It was kind of agressive to me. Not much, but a bit.
Divide that number by 2 and that's my HIM split with good accuracy but I obviously don't swim IM = 2xHIM.

I should probably change the thread title to 2.4 mile swim time predictor, as that is what is really being predicted. IM swims should be slower of course.

A really good question, and ultimately something that could add to the error due to the very simple math involved. The constant 3.94 was derived from 25 sprint estimates which would involve little or no breathing. If your breathing disrupts your propulsion to a greater degree, than you could either add some time to the estimate or, as you suggest, sprint a 25 with your long course breathing pattern.

We were doing sprints last night in my masters session. I don't like sprints. I am very definitely a slow twitch athlete. Off a wall push (fatigued, end of session) I got a 33s 50m. Could probably trouble sub 30s for a 50m off a block dive and fresh - the guy who I was chasing in the next lane last night swam a 26.5s 50m at the nationals a few weeks back.

I have an Ironman swim pb of 54 mins, and haven't swum a pure 2.4 mile TT to compare this with.

Using your calculator, and doing some rudimetary adjustment to take yards from metres it gives:

50m = 54.68 yards
Using metres, your calculator gives a time of 65:01 for the IM swim
To convert this to yards I took 0.91% which is what you get if you do 50 (metres) / 54.68 (yards)
65:01 x 0.91 Gives around about 59 mins 27s

About 5 mins off my IM pb, and I am currently swimming some 30s per 400m faster than when I set that, so reckon I would give 50 mins a good go at present if I were to go at it as a flat out effort.

I think your attempt at using this as an estimation is inherently flawed. The bloke above is a sprint monster - he goes around 26 for a 50m free. Put him in a 3.8km race though and I would swim circles around him. He has no endurance just as I have no speed. An elite age group sprinter might swim 25 seconds or so at a masters event for a 50m free, but it doesn't necessarily translate into endurance.

If you swim 30s for a SCM 50 from a dive, you're about 27 for the same in yards. A 27.0 50 yard free will be split in the ballpark of :12 / :15, which puts your 25 yard sprint from a push at maybe 14.0-14.5. Call it 14.25 and we come pretty close to your actual IM split.


You're a better argument for 3.94 giving reasonable estimates, not inherently flawed.

can you recalibrate it for metres?

---

They constantly try to escape from the darkness outside and within
Dreaming of systems so perfect that no one will need to be good T.S. Eliot

But I am a slowtwitch diesel engine. I think that the problem still stands for the sprinters amongst us. The guy I mentioned for instance who can go around 26s for the 50m free has a 200m free split in the region of 3 minutes. He just absolutely sucks at anything longer than 100m.

I guess the point I am trying to make is if Usain Bolt were to run a marathon, what do you reckon he would do? A similar calculator might put him sub 2 hours, but we can safely say he wouldn't be anywhere near that - he might not finish the thing!

My point is, I think you can sprint close to a 14.0 / 25 yards, which predicts a low 55. 3% faster is a mid 53, 3% slower is a high 56. So for your current IM PR, we nailed it.

I have already stated that for super fast swimmers, it will tend to underestimate. I have also stated that:

"if you are physiologically suited for the a 15-20 minute event, and trained to the limit of your endurance capabilities, then you should be able to average approximately 130% per 25 of your all out 25 sprint time, and you can do 140% per 25 in a multi-mile swim"

So the point I would make is that it is easier to predict a long distance swim from a 25 yard sprint, than to predict a marathon performance from a 100 meter run. And I just showed it. Sprint swimming and endurance swimming have more in common than sprint / endurance running.

With you. Carry on. I've had a few beers and maybe didn't get the gist of the thread.

No worries. It a simple relationship I derived just yesterday, so it ain't perfect and there are limitations of course. Same with heart rate training and Daniels VDOT. Understanding both the limits and potential is the key to all of these.

If you know your 25 meter sprint from a push time, I'd just take 91% of that for your 25 yard time, and then apply the 3.94 Hell, you could just round it to 4. It's not an exact science.

Does your sample include any actual sprinters? Or is it just long course triathletes who never actually train for sprints? The projections just seem wildly optimistic to me, someone who has one foot firmly in the Masters pool swimming world but who also dabbles in open water and triathlon. I can do a 12.79 25 yard free, off the wall. I'm a pretty unremarkable sprinter; there are over a hundred guys in my age group Nationally who are faster sprinters than me. But your formula suggests I should be able to keep pace with, or be slightly ahead of, the small group of guys in my age group who are contenders for the USMS National Championships in the 1000/1650/1 mile open water/2mile open water/2.4 mile open water events.

