
Extra Mass on Bike Wheels Is Worse than on Frames - Fjolsvith
http://www.wired.com/2016/06/cycling-physics-extra-mass-bike-wheels-enemy
======
rawland
Ex-Continental Tour Rider [1] & Computer Engineering Science PhD-student
talking here.

\---

TL;DR Considering reasonable wheels: Wheel stiffness is more important than
weight. A too light wheel, is not stable.

\---

Wired's physics are correct. However, neglect mechanical dynamics & handling.

Probably the biggest downside of light (& aero even more) wheels is: When your
wheels are very light, they are prone to cross winds and "jump around" a lot
due to their low inertia. And, well, you always have cross winds and bumpy
roads, because only very few of us are track riders.

Considering the acceleration, you lose a lot of energy by "twisting" the
wheel. That is: the hub starts to turn because the chain you pull with the
crank arm in front is forcing it to do so. Then, all this tension is
transferred to the spokes, rim and finally the tire. In that process most
wheels lose a significant amount of energy by simply storing it via elastic
torsion and releasing the energy without contributing to movement at all. As
already said in another comment, we "pulse" the energy to the back wheel, as
the maximum pulse comes due to our own biomechanics. And we have two pulses
per revolution with a zero at almost vertical crank arm alignment!

Therefore you want to have stiff wheels! Which stands in stark contrast to
light wheels.

The company Lightweight basically made its money by creating aerodynamic and
very very stiff wheels for the weight they had. These wheels, however, are not
maintainable any more & very expensive [2].

\---

[1]:
[http://www.uci.ch/road/ucievents/continentalcircuits/](http://www.uci.ch/road/ucievents/continentalcircuits/)

[2]: [http://lightweight.info/us/en](http://lightweight.info/us/en)

~~~
throwaway7767
Just out of curiosity, do you have any suggestions for stiff bicycle wheels?
I've been looking for a sturdy wheelset for touring with a fairly heavy bike,
but it's hard to navigate the offerings because they're all seemingly
advertised based on lightness.

~~~
wiredfool
In my opinion, If you want durable wheels, the best way to go is wheels built
by a _good_ wheel builder. That means properly tensioned (high), stress
relieved (for fatigue life), and lubricated nipples (so you don't wind up the
spokes). There are some places that will cater to tandems and touring bikes,
but you have to be careful. I've seen a tandem specialty shop lace up a
dedicated rear tandem hub to a lightweight mountain suspension front rim, with
predictable results. Note that this is not a cheap option, as I think there's
at least $150/wheel in parts here, as well as expert labor.

Parts wise, I'd look at something like:

* 36 hole hubs, either deore or ultegra level. 32 if you can't find 36. Not less than that. Some tandems go higher. This is more important on the rear wheel, where half (drive side) of the spokes are doing most of the work, because the other side's tension is so low.

* 3 cross, double butted spokes. It looks like the Dt Competitions are 2.0/1.7, which is a decent balance between elasticity and windup. 2.0/1.8 used to be my go-to choice, but that's hard to find now.

* Deepish section double eyelet rims, such as the Mavic Open Pro series. They should have closed section, not just a U for torsional rigidity.

* Grease the spoke threads and the nipple bearing surface.

* Tensioned just to the point of elastic instability in the rim, then backed off.

Reasoning:

* The key here is that you _never_ want a spoke to go slack under load. Once that happens, bad stuff happens with fatigue.

* 36 spokes puts either more spokes in the loaded zone.

* 3 cross lacing makes the spokes come in tangential to the hub, which reduces stresses on the spoke holes and prevents tearing of the hub.

* Double butted spokes allow the spoke to stretch more in initial tensioning for a given force on the spoke. As the rim deforms under load, the spoke will remain under tension to larger deformations.

* Eyelets make the nipples easier to turn in the rim, greasing even more so. Double eyelets also get support from second wall of the rim. I've had single eyelet rims (e.g. old MA series) fail where the inner wall of the rim pulled away from the braking surfaces.

* Grease the spoke threads and nipples. You want the nipples to turn on the spoke threads, not seize up and torque up the spoke like a spring. If you first ride a new wheel and hear it pinging, that's the spokes unspringing and unscrewing. Likewise, a good builder will always back off the tension a bit till there's no torque in the spoke.

* All other things equal, a wheel with twice the tension on the spokes will hold twice the load before you unload the bottom spokes, and have a much better fatigue resistance. So, take the tension as high as possible.

~~~
rawland
Ha, really love that one, wiredfool! :-)

Using 32 (front) and 36 (back) using your mentioned double eyelet rims
(tubular) in Cyclo-Cross racing these days.

