Synchronous belts were invented in the 1940s to synchronize shafts on sewing machines. They have since been widely adopted due to advantages over other transmission methods like gears, chains, and V-belts. Synchronous belts engage teeth in a smooth, rolling motion for precise synchronization without slippage. Modern belts use high-strength fiberglass or aramid cords and molded rubber teeth for durability and power transmission in a variety of industrial applications.

1. Introduction to Synchronous Belts

2. Introduction to Synchronous Belts
Timing belts were invented
in the late 1940’s by Richard
Y. Case, an engineer with
the former L.H. Gilmer
company, which was
eventually absorbed into
Uniroyal Inc. The sewing
machine provided the
impetus for the development
of a belt capable of
synchronizing two or more
shafts.

3. Introduction to Synchronous Belts
Applications required a very high modulus (no
stretch) tensile member to prevent distortion of
the pitch (the distance between the teeth) as it
rotated around the sprockets. Steel wire was
first used as a tensile member until later being
replaced by fiberglass and aramid fiber cords.

4. Introduction to Synchronous Belts
Synchronous drives represent
a modern and efficient system
of power transmission. They
essentially combine the
advantages of mechanical
components (gears & chain)
and flexible components
(flat & V-belts) while
eliminating the inherent
disadvantages of these
components.

5. Basic Design Principles
Synchronous belts operate on a basic principle:
molded teeth of the belt and mating grooves of the
pulley make positive engagement. The teeth enter
and leave the pulley in a smooth rolling manner with
low friction. This positive engagement results in:
• Exact shaft synchronization
• Elimination of slippage and speed loss common to
v-belts.
• Synchronous operation at speeds higher than most
chain drives.

6. Basic Design Principles
All synchronous belts operate on the positive
engagement principle. Chains operate on the
same principle but synchronous belts have many
superior characteristics. Synchronous belts wrap
around the pulley by means of flexion and not by
rotation of articulated parts (as chains do). This
eliminates one of the causes of wear and noise.

7. Basic Design Principles
To maintain the correct tooth
pitch as the belt flexes around
the pulley, the belt pitch line
(tensile cord) must coincide
with the pitch diameter of the
pulley. The difference between
pulley O.D. and pulley pitch
diameter is referred to as Pitch
Line Differential (PLD). For
proper tooth meshing the PLD
of the belt must match the PLD
of the pulley.

8. When to Use a Synchronous Belt Drive
• Synchronous transmission between shafts is a must
• High mechanical drive efficiency and energy savings required
• Precise relative positioning of shafts (non-slip and minimal
backlash)
• Compact drive layout is necessary
• Low maintenance is required
• Combines power transmission and conveying needs
• Low noise requirements (compared to chain)
• Environmental or contamination concerns (no lubrication
required)
• High torque, low RPM requirements

9. Synchronous Belt Advantages
vs. chain
• Increased service life for belts and sprockets
• No need for lubrication
- Improper lubrication of chain drives severely reduces life
- Lubrication attracts dirt and leads to wear
• Reduction in noise over chain (& polyurethane drives)
• Environmentally cleaner – no grease or oil
• Increased productivity — less down time
(vs. chain and v-belts)
• Increased efficiency and registration accuracy

10. Synchronous Belt Advantages
vs. chain
• Chain is heavier than belt systems
• Limited take-up or inaccessible drives - with synchronous
belts, the required take-up allowances for tensioning are
significantly less (v-belts and chain).
• No Hidden Costs — chain cost of lubrication, disposal cost of
lubrication, reservoirs
• Chain available only in full box lengths
- (Typically 10 ft. in box)

11. Synchronous Belt Disadvantages
vs. chain
•Less initial cost (although synchronous payback is rapid
due to reduced maintenance)
•Design Flexibility — larger availability of ratios and
lengths
•Less sensitivity to improper installation —
alignment and tensioning

12. tooth facing
teeth
tensile cords
rubber backing
The main components of a synchronous belt are the
tensile cords, the teeth, rubber backing and tooth
facing.
Belt Construction

