EastBiker

All this talk about small wheels doesn't change the fact that really small-wheeled bikes such as the CarryMe are a pain to use for medium to long range commutes. At least here in NYC. I tried one, and it was too tedious and uncomfortable, not too mention much slower than my Brompton or 26" or 700c wheeled bikes. Oh, and yes and the bike sucks when hitting potholes. No amount of theoretical analyses can overturn that experience.

I look forward to the folder chain lubing myth busters thread.

Bacciagalupe

Evidence: You can start with the very basic empirical fact that, as previously mentioned, a time trial bike is both heavier and faster than a standard diamond-frame bike. An über-light racing road bike can be 12-14 pounds, and an über-light TT is more like 16 or 17 and will leave the 12 lb bike in the dust. Similarly, as I previously mentioned, aero and disc wheels are much heavier than standard wheels but are faster (unless there's a stiff cross wind). Aerodynamics is far more important factor than weight.

You can continue by checking out the world's fastest HPV, the Varna Diablo II. Max recorded speed on the flats: 82.3mph. Weight: 60 lbs.

And keep going by playing around with the Kreuzotter calculator and examining their equations: https://www.kreuzotter.de/english/espeed.htm

I have heard of a study where a researcher plunked a 5lb weight in a downtube, and a group of pro racers couldn't distinguish between a loaded and unloaded bike. I'll see if I can find the reference.

If my own experiences are of any use to you: My Dahon Mariner weighs about the same as my steel road bike (26-28 lbs) but is substantially slower. This is almost certainly due to a very upright position that, on that particular Dahon model, cannot be adjusted. My Swift was also 4-6 lbs lighter than my road bike, but performance was too close to reliably say which is faster.


Theory, as best I understand it: Weight affects acceleration, and that's it. Once in motion, the primary force slowing down the bike is friction, specifically aerodynamic drag, which increases at roughly the square of velocity. Once you go above 12mph or so, even tiny increases in your drag coefficient will slow you down much more than adding weight. Above 18mph, you need huge increases in power output to gain tiny increases in speed.

Ergo, any recumbent rider who can't beat a diamond frame on the flats should be blaming the engine, not the bike.

When climbing, you're fighting gravity; most (non-pro) riders won't ride fast enough up a hill for drag to be a major factor. Even here, though, weight is a smaller factor than you think; Chris Carmichael, Lance Armstrong's coach, describes the impact of adding 2.5kg (~5 lbs) as adding 38 seconds off of a 20-minute long, 5km, 1200 foot climb -- huge for a pro, noticeable for an amateur racer, inconsequential for everyone else.

Subjective rider perceptions about weight are basically BS and highly inaccurate; the human body simply isn't that well calibrated, and has absolutely no reason to develop that ability, and cognitively it would be a very "expensive" one to develop. Perception of performance isn't much better, especially when a new or expensive bike is involved.

From what I've gathered, the only truly objective way to determine the efficiency / performance of a bike is with a power meter. Even an HRM might not do it since your biological efficiency will vary from day to day, so you'd need a large pool of samples.

Anyone willing to kit out a folding bike and a similarly equipped 700c bike with PowerTaps?

feijai

This one needs to be retracted. I believe small wheels are generally lighter and so have less forward inertia: and they are both lighter at the rim and have smaller radii, meaning they typically have significantly less rotational inertia. How does this not translate into faster acceleration?

You seem to be talking about some equivalence to the pedaling myth: but it looks nonsensical to me. It doesn't have anything to do with gearing.

noob_island

This so sounds like a MythBusters episode. Someone start a petition.

zonatandem

Now about tire wear: 16", 20", 26" 700c . . . Yup, bigger is better.

datako

Most of this stuff was nailed down as far back as 1896 (yes, over 100 years ago). Look for this book:

Bicycles and Tricycles -An Elementary Treatise on their Design and Construction
By Archibald Sharp (First Edition in 1896, but reprinted since)

A little simple mathematics shows the way.

There's also the much more recent Bicycle Science by Wilson.

I prefer the 1896 book because of the amount of stuff they have in it that has recently been re-invented and is being touted as the latest and greatest thing.

joose

https://books.google.co.uk/books?id=cAgLx-BHY80C&pg=PA279&lpg=PA279&dq=Bicycles+and+Tricycles+-An+Elementary+Treatise+on+their+Design+and+Construction&source=web&ots=OOsKjKA5ag&sig=31sLxw7c1bRIY7 cB6YFeVE_9T9E&hl=en&sa=X&oi=book_result&resnum=1&ct=result#PPA292,M1

makeinu

Well, sometimes reinventing something does make it the latest and greatest thing. As time goes on other new technology makes many old ideas viable.

