How Much Do The New Body Suits Help? A Coach/Engineer Sets the Record Straight -- May 30, 2000
By John Waring
Carleton University Swim Team
I have noticed a great deal of misinterpretation concerning the effect of drag reduction on final time reduction in swimming. In short, a 10% reduction in drag coefficient does NOT translate into a 10% reduction in a swimmer's final time.
I am an engineer, a swimmer, and a coach. As an engineer, I am ethically bound to tell you that I am under contract with Speedo America. Specifically, I invented a vortex modification to swimwear worn by Jenny Thompson and Lenny Krayzelburg when they set their world records at the '99 PAN PACs in Australia.
That being said, my purpose here is to clear up misconceptions in the swimming community concerning the effect on final time of ALL manufacturers'
reduced drag swimwear. Consequently, the information below is applicable to any manufacturer's claimed drag reduction.
The power requirement for a swimmer goes up approximately as the cube of velocity. This means that to go TWICE as fast a swimmer must work EIGHT
times as hard. However, power varies directly with drag coefficient. Doubling the drag coefficient requires a swimmer to work TWICE as hard to hold the same velocity. In effect, the power required to swim faster far outstrips the power reduction due to a "faster" suit.
I will not go into a detailed derivation here. However, if one assumes a constant power output (i.e. the swimmer is working as hard as he or she can), the
change in final time can be estimated as follows:
(New Final Time) = (Old Final Time) x [cubed root of](1 - drag reduction)
For example if a swimmer whose best time over 100m is 60.0 dons an ACME Drag-Be-Gone suit with a claimed drag reduction of 4% (note that 4% = 4/100 = 0.04), his new final time would be:
(New Final Time)=60.00*[cubed root of](1 - 0.04)= 59.19
That is an improvement in the final time of 1.3%
This is a very rough estimate and neglects, among other things, the effect of surface swimming versus underwater kicking. It does, however, give a much more accurate idea of the effect of a reduced drag suit.
In essence, while a better suit has an effect, it is far less than the effects of improved technique and fitness (i.e. showing up for workout and listening to your coach).
A more thorough examination of the effect of drag reduction on swimming can be found in my thesis at