I agree with @Pyrenean Wolf about not overthinking your weight. It sounds to me you're overthinking/overcomplicating things a little. try to eat reasonably healthy. a couple drinks aren't going to kill you. just keep it in moderation. as an endurance athlete I wouldn't focus too much on low carbs. you're already light. if you were an elite athlete and were eeking out those last couple watts on the bike or seconds on the run that's one thing. but I would focus more on good structured training and eating a reasonably healthy diet.

There isn't a formula that I know of.
That being said on the bike it's not going to help much unless you are going uphill. As mass increases surface area increases at a smaller rate. A 5% increase in mass may yield a .5% increase in surface area. Likewise a 1kg reduction probably won't decrease surface area at all. power/cda is a much, much, much more important metric when racing flat to rolling courses. If it's a hill climb p/wt ratio is much, much more important. If it's a rolling to hilly course then you need to figure out the ratio between flattish to hilly to figure out which ratio (p/cda or p/wt) is going to be more important.

On the run less mass helps to a greater degree when it's hot & humid. The more fat mass you have hanging around the harder it's going to be to shed body heat in hot/humid climates.

A 1 kg wt loss will help for increased running velocity but probably not as much as most on this thread seem to hope for.

On the other hand if you have a kg to lose losing it isn't a bad idea.

If I had to choose between losing a kg and revamping my training a bit to get more run frequency/volume and a 2-3 extra tempo sessions in that 6-3 week period prior to the race without a large increase in fatigue heading into a major race I know what I would choose.

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Brian Stover USAT LII
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There are calculators that would give some insight in what weight can do for your run time.

For example: https://runbundle.com/...t-vs-pace-calculator

Haven't tested it out with different weights to verify if there is any truth in it. But it will give an estimation of how much time you can save on the run.

Regarding cycling it is best to drop your weight in the last moment before a race. Because normally your power output will decline with your weight loss over some time and it will normalize around the W/kg that you had before. But by losing weight before your power drops you're able to gain some in the W/kg ratio.

Some additional info: https://www.yellowjersey.co.uk/...e-ideal-race-weight/

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He said he’s currently running that pace not racing a 70.3 run at the pace. The numbers don’t make sense. He wants to go 5:30. If he can swim 2:00/100m let be generous and comes out with transition at 45 mins. Running a 1:50ish would still give him 2:55 for the bike. If his ftp was over 200 watts on the bike and is sub 150lbs we’d be talking about under 5hrs not under 5:30.

200+ watt ftp, on a flat course at his size is easily 22-23 mph if not more. I did Florida 70.3 bike at 200 watts avg at 23.5mph and I probably had 20lbs and 6 inches on him at the time.

That's a really helpful run calculator. Thank you.

For the OP, here is a bike calculator to use as comparison. http://bikecalculator.com/
Keeping everything constant and just change your weight. Let's assume you maintain your power at 140 and drop from 68 to 65 kgs, over the course of an HIM, your bike split would change by about a minute. To me that is within the margin of error. It's also assuming that your power stays the same as you drop weight, which doesn't always happen.

On the run, based on runbundle calculator, you would save close to 4 mins.

So yes, you could acheive a theoretical 5 minute savings over the course of a HIM. If it's that important to you, then shed the weight. But if not, then eat clean and have a few beers once in a while man, you're 21 for crying out loud.

http://flocycling.blogspot.com/...-aero-vs-weight.html

This is a good read from Alan Couzens: Ideal Height Weight Ratios for Ironman Triathletes

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Benjamin Deal - Professional - Instagram - TriRig - Lodi Cyclery
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His 140W is really not that hard to believe given that he is relatively new to cycling.

I'm relatively athletic (3:04 marathon), weigh 60kg and when I started cycling last year I was at 120W. Within 3-4 months I got up to 150W and now I'm pushing 180 but the start was a huge struggle for me given my inexperience and lack of cycling muscles which take time to develop.

Perhaps most of you have been cycling so long that you forgot what it was like when you first started.

Not to hijack the thread, but I'm also FTP (according to Zwift) around 265. Would your target watts for an IM be 220?

+ mean.... +

I do believe some athletes will perform better at slightly higher numbers than what we think. I'm female, 1.8 meters tall. About 2 years ago I lost a bunch of weight, going from 84 kg to 65 kg. I pretty much held my bike power through the weight loss (FTP dropped less than 10 watts), and got much, much faster on both bike and run. However, the real speed breakthrough happened when I put some weight back on -- going to about 70 kg, and I've also made power gains on the bike that exceed that 5 kg increase (FTP pretty much back to where it was before I lost any weight). It's strange because I felt like I looked the part of where I wanted to be athletically at 65 kg, but I'm actually performing where I want to be at 70 kg. FWIW.