13. Steel was originally used as a tensile cord material. Most belts
today use high modulus (low-stretch) fiberglass or aramid fiber as
the tensile member. (Kevlar is the Dupont trademark for an aramid
fiber). Tensile cord is the load bearing element of the synchronous
belt.
The belt teeth are molded of a hard rubber compound jacketed with
a tough, abrasion resistant nylon tooth facing. The compressive
and shear strength of the teeth exceeds that of the tensile cords
when there are at least six teeth in mesh with the driver pulley.
Teeth in mesh is a critical design factor.
A durable rubber backing encases the load bearing tensile cord. It
protects the cords from dirt, oil and other contaminants, as well as
frictional wear when a backside idler is used.
Belt Construction

14. Belt Construction
“S” & “Z” Twist
" Z" twist
"S" twist
To reduce lateral movement, synchronous belts are constructed by
alternately spiraling “S” and “Z” type cords. The synchronous belt cord
is made up of a number of small fiber strands twisted together. These
strands can be twisted either clockwise or counterclockwise. The two
twist directions are referred to as “S” twist and “Z” twist.

15. Belt Construction
“S” & “Z” Twist
Most synchronous belts are made with both “S” and “Z” twist
cord to minimize belt tracking forces on the pulley flanges.
direction of
belt rotation
direction of
belt rotation
S - TWIST
(TOP VIEW)
direction of
lateral belt
movement
Z -TWIST
(TOP VIEW)
direction of
lateral belt
movement

16. Belt Construction
“Z” Twist
When necessary, the lateral movement of a belt can be pre-determined, if
the direction of rotation is constant (non-reversing drives).
A good example of this is Fin-Fan Drives. Because the fin-fan drive has a
vertical shaft, the belt is built with Z twist construction only. This gives the
belt an upward direction of lateral movement. This helps keep the belt off
of the bottom flanges and reduces excessive side belt wear. Carlisle offers
a special construction “Z” twist construction for Fin-Fan air-cooled heat
exchanger drives.
direction of lateral belt movement
direction of belt rotation
Side View
Z-Twist construction Fin-Fan Drive

17. Synchronous Drive Terms
Unlike the V-belt drive, the synchronous belt drive is not a friction
device. It is a positive engagement drive that is dependent upon
the meshing of the belt teeth with the pulley grooves.
The tooth profile indicates the type or shape of the belt teeth.
The spacing between two adjacent teeth on the belt (and pulley) is
referred to as the tooth pitch. The distance is measured from the
center of one tooth to the center of the next.
In synchronous belts, the belt length is determined by multiplying the
belt pitch by the number of teeth in the belt. This is known as pitch
length.
In synchronous drive systems, backlash is the necessary clearance
between belt teeth and pulley grooves for proper meshing.

18. Synchronous Drive Terms
The pitch diameter of the pulley or
(sprocket) refers to the diameter
determined by the tensile cord location
in the belt. Therefore, the pitch
diameter of the pulley will be
somewhat greater than the outside
diameter of the pulley across the teeth.
To maintain the correct tooth pitch as
the belt flexes around the pulley, the
belt pitch line (center of the tensile
cord) must coincide with the pitch
diameter of the pulley. The difference
between pulley O.D. and pulley pitch
diameter is referred to as pitch line
differential (PLD).

19. Synchronous Drive Terms
Tooth pitch is one indication of overall belt size. The larger the
pitch, the larger the teeth and tensile cord. The larger and stronger
the belt, the more horsepower it can transmit.
In conventional trapezoidal tooth profile belts, letters indicate
pitch, (MXL, XL, L, H, etc.) which are measured in inches.
In curvilinear tooth profile belts, pitch is measured in millimeters
(3M, 5M, 8M, etc).
The terms synchronous belt and timing belt are used
interchangeably.
Sprocket and pulley are also used interchangeably.

20. There are two types of synchronous belt tooth profiles that make up
the majority of synchronous drives in use today.
• Trapezoidal tooth profile — (original technology) refers to the
tooth configuration of MXL, XL, L, H, XH AND XXH type belts.
• Curvilinear tooth profiles — have rounded tooth profiles that
eliminate stress concentrations at the base of the tooth and allow
more uniform stress distribution. Curvilinear profiles transmit high
torque and represent the latest evolution of synchronous belt
technology. Available in 3M, 5M, 8M, 14M, and 20M pitch.
Synchronous Belt Tooth Profiles

21. Trapezoidal Profile
Carlisle Tooth Profile Evolution
Curvilinear (RPP Profile)
Original synchronous
belt tooth profile
Modern tooth profile
A trapezoidal belt
tooth has a constant
angle of pressure.
The profile of
curvilinear teeth has
an angle that increases
from the base, to the
top of the tooth and
allows for more
uniform stress
distribution resulting in
higher torque
transmission with
reduced occurrence of
tooth jump.

