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CRANKS AND PEDALS
Figure 1 - The two standard crank types
Bicycle cranks and pedals are pretty straight forward once you know which threads are reversed and
the basic differences between one piece cranks and three piece cranks. Tools needed: a 15mm box
wrench for the pedals, a pipe wrench if you plan on removing the crank set or axle from the bottom
bracket, and optionally, a crank puller to easily remove crank arms from a three piece bottom bracket
axle.
There are two types of crank sets and bottom brackets as shown in Figure 1. On the left is the one piece
crank set, which is often found on single speed BMX bikes and lower quality cycles. Single piece crank
sets are heavy because they are made of steel, but this also makes them practically indestructible, which
is why they are chosen for use on BMX cycles.
On the right of Figure 1 is a three piece bottom bracket and crank set. This type of crank set uses steel or
aluminum crank arms that are bolted to an axle. They are the most common type found on road and
mountain bikes.
If you are planning to build your own cycle, always choose a three piece crank set for any speed bike or
vehicle that is intended for serious riding, and use single piece crank sets for experimental bikes and fun
rides like choppers and cruisers.
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Cranks and pedals
Figure 2 - Single piece and three piece cranks
Both types of crank sets are available with varying lengths of crank arms, which typically vary in length
from 165mm to 175mm. The length of a crank arm is measured from its center of rotation to the center
of the pedal axle. Crank length preferences vary, and many schools of thought exist to what the best
crank length might be for a certain leg length or even bicycle type.
Shorter cranks are becoming a trend on recumbent bicycles, even to the point where builders are cutting
the crank arm shorter than the standard 165mm to re-drill and thread a new pedal hole. The best way to
determine which crank length suits your body and riding style is experimentation, but I have not noticed
any difference with varying crank lengths myself.
Oddly enough, pedals are not interchangeable between single piece crank sets and three piece cranks
sets. The threads on a single piece crank pedal are 1/2" by 20 threads per inch, whereas threads on a
three piece crank set are 9/16" at 20 threads per inch. It may seem odd that the pedal axle on a BMX
crank set would have a smaller diameter than a road bike, but since the BMX crank arm is made of steel,
it is more robust and will bend far before a pedal will strip from the threaded hole. I have seen many
stripped pedal threads on an aluminum crank arm, though.
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Cranks and pedals
Figure 3 - The right pedal has right hand threads
One thing all bicycle pedals have in common is that on the right side crank arm (chain ring side), pedal
threads are standard right hand threads, and on the left side crank arm they are reversed left hand
threads. Also, most pedals can be removed using a 15mm wrench, although some may differ or even
require a special thin profile pedal wrench. Figure 3 shows how to remove the right side pedal using a
counter clockwise rotation to unscrew the threads.
Figure 4 - The left pedal has reversed threads
Figure 4 shows the clockwise rotation used to remove the left side pedal, which has reversed threads.
Often, recycled bicycle parts have been well used and may be dirty or rusted, so don't be afraid to use a
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Cranks and pedals
few dirty tricks to free those stuck pedals. I have a few 15mm wrenches that I use specifically for bicycle
pedals, as there are times where a hammer is necessary to "help" things along.
Another trick you can use to gain leverage over a stuck pedal is to place a 2 foot long pipe over the
wrench for mechanical advantage, but be aware that you may snap the end from your wrench. A blow
torch can also be used to heat up the area around the pedal axle in order to expand the crank arm hole a
bit, but be careful not to melt the pedal bodies, which are often made of plastic.
Figure 5 - Right pedal on a three piece crank arm
By now, many astute garage hackers may be thinking, "Wait! The threads should be the other way
around on the pedals!" Really, the pedals rotate in the same direction that would actually unscrew their
threads, right? It does seem strange at first, but due to the fact that the bearings actually transfer force at
180 degrees to the other side of the race, the opposite is true. When a pedal is rotating in the clockwise
direction, forces are transferred around the bearings back to the pedal axle with counter-clockwise
force. Confusing, isn't it? But 120 years of engineering can't be wrong!
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Cranks and pedals
Figure 6 - Most pedals have their axles stamped
Rather than attempting to cross-thread the wrong pedal in a crank arm, you can usually just look at the
threaded end of the axle and see a stamp indication either "L" or "R". The pedals for three piece cranks
will not fit into a single piece crank set and vice versa, so that is not really much of a concern.
The only thing you need to be mindful of is the first few turns of a pedal into an aluminum crank arm. If
you can't get the first few turns in by hand, then either you have the pedal on the wrong side, or it is not
going in straight. Aluminum is lightweight, but it is very easy to damage, and a cross-threaded aluminum
crank arm is not repairable, even with a pedal threading device, since there will not be enough material
to cut new threads. Start a pedal by hand and then switch to your wrench after a few rotations.
