Be honest – when you paid for your first proper bike, did you even give the crank length a second thought? If you were lucky, the sales assistant steered you towards the bike with the most suitable cranks.
If your cranks are too long, your knees could be over-flexed, causing discomfort, maybe even injury. Too short, and while you likely won’t suffer ill effects, you’re forgoing the principle that crank length amplifies an input force. Find your Goldilocks zone – your local bike shop will be happy to help.
Keep it simple, just stay single
Chainsets are described by the number of chainrings around the crank. Count the number of teeth, and it gives you a number – this SRAM mountain bike chainset has 32 teeth, so you’d call it a 32. The higher that number, the more difficult the acceleration, but sustaining a top speed is more economic.
Wiggins opted for a 58 chainset for his Hour Record – perfect for a pro athlete in a velodrome, where changing speed is less important than efficiency. In comparison, the SRAM mentioned above is for mountain bikers who need agility, torque, and low gearing to change pace quickly and safely.
Fancy a triple?
The more chainrings you have, the more choices of gears you get. If your rear cassette has 9 sprockets, a triple chainset will give you a total of 27 gears. In practice, triple chainsets afford you a wider range of low gears to choose from.
Lower gearing improves torque, making it useful for touring cyclists who are packing more than their body weight. Think of it like the gearing in lorries and vans – low gears make it easier to get a heavy weight up to cruising speed. Triples also make it a lot easier to climb and conquer hills.
You’ll see the pro peloton using two chainrings around the crank, and many of us amateur riders are seduced by the notion that you don’t need triples if your ambition is to cycle like a pro. But the pro-peloton mechanics change the gearing ratio on a stage-by-stage basis, depending on the terrain.
In the 2015 Tour de France, Froome climbed a mountain in Stage 10 using 52/38 chainrings – whereas Dumoulin’s 2016 Olympic Time-Trial bike had a higher 53/42T more suited to the flat. In commercial terms, both chainsets would be considered “standard” chainsets but would be impractical for anyone other than a professional athlete on race day.
Compacts offer you a gear ratio somewhere between the hill-friendly triples and the standard chainsets that the professionals use – something like 50/34. You can always upgrade to a semi-compact 52/36 when you’re fit enough.
A friend of mine competes in amateur triathlons using a 48/32 “sub-compact” chainset on a cyclocross bike. I hated riding with him because even on a long flat ride he was faster than me on my standard-chainset road bike. Sometimes it just ain’t about the gear you use…