~~~
wiredfool
FWIW, nearly all that advice agrees with "The Bicycle Wheel" by Jobst Brandt,
with the exception of rim selection. Rim selection though is tricky these
days, as most wheels are now sold as a unit rather than parts.

------
jackmott
This is one of the most persistent and silly myths in cycling.

When biking at a steady speed, _even_ when accounting for the fact that steady
speed isn't entirely steady because humans pulse their power a bit, wheel
weight is not worse than frame weight (the extra effort of each micro-
acceleration is offset by the reduce slowdown between micro-accelerations _and
then some_ )

When climbing a mountain, wheel weight is not worse than frame weight

Yes, when accelerating, wheel mass is worse than frame weight, but only a tiny
amount. source: physics:
[https://docs.google.com/spreadsheets/d/1N2aS3E0K4wrTa5jKqed7...](https://docs.google.com/spreadsheets/d/1N2aS3E0K4wrTa5jKqed7etJY_0XEyA6-23kUFR3KNmI/edit#gid=0)

That is my spreadsheet, it is very very basic physics and it drives me crazy
that people spew pseduo physics and comment on this "without taking the time
to comapre the sizes of the effects"

take the time!

TLDNR; don't worry about wheel weight any more than frame weight. Addendum:
don't worry about frame weight much either.

~~~
Maarten88
> That is my spreadsheet

I think your spreadsheet makes several assumptions that are only true in
theory.

As other have said, acceleration costs more energy. You don't get that back
when braking.

More importantly, in practice, the road is not flat at all. There are small
movements at every brick / stone that you cross, slightly rotating the bike
forward and back. The momentum (MOI) multiplied with the weight of the bike
for those those small movements is lost in energy. Weight at the ends of the
bike (mostly the wheels) increases the momentum of the bike far more than
weight in the center of the bike. I don't remember the exact energy formula,
but think there is a power of 4 with the distance from the center in it...

~~~
IshKebab
I too have done the calculations, and with reasonable weight wheels it is
totally trivial. Actually the weight of the bike itself is fairly trivial too
unless you are a professional cyclist or regularly ride up mountains. The
biggest difference it makes is how hard it is to pick the bike up.

------
mikestew
The article's conclusion isn't entirely correct. Mass on the wheels also
affects braking (the reverse of acceleration), and handling (gyroscopes with
less mass turn more easily). But otherwise, yeah, the standard line amongst
racers is to upgrade your wheels before anything else (albeit racers do a lot
more accelerating and braking that your average Sunday rider). Lighter wheels
are like the SSDs of cycling: biggest bang-for-the-buck.

As a sidenote, the picture looks to be a late-1880s Columbia of some sort.
Yup, same Columbia from whom you can buy a bicycle today (well, at least
something bicycle-shaped; they haven't made good bicycles in over 100 years).

~~~
jackmott
"Lighter wheels are like the SSDs of cycling: biggest bang-for-the-buck."

Completely wrong. Biggest bang for the buck is low CRR tires, then skinsuits,
then, I don't know, maybe helmets. Then 100 other things, then light wheels.

~~~
mikeklaas
Completely agreed. Tires a neglected by most cyclist. It is shocking how many
people buy a nice bike and keep the stock tires, or worse, slap on conti
gator-skins.

~~~
panglott
Gator skins are heavy, but they do protect you from punctures on the road.

------
thedufer
I haven't taken the time to compare the sizes of the effects, but it doesn't
sit well that they blow past seemingly obvious ways extra wheel mass would go
in the opposite direction. I see at least two places they do this:

Air Resistance:

> However, this force will produce a greater change in speed on the bike with
> less mass.

But the wheels act as (unsurprisingly) flywheels. Extra weight in the wheels
adds both momentum and angular momentum, while frame mass adds only the
former. This is exactly symmetric to their acceleration argument, so it's kind
of shocking they skipped it.

Internal Friction

> More mass on a bike can increase the friction in the bearings—but again,
> this won’t matter where the mass is located.

As an extreme example, a massful wheel with a massless frame clearly has no
bearing friction. I'm pretty sure wheel weight does not contribute to bearing
friction.

Does anyone have any insight into why these matter less than the acceleration
bit?

