While hippos are known for their speed both on land and in water, they would face insurmountable difficulties during a the biking portion.
Hippos have short, stout legs relative to their bulky body size. Even if we entertain the hypothetical scenario of a hippo magically being able to ride a bike, these short legs would severely restrict their pedaling efficiency.
Their weight, coupled with the slow biking speed resulting from their short legs, would most likely cause any lead from the swimming and running stages to dissipate rapidly.
Additionally, despite their intimidating size and strong jaws, hippos are not carnivorous by nature, but rather herbivores with a diet primarily composed of grasses. While they can be aggressive if they perceive a threat, they don't typically target humans as food. Therefore, the scenario of a hippo eating a competitor during a the other stages is extremely improbable.
All things considered, a relatively fit human athlete would still have a considerable edge in a triathlon competition against a hippo.
While hippoes are surprisingly agile in water and surprisingly fast runners, they are not known for their endurance.
Hippoes would probably have an advantage while swimming due to a body adapted to water.
Hippoes don't sweat and have a very thick skin, so they would overheat quickly when running. The same thing applies to cycling, but with a bike designed for their body, I'd think they'll do better cycling than running. Their hind legs are about 70cm long (according to ChatGPT), so not that short. Shorter crank arms are required. The hind legs are super strong, so that would be a significant advantage, especially when the bike is holding their body weight.
Let's incorporate some numbers into this scenario for a clearer perspective.
Assume a standard Olympic triathlon, which includes a 1.5-kilometer swim, a 40-kilometer bike ride, and a 10-kilometer run. Hippos can swim at speeds around 5 mph (8 kph) and run at up to 20 mph (32 kph) but these speeds are only in short bursts, not sustained over long distances.
For the 1.5-kilometer swim, at an average speed of 8 kph, a hippo could theoretically complete this segment in roughly 11 minutes. A well-trained human could complete the same distance in around 20 minutes.
However, the biking and running segments are where the hippo would struggle due to its short legs and lack of endurance. Even with a specially designed bike, let's assume a hippo could bike at a generous speed of 5 kph due to their physical limitations. Therefore, it would take them around 8 hours to complete the 40-kilometer bike segment. In contrast, a well-trained human could complete this in around 1 hour.
For the 10-kilometer run, even if the hippo could sustain their top speed of 32 kph (which is unlikely), they could theoretically finish in under 20 minutes. However, due to their poor endurance, a more realistic time might be around 1-2 hours. A well-trained human could complete this segment in under 40 minutes.
In summary, even if a hippo performed at its absolute best and a human performed at average speeds, the human would finish the triathlon in roughly 2 hours, while the hippo would take around 9-10 hours. The limitations of the hippo in biking and sustained running, even with hypothetical specialized equipment, make it highly unlikely they could compete effectively in a triathlon.