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-   -   Bicycle weight doesn't matter? (myth) (https://www.bikeforums.net/general-cycling-discussion/1149472-bicycle-weight-doesnt-matter-myth.html)

Metieval 07-12-18 08:06 AM

Bicycle weight doesn't matter? (myth)
 
So I have been looking at cargo vans, and the economy of those cargo vans.

there is a pattern with fuel economy. unloaded economy is always higher than loaded economy.

the same can be said for hybrid cars. If you want the 'listed' estimated economy numbers, you better haul nothing and haul no other passengers. Because 4x 200lb guys in a Prius will lower the economy of said Toyota Prius.

so how is it that a heavier bicycle won't require more fuel for the given distance when compared to a light bicycle?

indyfabz 07-12-18 08:09 AM

Subscribed.

JonathanGennick 07-12-18 08:09 AM

Bicycle weight does matter. Some riders put too much emphasis on weight though, and that leads to a backlash in which other riders downplay the issue of weight.

gregf83 07-12-18 08:12 AM


Originally Posted by Metieval (Post 20443179)
so how is it that a heavier bicycle won't require more fuel for the given distance when compared to a light bicycle?

A heavier bike takes more fuel, it's just an insignificant amount not worth worrying about.

Metieval 07-12-18 08:19 AM


Originally Posted by gregf83 (Post 20443198)
A heavier bike takes more fuel, it's just an insignificant amount not worth worrying about.

I searched the Bike Forums for 'bonk' and 'bonking'....... apparently fuel is pretty significant with cycling. :)

Koyote 07-12-18 08:20 AM

This has been beaten nearly to death.

Short answer: weight does matter, but how much it matters depends on many other variables, including rider weight, elevation change, etc. Then you can start comparing the effect of weight relative to aero drag, mechanical drag, wind speed, etc.

DanBraden 07-12-18 08:26 AM

Yeah... Weight loss costs money... My commuter, an amalgamatiin most wouldn't be caught dead on, is all price conscious function over weight savings. At one point I obsessed and worried over my fat Franken-fritz, then I just said "screw it! I want ALL THE THINGS!"

Now Fritz is probably in the 40 pound range (I haven't weighed him in a while) and he's my rugged go everywhere bike. In Austin there's no shortage of steep but small hills and I huff and I puff but I get to where I'm going in ok time. Am I wearing myself out? Maybe if didn't ride everyday I would, but as it is we have a good groove and I'm not exhausted. As an aside, I'm not super calorie conscious, so if Fritz's weight makes be burn extra calories, I've got plenty to spare.

All that being said, I do have my MUCH lighter carbon TT bike, Horse-feathers. He's as light as the day I made him, but it came at a price. After spending a week on Fritz, I really notice the weight difference and it... Is... EXHILARATING!!!

I love all my bikes, skinny, fat, and junky! They're mine and have my sweat and sometimes blood in them (Fritz will bite me if I'm not careful and I the scars to prove it).

Caliper 07-12-18 08:36 AM

I've never thought it doesn't matter, just not as much as some think. So the web says a 2018 Prius weighs 3075#. 4x200# guys in a Prius takes the car from 3275# (one 200# driver) to 3875#, or a 18% weight increase. If we have a 20# bike and 180# rider, that's like adding 36#. You're talking bike touring territory there and nobody argues that a loaded set of panniers "doesn't matter".

So, maybe you save a massive 5# from the bike and the vehicle (bike + rider) goes from 200# to 195#. That's 2.5%. To compare to the car analogy, that's about 82# in our Prius, maybe the weight of a kid. It's not much, and dropping 5# is a major upgrade in a bike.

Let's say you drop 0.5# with some new carbon parts, that's now 8.2# in our hypothetical car. It's like putting a gallon of milk in the car, or 1.35 gallons of gas. Can you calculate the change in fuel economy? Sure, it has some effect. But it's going to be pretty small. Will you even notice it at the pump without keeping careful records and compensating for weather conditions?