22. Trapezoidal Profiles
Pitch Pitch
Designation Distance
MXL = 0.080”
XL = 0.20”
L = 0.375” (3/8”)
H = 0.50” (1/2”)
XH = 0.785 (7/8”)
XXH = 1.25” (1-1/4”)
Trapezoidal profile belts are available in the following pitches:
tooth pitch

23. Trapezoidal Pitch Sizes
MXL = Mini Extra Light
XL = Extra Light
L = Light Duty
H = Heavy duty
XH = Extra Heavy Duty
XXH = Double Extra Heavy Duty

24. Trapezoidal Construction
• Fiberglass tensile
member
• Synthetic rubber
compound body
• Nylon tooth facing

25. Trapezoidal Features
• Fiberglass tensile member
– High breaking load, length stability (low stretch)
– Good resistance to repeated flexing
• Belt body synthetic rubber
– Good resistance to fatigue
– Resists heat, oil & ozone
– Ground back for smooth operation – low vibration
• Nylon tooth facing
– High resistance to abrasion
– Low coefficient of friction for smooth engagement
– Extended sprocket & belt wear
• Low backlash
– Good for applications where high positional accuracy is
required

26. Explanation of Part Numbers
300L100
300 ÷ 10 = 30 inch pitch length
Pitch Length designated in tenths
of an inch
(hundredths of an inch for MXL)
example: 440 MXL 025
440 ÷ 100 = 4.4 inch pitch length
L = 3/8”
Tooth Pitch
100 = 1.0”
Belt Width
in hundredths
of an inch
D300L100 = dual sided

27. Sycnhro-Cog® Dual Timing Belt
belt belt belt pitch length
type pitch (inch) pitch (mm) range (inch) standard widths (inch)
DXL 0.20 (1/5) 5.080 15.0 – 33.0 .025 - .037
DL 0.375 (3/8) 9.525 15.0 – 66 .050 - .075 – 1.0
DH 0.50 (1/2) 12.7 24.0 – 140.0 .075 – 1.0 – 1.5 – 2.0 – 3.0
Standard Lengths and Widths

28. Curvilinear Tooth Profile

29. Advantages of Curvilinear Profile
vs. Trapezoidal Profile
•Higher power ratings allow narrower widths to be
used than trapezoidal timing belts
•More compact drives
•Lower overhung bearing loads (narrower widths)
•Quieter than comparable trapezoidal belts
•Covers wider range of power
•Reduced sprocket wear

30. Evolution of Curvilinear Tooth Profiles
• HTD - Curvilinear - Introduced by Gates in 1971
• STPD - Modified Curvilinear - Introduced by Goodyear
in the early 1970’s
• GT - Modified Curvilinear - Developed by Gates in the
late 1970’s
• RPP - Parabolic – Dayco (Carlisle) introduced in the
USA in 1985

31. Curvilinear Profiles
Pitch Pitch
Designation Distance (mm)
3M = 3
5M = 5
8M = 8
14M = 14
20M = 20
Curvilinear profile belts are available in the following pitches:

32. Advantages of RPP Profile
•Interchangeable with existing deep groove
profiles (HTD, HPPD, UPD)
•Sprocket availability - most major sprocket
manufacturers provide RPP profile
•Sprockets use readily available QD bushing
•Quieter than competitive curvilinear belts
•RPP profile reduces sprocket wear

33. RPP Plus Synchronous Belt
• Highly energy efficient
• High Torque capability
• Provides up to 50%
more horsepower
capacity than first
generation high-torque
belts (HTD)

34. RPP Plus
Tooth Indentation
• Shock Absorbing
• Reduces Noise
Extra Strong
Fiberglass Cords
Precision Ground
Neoprene Backing
Patented nylon self-
lubricating graphite
loaded tooth facing
Neoprene Rubber Belt Teeth

35. RPP Plus
available in pitches of *3M, 5M, 8M, 14M, 20M
Reinforced Parabolic Profile
Wide range load capacities & speeds
No lubrication
High mechanical efficiency
Does not require friction to operate
Positive slip-proof engagement
No speed variations
Speed range more than double of chain
High torque capacity
Wide range of applications
Clean, maintenance free
Energy savings
Reduced overhung bearing loads
Improved motor life. Less heat build-up.
Reduced maintenance
FEATURE BENEFIT
* 3M is non-stock. Contact Carlisle for availability.