You yourself were quoted as saying although you prefer singlespeed, you'd use a multigeared bike for riding with heavy loads. 110 years ago your bike would itself be a heavy load. So there you go, the old singlespeed technology has suddenly found new life in conjunction with lighter manufacturing.

Of course, Bacciagalupe is arguing that weight doesn't matter...

I don't think the trained muscles of pro riders are necessarily comparable to our muscles (it's like saying that since you can lift 5 pounds in your arm with only negligibly lower speed than just your arm and then concluding that a baby should be able to do similarly) and I think you're cherry picking situations where aerodynamics are way more important than they would be in normal riding.

A rider averaging 15 mph will spend a significant portion of the ride below 12 mph and if the muscular losses in that region are large enough then the increased load of accelerating extra weight could very well result in weight being a significant factor. Obviously weight only affects acceleration, but the point is that if it affects it enough then that's all it has to affect because acceleration is the gateway to all motion.

While subjective rider perceptions of weight and performance might be BS (which I'll take your word on as you seem to know more about psychology than me), I can confidently say that the Kreuzotter calculator is also BS because it tacitly ignores the very place where we would measure losses due to extra heft (in the muscles).

I actually think a heart rate monitor might do quite well to measure how weight affects the amount of energy needed to ride a course in a given time, but I'd expect to find that pushing a heavier bike will, on average, require a significantly higher heart rate to achieve the same overall speed (that is, on average, and not just the most exotic and egregious riding like the varna diabolo in the flat desert or lance armstrong making minced meat out of 5 pounds with his pistons). A power meter would be less reliable because you wouldn't be able to tell if the rider is just working harder to muster that power...whereas the heart rate monitor would actually be measuring power at the source. In fact, since you're so convinced that people can't tell what gets their heart pumping, I think I'll buy a HRM to see for myself.

invisiblehand

I think that on any club ride with some drafting falling out of the group -- which the five pounds would do with riders of equal strength on a moderate hill -- will have a big effect since once it brings you out of the paceline, you have to work hard to get back in.

Bacciagalupe

Does weight matter?

I say: No and yes. "No" in that weight will have a minimal effect on the general rider, especially one who doesn't care about performance. Also, in terms of our discussion, "no" in that folding and non-folding bikes are usually very close in terms of weight anyway.

"Yes" in two senses. One in that for an elite handful (specifically, pro racers), 3 seconds at the end of a 40 mile time trial can be the difference between 1st place and 20th. Two in that if you have to carry the bike up a flight of stairs or onto mass transit, a lighter bike is much more convenient.



At the risk of a bit of repetition: the primary issue, which I think you're starting to understand, is that weight only matters when you're accelerating. Once you have achieved a specific velocity, though, the force that will slow you down is friction: drag (which is the largest factor), rolling resistance and drive train efficiency.

The trick is, you aren't spending a lot of time accelerating, and the effects of 10 pounds to a system that totals, say, 150 - 280 pounds is small to begin with. Most of the time you're trying to maintain a certain speed.

This is why you can have strong and consistent subjective experiences that a heavy bike is slow (because it doesn't accelerate quite as fast) or that small-wheeled bikes are more fun (because they do accelerate faster, and that can be more pleasant). However when you add everything up, because you spend so much time at a more or less constant speed and fighting drag rather than gravity, the slower acceleration actually winds up being less significant than it feels.

By the way, drag has an impact at all speeds. It's the biggest opposing force you're dealing with as a cyclist. It is more significant for riders with higher power outputs (or, to be specific, higher power-to-weight ratios) because they are riding faster. However, drag is still far, far more important than weight even at slower speeds. [FYI the Kreuzotter does account for this, as you can modify the rider's power output.]


As to objective measurements: A HRM does objectively measure the rider's exertion. However, this is not necessarily going to be a consistent factor, because your cardiovascular abilities can change from day to day -- especially if you happen to be training. I think you'd need a pretty large pool of samples to try and correct for this.

The reason why a power meter will be more objective in terms of measuring a bicycle's performance is that it precisely measures power output, which is what is propelling the bike. It doesn't matter if it's a pro or an amateur or a robot, 200 watts is 200 watts is 200 watts.

So if you know that Bike 1 travels at 15mph when the rider applies 200 watts of power, and Bike 2 travels at 16mph at 200 watts, and the environmental conditions are consistent between tests, you will know exactly which bike performs better and by how much.