~~~
davidw
In a road race, you have to attack to get away from the group, or win the race
in a sprint. Either way, acceleration is critical.

~~~
thedufer
That seems like a very reasonable observation, and I would accept that as an
answer if this were a discussion about road racing. However, the completely
unqualified title (including the word "prove") implies something deeper. Road
racing is never mentioned.

~~~
mikekchar
It's very common for bicycle enthusiasts to equate "better" with road racing.
It's not just acceleration away from the group either. Almost all the effort
you put into cycling at high speeds (say over 30 km/h) is overcoming wind
resistance. You can save a huge portion of that effort by drafting behind
someone. So in terms of saving effort (or making other people hurt) making and
closing gaps is crucial.

But of course most people riding a bike are not racing. Even still
acceleration is quite important. When you are on a relatively uniform gradient
you can judge your power easily and make sure you don't go anaerobic. It's
when you have to push hard to get over a small bump, or sprint ahead to get
out of traffic, etc that you get into the red zone. Making those situations
easier will make your whole ride easier.

But it is fair to point out that "good" bikes are really only "better" for
certain situations. For example, my wife almost never travels faster than 20
km/h. Many of the things that are absolutely necessary on a "good" bike that
is travelling at 40+ km/h make absolutely no difference for her. Lot's of
people tootle around at 10-15 km/h. Any well maintained bicycle will be
completely fine. In fact a "good" bicycle will be unsatisfactory because it
will be hard to handle.

It's all about context. And in the context of talking about which bicycle is
"better", the convention is to assume you are talking about road racing unless
otherwise stated.

~~~
eru
If you are not racing (and thus not subject to racing conditions) and you want
to go fast, you should be riding a fully covered recumbent.

There's only so much that toying around with slightly better uprights can do.

~~~
mikekchar
I have never ridden one (and I really want to ;-) ), but I've heard mixed
reports on hills. You can push against the back of the seat, but you lose the
advantage of using your weight on the pedals. Can anyone comment on what it's
like for difficult hills? I have lots of gradients over 20% here and one of
the hills I ride has a 30% section!

~~~
BenFrantzDale
I have never ridden one either but weight on the pedals shouldn't matter. If
you push down on a pedal as you extend your leg leaving your body at a
constant height, that should be the same work as pushing just as hard over
just as far against a seat. I'm sure there are subtleties – you can push more
than your weight against a seat but a seat absorbs energy – but to first order
it should be a wash.

~~~
davidw
I'm skeptical. When you're up out of the pedals and sprinting on a bike, you
are transmitting an awful lot of energy. I don't quite see being able to push
quite so hard when sat down.

~~~
BenFrantzDale
One way of thinking about it is that work is force times distance, so if you
aren't moving WRT the bike, and push just as far work goes by force. Assuming
you don't have toe clips and so aren't pulling up with one foot while you push
down with the other, then at most you can push down with your body weight.
(You could push harder but that would leave your body accelerating up at the
end of the stroke.)

~~~
davidw
You're thinking about it from a physics point of view, which is kind of
abstract, and possibly not considering all the movement involved. I'm thinking
about it from the point of sprinting for the finish line at a race last
Sunday. I really don't think I could have brought the same force to bear while
sitting down.

Also: modern bikes have clipless pedals, not toe clips.

------
freehunter
>Here’s The Thing With Ad Blockers

Here's the thing with "I'm a print subscriber but hate having to log in on
every device I might read your site on".

------
3pt14159
Last year I paid the $700 for custom made wheels. I fairly regularly go down
short staircases (3 or 4 steps, or big curbs) and I used to blow through
spokes like birthday cake candles.

No longer. Screw minimizing wheel weight. I want my bike to be an extension of
myself. I want to be able to push it and for it to deliver. If I need to spend
some extra joules on angular momentum, fine. My thighs need the workout
anyway.

~~~
collyw
How much do you weigh? I (used to) regularly drop off of stuff a foot or two
and I never had any problems. My bike wheels can't have come close to that
price. (I did need to move to downhill tubes as those kept getting pinches).

~~~
lostlogin
Tall guy who used to bmx here. Never broke a spoke but munted a few few wheels
and one set of bearings. I dearly wish for a bmx scaled up by something like
1.3x or 1.5x. My neck has never recovered from the stupid head-tilted-up pose
that bike forced me into. Loved the bike though!

~~~
eckza
How tall are you? We've got all kinds of stuff for tall people. Check out 24"
BMX bikes (aka cruisers) - a cruiser with a long frame and 7" or 8" bars would
probably suit you well.