36. RPP Plus
available in pitches of *3M, 5M, 8M, 14M, 20M
High torque capability
Precision ground rubber backing
Fiberglass cord
Nylon fabric tooth cover
Compact drive package
Lower cost
Consistent uniform thickness
Reduced vibration
Compatible with backside idler
Length stability
High belt strength
High resistance to wear and shear
Longer belt life
FEATURE BENEFIT
* 3M is non-stock. Contact Carlisle for availability.

37. Explanation of Part Numbers
800-8M-30
800 = 800 mm pitch length 8M = 8mm pitch 30 = 30 mm width
RPP Plus

38. RPP Plus
belt belt pitch length
type pitch (mm) range (mm) standard widths (mm)
*3M 3 159 – 1263 6 – 9 - 15
5M 5 350 – 2525 9 – 15 – 25
8M 8 480 – 4400 20 – 30 – 50 – 85
14M 14 966 – 6860 40 – 55 – 85 – 115 – 170
20M 20 2000 – 6600 115 – 170 – 230 – 290 - 340
Standard Lengths and Widths
* 3M is non-stock. Contact Carlisle for availability.

39. - Used to drive shafts on (serpentine) multiple
pulley drives in opposite directions
- Available in RPP 8M & 14M profiles
- RPP molded teeth both sides - full power rating on both sides
- Goodyear molded teeth one side – Ground teeth on opposite
side - 33% rating reduction on ground tooth side due to lack
of fabric reinforcement on teeth
Dual RPP Plus

40. Dual RPP Plus
belt belt pitch length
type pitch (mm) range (mm) standard widths (mm)
8M 8 720 – 4400 20 – 30 – 50 – 85
14M 14 1400 – 4956 40 – 55 – 85 – 115 – 170
Standard Lengths and Widths

41. Explanation of Part Numbers
D800-8M-30
800 = 800 mm pitch length 8M = 8mm pitch 30 = 30 mm width
Dual RPP Plus
D = Dual Sided

42. Introducing the New RPP Panther®
The Panther Rules!
The new RPP Panther
with ULTRA-CORD and
Able compound provides
fierce, unequaled
strength, efficiency and
durability.

43. New RPP Panther with “Able” Compound
The “Able” Advantage
Reduces Tooth Shear
The new “Able” compound is
reformulated for increased
performance. This advanced
polymer provides increased
resistance to tooth shear and
tooth jump.

44. New RPP Panther with “Able” Compound
The “Able” Advantage
Better Adhesion
“Able” adheres to the belt cords and
nylon tooth facing better than the old
Panther compound. This allows for
reduced tooth deflection and improves
belt life.

45. New RPP Panther with “Able” Compound
The “Able” Advantage
More Robust
The “Able” compound
is a robust material
that improves product
consistency.

46. New RPP Panther with ULTRA-CORD!
The ULTRA-CORD Advantage
Reduced Tension Decay
Holds drive tension better
than belts using aramid
fiber cords thus providing
dimensional stability for the
life of the drive.

47. New RPP Panther with ULTRA-CORD!
The ULTRA-CORD Advantage
Lower Installation Tensions
With ULTRA-CORD, there is no need to
“over-compensate” for aramid tension
decay. Lower tensions put less strain
on drive components such as bearings
and shafts.

48. New RPP Panther with ULTRA-CORD!
The ULTRA-CORD Advantage
Doesn’t Absorb Moisture
The use of ULTRA-CORD eliminates the need
for special handling such as plastic bags and
desiccants used with aramid belts to prevent
shrinkage from moisture absorption.

