Despite using an 11/23 rear cassette with 39/53 front chain rings for many years, our favorite gearing for racing and training has shifted to an 11/26 rear cassette and 39/53 front chain rings. This set up allows you to keep a higher cadence on hills and prevent that excessive leg burn that can be so detrimental to finishing your race with a strong run leg. On extremely hilly, long-distance courses such as IM St. George, we’ll even use a 12/28 rear cassette. A general rule of thumb is that if there is any question at all – go with the easier gearing.
Long, steep climbs aside, having the larger gears in back can also help save you from that oh-so-annoying shift to the small chain ring when you hit some small rollers or false flat sections. Having the ability to stay in your 53 front ring and get into the 23 cog on the back without crossing the chain over too far can be nice advantage.
One small disadvantage to having a cassette like a 12/28 is that you lose the ability to pedal hard at over 40 miles per hour. I.e. when you’re going downhill. In our opinion that little bit of lost speed on fast downhill sections is more than made up for on the rest of the hilly course.
When making equipment decisions it is important to look past the macho stigma of pushing big gears. There is no shame in throwing on a 28 tooth cassette if it’s going to help your overall finish time – and it always feels good to cruise up a hill past all those mashing away and having to stand in their 23.