You're right in that the KOM guy probably could lose some weight and go faster but he doesn't need to, and in fact to maximize flat land performance it maybe be that he's maximized his power and not worried about a bit of extra fat.

If weight was an issue in track racing then we'd see skinny sprinters, not the Chris Hoys and the like.

To put the car thing back to bikes, a typical regular racer (Cat 3) might have a 1000-1500w peak jump, with maybe a sustained 800w 20 second sprint. For me I can do a 1500w peak jump, 1100w for about 18-19 seconds. My max minute is 587w.

A local rider, former US cycling track rider for the team sprint, said that he peaked at 2400w, could do 1800w for something like 10 or 20 seconds, and could average over 1000w for a minute. He's not light but holy smokes he's fast. And he never did well internationally, meaning he was never on a podium or even close. If he lost 10 or 20 pounds would it make a difference? Maybe. But if he's being out powered by 500w peak and 200-400w for a minute then that 10-20 lbs isn't going to help.

Finally Strava doesn't differentiate between single riders and groups of riders. If that guy can draft before the segment, or even during the segment, it really reduces the need to be lighter.

I'm a far heavier than optimal rider that does fine on flat races and immediately gets shelled in hilly ones.

Once he's at top speed, he has momentum. Air resistance and rolling resistance are the only things slowing him down at that point. So if a 230lb rider and a 200lb rider with exactly the same aero profile get to 40mph at the same time and both stop pedalling, the smaller rider will slow down before the larger one.

Weigth makes a difference, but not much compared to aerodynamics. If you check this link for an equation to calculate power to move a bicycle: Cycling: Uphill and Downhill then you'll see that power to overcome rolling resistance (where weight is considered) is proportional to speed whereas power to overcome air resistance is proportional to speed to the third power.

It depends on what the 30 lbs consists of. 30 lbs of fat and his speed would go up, 30 lbs of muscle it might very well go down. I'm in a situation now where I'm getting smaller but not losing weight. The added muscle has absolutely help my speed (which is still pretty slow).

if your estimation of the consensus is true then the "consensus is wrong" IMO.

what i think people are missing is that a bicycle at motion relative to the road is under acceleration at all times while pedaling. just stop pedaling sometime and see how long it takes to come to a stop. something is slowing us down, so if we are maintaining a constant relative speed to the road we are applying power to overcome it, and the power necessary to maintain that speed is proportional to the weight.

the force it takes to overcome air resistance is substantially higher at normal cycling speeds then the effect of weight. I can even sit up higher on my bike and slow myself down after coming down a hill.

i believe you.

Few routes are totally flat also, so even slight rolling hills (even in Kansas) means heavier rider will be doing more work on small climbs. Also every time rider slows slightly then accelerates more work will have to be done by a heavier rider, all things else the same.

Why?

air resistance gets exponentially higher as you go faster.

No, it's not. The definition of acceleration is change in velocity with respect to time (dv/dt). If the velocity doesn't change, acceleration is zero. period.

There are forces on the bike that will result in negative acceleration if not balanced by a force in the opposite direction (the rider's pedaling).

Wrong again. The power necessary is proportional to the forces acting on the bike. Only one of them (rolling resistance) has weight as a factor. Don't take my word for it. Pull up any bike calculator and look a the power required for a rider to maintain 20 MPH. Now drop the rider's weight by 50%. Does the power drop by 50%? Nope.

Yes, he'd be significantly faster. Rolling resistance is lower so he'd be saving 5-10W, his aero profile would improve due to smaller size and better ability to get into an aero position (less fat in the way) and he'd be more efficient. If you add 50 lbs of weight a good portion of that extra weight will go to your legs which go up an down about 90 times per minute. Moving an extra 10 lbs up and down on your legs is just a waste of energy that's not going to the pedals.

Don't kid yourself, dropping weight will always make you faster. OK if you're at 8% bodyfat then possibly not but for 99% of the population this would hold true.

Here's my take. At 215 lbs, I have some experience in the subject.

If the OP's riding buddy dropped 30-50 lbs, he'd probably be faster but most of that would be better aerodynamics.

Heavier bike/rider combinations would flex the sidewalls of the tires more creating some friction. Or, as in my case, need to go to fatter tires such as 700x25s which are a little heavier and a little less aerodynamic. I also had to go from wheels with 20/24 spokes to 32 spokes. Ironically the new wheels were a little lighter, but the extra spokes probably cause more aerodynamic drag.

Even on flat ground, more weight is harder to accelerate such as from a stop or even yo-yoing on the back of a pace line.

There is seldom any truly flat ground. There are always some slight ups and downs. A 1% grade may look flat, but isn't.

I have a relatively light Giant Defy Advanced with 700x25 tires and a much heavier (about 12 lbs) Windsor Tourist with 700x32 tires. I have both set up about the same with maybe being slightly more upright in the Tourist. I've ridden both on the same relatively flat loop a number of times at similar levels of effort as judged by heart rate. I'm about 5% slower on the Tourist. Ideally I'd be fitted exactly the same; have the same size tires and wheels; plus have a power meter to judge effort when comparing the two; however, I firmly believe I'd still be slower on the Tourist.

Of course the differences between both of my bikes really get wide as the hills go up. I can really feel that extra dozen pounds on steeper grades. Speaking of weight, a few years ago I dropped 20 lbs and was much faster up the hills and a little faster on the 'flats' after dropping the weight. Too bad I put it back on.

That's true, and your torque on the pedal arm varies trough the stroke which means you'll constantly have some acceleration. It's one reason that a smooth stroke is more efficient. But it turns out that the difference that the extra weight makes with these tiny accelerations doesn't amount to much.

Rolling resistance is proportional to weight and at lower speeds it predominates over aerodynamic drag. Even at 18-20 mph where air resistance is the biggest factor the rolling resistance is still a significant portion (by significant I mean that it definitely, noticeably slows you down), so I can't really agree that weight makes "no difference" or is insignificant on flat ground. It makes less difference than other things depending on the speed, terrain, and rider and ride profile, but it does make a difference.

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.