Wetsuits are common in triathlons, but not universally allowed. Most triathlons allow wetsuits if the water temperature is going to be below a certain level. The most hard and fast rule about what temperature makes a race wetsuit-legal comes from the USA Triathlon association, which states that swimmers using tri wetsuits at water temps of about 78 degrees are not eligible for official race awards. In addition to the USAT’s stated guideline, the following rules of thumb are common based on many years of observing race directors’ decisions, racers behavior, and published race rules on the open water swim portion of a triathlon.
(all temps refer to surface water temperatures)
Under 50 degrees: Not suitable for open water swimming, even with a wetsuit
50 to 65 degrees: Suitable for open water swim, but wetsuit is highly advised
65-78 degrees: Suitable for swimming with or without a wetsuit. Sleeveless suits are popular at this temp.
78-84 degrees: Race directors use their judgement to allow or not allow wetsuits at this range
Over 84 degrees: Wetsuits not allowed
The range of 50 to 78 degrees is therefore the ideal range for using a wetsuit. Any warmer, and the swimmer may actually overheat due to the wetsuit’s insulative qualities. Any colder, and the water is dangerously frigid for a swim. Keep in mind that even with a full-length wetsuit, you have a layer of water against your skin (that warms up gradually) and that your head, forehead, and neck are still exposed to the cold water. It is very common to have an otherwise comfortable swim where your forehead is so cold it makes for an uncomfortable swim.
Of course, it is not just about the rules. The wetsuit answer might be different for every individual. Here are a few factors that you should weigh, in addition to the race director’s rule, regarding using a wetsuit:
Swim Ability: This one is pretty obvious, but if you are a weaker swimmer you may want to use a wetsuit if it is allowed, no matter what. Wetsuits help your bouyancy, and that can help your swim performance both physically and psychologically in addition to adding an element of safety. Having an open water swim “panic” is very common, and you are more likely to work through it if you know that the wetsuit is giving you some extra lift.
Conditions: Swimming on a windy day or in salt water can introduce unpredictable variables. When in doubt, you may want to use a wetsuit if the day’s conditions create factors that you don’t feel as comfortable in.
Your Training: “Nothing new on race day” is a common matra of seasoned racers. Race day is not the time to test a new approach or technique. If you have only trained in wetsuits when in open water, use one on race day. If you have never tried a wetsuit, you may want to forego one for the race (unless that is also your first open water swim as well — in which case, shame on you for not practicing in open water sooner).
Distance: With the advent of many shorter races, modified sprints, the swim distance can sometimes be so short that any time you save in the water by wearing a wetsuit can easily be lost in the transition. Taking a wetsuit off in T1 can easily take 60 seconds alone. If the swim is only 1/4 or 1/3 of a mile, you might be better off, timewise, by not having to contend with the suit during that first transition.