Ergo, in terms of the myths: Although I haven't proven it using objective tools, from what I know the performance differences between 20" and 700c bikes are usually a wash. The smaller wheels are faster, but less comfortable, so the designers almost always adjust for this via methods that induce a performance penalty that, in most cases, is acceptable to the rider.

So the myth that "you have to pedal more" or "smaller wheels must be slower" are incorrect, while "smaller wheels are harsher" is true specifically when you are comparing equivalent tire types.

127.0.0.1

all I know is

on my stock L3 brommie, 100psi, head down and hammering

-I do have to work harder to keep up with someone on a 700c. mostly because I can only
pull 'so hard' on those bars vs normal drop bars and position. plus once you run out the 3rd
gear, you need clips to get an effective cadence above 110. no clips....stock.

-and it steers incredibly well, so I need to be more caring with my control and steering input

-and on the cobbles and wet tracks in amsterdam, barreling along, then hitting sidewalk repairs
which are dirt and plywood cover then dirt again...I can plow that brommie through it all and
I feel safer on the brommie than my mountain bike in the city. something about it makes me ride better
if that makes any sense ? also with all the people around i can slow and stop and turn 90deg easily.
I guess because I can turn on a dime. literally. [and i am an expert norba racer.] I dunno, I just pound on the brommie and it delivers

-as a dirt trail bike, it is dog slow but servicable. tire diameter.

-I will challenge all on the brommie, and surprise most people and change thier mind about tiny wheels.
the thing smokes if you are motivated
it delivers (though in a bendy way sometimes when i really torque on it)

makeinu

I think weight is more important for the general rider who doesn't care about performance, because this is the rider that would be content coasting after accelerating. So whatever portion of the effort pie acceleration is for the performance cyclist gets multiplied to as much as 100% for the general rider and the affect of weight gets multiplied along with it. Of course, not every general rider will simply coast after accelerating, but in my opinion most riders spend much more time accelerating than they do maintaining a certain speed. Racers don't, but riders on streets with stop signs, lights, and other traffic do and although it all depends on where you're riding and how far you're going, let's face it, a bicycle is a vehicle much better suited to short trips in dense environments then brevets. That's why the winner of the TDF gets fame and prestige, while the guy delivering chinese food by bike or the guy that drives his car 200 miles to work everyday gets squat.

I would also contend that folding and nonfolding bikes are close in terms of weight because they are too close in terms of wheel size. In my opinion, the conclusion we should draw is that smaller diameter wheels are better because they have few inherent disadvantages and can be made lighter. If 20" wheels are not making a notable difference it's because they're still too large, not because weight doesn't matter.

To be clear Kreuzotter does not account for weight because, although you can modify the rider's power output, you can't simulate how much operating at a given level of power output will fatigue the muscles, in turn, reducing the rider's power output. There's no feedback. It is assumed that the muscles are a perfect power source whose internal losses are independent of the load, which is false.

You see, 200 watts is not 200 watts is not 200 watts. 200W evenly delivered over one second is not the same as 200 million watts delivered for a millionth of a second followed by nothing for the rest of the second is not the same as delivering nothing until the last millionth of a second and then delivering 200 million watts. Although they're all 200 watts, the first one would have the lowest losses, the second would have internal losses so high they'd destroy your leg just as you started, and the third would allow you to cover ground with your previous momentum before destroying your leg.

Accelerating a large mass has the effect of creating exactly this sort of uneveness. When your muscles have to work harder to accelerate a larger mass they get hotter, more fatigued, and waste more energy to deliver more power now and they don't get that waste back by delivering less power maintaining speed later on. That's why lifting a box and putting it back down is hard work, even though the average power delivered to the box is 0 watts!

Muscular efficiency is generally quoted as being only around 15% and can be as low as 0%. So while I may be able to funnel 200W out of 1000W of total exertion while riding a 15 pound bike, all but 1W may be lost while exerting 1000W to try and push a mac truck. The question is, what about a 20 pound bike, or a 30 pound bike? How many watts get delivered to the pedals for a given exertion?

The thing that makes it so difficult for me to ignore subjective rider opinion of exertion is that it's the only frequent recorded measurement of what is obviously the overwhelmingly largest mechanism of loss. Things like rolling resistance, aerodynamics, and friction are generally quoted at maybe 10-20% total, but when it comes to the biomechanical losses we're talking 75% or more. So the subjective observations would have to be really way off to reverse the conclusion...which begs the question if there's a total disconnect between the feeling of exertion and actual exertion then shouldn't we be more concerned with the feeling of exertion anyway? After all, the feeling is the basis of your decision to push yourself harder, or to stop riding, or to continue that long commute. So shouldn't that be the important parameter?