The main message about "weight doesn't matter" is that many of us try to buy our way to better performance by sitting on our butts and ordering trick parts off the internet when the truth is we should be out riding whatever bike we have today and upgrading the motor. A fit rider on a 20 year old bike will outpace a weak rider on a modern carbon bike any day.

livedarklions 07-12-18 08:47 AM

No one claims it makes no difference--the questions are whether you'll notice the differences and how much those differences are going to cost in terms of money and impacts on performance for the task you're using the bike for. DanBraden's example is perfect--if he used his TT bike for a commuter, he wouldn't spend as much energy on the ride and he would definitely notice the difference, but it would come at the cost of probably destroying the TT bike over time, and making for a really impractical commute.

Now, that being said, is there anything funnier than a really overweight guy trying to convince you that you should spend an additional $400 on an accessory like he did in order to save 200 grams? I know, that's kind of mean, but still....

livedarklions 07-12-18 08:53 AM


Originally Posted by Metieval (Post 20443216)
I searched the Bike Forums for 'bonk' and 'bonking'....... apparently fuel is pretty significant with cycling. :)


Sure, but if you're using the bike for short hops back and forth to work, those fuel savings will mean almost nothing. If you're riding long distances and/or high speeds, marginal differences in calorie demands make a much bigger difference.

I've actually ridden solo centuries on a bike that probably weighed 45 pounds. There isn't enough food in the world. Now that I have a lighter bike, I can fgo much farther and eat a bit less.

Machka 07-12-18 08:54 AM


Originally Posted by Metieval (Post 20443216)
I searched the Bike Forums for 'bonk' and 'bonking'....... apparently fuel is pretty significant with cycling. :)

Really? Huh ... who would have thought?

Happy Feet 07-12-18 08:55 AM


Originally Posted by Metieval (Post 20443179)

so how is it that a heavier bicycle won't require more fuel for the given distance when compared to a light bicycle?

It is a question built upon a faulty premise.

I've never heard anyone say weight doesn't matter. As some have already said, it is only a question of degree.

If you are currently participating in the TdF it will a lot, but if you are only imagining you are it will not.
If you are riding 200km it will, but if you are riding 2km it will not
etc...

If you want a more intellectually honest discussion why not define the question more.

NomarsGirl 07-12-18 08:56 AM

I figure I'll worry about the weight of my bike when I can no longer decrease the weight of the rider. Maybe I can buy a lighter bike. It may cost me $1200 or probably more to save a couple of pounds. Or I can take 10 pounds off myself for free.

I don't race so I have no need to have the lightest bike. And if I burn more fuel, so much the better. I like food.

Marcus_Ti 07-12-18 09:00 AM


Originally Posted by indyfabz (Post 20443185)
Subscribed.


Nah...rally doesn't have much potential for shens. Too troll-y, too soon.

Metieval 07-12-18 09:01 AM


Originally Posted by Caliper (Post 20443257)
A fit rider on a 20 year old bike will outpace a weak rider on a modern carbon bike any day.

the cargo vans and the Prius example didn't do engine swaps. So why are you swapping engines?

Metieval 07-12-18 09:05 AM


Originally Posted by Happy Feet (Post 20443300)

I've never heard anyone say weight doesn't matter.



so because you have never heard it said, that means it has never been said? Interesting logic!

Caliper 07-12-18 09:06 AM


Originally Posted by Metieval (Post 20443309)
the cargo vans and the Prius example didn't do engine swaps. So why are you swapping engines?

Who said it was an engine swap? Maybe they just cleaned out the sludge, changed the oil and air filter, upped the compression ratio and swapped cams?

livedarklions 07-12-18 09:23 AM


Originally Posted by Metieval (Post 20443316)
so because you have never heard it said, that means it has never been said? Interesting logic!


OK, who did you hear say it? Did they qualify it? Put it in context?

If you say something is a "myth", it implies that it is often told. So yeah. "I've never heard anyone say that" is actually a valid data point.

Basically, I think your Prius example is arguing with a straw man.

BTW, I just added a half pound of battery charger to make a hilly 140 mile ride last Saturday. I don't think I was particularly hungrier than I would have been without that charger, but if I was, it was too small a difference to notice.

TimothyH 07-12-18 09:31 AM

Bike weight matters less to heavier riders.

