Having the run of a French wheel testing facility was like ‘us kids’ being locked in the proverbial sweet shop for a day.
Not that this was ‘play’, you understand. We donned white coats and safety glasses and got to grips with the sophisticated equipment – eight different tests in all – to gather a ton of data to crunch. As much as possible everything was standardised, and always the recorded value was the average of three trials. The sections that follow outline our test protocol.
Test one: weight
A pretty self-explanatory test and certainly not rocket science, but in a laboratory setting multiple decimal places are the order of the day. A specifically modified set of scales meant we could be über accurate, every time. Weights include the supplied rim tape in all cases.
Test two: inertia
Measured using strain gauges on a central axle, about which the wheel is rotated, using a predetermined force. Potentially one of the most useful tests for predicting potential ‘ride feel’ and characteristics of a wheel, essentially quantifying its resistance to motion. For example, a wheel with a low inertia will feel very responsive, requiring less energy to alter its rotational speed, hence it will accelerate easily. At the other end of the scale a wheel with high inertia may not accelerate rapidly but should deliver more of a flywheel effect, and carry speed well, but at the same time will also be harder to stop. Inertia impacts performance whenever there is a change in speed (either acceleration or deceleration) so is a key test. Rotating mass clearly plays a big part in this, and obviously there is a balance that needs to be achieved for a good all-rounder.
Test three: lateral rigidity
This test was designed to simulate the lateral loading a wheel is subjected to by a pro rider going full steam in a finishing sprint. In the lab, that translates to a sizeable side force being applied to the wheel rim, while the spindle is firmly clamped, and the amount of deflection/distortion measured, to the nearest 100th of a millimetre. Standardisation and replication being the name of the game again, each measurement is taken at the valve hole as the point of reference. The benefits of performing well in this test are usually reflected in a wheel that feels solid during sprinting and suffers neglible loss of energy, and hence good transfer of power.
Test four: opposite displacement
In a nutshell this measurement is what’s happening on the opposite side of the rim when the lateral rigidity force is applied. It too quantifies the displacement/distortion that occurs at the rim and is also measured to an accuracy of 100th millimetre. The results of this test do not so much reflect the stiffness of the rim itself (although that is still partly responsible) but how well the spindle/axle is supporting the wheel. Significantly higher opposite displacement values would suggest a wheel that is likely to rub the brake blocks when loaded by standing climbing and/or sprinting.
Test five: frontal stiffness
Here the measured load, or force, is applied radially ie directly downwards on top of the rim, as the wheel is clamped vertically, as if in a bike. Again, this is a measurement of distortion under a given load, expressed in N/mm and suggests the likelihood of how well the wheel will react to bumps and impacts, related to both durability and comfort for the rider. It also clearly shows the effect different spoking patterns have, as it highlights the loading and unloading of spokes as the rim shape distorts.
Tests six, seven and eight: friction torque – breakaway
A highly sensitive gauge is clamped directly over the freehub body (test six) or the axle (tests seven and eight), then a rotational force is applied, by hand, until the friction in the system – created by a combination of the bearings and seals – is overcome and the freehub begins to turn. This measures how much force is required to get the thing moving. This will manifest itself as drag, and every bit you can reduce the better. Bear in mind though that the drag is more often caused by bearing seals but these also protect the hubs from water and dirt. As with most things, a balance needs to be struck.
Exactly as per tests six and seven, but taking the reading from the gauge once the wheel had begun to rotate. This gives the total drag being caused by the bearings and seals within the hub. Bear in mind this test did not take into account loading of the system by the weight of the rider or riding forces applied, so is slightly limited in its application.
Click on the table below to enlarge it in a new window so that you can actually read it