Yeah, but that depends on whether the heavier larger diameter tires can really be called equivalent (which I believe we still haven't settled). If heavier wheels are worse then the equivalent tires would need to be skinnier, thus, pushing us towards parity of harshness.

staehpj1

Not my typical riding situation. That is true for a situation where acceleration is not a factor, drafting is not a factor, and climbing is limited.

Again hardly a normal riding situation. Dead flat and probably pushed or towed up to speed

I am pretty sure they didn't climb any mountain passes in that test.

In practice when riding with others accelerations are frequent and important if you intend to stay with a group. Accelerating out of corners is where folks most often are dropped in my experience.

I don't consider 38 seconds inconsequential if riding with others who I have to work hard to keep up with. At that point it becomes VERY consequential. Another way of looking at it is that no matter what your energy output is still increased by lifting 5 pounds 1200 feet.

it isn't all that subjective if you ride with the same people and drop them or get dropped depending on which bike you ride.

So basically if I disagree I need to have a large pool of samples, but you can cite your own impressions and irrelevant time trial and HPV references.

feijai

What part of "HPV" did you not understand?

staehpj1

Regardless of my lack of knowledge of HPV rules the example is not all that relevant to real world riding since there is no climbing and the need for acceleration is minimized. I may be mistaken about the assisted starts. I thought I recalled from the distant past reading about assisted starts due to the very high gearing used. That may have been from something like John Howard's 152.2 mph speed record which was motor paced and maybe assisted start as well,my memory is not clear on the specifics.

82.3mph and a weight of 60 pounds was mentioned for Diablo II. I am pretty sure these are "flying start" times right? Correct me if I am wrong but that is probably a long un-timed lead up run and the speed is timed through the "traps" that are a couple hundred meters apart. There is not much in common with any riding any of us are likely to do.

pm124

Agree that potholes are a big problem. Disagree with the panic stop comment. That has to do with the amount of weight distributed on the front and rear wheel, wheel base, even the brakes themselves. In a panic stop, I would much rather be on my Birdy than a narrow wheelbase road bike. Better still, put me on a recumbant with disk brakes. But I'll take a road bike for a pothole any day.

noteon 

I agree, actually. In my limited experience with panic stops on one 20" folder, one 26" folder, one 700cm hybrid, and one 700cm road bike, what feel like (yes, I know, but I don't carry a slow-motion camera rig with me) the biggest factors in whether the rear kicks up are my position relative to the front wheel and the overall length of the bike.

I've never had a bike threaten to pitch me over the handlebars like the Swift does in a panic stop, and it feels as though (1) I'm closer to the fulcrum (the contact patch), and (2) there's not much bike weight behind me to help counter the movement.

Perhaps incorrectly, I do attribute this to the nature not of small wheels, but of the kind of frame geometry you're likely to encounter on a small-wheeled folding bike.

PS Was that you on the greenway Tuesday morning?

feijai

They are not. The riders get up to speed on their own, at which point they are timed in the traps.

That's why it's called a "Human Powered Vehicle" competition.

staehpj1

I said:
And you replied with:
Actually the times listed are "flying start" times. I just looked them up and sure enough they are listed as "flying start" times. Don't believe me look them up yourself. Flying start does not imply that they didn't attain that speed on their own, but merely that they are not timed except in the traps. I had suggested that they were assisted in attaining speed in an earlier post and acknowledged the error in the post you were quoting.

My original point was that this is a very specialized example with little in common with the riding that most of us do. I know that most of the riding I do involves lots of accelerations interspersed throughout the ride and lots of elevation gains and losses. These real life factors make weight a much bigger factor for this riding than either the time trial example or the HPV example.

None of this pointing out my ignorance of HPV's or yours of what "flying start" means is all that relevant to the point I was making anyway. That point is that Bacciagalupe was making an argument about the effect of weight on normal riding by using a couple extremely specialized examples that both were limited much more by aerodynamic drag and much less by weight than most other forms of riding.

Bottom line, I still fail to see how riding a 60 pound streamliner through traps 200 yards apart proves that weight is not important in regular "normal" riding of the sort many of us are likely to do..

pm124

This morning, no? Someone said hello, but I think we passed each other quite quickly.

noteon 

Hey, it was you! Yeah, I braked, but you were still (or again) heading uptown.