This assumes he has been properly fit in an optimal aero position. He could be riding a road bike and wearing a baggie bike jersey and spends half his time sitting up on the horns.

Not really, I didn’t say he sucked, he’s an average half Ironman racer at 5:30 on a flat course, it’s just reality. But he's running a 50 min 10k pace and swimming at an average swim pace. It would be odd for him to just starting out cycling with those two numbers, and have an FTP of over 3.0.

I swam a 47 something in my first Olympic and ran over an hour. I’ve been slow as shit, so not talking down to him at all.

Read these two quotes:


"The best predictor of performance is performance itself." - Andy Coggan

"FTP = how fast you can go. CTL = how long you can go fast." - Rick Murphy


Now sit back and think about what they are telling you. Not only do they answer your question they also lay out a road map how to train for your IM.

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Brian Stover USAT LII
Accelerate3 Coaching
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1kg? Not a lot, 3 to 4 kgs? A grip.

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Washed up footy player turned Triathlete.

Body fat also plays in.

2-3% body fat and anything you lose could be muscle and detrimental to performance.

10-15% body fat and you have some wiggle room.

Losing 1 kg probably isn't going to swing you one way or the other much. I lose that much in water weight on a long run.

I also know 97 kg guys around 183 cm that CRUSH IRONMAN races and look like it's nothing. Depends on the engine as well as the body makeup.

Focus on fitness and eating right and the weight will fall to where it needs to be. Don't get stuck on the numbers.

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Ryan
http://www.SetThePaceTriathlon.com
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If you're FTP is 2 watt/kg, there is absolutely no way you're going to go 5:30 in an HIM unless your bike has a hidden electric motor on it. Either your power meter is completely useless, or you might want to adjust your expectations. When I did my first HIM, my bike split was 3 hours and my FTP was about 2.9 watt/kg, and I probably was a bit overcooked (under-performed relative to my running potential, 2 hour HIM run vs 1:40 open 13.1).

More constructively, studies have shown that a 1% decrease in EXCESS body weight roughly results in a 1% decrease in your marathon time.

In hindsight, absolutely. I will have to redo the test with this in mind, avoiding embarrassing results this time!

That's a great way to look at things. I have probably gotten too obsessed with the numbers that I've lost sight of what they actually mean when it comes to race day. Triathlon seems to be all about finding a balance between obsessing over the data and knowing how to use them... I'll work on the latter.

Unless I`m mistaken, you're not able to hold your FTP for a half. He would probably be riding at 150-170, at most, with an FTP at 200 and that does not equate to 22-23mph on any course. Probably not even 20

When you retake your FTP test, keep a trash can nearby. Your not done the ramp test until you feel like barfing in the trashcan.

Like you said, 1 kg probably isn't that true. Based on my informal results I've noticed the following....

In 2017 I raced 70.3 worlds and IMFL around 180 lbs and am 5'-11". At 70.3 worlds the weather was mild with little humidity and I had a good race. At IMFL I really struggled on the run and it was warm (no shade). Looking back I really felt like weight played a part on that run. I guess I'd describe my racing performances as having a strong bike but then giving up a few spots on the run.

Last year I got control of my diet and got down to around 173. I did a few smaller halfs and was surprised that I either came off the bike in the front and didn't lose ground or would run down people in front of me. At IMchoo it was warm, but I felt like I had one of the best runs I've had in an IM. I came of the bike in the top 10 and while I didn't move up, I also didn't lose ground either. Granted there wasn't a swim which could have caused things to play out differently

Disagree on the speed part. Even at 150 watts on a flat course at his weight he can be pushing 20+mph You can look at the numbers on bike calculator. Obviously it depends on position and set up but not out of the realm of possibility anyways.

There are a couple people saying that he’s probably over 200 watts ftp, it just doesn’t make sense. Anything over 200 you’re really getting into the 20s on a flat course with a good set up.

Don’t focus on weight loss, but rather reducing body fat percentage. Obviously weight loss is a part of reducing body fat, but it’s only part of the equation. If you lose muscle (weight) then you could lose a lot of bike power as others noted. Can you see your abs? If not then you could probably make some adjustments to your diet in terms of the quality of calories consumed. It doesn’t mean drop 20-30lbs though. Cut back on the pizza, burgers, beer, cookies and cake and watch the fat fall off.

Yes, it matter. It matters more the hillier the course. Heat can also affect you more the heavier you are, as you ability to cool is more difficult the larger you are.