Every part of the modern bicycle has been developed since the first pedal powered bikes were introduced and though they say you cannot reinvent the wheel, bicycle designers have had a good try.

General Construction

A bicycle wheel comprises a rim and hub held together by spokes. Spoke patterns are known as lacing, spokes are held in the rim by nipples. The wheel rim is surrounded by a tyre, the type of tyre affects the design of the rim. Brakes also affect rim design and the lacing pattern. The gear type changes the width of the hub and this in turn affects the angle of the spokes which may in turn affect the rim spoke hole construction. Hubs include bearings and an axle and a means of attaching sprockets.

Souplesse is a cycling term which describes a state of harmony and smoothness in the way a rider propels their bike. This may seem an aspirational and exotic goal for ordinary riders, but all of us can  appreciate how a  good set of hoops contributes to the smoothness of a bike. A caveat is that choice of tyres and tubes can be a net benefit or a detractor to souplesse.

Materials used in wheels can vary from plastic in BMX and children’s bikes, steel or aluminium alloy and even wood.

Rim shapes

The external shape of a rim is determined by tyres and brakes.

Rod pull brakes as used on vintage bikes pull the pads onto the inner surface of the rim and the rim pattern is a Westwood rim. Westwood rims feature a curved edge and a central ridge so pads miss the spoke nipples. An Endrick rim with square sides is used for cantilever and caliper brakes used on most modern bikes. Disc braked wheel rims are not constrained by brakes, but designers apply aerodynamic principles to optimise the shape. A hybrid rim pattern known as Westrick was developed by Raleigh to allow them to fit both older brake styles.

Tyres can be generally described as Tubular or Clincher style. Rims for tubs or sprints have a flatter surface designed to glue tubs too, these are a specialists choice and used by professionals and time trial racers. Tubs can be more tricky to repair as they have a tube sewn into an outer case, one reason why professional riders still use them is that they remain attached to the rim if you puncture which is safer and means they can limp on until the team car catches up. I put this to the test recently while test riding a classic Bob Jackson I was fixing up, the tub punctured near home and I was able to cautiously continue. Most popular tyres are clinchers, where the rim clinches the tyre when it is under pressure. A modern development is the tubeless tyre, there is a subtle difference in the internal rim shape to seal the tyre against the rim. It is essential for safety that tubeless tyres are only fitted on tubeless design rims.

Spokes, Nipples and Lacing patterns

Rim and disc brakes produce different forces on the wheel and the construction is adapted accordingly. Disc brakes require stronger hubs and allow lighter rims. A key but subtle difference is the lacing pattern. Lacing designs used to save weight on rim brake wheels are not suitable to use on a disc brake wheel where the torsional forces are different.

The most common spoke lacing pattern is a 36 hole 3 cross, but conventional spoked wheels may have as few as 12 spokes. Solid moulded wheels may have only 3 ribs instead of spokes.

Spokes may be galvanised steel, stainless, painted. They are measured by length and gauge and also have different profiles and ends, this means there are endless permutations which is a headache for a cycle shop. The best spokes are butted which means the diameter varies along the length, surprisingly these are not only lighter but also stronger and may improve the ride quality of the wheel.

Nipples are threaded inserts which feed through rim holes and screw on the spoke. They can be made of brass, steel or aluminium. It is important to check the spoke tension regularly as spokes may break or nipples unscrew. Also alloy nipples used in wet conditions may corrode and fail without warning, so should be checked regularly and probably best avoided if you are not a weight weenie.

The strongest rims have eyelets in the spoke holes and nipples may have washers to spread the load.

Assymetry

The design of the hub may require the wheel to be asymmetric, this can take the form of different numbers of spokes on the drive and non drive side, or rims may be drilled so spokes enter at a different angle each side to reduce stress on the spoke.

Hubs

I was amused by a recent post on a bike mechanic forum. A rider asked after changing his rear hub to add a fixed sprocket, why his legs were being pushed round as he slowed. He had misunderstood the difference between a fixed wheel and a single speed. A fixie is the purest form of bicycle transmission  favoured by cycle couriers and track racers as it is the lightest possible transmission and has minimum moving parts. A single speed has a single sprocket, but a freewheel is incorporated to allow the pedals to remain static when riding down hill or slowing down.

Dyno hubs used to be popular and saved buying batteries for lights on utility bikes. They are a simple direct current dynamo built into the hub and may be combined with a hub gear on the rear. Modern designs are more efficient and lighter, I have only seen them as front hubs. They are very popular in Germany and on the continent or with long distance tourers who use them to charge essential electronic devices and run lights.

Hub gears are also called “coke cans” as the gears are enclosed in a metal cylinder. This protects them to improve longevity and reduce maintenance, the trade off is additional weight. However, long distance riders accept this compromise and premium brand Rohlhoff’s impressively engineered  designs can contain up to 16 speeds.

