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A road bike wheel makes almost 500 rotations for every kilometre that is travelled. During that time, the rim is constantly compressing under the weight of the rider, such that every spoke is loaded and unloaded with each rotation. This ongoing cycle of radial load takes its toll on the wheel, inevitably producing fatigue in one or more of the components, though it’s the spokes that typically suffer the most.
Lateral loads also contribute to wear and tear of the wheels. These forces are generated as the rider transfers their weight from one side of the bike to the other when pedalling out of the saddle. Lateral loads are at their greatest during sprinting and climbing efforts as the bike is violently tipped from one side to the other.
The drive-train places extra load on the rear wheel in the form of torsion of the hub. Once again, there is an ongoing cycle of loading and unloading for the spokes, and that contributes to the development of fatigue.
There are no outward signs of this fatigue until the spoke and/or nipples start to break as a result. The rate at which it develops depends upon the design of the wheel, the qualities of the starting materials, and the way in which the wheels are used. Heavy loads in particular typically accelerate the development of spoke fatigue.
The only remedy for spoke fatigue is to replace them, however, in the time the fatigue takes to develop, the rims will undergo a significant amount of wear and tear too. This is especially true for road bikes with rim brakes, since the brake pads are constantly scouring the surface of the rim, slowly eroding the material.
The effect of rim brakes is almost as subtle as spoke fatigue. If the brake track has a surface finish (such as black anodising), then riders might notice when it disappears, or if it is polished, the black marks that slowly appear. Both are of little consequence to the integrity of the rim, but they are the first signs of the gradual erosion that is caused by the brake pads.
Over the course of many months, years even, the sidewalls of the rim will become concave as the pads scrub away at the material. It’s an inevitable by-product of rim-braking that affects both alloy and carbon rims. The combination of rain and dirt/debris will enhance the abrasive effect of the brake pads to accelerate the process while soft-compound brake pads (eg. Swissstop BXP) can be used to slow it down, however, the only way to eliminate it is to switch to disc brakes.
For riders using rim brakes, it’s important to monitor the brake track of the wheels. Rubbing a finger over the track will reveal any concavity and a straight edge can be used to gauge how deep the concave is.
Rim walls are typically less than 2mm thick, so any concavity approaching 1mm is very significant (and worrying), especially for clincher rims. That’s because the hooks of the rim will get weaker as the brake track is worn away. There will come a point when sidewalls will flare from the pressure within the tyre. Tears will appear in the brake track and one or both hooks will fail, leading to a blowout for the tyre.
It is difficult, if not impossible, to anticipate when this will happen. Some rim manufacturers position wear-indicators in the brake track, recommending that the rim be replaced once those indicators are no longer obvious. In the absence of such indicators (typical for carbon rims), owners must decide the risk for themselves.
The hubs and wheel bearing are also subject to wear and tear, where the biggest threat comes from the gradual accumulation of dirt and debris and the ingress of water. The former will have an abrasive effect on the balls and races while the latter will promote rust.
Regular hub maintenance will go a long way to prolonging the life of the bearings, however the eventual demise of these moving parts is inevitable. For those hub using cartridge bearings, the entire unit can be replaced when balls or races are damaged. Similarly, cup and cone hubs can be overhauled with new parts (cones and bearings) though not all have replaceable cups, so once pitted, the hub will have to be replaced.
Any play in the bearings or hub axle can be indicative of wear, so it shouldn’t be ignored when it appears. Similarly, any roughness or catches in the bearing-action when the axle is turned by hand is enough to warrant a service so that all of the parts can be cleaned and inspected to accurately determine the cause of the problem.
Most riders intuitively understand, or have had first-hand experience of what kind of effect an unexpected impact, crash, or collision can have on a wheel. Potholes, rocks, drainage grates and gutters: there is only so much force that a wheel can resist before it is overwhelmed by an impact.
Under these circumstances, a rim that is bent, dented or cracked is normally beyond repair. In contrast, broken spokes and nipples can be replaced, though proprietary spokes and nipples can be difficult to obtain at short notice.
In those instances where there is a minor lateral bend in the wheel, the spokes can be re-tensioned to straighten the rim. This will come at the expense of even spoke tension, which will place extra stress on the spokes concerned. In contrast, radial damage (i.e. a flat-spot in the rim) cannot be repaired in the same manner.
Lift each wheel off the ground and give it a spin. Watch from above and take note of any wobbles; watch from the side and look for any rise and fall.
Stand to one side of the bike, pinch the rim, and try to wobble it from side-to-side. Any play in the hub/axle will be felt as a rattle.
Squeeze every pair of spokes on each side the wheel. The amount of tension in each should be evenly matched and require some effort to displace. Take note of any broken or wobbling spokes.
Early cracks can sometimes be identified in the rim and hubs, but these typically develop very quietly and only have an effect on the wheel once they have progressed significantly.
Every tyre has some kind of line/ridge near the edge of the rim for assessing the seating. If this is uneven, the tyre needs to be re-seated.
It should be smooth and consistent without obvious dents, bulges, cracks, or any other inconsistencies. Take note of any concavity in the brake track.
Most pads have slots; when these have disappeared it is time to replace them. If there are obvious slots, inspect the surface for embedded debris and uneven wear.
Remove each wheel and roll the axle between the thumb and forefinger. It should turn freely and smoothly without any roughness or catching.
The decision to repair or replace a wheel ultimately depends on the nature of the problem and whether it is possible to obtain replacement parts. This can be difficult and/or expensive for factory-built wheelsets, even those from major brands like Shimano, Mavic, DT Swiss, Campagnolo, and Fulcrum.
Nevertheless, for those issues that only affect one wheel, it’s normally worth repairing, especially if the problem that doesn’t involve the rim. Any problems with the bearings can normally be attended to relatively easily and inexpensively unless the damage is considerable and affects the hub shell.
A single broken spoke or nipple is always worth replacing, but once it becomes an ongoing problem, then it is a clear sign of fatigue. Re-lacing a wheel is often expensive because it involves the cost of the spokes and the labour to carry out the work.
For those riders that regularly replace wheelsets, it might be worth considering a bespoke product. Custom wheels may cost a little more but each part is hand-picked by the customer to suit their needs. Such wheels are normally more feasible to repair and the rims, once worn, can be replaced at a fraction of the cost of a new wheelset.