Rim - Round and Round We Go

Rim - Round and Round We Go

What good would a bike be without wheels?  It would be a bi... the cycle-type things define the beast.  The frame would get nowhere without the wheels.  The hubs are necessary, as they support the axle.  In terms of bike wheels, the hub contains the bearings, any extra gearing or brakes, freewheel, and house the skewer.  It also anchors the spokes that connect it to the rim.

The rim is the metal hoop that also anchors the spokes. The rim also supports the tyre, the inflated rubber tube that ideally is the bike's only contact with the rest of the world.  Crashing changes that, but that can wait for another entry.

A simple arrangement, but with a few issues and a history of its own.  If you step sideways to older forms of transport, we can see wagon wheels have the same arrangement of hub, spokes (wooden!) and rim, with an iron band to stop the rim wearing away.  This was the same design as the first bikes.  Even as late as a few decades ago (the realm of living memory!) the top-line racing wheels used wooden rims.  
As a material wood can be as strong as steel in tensile strength, and is much lighter.  The classic examples of wood used in high-tech structures is in aircraft, notably the De Havilland Mosquito fighter-bomber, and then the Vampire jet fighter of the 1950s.  
The main issue with bike wheels is that rim technology advanced beyond the scope and strength-weight limits of wood, which has to always be solid.


The first steel rim was the Westwood, essentially a single flat strip of steel press-formed into a ridge with rolled edges to support the tyre.  These rims are still being made in India...
This progressed to the Endrick rim (also available new from India!), the first design that gave a hollow, box-section rim. The square tube was pressed into the collapsed box shape, and was still found on bikes through to the eighties.

Modern rims are now engineered around a V-design, providing greater torsional and compressive strength, and allowing for aerodynamics.  As the bike moves forward air strikes the inner edge of the rear rim surface.  Older square profiles were lousy in terms of aerodynamics, as the air would be striking a flat surface.  The development of the V-rim allowed a smoother, shaped airflow around the wheel.  Also, as the tyre strikes the oncoming air, the deep V gives the wheel a leading-edge profile similar to an aircraft wing, whereas the old square rims simply created a zone of turbulent air amongst the spokes.  If you like to have a stable, smooth ride this is not the way to go.  


Today, modern companies, for example Zipp, continue to develop aerodynamic rim profiles to give not just a smooth, controlled ride, but to achieve the time-energy boosts from having low-turbulence wheel-air interactions.  The drive to develop the perfect aero wheel gave us the disc wheel, which eliminates the turbulence generated by spokes and also eliminating the slight, but distinct flattening of the wheel shape at the road contact point.  Trouble is, these wheels can only be practically used in indoor velodromes, as they become wind-traps as soon as you venture outside.

My hubs are 28h, so the rims for the build have to match. Of course.  Also, I want regular clinchers, as I like to be able to repair flats alongside whatever road I may puncture on.  I cannot afford a team support car to follow me everywhere with spare tubeless set-ups.  Surprisingly, there is not a terrific range of rims available internationally online (posting to New Zealand). Sun is common, but also available are Velocity rims and, my preferred rim, DT Swiss.

Founded in 1994, the Swiss company expanded its business from spokes to everything attached to them, and they do it well.  My last build used a DT Swiss RR415 rim, and I am staying with this rim.  Of note, the DT model number is the rim weight - the RR415 weighs 415 grams. Rim weight does have some effect upon the performance of the wheel, mainly through rotational momentum.  

To those students of physics, this is angular momentum. A 700c rim has a diameter 622 mm, and radius of 311 mm. It's circumference is (622 x π =) 1953 mm. A rim mass of 415 gm at 0.311 m from the centre has a momentum of (415 x 1.953 x 0.311 =) 252 gm², for one revolution.  Boost the rim weight to, for example, 450 gm, and the angular momentum goes up to 273 gm². More energy is needed to get the wheel turning, and any time that you want to accelerate you use proportionally more energy. Being a middle-aged kind of bloke, that is energy that I am not too keen to use needlessly.  Fortunately I am light enough (78 kg and holding...) to get away without a heavier rim.  So long as I can see my toes when I look down I should be fine.

I bought the rims from Chain Reaction Cycles, far away in Northern Ireland. Two rims and postage to New Zealand, from Ireland, cost me NZ$187.33 (US$151.50).  Really, for what you get (Swiss rims!), and delivery time of 7 days and 10 hours from the other side of the world, is an unbeatable deal.