Figure 7 - Two sizes of pedal threads shown
The larger 9/16 inch threads for three piece cranks are shown at the top of Figure 7, and the smaller 1/2
inch threads used on single piece crank sets are shown in the lower part of Figure 7. Pedals are also
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Cranks and pedals
available in a wide variety of styles and types, some of which hold the pilot's shoes in place using some
type of clip or strap system. Clipped pedals require a special cycling shoe and allow the rider to push and
pull on the pedal, allowing the legs to deliver force to the drive system at all times during a pedaling
rotation.
Clipped pedals are generally used by more serious long distance cyclists as they require special shoes,
as well as the confidence to ride with their feet somewhat bonded to the pedals. Although the rider's feet
can be removed from both clipped and strapped pedals without much difficulty, it could still become a
problem in an emergency situation.
The typical and most common type of pedals are platform pedals (shown on this page), and have no
constraints since the rider simply pushes down on them. Platform pedals only allow force in the
downward direction, but for most cycling, this is more than enough efficiency. In defense of clipped
pedals, a foot slipping from a platform pedal on a very low recumbent can cause the rider's foot to catch
the ground and be pulled under the cycle, so consider your choice of pedals based on our riding style
and bicycle type.
Figure 8 - There are several bicycle chain widths
There are two basic types of bicycle chain: single speed chain and multi-speed chain. Single speed chain
is mainly used on kids' bikes, BMX bikes, coaster brake cruisers, and heavy cargo bikes. Multi-speed
chain is used on standard speed bikes and mountain bikes that require the use of a front and rear
derailleur to change gears. Both types of bicycle chain have a pitch of 1/2 inch (ANSI standard #40). This
measurement indicates the length of the links. Although every type of bicycle chain and freewheel have a
1/2 in pitch, the width of chain varies quite a bit, from 3/32" to 1/8".
Single speed bicycle chain is wider, having a width of 1/8 inch. This type of chain will not fit a multispeed freewheel or will it fit properly through a derailleur cage. Multi-speed chain comes in various
widths, with 3/32" being the most common size. Multi-speed chain is designed with a lot more side-toside flex to allow it to function properly with a derailleur system. Flexibility is very important in a multispeed system as the alignment of front and rear chain rings could be off by as much as 3 inches,
depending on which gears are being used.
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Cranks and pedals
Figure 9 - A crank puller is a nice tool to have
To remove a crank arm from a three piece bottom bracket axle, you must remove the axle nut (or bolt)
and then pull the crank from the square axle, as it is forced on very tightly by the axle nut. Hammering
on a 6 inch rod or bolt placed behind the crank arm as close to the axle as possible is usually enough to
free a crank arm, but often the aluminum has oxidized around the axle, making this job very difficult.
If you plan to work on bicycles a lot, then the crank pulling tool shown in Figure 9 can make your life
much easier, as it will help you pull a crank with minimal effort. The crank pulling tool threads into the
opening where the plastic dirt cap threads are, and forces a pin down on the bottom bracket axle, pulling
the crank away from the axle. For very stuck cranks, a little heat around the axle area from a blowtorch
can also do wonders.
Figure 10 - A common three ring crank set
Typically, mountain bikes have a triple ring crank set like the one shown in Figure 10, with rings having
something like 32, 48, and 52 teeth. Road bikes have a similar set of chain rings, although often without
the smaller third ring, which is primarily used for extreme hill climbing or load pulling. The same typical
triple ring system can be found on the less expensive single piece crank sets as well. Lower quality crank
sets have steel stamped chain rings, and the more expensive and lighter crank sets use machined
aluminum chain rings, which are often interchangeable.
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Cranks and pedals
Figure 11 - A crank arm with a removable chain ring
Higher quality crank sets will have what is called a "spider" (Figure 11), allowing the chain rings to be
removed. This allows worn chain rings to be replaced and for experimentation with different sized chain
rings. Since many recumbent cycles use a rear wheel smaller than 26 inches, it is often necessary to have
a front chain ring with many more teeth in order to achieve the higher speeds the cycle is capable of.
Many of the fully faired racing recumbent cycles have custom made front chain rings with 80 or more
teeth to allow the cycle to reach much higher speeds. Typically, 52 teeth is about the largest chain ring
that can be purchased, and with a 20 inch rear wheel, this can be very limiting. Some garage hackers
have actually created their own large chain rings by printing out a template to cut an aluminum disc,
which is then hand drilled and filed to create every single
tooth!
If you have questions about pedals and cranks or need
more information about them, log onto the AtomicZombie
builders forum. There are forums specifically on bike
parts and general forums where you can get some help.
See you there.
Free bike building tutorials:
Using a chain link tool
Basic fishmouth cutting
Arc welding
Cranks and pedals
Front derailleur
Cables
Coaster brakes
Free bike projects:
Kids electric trike
Choppers
Mountain bike tandem
Bicycle bearing basics
Lacing wheels
Frame chopping
Bike chains
Rear derailleur
Freewheel
Head tubes
Sidewinder stunt bike
Velomobile
World Record SkyCycle
Head tube bearings
Salvaging wheel parts
Bicycle autopsy
Rake and trail
Brakes
Gooseneck
Detachable tandem
Tall bikes
Spin Scooter
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Simple SWB recumbent
and more!
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