26 September 2020 | New Scientist | 55Tom Gauld
for New Scientist
Answers
Matt Chamings
Barnstaple, Devon, UK
Steering is one problem associated
with extending a bike for more
than one person. Turning a bike
involves leaning into the turn.
With more weight shifting off
the centre of balance, the person
holding the handlebars would
need enormous strength to stop
the whole thing toppling over.
Adam Osen
Harlow, Essex, UK
The previous discussion on
tandems focused mainly on
the hardware. The software is
important too. A few years ago,
my daughter and I rode a tandem.
When we got back, I remarked
that it was surprisingly hard. She
smiled. Apparently, I had been
doing all the work, while she
enjoyed the ride. On the other
hand, when I rode up a hill with
my son on the back, it was like
having an electric motor. Perhaps
an app that displayed the power
being provided by each rider
might help the efficiency gains of
the tandem to be better realised.
Richard Ellam
Bristol, UK
The discussion about multi-
person bicycles assumes that
triplets are more efficient than
tandems, which in turn are more
efficient than solos. Practical
experience suggests that this
isn’t always the case. The truth
of the claim rests on the definition
of “efficiency”.
A tandem bicycle with its riders
will be lighter than the same riders
on two solo bikes and will have
roughly the same air resistance
as a solo. So, with about twice the
power available, it can be ridden
faster than either rider can
comfortably pedal a solo when
air resistance is dominant, for
example on flattish roads and
when riding into a headwind. But
not when it comes to hill-climbing.The ability to climb steep hills
depends on the power-to-weight
ratio of the bike and its rider or
riders, not on the power-to-air
resistance ratio, because most of
the riders’ efforts are devoted to
increasing gravitational potential
energy, not pushing the air aside.
The fact tandems climb poorly
suggests that their actual power-
to-weight ratio is less than that of
good solo bikes. That is probably
because of increased losses in the
transmission due to the chainsets
being coupled and difficulties in
the riders synchronising their
physiological efforts, despite
being mechanically coupled.
My wife and I rode a tandem for
several years. When riding with
solo cyclists, it was common for
the solos to pass us on climbs.
On the descent, we would
catch up and overtake them in
short order as we were much
faster downhill. Even with very
low gear settings, climbing our
local hills, which we can do quite
comfortably on our solo bikes,
could be pretty purgatorial on
the tandem. ❚Quick quiz #70
Answers
1 Australia. It was detonated in a
lagoon of the Montebello Islands,
an archipelago off the country’s
west coast, on 3 October 19522 Ammonia3 53. The chip’s 54th qubit failed4 Hyperbolic planes – surfaces
where the space curves away
from itself at every point5 The earCryptic
Crossword #40
Answers
ACROSS 1 Peat, 3 Price war,
9 Algebra, 11 Testosterone,
13 Sirius, 15 / 10 Alfred Nobel,
17 Osteoporosis, 20 Oxeye,
21 Truffle, 22 Halloumi, 23 PansDOWN 1 Phantasm, 2 Aegis,
4 Reacts, 5 Control group,
6 Webinar, 7 Roll, 8 Absolute zero,
12 Odysseus, 14 Roswell,
16 Sputum, 18 Sofia, 19 Moth#77 Sir Prancelot's
archers^
SolutionThe eight archers at the turret
must alternate odd/even, so the
napping archer must be an odd
number. The four evens at the
turret add to 20, so the four odds,
which must also sum to 20, can
only be 1+3+7+9, meaning the
napping archer is number 5.There are two possible
arrangements of these eight
archers around the turret:
12389476 and 12983476
(clockwise or anticlockwise).“ On steeper hills,
the main influence
on progress was
how soon one of
the riders needed
to pause for breath”