49. Improved Flex Life
Aramid tensile strength
degrades over time with
repeated flexing.
ULTRA-CORD resists tensile
degradation & dramatically
improves belt life and
shock load resistance.
New RPP Panther with ULTRA-CORD!
The ULTRA-CORD Advantage

50. New RPP Panther with ULTRA-CORD!
The ULTRA-CORD Advantage
Improved HP Ratings
The new RPP Panther
construction permits
increased drive horsepower
ratings as much as 20%
over the previous Panther.

51. The New RPP Panther…
Some things didn’t need to be improved…
SAME Great RPP Tooth Profile
The new RPP Panther still
utilizes the same RPP tooth
profile for reduced noise
levels, resistance to tooth
jumping, and improved
meshing with either RPP or
HTD sprockets!

52. The New RPP Panther…
Some things didn’t need to be improved...
SAME High Quality Fabric Facing
The New RPP Panther still
utilizes the same graphite-
loaded, self-lubricating nylon
fabric facing for exceptional
wear resistance, low
coefficient of friction, and
superior drive efficiency.

53. The New RPP Panther…
Some things didn’t need to be improved…
SAME Industry Standard Sprockets
The New RPP Panther still
operates with the same
readily available, industry
standardized RPP Panther
sprocket systems.

54. The New RPP Panther…
Some things didn’t need to be improved…
Still Works on Backside Idlers
The new RPP Panther is still the
best choice (and sometimes
your only choice) for high
torque drive systems that
require backside idlers.

55. Nylon Tooth Facing
• Graphite-loaded
• Self-lubricating
• Wear resistant
Tooth Indentation
• Shock absorbing
• Reduced noise
Proven RPP Profile
• Greater transfer of power
• Jump & shear resistant
• Reduced sprocket wear
ULTRA-CORD
• Improves belt life
• Higher strength
• Reduced tension decay
• Dimensional stability
Precision Ground Backing
• Smooth operation with backside idlers
The New RPP Panther® Synchronous Belt
Able Compound
• Engineered polymer
• Increased performance
• Increased belt life

56. • Panther improves energy efficiency
- 98% operating efficiency
• Reduces energy consumption
- As much as 5% over other PT systems
The Energy Efficient RPP Panther®

57. Explanation of Part Numbers
3600-PTH8M-35
3600 = 3600 mm pitch length PTH8M = 8mm pitch 35 = 35 mm width
RPP Panther®

58. Belt Belt Pitch Length
Type Pitch (mm) Range (mm) Standard Widths (mm)
8M 8 480 – 4400 12 – 22 – 35 – 60
14M 14 966 – 4956 20 – 42 – 65 – 90 – 120
Standard Lengths and Widths
RPP Panther®

59. Panther Advantages
over Poly-Chain
• Poly-Chain has a ribbed belt backing that does
not work well with backside idlers.
• Poly-Chain is made of polyurethane and has a
lower maximum operating temperature (185° F).
• Panther belts (rubber) have lower noise
characteristics than (polyurethane) Poly-Chain
belts.

60. Panther vs Competitive System
Test on belt pitch 8 mm / 20 mm wide, 2 pulleys Z=44, tension 46kg/strand
NOISE COMPARISON
rpm
600 1200 1800 2200 2800 3500
65
76
82 84
90
88
57
67
73 76
83
80
0
10
20
30
40
50
60
70
80
90
RPP PTH POLYURETHANE
RPP Panther®

61. Energy Efficiency
• One third of the electric motors in the industrial and
commercial sectors use belt drives
• Certain types of belts are more efficient than others,
offering energy cost savings
• V-belts can have a peak efficiency of 95% to 98% at the
time of installation but deteriorates by as much as 5% over
time
• Synchronous belts offer an efficiency of about 98% and
maintain that efficiency
• V-belts have a sharp reduction in efficiency at high
torque due to slippage

62. Selling Energy Efficiency
• Conduct a survey of belt driven equipment in a plant or
facility. Gather application and operating hour data.
Then, determine the cost effectiveness of replacing existing
v-belts with a synchronous system.
• Replace wrapped v-belts with Gold Ribbon Cog Belts
where the retrofit of a synchronous belt drive is not cost
effective.
• Consider synchronous belts for all new installations
because the payback overcomes the price premium over
v-belt drives.

63. U.S. Customer Service: 866-773-2926
Canada: 866-797-2358
www.CarlisleBelts.com
info@CarlisleBelts.com