So many variables. It depends on weight, sweat rate, intensity, how fast you finish swim, target bike finish time and overall race finish time. No straight up answer to this. Also be attentive to how many calories thru liquid, and dilution of blood sodium through amount of drinking vs amount of sweat and how much sodium you may or may not be getting through your drink mix. again, overall race time, splits in each sport and weight and sweat rate will factor in. then there si the entire hot race-cold race angle. Sooooo it depends. I have raced Kona off 4 bottles of Gatorade on the bike and had a solid day for me, but I weighed 136 lbs for that race. Others same day may have gone through 10-15 botttles.

Some days when I’m riding in my garage for an hour I can drink three bottles, others I don’t even finish one

Really depends on the day

I’d guess 1-2 is normal.

I weigh myself first thing in the morning (before I ride) everyday. I try to always weigh myself after the ride / breakfast and like to see myself at the same weight or higher ... so it’s my way of saying “did I drink enough water”

You only drink 1-2 bottles for a IM ride?

Personally, I can handle ~40oz/hr. (but can also do 400kcal/hr on the bike w/o issue)

Lionel Sanders said he aims for 1.5l/hr.

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My last full distance race I took a 20oz bottle every 45 minutes, so ~27oz an hour. But bearing in mind that I'm on liquid calories, so part of the control around that was delivering the preferred number of cals/carbs per hour too (275 cals/ 69g carbs). I carried a plain water bottle too but don't really remember drinking much from it.

Whilst this race was Norseman, it was a very hot day for that part of Norway.

60oz an hour sounds nuts to me.

1-2 bottles / hour ** :)

I run 480 calories per bottle (2 bottles) for a concentrated mix. And I try to drink 7-8 bottles of water from aid stations. A good rule of thumb is ~10-12 oz/100 cal. If it's really hot, go up to 14 oz/100 cal.

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I drink 40-45oz/hr indoors for long rides, which probably more approximate conditions for a hot IM. Maybe closer to 30-35oz outdoors in ‘regular’ conditions, and fewer yet if it’s cold.

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Dimond Bikes Superfan

I am glad you asked this question because it's been on my mind a lot as I prepare for my first IM in 8 weeks. I've been trying to figure it out through experimenting in training, but it's not easy since I live in Chicago where I train indoors and my race will be in TX.

My last ride was 3.5 hours at my IM power target of 67% FTP and I drank 26-27 ounces per hour of Infinit GoFar. I also ate four GUs and took three Gu Roctane Ultra Endurance capsules. I was aiming for ~90 g. of carbs and 750 mg of sodium per hour. I more or less hit the target.

It was between 70-75 degrees in my pain cave and the humidity started at 45%, but was at 60% after about 90 minutes. I ran a dehumidifier to keep it at 60. I have only a single fan and it's kind of weak so I sweat steadily, if not profusely. I lost 2.9 pounds, which is almost exactly 2 percent of my body weight. I did pee three times (too much pre-ride coffee), so I'm guessing my sweat loss was between 1-1.5 pounds.

I did a one-hour brick run afterwards and for the first 2-3 miles I was close to having too much in my stomach. I was not hungry or thirsty at all during the run. My sense is that if I had consumed much more I would have had a sloshing stomach. This ride is probably pretty close to my race day plan other than I intend to mix in some water for washing down the GU products.

Without training, most folks can consume 32-36oz per hour during IM-level intensity cycling. I would imagine this might improve slightly with training, but have no evidence to back it up. Certainly carb absorption rates do improve with high carb fueling rates.

I have not done an IM.

On long rides at similar efforts, I can comfortably consume 40-45oz in an hour if I have fallen behind the previous hour, but not so far behind that I've lost significant systemic hydration (~2% body weight loss from sweat). Reduced hydration impairs absorption ability of carbs and fluid.

3x20oz bottles an hour is far outside what's tolerable for most folks.

Key to maximizing fluid absorption: consume often and keep stomach at >60% capacity at all times. The more full, within comfort constraints, the faster fluid moves through it. The more often you consume, the faster fluid moves through it.

Direct answer to your question: yes, 20oz per hour for an IM bike is suboptimal... though probably not abnormal. Lots of folks do lots of suboptimal things.

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Dr. Alex Harrison | Founder & CEO | Sport Physiology & Performance PhD
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My goal was always 1x20oz bottle with 100cals of nutrition in it plus 1x20oz bottle of plain water. I almost always got through the nutrition bottle and usually drank about half of the water and dumped the rest on me at some point.