Upgrading your chainset can be a bit of a minefield. The march of product development and the one-upmanship of manufacturers have left us with numerous systems that are not compatible with one another. It's not as bad as it sounds though, and there are similarities that lessen incompatibilities.
As a general rule you can't mix and match parts. For example a Shimano crank will not fit onto a Campagnolo bottom bracket. If you decide to go down a certain route stick with that manufacture and don't try to over complicate things. Hopefully this guide will lead you through the different type of chainset design and shed some light on the different systems.
Anatomy of a chainset
|Crank Arms:||The cranks are the 'arms' of the chainset and are made from either carbon fibre or aluminium, or in some cases entirely of steel if you're a BMXer or old school aficionado. The latest generation of two-piece cranksets from the likes of Shimano and FSA use an oversized steel or carbon fibre axle that's integrated with the right- or left-hand crank.|
|The Q-Factor:||This is the overall width of an assembled crank system, measured from the crank eye outer surfaces. For example a triple chainset has a slightly wider Q-factor, which can initially make the rider feel a little bow-legged|
|Chainring Bolts:||These bolts secure the chainrings to the crank's spider. Most use a 5mm Allen key at the front and a special chainring bolt spanner holds the female part of the bolt in place at the rear during assembly. Alloy chainring bolts are lighter than steel but steel bolts are stronger and less prone to creaking.|
|Spider:||As part of the right-hand crank, the spider is a hand-like aluminium forging or carbon moulding that holds the chainrings. It is usually a five-arm configuration, though Rotor and some off-road Shimano cranksets have four arms. Some spiders are also detachable.|
|Chainrings:||These are usually made of aluminium but the smaller ones are sometimes steel to reduce the rate of wear. Carbon chainrings are available but they barely save any weight and we've yet to find one that shifts the chain as smoothly as an aluminium one. The variety of chainrings available range between 22 and 54 teeth, though larger ones are available to special order. Compacts are usually fitted with a 34/50 tooth combination, conventional road doubles use a 39/53 and road triples are usually 30/40/50 or 30/42/52.|
|Pedal Thread:||This is the bit that the pedals screw into. The right-hand pedal will tighten clockwise onto the crank whereas the left pedal will tighten on to the crank by turning it anti-clockwise. To reduce the likelihood of cracks at the pedal eye, some cranks are supplied with a washer that's to be placed on to the pedal thread prior to installation. This reduces the risk of gouges because the pedal will be tightened down to the face of the washer instead of the pedal eye.|
|Bottom bracket interface:||This is where the spider and crank arm attaches to the bottom bracket's spindle. Nearly all cranksets run on their own type of dedicated bottom brackets. The general rule is no mix and match between manufactures.|
Bottom Bracket Types
All cranks attach to a bottom bracket bearing assembly that fits inside the frame's bottom bracket shell. Each crankset runs off its own bottom bracket design so it is important to it match crankset to the correct bottom bracket. The following is a list of the most common bottom bracket designs in use today.
The original and proven method of fitting bottom brackets to cranks, the square taper is now well on the way to being replaced by other systems, but it is still used by Campagnolo (at the lower end of their range), TA and is commonplace on many budget chainsets.
ISIS(International Splined Interface Standard)
ISIS is the non-Shimano manufacturer's take on Shimano's Hollowtech II 'two-piece' crankset. It is similar but with a more pronounced spline on the bottom bracket axle and crank arms. FSA and TruVativ are examples of crankset running on the ISIS spline. The two piece cranksets locate the bottom brackets externally to the bottom bracket shell. ISIS bottom brackets are also available for three piece cranksets.
Shimano Hollowtech II
Shimano's Hollowtech II system is used from the top-end Dura-Ace crankset right down to the enthusiast's Sora crankset. It's fair to say that it is fast becoming the standard across Shimano's range for road and mountain bike. Sometimes referred to as a 'two piece', the bottom bracket axle is an integral part of the left side chainset. The bottom bracket sites externally to the frame's bottom bracket shell.
The Octalink spline system is Shimano's predecessor to Hollowtech II now being seen much lower down on the big S's groupsets and it looks like it will eventually be phased out. However, it's still in wide circulation and as a testament to its reliability there are still plenty of chainsets running on Octalink cartridge bottom brackets. The picture shows the longer, deeper-splined Octalink bottom bracket as used on Shimano's off-road groupsets including the tourer's favourite Deore, while the shorter spline variety is the road version. If you're replacing an Octalink bottom bracket ensure you install one with the correct splines.
Campagnolo's Ultra-Torque has large diameter out-board bearings à la Dura-Ace/Mega Exo and all the other modern two piece cranksets but the central axle interlocks with a splined interface. Campagnolo claims it has a lower weight and smaller Q-Factor than its competitors.
Tune Six Pack
A hexagonal two-degree tapered axle gives excellent fit and massive stiffness. So far it's only being used by inventors Tune, but rumour has it that Storck and Campag will offer it as an option on their cranks.
Bolt Circle Diameter
The Bolt Circle Diameter (BCD) of a chainring needs to match that of the crankset.
|130mm or 135mm BCD road:||To the hardcore roadie, two's company and three's a crowd when it comes to the number of chainrings they'll use. These cranks are typically fitted with 39/53t or 39/52t chairing combinations, and will only accept a minimum count of 38 teeth, but this gearing is usually sufficient for the competitive cyclist on UK roads.|
|110mm BCD compact:||Compacts use smaller chainrings than a traditional road crankset (typically 34/50 teeth) and these low ratios have proven to be popular with fitness, recreational and sportif riders looking for less weight than a triple chainset - though the difference is actually quite negligible.|
|110mm BCD triple:||The three chainrings of a 'triple' chainset provide a more even spread of gears than any other, so they are perfect for all types of road bike that are used in hilly regions. The ratios are usually either 30-40-50 or 30-42-52 teeth.94mm BCD micro-drive triple: Originated by Suntour, this standard is used on many Mtbs and lends itself very well to heavily-laden tourers. It uses the smallest BCD available at 94mm. Chainrings are typically 22-32-42.|
|Single Chainring:||Wherever there's a need to save weight or keep the range of gears simple, a single chainring can be used with several different standards. Road fixers, time triallists and track riders select anything from a single 38-56 chainring fitted to a 130mm or 135mm BCD crankset. However, off-road singlespeeders typically prefer a 32-38 chainring fitted to a 110mm or 94mm BCD crankset.|