~~~
lostlogin
1.95m. And thanks!

------
walrus01
Road bike nerds have known this for a while. If you ride a lot you will
immediately feel the acceleration difference in a wheelset that totals around
1450g front and rear with hubs, spokes, nipples and rims (example: White
Industries road hubs, Sapim CX-Ray spokes, medium profile high quality
aluminum rim) vs the same spoke count "cheap" wheelset that might weigh 1800g.

That is all before you get into the category of exotic and expensive deep
profile CF rim wheelsets that cost $1500+/pair...

~~~
brianwawok
And us tri dorks don't care what we weigh because aero beats weight on most
courses that we ride.

The science of bikes is pretty great.

~~~
outericky
That's why we buy $3800 Zipps. Though they are both aero and light.

That said, got mine used for $1800. Sold them 2 years later for.... $1850.

~~~
brianwawok
ya zips are spendy (but very nice). I am more of Flo fan for me $900 for a
pair.. plenty aero.. fairly heavy.. but I can lose 1 pound from my belly for
less than the $3000 nicer wheels would cost me to lose a pound.

------
dahart
> You will have double the increase in energy by adding mass to the wheel.

Is this always true regardless of wheel radius? At first I was thinking it has
to depend on radius, but then thought about how the ground contact point has a
zero velocity, and the exact other side of the wheel is always double the
velocity of the bike frame relative to the ground, regardless of wheel radius.
I'm not sure if this is a reasonable intuition. Maybe it makes sense that a
gram added to the rim is always double the difference in effort that a gram
added to the axle or frame or rider is.

~~~
brianwawok
Well for adult bikes you are pretty much fixed at 700C. If making a bike
pedaled contraption not so much.

~~~
jean_claude
>Well for adult bikes you are pretty much fixed at 700C. If making a bike
pedaled contraption not so much.

For racing/road bikes, maybe. You're leaving out the 26" wheel adult bikes
(which over time has encompassed 5 different rim diameters[1]) and 24" wheel
bikes that are targeted at youth, but smaller adults sometimes prefer (well,
those that have been give the option).

My bike pedaled contraption is a rear suspension compact long wheelbase
recumbent with two real 20" (406mm rim) tires and they're spectacular.

[1] [http://www.sheldonbrown.com/26.html](http://www.sheldonbrown.com/26.html)

~~~
brianwawok
I feel like less and less bikes are going for 26s. It used to be that the
smallest bike or so from each manufacturer used 650C, then everything else
used 700C. Seems like most manufactures just went to 700C for all adult bikes
over the last few years...

------
slashdotdash
Aerodynamics trumps weight for cyclists, even for wheels.

"In summary, wheels account for almost 10% of the total power required to race
your bike and the dominant factor in wheel performance is aerodynamics. Wheel
mass is a second order effect (nearly 10 times less significant) and wheel
inertia is a third order effect (nearly 100 times less significant)."

[http://www.biketechreview.com/reviews/wheels/63-wheel-
perfor...](http://www.biketechreview.com/reviews/wheels/63-wheel-performance)
[http://www.slowtwitch.com/Tech/Why_Wheel_Aerodynamics_Can_Ou...](http://www.slowtwitch.com/Tech/Why_Wheel_Aerodynamics_Can_Outweigh_Wheel_Weight_and_Inertia_2106.html)

~~~
slashdotdash
Some worthwhile further reading, including worked examples, comparing a
wheelset with superior aerodynamics versus one that is lighter.

"... the point of all this was to demonstrate the relative unimportance of
wheel rim mass and why aerodynamics matters even when accelerating"

[1] [http://alex-cycle.blogspot.co.uk/2014/12/the-sum-of-parts-
ii...](http://alex-cycle.blogspot.co.uk/2014/12/the-sum-of-parts-ii.html)

[2] [http://alex-cycle.blogspot.co.uk/2014/12/the-sum-of-parts-
ii...](http://alex-cycle.blogspot.co.uk/2014/12/the-sum-of-parts-ii.html)

[3] [http://bicycles.stackexchange.com/questions/15047/are-
aerody...](http://bicycles.stackexchange.com/questions/15047/are-aerodynamic-
rims-worth-additional-weight)

------
dbg31415
>Here’s The Thing With Ad Blockers

Today I learned that a VPN counts as an ad blocker. Hooray.

------
jdc0589
This is pretty standard stuff in automobile land. Unsprung weight (includes
slightly more stuff than this, but same basics) is known to have a
disproportionate effect relative to, say, the driver gaining a couple lbs.
People don't talk about it as much as other performance factors, but this is
why magnesium wheels have existed for upper end cars for a while, and carbon-
fiber more recently.

On the flip side, this is also exactly the same reason why flywheels outside
of automobile land, when used as energy storage devices, are hugely massive.

------
shermozle
Or to take the alternate view, if you want to get fit, get a heavy wheel. I'm
having a super strong one built right now, and extra weight is fine by me.