Derailleur gear hubs are probably the most common hub we see in Riley’s workshop due to their lighter weight and simpler design. These have exposed sprockets called a cassette, mounted on either a freewheel or freehub. A freehub is a part of the hub and should be serviced with the rest of the wheel. Both suffer from road grit and wear. Freehubs are a serviceable or replaceable part depending on the design. A freewheel is built into the cassette and on cheaper models is not designed to be serviced.

All hubs contain bearings and the quality of these affect how smoothly and freely the wheels run. Basic bearings have a bearing surface built into the hub, loose ball bearings, a cone and some form of seal to keep grease in and water out. If used in wet conditions and not serviced bearing surfaces wear and the hub is scrap. Recent designs favour cartridge bearings, their benefit is that when the bearing wears it can be replaced with a new one and different grade bearings are available including ceramic for high performance applications. Friction is the cyclists enemy and smooth, freerunning bearings contribute to how well a bike performs.

Development

Early rims were made of wood or bamboo and you can still obtain these. Steel was a popular choice for many years and stainless rims and spokes are long lasting. Aluminium alloy is more commonly used now.

Rim Construction methods

Metal rims are made from an extrusion which is curved and joined. The join may be welded or pinned. There is usually a hairline at the join which manufacturers cover with a decal.

The grade of alloy is selected more for price and weight rather than longevity and modern  rims seem to wear more quickly, however this may be because modern brakes are more powerful and exert more force. Andy, one of our regular customers covers a high mileage each year of well over 10000 miles and wears out his rims in under two years.

Carbon rims are moulded and easier to produce in aero shapes. Some extreme deep rims are a composite construction of an aluminium rim with a carbon fairing. The quality of the carbon and resin varies and cheap Chinese rims may be made with a resin that softens at a lower temperature than higher quality brands, the rim may deform under breaking due to the heat generated and cause a catastrophic failure and a potential crash.

The braking surface on carbon and alloy rims may be coated to protect the rims and dissipate heat,  note that the braking performance of carbon wheels is worse than alloy rims under most circumstances.

A member of a group I ride with pointed out that his best bike’s alloy Mavic rims have a ceramic coating and the pads and rims are barely worn. I had a wry thought that may be because the bike is on the wall of his garage while he is riding his winter bike. Another rider did a test when he found his rim had worn to less than 1mm thick and inflated it to a pressure over 100psi and the worn rim collapsed under the strain created by the tyre pressing outwards.

Pre Ride checks

Check for rim wear and defects such as dents and that the rim runs true by spinning it and watching the gap against a reference point. Ensure tyres are correctly inflated. Spokes can break or work loose, so grasp them as a pair on the same side and squeeze them lightly to feel the tension, work your way round the wheel noting any slack spokes. If you find a damaged spoke replace it ASAP.

Caring for Your Wheels.

A simple check is to feel with a fingertip if the rim is concave or put a straight edge against it and check by eye. Rim wear indicators take different forms, a continuous black groove or a small circle often opposite the valve hole, the latter can be misleading though as they may clog with muck.

As well as general wear due to road grit, I have seen folks let their pads wear excessively and the metal inserts score the rim, leading to premature failure or a piece of grit stuck in the pad can have the same effect.

Some brake pads are less harsh on rims than others. I prefer Koolstop and Swisstop brands, they cost more than basic pads, but wheels and rims cost even more. It is also important to buy pads designed for the material your rim is made of.

Keeping tyre pressures at their recommended pressure is the easiest thing you can do to protect your rims from damage Also avoid pot holes and kerbs if possible, but do not swerve in case a vehicle is about to pass you. On Mountain Bikes it is possible to put a foam insert into the tyre to protect the rim at low pressures.

Take out the wheel so you can inspect the brake pad thoroughly to reveal particles embedded in the brake pads, these can be hooked out with a sharp podger. Washing off the rims after each ride and rinsing brake blocks with a watering can or hose helps rinse away grit, I know it is not appealing on a chilly day, but if you do it while still togged up after your ride you will not notice the cold and a virtuous glow will warm you from the inside.

If your rims are worn, unless the hubs are of a quality to justify it, a new wheel may be the answer as the hubs may also have deteriorated. Wheels can be rebuilt if it is cost effective with new rims and spokes and the bearings serviced.

One option to avoid rim wear is to choose a bike with disc brakes.

Servicing

It is advisable to service wheels annually especially if ridden in all weathers. Clean the wheel then Inspect all components, check spoke tension and adjusted if required, true the rim to remove buckles, clean bearings and regrease or check for roughness and wear depending on bearing type. We have saved customers the expense of new wheels by servicing their hubs before they are ruined and extended their life significantly.

Stay safe!

Mike Riley