I'd say 2-3'' slower per 100

http://www.trinewbies.com/swim_pace_chart.asp

sorry for putting a non-ST site on here... this is pretty helpful to get a general idea, i find.

I use the following formula for "scaling" race performances to different distances. It predicts best if the ratio of the two distances is between 1/2 and 2.

t2 = t1*(d2/d1)^1.06

So for estimating a 1.2 mile (1930 meters) from a 1500 meter time, multiply your 1500 meter time by (1930/1500)^1.06 = 1.307. For example, if you swam 1500 meters in 25:00, your 1.2 mile estimate would be 25*1.307 = 32:41

Gonzobob's formula does a good job of comparing swims over any differing distances, however I'd suggest that you use a power of 1.05 rather than 1.06. Current world records fit well to a curve when using a value of a bit less than 1.05.

For running, use gonzobob's formula but with a value of about 1.07 to 1.08. This is because in running we're not constrained by a fluid with a cube rule relating power to speed.

Of course, this formula predicts what your capable of in a 1.2 ml swim race. But that's not what you're doing, rather you're goofing the swim, with drafting, with a wetsuit, without flipturns, and saving it mainly for the run. Looking at several other swimmer/triathletes I know, I'd suggest applying gonzobob's formula with a power of 1.05, then adding at least 1.5 to 2 minutes. For a simple approximation, I'd say multiplying your 1500m pool race time by 1.38 to 1.39 gives an estimation of what you ought to be doing for a half ironman swim.

This is a nice chart, but not really appropriate for these purposes. All it does it scale a given time for a set distance to another distance. What we want is some way to estimate how much slower your pace will be over a longer distance. I think the exponential formulas are the best for this.

-Colin

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Any run that doesn't include pooping in someone's front yard is a win.

Have people used these formulae for whole triathlons, not just swimming or running?

-Colin

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Any run that doesn't include pooping in someone's front yard is a win.

You have so many variables (how well you do flip turns, are you wearing a wetsuit, how much the wetsuit benefits you if you are wearing one, are you lucky enough to find the right person to draft off of, how well do you navigate that day, how accurately is the course marked off) that all you are going to get it a good guess.

Not as far as I'm aware.

Exponential formulas are the way to go as regards predicting performance based on results at a different distance, but you can't apply them across three different sports at the same time, all which require ratios raising to different powers due to the nature of the fluid you're moving through in the sport.

Those same factors also dictate that one should NOT be applying the same effort throughout a triathlon, but rather should be applying less than the mean effort during disciplines where you are constrained by a more viscous fluid (e.g. swimming), simply because the effort required to gain, say a minute, is a lot more than the effort that would be required to gain a minute later in a discipline where you're not constrained by the fluid (e.g. running, where power is almost proportional to speed).

Those are the rules I go by, I used to try to maintain the same effort throughout a triathlon, but now I realise that you can go faster on less total effort by goofing the swim, going steady on the bike, then running hard. I also try to negative split slightly within each discipline, which is also very effective but for different reasons.

[reply]What we want is some way to estimate how much slower your pace will be over a longer distance. I think the exponential formulas are the best for this.[/reply]

on the other hand, 1.2 miles is only 430m longer than a 1500m. In my experience pace over 1.2 in a race situation is not significantly different from pace for 1500m in a race situation.. it's not a lot longer. 3.8 is certainly different, and I agree the exponential formulae are better here. But for the original question, I think a linear projection is not unreasonable.

I do. I apply the exponential formulas to each leg of the triathlon (or duathlon) and then add them up to get a total time. I use 1.06 as the exponent for the swim and bike and 1.08 as the exponent for the run.

Also, swim courses are rarely veyr accurate. Not only may they be guesstimated, but current, zig-zag swimming & drafting will effect you in positive or negative ways. Last August I did an Olympic race and a half within two weeks of each other. My swim for the half was 1:30 faster than for the Olympic... and the half was in the ocean.