How a water-logged wetsuit affects your swim speed

Have you ever borrowed someone else’s wetsuit for a race, only to find that it didn’t fit very well and filled with water? It is not a fun moment of discovery on race day. But, how much of a difference in speed does it make if your wetsuit fills with water while swimming? If your wetsuit is obviously larger, it makes sense that it would make you slower. But how about wetsuits that feel tight when you put them on and collect about a centimeter of water around your waist, shoulders and arms? Does this small amount of extra water weight affect your top swimming speed? And if so, by how much?

In this experiment, the author (Duane Dobko) swam a total of eight 25 yard sprints. In the first four, a Men’s Small wetsuit was worn, and for the final four, a Men’s Medium wetsuit was used. Both wetsuits were from the same manufacturer and model (Quintana Roo Superfull). The superfull is a full-body wetsuit, meaning it covers the torso, arms and legs, leaving only the hands, head and feet exposed. The Men’s small was the 2007 model while the Men’s medium was the 2004 model. It is not known how much of a difference the year classes make.

What was certain was that the two sizes of wetsuits had a dramatic impact on amount of water that filled the suit. The Men’s Small was so tight it almost felt like it would burst when I put it on. But very little water filled the suit, even when pushing off the wall or during flip turns. The Men’s medium also felt tight while putting it on, but not quite as much as the Men’s small. But it filled with water; about a centimeter around the torso, shoulders and arms. Most of the water filled during starts and turns, but the filled water never went away while swimming.

Here are the results. There was a difference in swimming speed with a water filled wetsuit versus a tight fit suit. And the magnitude of speed loss when a wetsuit filled with water was BIG. The water filled wetsuit (even with 1 centimeter of filled water around the torso) was 5.1% SLOWER than the wetsuit that didn’t fill with water. See Figure for details and data. A speed loss of 5.1% is dramatic, as it virtually wipes out the gains you could expect by the wetsuit in the first place. Other experiments here on Dobkanize have shown that the gain in speed associated with a full-sleeved wetsuit is 7.9%. Therefore, a 5.1% loss means you lose over half of the benefits.

The difference in swimming speed was so dramatic that I could sense it while swimming. The Men’s small felt extremely tight, so tight that it took extra effort to swim freestyle properly. But I felt like I was so buoyant in the water that it didn’t matter. Conversely, I felt like I was drowning in the men’s medium suit. There was so much water that filled in the torso, shoulders and arms that I just couldn’t get high in the water. And the water that left the arms and legs got quickly replaced. I could feel jets of water spraying over my hands for every sprint (just because the water was warmer coming out of the wetsuit). Even if I didn’t know the times, I knew the smaller suit was faster.

The results suggest profound implications for wetsuit optimization. So much focus is placed on how slippery a wetsuit surface is in the water, or how easy it is to take a wetsuit off in transition. I must admit, advertising slogans like “50% less drag coefficient!!!” sound pretty cool. But this experiment says that a wetsuit that fits well will make you much faster than a slippery one that doesn’t fit well. It may not sound as cool to say, “…our wetsuit lets in less than a shot glass of water!!!”. But, at least it is an accurate claim to increase speed!

The experiment results also suggest that much work can be done to improve wetsuit design. The wetsuits used in this experiment were Men’s Small and Men’s Medium, both from a top of the line manufacturer in triathlon gear. At the time of the experiment, I weighed 195 pounds, with height of 6 feet, 2 inches. I should not be men’s small material! Most of my clothes are XL or XXL. My pant size is 36. In fact, it has taken only 2 seasons of racing with the Men’s small to burst at the seams. But, I would rather sew it up than wear a wetsuit that I am supposed to wear for my size. It is just that much faster.

If a manufacturer can find a way to make a wetsuit fit well, all the time and for everyone, then their wetsuits are going to be fast. There are many ways to accomplish a good fit. There is of course the expensive way (custom tailored wetsuits!!!). But a suit doesn’t have to be perfect, it just has to let a shot glass (or less) of water to run through. There has to be some way out there to make this happen.

Hopefully, this article has enhanced your understanding of the difference between a wetsuit that fits well and a wetsuit that does not. Even a modest amount of water filled inside a wetsuit (like a centimeter around the torso), makes you 5% slower than if you had a wetsuit that fit perfectly. You swim so slow with a poorly fitted wetsuit that it almost negates the speed benefit of wearing a wetsuit in the first place. So, if you are in the market for a wetsuit, do make sure you shop around, try it on, and buy from experienced professionals who know how a wetsuit should feel when the fit is right. Until next time, happy training!

You could be right on your conclusions but I am not convinced. Number 1, older wetsuits are slower (small 2007 vs. medium 2004). My older versions of the same wet suit are a lot slower (design not as good seems not as tight cracking or damage to rubber). Number 2 you did not prove your hypothesis. You had an observation on taking in water and did not prove this hypothesis. If you took the smaller suit and purposely put a shot size of water in it and it slowed you down the same amount I would believe you.

It may be that wearing a tighter wetsuit just makes your muscles perform more efficiently, and have nothing to do with water getting inside the suit.

A centimeter of water in a wet suit is massive and I have a hard time believing that there would be that much water intake on a medium suit knowing your size. If the experiment was done off a block start then I would believe water would inter, but in a tri there are very few dive starts. Most wetsuit fitters would put me in a medium suit. But I've done my own tests with suits up to x-large and the ability to breath and expand my chest in the big sizes, gives me far more benefit than a tight, restrictive suit.