Mountain bike frame
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Light weight
Strong
Durable
Water resistant
High strength to weight ratio
Reasonable cost
High resistance to corrosion
Some flexibility required
Density
Yield strength > service load
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Built tough to withstand jumps and drops.
Created for off-road cycling.
Traversing of rocks and washouts
Steep declines
Hill-climbing
Dirt trails, logging roads, and unpaved environments
These bicycles need to be able to withstand the stresses
of off-road use (logs and rocks)
Full front and rear suspension
seat tube angle around 73 degrees
head tube angle of anywhere from 60-73 degrees
In general, steeper angles (closer to 90 degrees from the
horizontal) are more efficient for pedaling up hills and
make for sharper handling
Mechanical Properties:
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Some flexibility required: Young’s Modulus, 60-175
Yield strength > service load 540-1,000,000
Strong: Compressive strength 450-850MPa, Fracture toughness 7-20MPa^5
Density: 1.5x10^3-1.7x10^3Bike weight is a key quality indicator! Quality and performance ^
with ρ
 weigh 10 to 18 kilograms
 Typical "medium" sizes are 54 or 56 cm
General properties:
 pivoting rear triangle to actuate the rear
shock absorber
 Reasonable cost: Price
 two triangle design
 High strength to weight ratio: Density
Durability:
 Water resistant:
 High resistance to corrosion
Process ability:
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Weldablilty
Machinability
Possible materials:
Hybrids, Composites, Metals and alloys
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Steel
Aluminium alloys
Titanium
Carbon fibre
Possible designs:
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Dual or full suspension: A front suspension fork and rear suspension with a rear shock and
linkage that allow the rear wheel to move on pivots.
Soft tail: A frame with small amount of rear suspension, activated by flex of the frame
instead of pivots.
Hard tail: A frame with a front suspension fork and no rear suspension.
Rigid: A frame with a rigid fork and fixed rear, no suspension.
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Density (or specific gravity) is a measure of how light or heavy the
material per unit volume.
Stiffness (or elastic modulus) can in theory affect the ride comfort
and power transmission efficiency. In practice, because even a very
flexible frame is much stiffer than the tires and saddle, ride comfort
is in the end more a factor of saddle choice, frame geometry, tire
choice, and bicycle fit. Lateral stiffness is far more difficult to achieve
because of the narrow profile of a frame, and too much flexibility can
affect power transmission, primarily through tire scrub on the road
due to rear triangle distortion, brakes rubbing on the rims and the
chain rubbing on gear mechanisms. In extreme cases gears can
change themselves when the rider applies high torque out of the
saddle.
Yield strength determines how much force is needed to permanently
deform the material (for crash-worthiness).
Elongation determines how much deformity the material allows
before cracking (for crash-worthiness).
Fatigue limit and Endurance limit determines the durability of the
frame when subjected to cyclical stress from pedalling or ride bumps.