~~~
adriand
Or take another alternate view: if you want to have a lighter bike and you
don't want to pay for it, lose body weight instead. Then you'll be both
lighter and fitter. Only once you've lost as much body weight as you can
reasonably lose does investing heavily in a lighter bike make sense!

Naturally this doesn't, of course, diminish the fact that lighter wheels give
you more bang-for-the-buck than lighter anything-else, due to the physics
described in the article. But if the difference between heavy, cheap wheels
and light, expensive ones is a few hundred grams and a few thousand dollars,
losing a pound of body fat is likely a better bet.

~~~
eru
Depends on how much body weight you start out with. There's such as thing as
too skinny.

~~~
marvin
Yeah, this advice isn't good for my 147-pound, six-feet frame ;)

------
peterwwillis
Increase in unsprung weight is also bad for suspension[1] and handling[2].

Here's something they don't mention in the article: the location of the mass
in the wheel has a direct relationship to torque. The same mass located in the
hub will take less torque to move than if the mass were located in the rim. So
acceleration could in part be improved merely by relocating mass in the wheel.
(But that's just wheel acceleration torque; you'll still need to do the same
amount of work to move the same total mass of the bike at the same speed)

Also, for the same weight tire rubber, wider tires would create increased
friction and slow the tire down more.

[1]
[https://en.wikipedia.org/wiki/Unsprung_mass#Effects_of_unspr...](https://en.wikipedia.org/wiki/Unsprung_mass#Effects_of_unsprung_weight)
[2]
[http://www.formula1-dictionary.net/unsprung_weight.html](http://www.formula1-dictionary.net/unsprung_weight.html)

------
davidw
I'd be curious to see the math on 29 inch mtb wheels vs other sizes. Of course
there are other things in play there like the ability to roll over obstacles
(29ers do this well) and maneuver in tight spaces (not quite so good).

~~~
niels_olson
[http://hyperphysics.phy-
astr.gsu.edu/hbase/ihoop.html](http://hyperphysics.phy-
astr.gsu.edu/hbase/ihoop.html)

------
ars
There is a similar concept with cars:
[https://en.wikipedia.org/wiki/Unsprung_mass](https://en.wikipedia.org/wiki/Unsprung_mass)

The same conclusions about mass hurting acceleration also occur with the car,
but the relative masses are so different, it's mostly irrelevant (cars are a
lot heavier than bike frames).

The main difference comes with the ability of a lighter wheel to be able to
fully track the road, and not leave it on a bounce. This gives better
traction. (But somewhat greater vibration in the cabin.)

~~~
taneq
Unsprung mass is more about the effectiveness of suspension in keeping the
wheel on the road. This is about rotating mass and the fact that you have to
'speed up the wheel twice', once in translation and once in rotation, and so
rotating mass stores more kinetic energy than non-rotating mass.

------
cellis
Taken to the extreme, what is going to move faster, a thin strip of steel on 6
logs, or 6 logs on a thin strip of steel with, say cartwheels wheels under
that?

------
gooseyard
in racing I've heard this referred to as "unsprung weight" or mass. Makes it a
little easier to find more information if you're interested.

~~~
recursive
I think "unsprung weight" is a different idea, at least in bike racing.
Unsprung weight represents the weight not supported by suspension. In road
racing, the suspension is the rider, so the entire bike is unsprung weight.

------
WalterBright
Drag racers have known this forever :-)

~~~
taneq
The rule-of-thumb I've always heard is that 1kg off your wheels is equivalent
to 4kg off the weight of the car.

~~~
lostlogin
Wonder if you can apply the same theory that had me shaving the crank on an
old car a bike...

------
gerbilly
I never was a weight weenie in my cycling. I never understood the obsession.

Humblebrag: I could bunny hop my 28 pound trial bike 2 ft, and sidehop 30
inches too.

------
caycep
is this something about unsprung weight? Similar rational for using carbon
wheels on the new Mustang GT350R

------
RP_Joe
The comments here are better than the article.

