Monday, March 28, 2011

School is in! on the PZ3TX and how it makes you faster

TriSports University takes a look at the blueseventy PZ3TX swimskin.
By Tom Demerly.
Go to article at

The Beijing Olympics established a precedent for new swim skins as being measurably faster in the water. The blueseventy PZ3TX leads the swim skin category for triathletes.

When the water is too warm to wear a wetsuit, speed suits make you faster in the swim.
If the incredible number of swimming records in Beijing didn’t convince you, then the FINA rulings on speed suit use should. Bottom line: You’ll go faster in the water with a speed suit. The only debate is how much faster.

It’s true that strong swimmers duking it out for a handful of seconds over 1500 meters or 2.4 miles for the Kona swim prime are the primary market for swim skins. But anyone looking for that handful of seconds out of the water will benefit. For the good swimmers a swim skin makes them faster. For the rest of us a swim skin makes us less slow.

The early swim skins worked by providing a small degree of positive buoyancy while improving hydrodynamics. Swim governing bodies quickly outlawed the positive buoyancy suits. The next generation suits went for extremely snug, compression-benefit fit and non-absorbent fabric. This final generation of suits including the blueseventy PZ3TX combine all allowable technologies with the addition of hydrophobic – water fearing – performance and improved hydrodynamics along with fine details like no stitching to absorb water. Finally, the patterns for the suits – where they close at the arms and neck – have finally been optimized to manage the layer of water surrounding the swimmer.

Because the PZ3TX works partially due to compression it takes a little effort to get on.
An impressive automatic opening zipper makes removal extremely fast. 
Swim skins work most prominently by making your body smoother and smaller in the water. They cover and compress protrusions making the overall shape of the body smaller and smoother. For females, they compress the chest and block entry of water in the bust that can increase resistance. The larger your bust, the greater the potential improvement in hydrodynamics and efficiency as long as the suit provides adequate compression and a tight enough neck seal.

Additionally, while swim skins cannot be buoyant by definition, they can resist water intrusion or becoming permeated with water which would increase their tendency to sink.

The blueseventy PZ3TX uses a hydrophobic, non-absorbent fabric called BLU-TX that also has significant compression. This fabric accomplishes two agendas: It provides compression for muscular support and improvement of body hydrodynamics by smoothing and reducing the body shape in the water, and: It uses non-absorbent fabric and seams so it does not become water soaked and negatively buoyant. In short: The suit makes you smaller, smoother and doesn’t soak up water.

“In short: The suit makes you smaller, smoother and doesn’t soak up water.”

One of the innovations on the blueseventy PZ3TX is the seams. The suit is not sewn together using thread and stitching but welded together using radio frequency and heat to melt the edges together under a seam-sealing, non-absorbent fabric tape. This process is extremely strong. By flipping the charge of the molecules from positive to negative thousands of times per second they heat up, creating friction from the inside going out. A die exerts pressure on the overlapping edges of the fabrics as they near a molten state. On a molecular level, they melt together. The joint is reinforced by fabric tape welded on in the same process. The seam is waterproof, smooth, hydrodynamic and utterly non-absorbent. It is also extremely strong, effectively making the entire garment into one continuous piece of fabric – like a tight fitting “tube” you squeeze into.

At the outside edges of seams there are bar tacks to join and reinforce several seams simultaneously, but that is the only thread on the garment.

Details on the PZ3TX include the taped/welded seams that are stronger, less absrobent and more hydrodynamic than conventional sewn seams.
Notice the bar tacks in the center photo near the end of the seam finish at the leg, a durable reinforcing detail.

The blueseventy PZ3TX is donned and doffed by a zipper in the back. The zipper is 14.5 inches or 37 centimeters long, zipping down to the upper portion of the small of your back. The YKK zipper closes extremely tight and is self locking so it will not open during the swim. The zipper is a quick opening design that can be automatically disengaged for near instant opening by pulling the top of the zipper apart. The zipper is backed by a 1mm thick, two sided nylon, open cell foam draft flap that is 45 mm wide and is stitched on as with the rest of the zipper.

With minimal practice the suit comes off in a flash, the quick opening zipper is a thoughtful detail that stays securely closed while swimming. while you may need an assistant to help zip you up before the race, getting the suit off is fast.

To me the important question is: How much faster will a PZ3TX make you in the water? How much time will it save? I’ll suggest this is a nearly impossible value to quantify. The suit will not take on negative buoyancy as the swim duration increases due to the non-permeable fabric and that it exerts an improvement in hydrodynamics. It won’t get waterlogged. Perhaps the larger performance advantage may be streamlining the body through compression and “fairing” of body contours.

A confounding question of whether or not a swim skin like the blueseventy PZ3TX makes us swim faster would be easily answered with that one “golden BB” metric that proves how much time the suit saves over a given distance. Something similar to aerodynamic tests that suggest a given aero helmet will save 30 seconds over a 40 km time trial at a certain speed. I can’t provide or verify that metric.

“Basically, when wet- the PZ3TX is nearly a half pound lighter than a standard tri suit. Almost a half pound.”

We did discover this: When we weighed the PZ3TX dry it weighs 140 grams in a women’s size small. When we weighed the blueseventy Triathlon Enurance Suit dry it weight 169 grams. The Endurance Tri Suit has a chamois pad for the bike while the swim skin does not. The difference in dry weight between the suits is 18%. When we immersed the PZ3TX for ten minutes at the bottom of a four foot deep pool, along with the Triathlon Endurance Suit- then pulled them out of the water and drained them for 30 seconds before weighing them wet the Triathlon Endurance Suit weighed 429 grams wet while the PZ3TX only weighed 243 grams wet for a 44% decrease in weight when wet, a weight savings of 186 grams or 6.5 ounces or over .4 pound. That is a lot of weight in the water. Basically, when wet- the PZ3TX is nearly a half pound lighter than a standard tri suit. Almost ahalf pound. To calibrate that, put anything in your back pocket that weighs a half pound and swim with it- like a half dozen gel packets. While it is impossible for me to translate this additional weight to any potential time savings in the swim, it isn’t difficult to imagine that lighter in the water is likely faster in the water.

The one paradox to the use of a swim skin like the blueseventy PZ3TX is that, if the swim skin is worn over a standard tri suit, is there any advantage? Does the tri suit still soak up the same amount of water as it would when worn alone in addition to the (much smaller) amount of water absorbed by the swim skin? The suit still changes the hydrodynamics of the swimmer by acting as a fairing over the regular fabric tri suit. Especially in long distance events where you may wear a tri suit with back pockets, swim skins like the PZ3TX will keep pockets from acting like a drag sit in the water.

Triathlete Magazine’s Aaron Hersh recently wrote a column that included data from a trial that included three swim skins compared to a swim brief. Hersh measured overall time, heart rate and stroke count. He tested the TYR Torque Elite, TYR Torque Pro and Profile Design Mako speed suits against. His article is here.

While the validity of test protocols can be debated ad nauseu, and Hersh likely tested the suits worn by themselves (not over a tri suit), Hersh’s test does establish a trend that swim skins test faster. He estimates up to a 1:36 time savings over a 2.4 mile swim.

Ultimately a data-driven case for swim skins is difficult to produce. Tests suggest they are faster. If you put one on and swim in it, and you feel faster and have test results to show faster swim splits individually, that is a compelling argument for swim skins providing an advantage in your next race.

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