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Rigidity tests for frames
Rigidity is an important quality characteristic when manufacturing frames. So much so, it is now even being tested all the more frequently by specialist bike magazines.
For detecting production defects, quality control often is monitoring the rigidity of Carbon frames. Then, after accidents, a comparision with the original data may be an indicator for internal damage of the material, that is not indicated by surface cracks and delamination.
1. Frame Track-holding rigidity
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Especially high-quality, lightweight frames can make a sloppy, inaccurate handling feel, if the bike’s stiffness properties were not sufficiently considered during the construction process. Certain circumstances, i.e. depending on the wheel model, tyres, air pressure, front fork, head tube bearing clearance, carrier rack load etc., can lead to irritating vibrations (shimmy effect).
The track-holding rigidity (also called torsion rigidity) is a measure for the track consistency of the bike. The lateral displacement of the head tube axle near the front wheel contact point is measured by securely fixing the rear wheel axle, centrally supporting the head tube, and by using a defined lateral load. The lateral load to displacement ratio is referred to as the bike’s track-holding rigidity. It is measured in N/mm.
2. Frame Out-of-saddle rigidity
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The out-of-saddle frame rigidity test (bottom bracket rigidity) is a method for measuring the resistance a frame exerts against the out-of-saddle forces. A high level of out-of-saddle rigidity ensures a good conversion of rider performance into driving power.
The frame is supported appropriately, allowing for all necessary degrees of freedom used in a bike’s standard operation. The testing load is applied at a defined distance from the middle of the bottom bracket at a specific angle onto the (extended) bottom bracket axle. The displacement of the load input point is measured in the direction of the testing load. The testing load to displacement ratio is referred to as the out-of-saddle frame rigidity. It is measured in N/mm.
3. Out-of-saddle rigidity of the frame/fork unit
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On racing bikes, frame sets often are treated as complete units, so that out-of-saddle rigidity can be determined on the complete frame set. The unit consisting of frame, fork and headset always has a lower rigidity than the frame alone.
Download test order form
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Nm per degree?
Stiffness is measured in N/mm.
Under pure torsional load,
such as track-holding rigidity,
the stiffness can be calculated
to Nm/°. 1 N/mm is equivalent
to 12,6 Nm/° (using a standard
lever arm of 850 mm).
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