Technology is changing everywhere, and this includes cycling.
"The bike is the perfect marriage of technology and human energy."
--Jeremy Corbyn
Let's look at some of these changes, and how they can impact you as you look to upgrade your triathlon bike(s) over the years.
Brakes:
The most recent trend in triathlon (and road) bikes is the introduction of disc brakes. Traditionally bikes have used caliper brakes, and caliper brakes are reliable, easy to service, and can be worked on by most home mechanics. So why disc brakes? Disc brakes are stronger, more progressive, and their braking abilities are not affected by rain.
Gearing:
Upfront, the 'big' chain rings have recently shown a large number of riders utilizing a compact crank. A compact crank has 50/34 teeth (Big/Small ring) while a traditional crank has 53/39 teeth. The compact crank helps the rider have a faster cadence, getting away from grinding up hills. On the rear gearing has also changed, from 10 to 11 rings, allowing for a wider range of teeth options. Ultimately it allows you, the rider, to be more efficient on flats, hills, and just spinning at a faster rate.
Electronic Shifting:
Instead of traditional shifting which involve a cable running from the headset to the front and rear derailleurs, electronic shifting provides the ability to shift more rapidly, under extra conditions, without the issues that stretching cables can cause. The three biggies in the electronic shifting world are Shimano (Di2), SRAM (eTap), Compagnalo (EPS). One huge advantage for triathletes is the location of the shifters on a tri bike. In addition to the traditional location on the aero bars, now shifters can be included on the bullhorns near the brakes. The location changes, and the less physical involvement needed when manually shifting, can be a huge advantage for the triathlete.
Wheels:
Wheels are getting lighter and lighter. Manufacturers are taking advantage of wind tunnels to truly make fast wheels. Combine that with wheels that no longer need brake trakes (thanks to disc brakes) are lighter and faster than ever before.