A couple pound lighter bike does little for a 250 lb rider but it is can be a significant difference for a 100 lb rider.

Ironfish653 07-12-18 09:42 AM

I really don't want to break down the physics of it, but on a flat road, at constant speed, weight doesn't matter much. Aero, rolling resistance / friction, and cadence / gear selection will have much more of an effect on your efficiency. Usually going to a lighter (read newer / nicer) bike brings increases in aero and mechanical systems, which means you either go faster, or with less effort.

Climbing hills, is another story, where you will have to lift that weight a fraction of a meter, for every meter you travel down the road. Usually, us mortals get over that by choosing lower gears for more mechanical advantage at the expense of speed. That's why heavy bikes like tourers have those 22t triples, and MTB cassettes have gone over 40t.
If this is a road racing stage, then every gram you can eliminate is one that you don't have to lift on the climbs. Hence, the quest for lightness. The less weight you have to lift, the more of your effort goes in to making the bike go forward. Hence, the theory of incremental gains.

Paul Barnard 07-12-18 09:44 AM

I am not sure how much this translates into road biking, but it made a massive difference years ago when I raced mountain bikes. I raced in rain and muddy conditions at times. On one particular course there was a section of wet red dirt/clay. It stuck to my tires and didn't let go. Even when I hit dryer firmer ground the weight of my wet shoes and the mud laden tires were a major drag. Can we say that where the weight is carried matters perhaps more than the overall weight?

gregf83 07-12-18 09:52 AM


Originally Posted by Metieval (Post 20443216)
I searched the Bike Forums for 'bonk' and 'bonking'....... apparently fuel is pretty significant with cycling. :)

Feel free to run the calculations to determine the number of extra calories used per extra pound of bike weight for two conditions: riding on the flats for one hour at 20mph and riding up a 6% hill for one hour.

The 6% hill I think works out to around 5 or 6 extra Cals If youíre riding at 300W for an extra lb of weight. On the flats itís likely well under a Cal.

fietsbob 07-12-18 09:52 AM

with the frontal area of a van the air resistance increases the faster you drive.. and gas mpg gets worse.
work thru your analogy to bikes with that.

OneIsAllYouNeed 07-12-18 09:56 AM

Don't be afraid to work it out. Here are some steady state power numbers. Accelerations consume additional fuel, but you didn't provide drive cycles.
A 70kg (154lb) on a 14lb road bike with 0.006 Crr tires needs to produce 224.5W to go 20mph on flat ground.
A 70kg (154lb) on a 22lb road bike with 0.006 Crr tires needs to produce 226.4W to go 20mph on flat ground.
8lb of bike requires 0.8% more fuel.

A 3900lb Toyota Prius with 1X 110lb passenger and 0.006 Crr tires needs to produce 7557W to go 55mph on flat ground.
A 3900lb Toyota Prius with 4X 200lb passengers and 0.006 Crr tires needs to produce 7934W to go 55mph on flat ground.
690lb of passenger requires 5.4% more fuel.

Happy Feet 07-12-18 09:57 AM


Originally Posted by Metieval (Post 20443316)
so because you have never heard it said, that means it has never been said? Interesting logic!

Well, let me rephrase it so you can't argue what should be a simple concept by obfuscation.

I have never heard a reasonable person suggest that weight does not matter in broad general terms without defining just what it is they are discussing. Reasonable people define parameters because they know context matters if they actually are interested in answers.

And to add to the reasoning that context matters: As I already indicated, If you are riding 2kms weight will not matter in regard to fuel requirements as you will not deplete your stored glycogen stores and thus, require no additional fuel. Most reasonably fit humans have a constant fuel reserve such that riding a short distance on a heavy or light bike will not unduly effect them. If however, you ride 200kms, you will deplete those glycogen stores, more so on a heavy bike, and will need to adjust accordingly.

Until you define what you are doing on the bike how can anyone intelligently discuss whether fuel considerations matter or not.

And, livedarklions gets it. This is just an open ended question based on a fallacy of the opinion being generally held (it is not) which just generates random opinions that do not in any way really answer a question.


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