And now, I have to find not just spokes, but a truing stand to build the wheels on...

Rub-a-Dub Hub

Rub-a Dub Hub

Bicycle.  A simple word, meaning two cycles.  Frame, group set, saddle, handle bars.  All well and good, but rather pointless if there is not a pair wheels in line with each other, and both able to turn freely.

The wheel is arguably one of the greatest inventions ever.  Chariots, windmill wooden peg gears, clockwork mechanisms, rail rolling stock, gyroscopes, and the space station from 2001.  All use the wheel.  Even the steel castors that tea trolleys are pushed around on.  But in terms of technology and attention to design detail you would be hard pressed to beat the modern derailleur hub.

The first rear derailleur hubs had the cassette (typically just a few sprockets) screwed on to the hub as a separate unit.  One of the first popular units was the Bayliss hub, an example is shown here from Dave Moulton's site.  This design was introduced in 1938.

One might argue that hub gears are technically more advanced than current derailleur systems, but they have their limitations.  Take a look at this exploded view of a typical Sturmey-Archer 3-speed hub unit.

There is a lot of iron packed into that space, and most of them are moving parts.  Which is a good time to remember a good rule of thumb - the more moving parts there are, the more this is to go wrong.

Internal hub gears are heavy, have a much lower effective range of gearing ratio, with fewer gears to choose from (even with the modern Sturmey-Archer hubs that give up to eight gears across a claimed range of 325% from below to above direct drive, they cannot compare to the Campagnolo 11-gear cassette), and need a lot of maintenance to keep the gears from seizing.  So, they remain the preserve of city cruisers and tourers.

The freewheel system allowed the installation of the cassette as a unit, and is still used on many cheaper BMX and single-speed bike hubs. A half-way step is the freehub system with open bearings, used on mountain bikes.  Personally, I loath this system, as the bearings have to be individually placed each time the cassette is removed, for example replacing spokes.  Grease, tweezers, and finding the last dropped bearing.

Shimano and Campagnolo independantly developed a freehub system, although the name freehub is copyrighted by Shimano.  The difference between freewheel and freehub systems in best shown in this diagram.

The freehub bearings are enclosed beneath the ratcheted splines.  The cassette slides onto the splines and are locked into place with a single lockring, no bearings in sight.  In terms of maintenance and simplicity of design, it is ideal.

For my weight and riding style, I have found that 28 spokes is a good minimum build. Several years ago my brother-in-law gave me a Shimano wheelset, both wheels laced with 16 aero spokes.  The front is still performing perfectly, but the rear popped a spoke every 300 km.  A 20-spoke build lasted until the spokes pulled through the rim holes, and a 24h build lasted a few thousand km, but I retired it when hairline cracks appeared around the eyelets.  The 28h build I am currently using is flawless, and has given me over 2600 km without needing any truing. I built it using a Novatec F162SB 28h hub, laced with round spokes to a DT swiss 28h  RR415  rim.

Also of issue are the skewers.  Once upon a time all bikes were secured by an axle that was simply a long bolt.  Many cheap department-store bikes still have wheels secured by a bolt.  If you are in a race and have to swap a wheel or tyre, you really don't want to be mucking around with a spanner.  Wikipedia have a good summary of the quick-release history, from its invention in 1927 by Tullio Campagnolo onwards.  

And now to the market.  First off, if I were to buy skewers separately, I would be looking at about NZ$10 each.  I had been planning on repeating the current rear build but using aero spokes, but the Novatec hubs cost US$70 each. A deal on eBay offered a pair of gold novatecs (20/28h) with skewers for NZ$112, indicating that a bundle would be a better deal.  Scouring the net, there are few affordable 28h Shimano-compatible rear hubs, but the deal came via Wiggle.  For a grand total of NZ$133.99 I acquired a boxed pair of Miche 28h hubs with Shimano freehub, and matched Miche skewers.  Is this a good deal?  I like to think so.  Miche are an Italian component manufacturer with over 70 years experience.  The hubs are forged aluminium, use sealed bearings, are compatible with the Shimano 10-speed cassettes, and weigh 433 grams for the pair.

A touch of Italian style for the ride, and the one box takes care of both wheels, leaving the rims next, and then I can calculate the right spoke lengths for the build,