I'm off the greenway until next Wednesday. See you then, maybe...

feijai

They are exactly as I described: they have four miles to get them up to speed, then are timed in the traps. It's good that you're seeing it that way now. :-)

You originally claimed these bikes were being assisted by motors etc. They are not. The speeds achieved were entirely by human effort. I'm just trying to get you to back off of your original claim.

arctos

Alex Mouton is an engineer who has been designing and manufacturing small wheeled bicycles for fifty years. Here is his list of answers to questions about small wheeled bike performance:

1. Why the small wheels? The small wheels are an essential feature of the Moulton concept. They offer many advantages.
With only half the rotating mass of the wheels on a 'conventional' bicycle, it is possible to accelerate faster.
They are extremely stiff and much stronger than larger wheels because of the short spokes.
The aerodynamic drag is lower; there is less frontal area and less spoke area causing turbulence to slow you down.
The centre of gravity is lowered, resulting in improved stability.
The small wheels free up space normally occupied by large wheels, allowing luggage to be carried lower. 2. Aren't smaller wheels harder to pedal?
No, because:-
The gears are chosen so that they correspond to pedalling a bicycle with large wheels.
The smaller frontal area results in less aerodynamic drag.
The lower inertia means that you can accelerate faster.
If you are still doubtful, consider the HPVs (Human Powered Vehicles) developed for the ultimate performance - many
of these use the unique 17" Moulton wheels and tyres fitted to the AM series bicycles.
https://www.alexmoulton.co.uk/FAQ.htm

Which engineer should we believe?

In my unengineered ignorance I only know that riding my Moultons has been a supremely comfortable, fast and pleasurable ride over the last twenty years.

datako

Just to be nitpicky, they're not lighter. Somehow we have managed to keep the weight of a single speed bike about the same as a 1900s one My latest bike build (Singular Peregrine) came out at 12kg which puts it bang in the weight range of a similar sports bike of the early 1900s.

I was referring to luggage loads of around 60-70 lbs on top of bike weight.

Bacciagalupe

A few specific points:

• I agree that urban cycling / commuting will involve a lot of stops and starts, and will have a lot of acceleration. I'd also agree that in terms of road feel, a snappier bike will feel better and be more fun for that specific environment if you're constantly stopping and starting (hence all the track frames around NYC). However, the effect of weight is so small that other interruptions and variants will overwhelm any performance impact of the added weight. Geometry can also have as much to do with "feeling snappy" as wheel weight -- possibly more.

• I thought it was screamingly obvious that when I suggested using a power meter to compare the performance of 2 bikes, I was talking about comparing periods of consistent power output (e.g. "10 minutes @ 200 watts").

• Subjective perceptions of rider efforts are notoriously inaccurate. You can't tell based on feel if you are below, at or above LT. You can't tell based on feel what your average or max heart rate is. You have no idea of your actual power output at any time. You can't tell your actual speed, or rate of acceleration, or bike's weight based on feel. Stories abound of mismatches between perceived effort and data collected by HRM's and/or power meters.

Plus, various physiological, environmental and psychological factors -- especially expectations -- can strongly bias a subjective perception. That's why if you are serious about training, you need a HRM and/or power meter to objectively record your efforts.


And for staephj1:

• If you're getting dropped on a club ride, it's not because you have an extra 5 pounds on the bike. It's the engine. You know it, I know it, and everyone else on the ride knows it.

• I would hope it was screamingly obvious that I didn't mention the HPV World Record as an example of a "general" or "typical" cycling effort. The point was to illustrate that friction, primarily drag, is the biggest factor that effects performance. If you read up a little on the Diablo, by the way, you'll see that they do everything they can to reduce friction; to break their previous record, they pumped up the tires to reduce rolling resistance rather than toss 5 pounds overboard.

(By the way, TT's and solo rides are far more abundant than you suggest in your posts.)

• I'd hope we can agree that for most "general" rides, 38 seconds over 20 minutes is not only insignificant, but almost certainly overshadowed by other factors like rider fitness and drag. Most "general" riders don't even have the tools to accurately measure a change like that, let alone isolate it to one specific cause.

If 38 seconds out of 20 minutes is critical, it's not because it's a large amount of time, it's because you happen to be in one of the situations where small changes in performance are significant (let alone actually measured).


Last but not least... I'm no longer accepting the assumption that "added weight produces a significant performance loss on the flats" without some kind of proof. (The losses on a climb are pretty well understood, and may or may not be significant depending on the context.) So if you want me to believe that an extra 5 or 10 pounds is actually going to make a difference, prove it. One possible option is:

- quantify the effect of adding weight as best you can, in various scenarios
- compare it to the effect of an increase in drag
- compare it to the effect of an increase in RR
- and if weight does prove to be a primary or even notable factor, compare your results to this guy here, along with how and why you differentiate from his findings.

Or: Get a power meter, plant a 10 pound weight in your downtube, and quantify the results. It ought to cost you about 1-2 watts.

Have fun with that.