---

"They're made of latex, not nitroglycerin"

I can swim 13-13.5 or so from a push. I have never done an IM but swim 20 minutes in an open water 1500m. I am a runner by trade and my stroke falls apart with longer distances unless I am swimming at least 15 to 20k a week.

Your 12.79 / 25 yard sprint predicts a 2.4 mile swim split of mid 50:xx Call it a 50:30 (3% slower is roughly 52 flat. 3% faster is roughly 49 flat) As I said, the faster you go the more it tends to underestimate, so if we give you a 5% range, on the high end you're looking at a 53 flat. Are you saying you could not do that if you were well trained for it?

My original sample was done by estimating the speed degradation of excellent distance swimmers. I calculated their 25 yard splits in a mile swim being 130% of their estimated 25 yard sprint speed, and used 140% for their 2 mile+ 25 yard pace.

I'll use13.25 and simplify my constant to 4 (instead of 3.94), giving a 2.4 mile time of 53 flat. So roughly 22:00 per mile. (+/-3%)

If you are 20:00 for an open water 1500, you are ballpark 21:30 for an actual mile (1609m) So 22:00 per mile for 2.4 miles may be a bit optimistic, but well within the +/- 3% range.

Next?

15 sec 25 yards comes to a :59 IM
My best IM is 1:04.

I wish this was accurate for me!!

Well, not too far off. I think I will make it simpler and just use a coefficient of 4 instead of 3.94 So your :15 seconds sprint comes to 60 minutes, 3% slower is a high 61:xx. How much did you train to hit that 1:04? How straight did you swim? How hard did you push?

I see a reasonably local opportunity to collect some data towards validating or adjusting the model.

2018 U.S. Masters Swimming Open Water National Championships

USMS Middle Distance Open Water National Championship (2 miles)
Reston, Virginia, May 27, 2018

I was in good swim shape which isn't saying much.

It was at placid and I followed the cable.

My stroke goes to crap after about :30minutes.

I just joined a masters group and I hope this gets me motivated to go under 1:04.

I was expanding on my earlier post where I said I was about 16 the last time I tried a 25 but have swam a 59 in an IM swim. I am not sure what my 25 time would be now but I THINK I can get a mid 50's IM swim now, or I hope so! But that all depends on the course, conditions, and if I can find a group. But Jonnyo is killing me in the pool so I trust I will get where he wants me to be!

---

Twitter - Instagram

There was a thread recently where a guy was saying he had done a 50+/52/53 for his ironman swims. And based on his pool 400/1000 it seemed as if he was swimming too fast for those IM swims, but then I drilled down a bit. Those are all wetsuit swims, as I presume are all the IM times people are giving you here. When I pointed this out he said oh ya, by the way I did a 57+ at Kona..SO that made a lot more sense in his predictors, I think your formula is having the same problem, only in reverse. If guys here were actually giving you Kona or Florida swim times(without rubber on) the formula would be much further off on the pointy end.

I think you have a good start, but somewhere under 16 seconds it has to be adjusted or you will have everyone swimming sub 50 IM swims without wetsuits. You know how hard and rare that is, especially to the average AG swimmer who can easily push a 13+ 25yd.

And your assumption that IM swims are slower given a pretty close distance is really off when you figure in the wetsuit and the drafting. Sure you back out turns, but that is not enough to negate the other two things, and if salt water, well that is another huge plus for swimming faster times It's too bad that virtually no one here or elsewhere actually swims an IM swim in the pool, that would be an interesting comparison if there were enough data. Best you could hope for is a 25 sprint vs maybe a 1000 time predictor? Drill that one down to a small +/- and you wont be that far off of getting a good 4k predictor. And lots if not everyone has done a 1000 for time, or could if they wanted to see where they stacked up in your formula..

Continue on, just my 2 cents.

Spot on.

I can do 19sec 25scy on wall push, your prediction of a 76min 3800m swim would be close (not counting currents, chop etc) based on my 103 minute 5200m cross lake swim (completed on ~5K/week for 2 months training).

People who swim 90minutes for 3800m despite being able to do a 19 sec SCY likely have poor technique and/or poor swim endurance but lots of upper body power to muscle through a short distance. I have no upper body strength, but good enough technique and good swim endurance.

---

Two wheels good. Four wheels bad.