Out of the Water With the Right Group: The Pack Effect on a Non-Drafting Bike

Ask experienced age-groupers what changed when their swim improved, and many give the same answer: "I started coming out of the water with better people, and my bike got faster too." It sounds like it shouldn't matter in a non-drafting race. You can't sit on anyone's wheel, so why should it make a difference who's around you?

There are good reasons to think it does, but they're a mix of solid evidence and reasonable logic. This article separates the two. It covers what happens in the water (where the evidence is strongest), what happens on the bike (where the logic does more of the work), and the risks of getting it wrong.

To be clear about scope: this is not about drafting on the bike, which is illegal in non-drafting races, unsafe in age-group fields and not what's being described. It's about the legal advantage of riding among stronger athletes.

Part 1: getting there cheaper

Swim drafting is legal and effective

Unlike on the bike, drafting in the swim is allowed in age-group racing. Its effects are well documented in the lab.

Chatard and Wilson (2003) had 11 swimmers swim at 95% of their 1,500 m best pace, first alone and then directly behind a lead swimmer at distances of 0, 50, 100 and 150 cm. In every drafting position, oxygen uptake, heart rate, blood lactate, perceived exertion and stroke rate were significantly lower, and stroke length was longer, than when swimming alone. Passive drag fell by about 21% right on the leader's feet and about 20% at 50 cm.

A 2008 computational fluid dynamics study by Silva and colleagues modelled how this changes with distance. The trailing swimmer's drag was about 56% of the leader's at 0.5 m behind, rising to about 84% at 6 m, and only matched the leader's beyond about 6.5-9 m. So drafting benefits fall off with distance, but don't disappear immediately.

And it carries over to the bike

Delextrat and colleagues (2003) tested whether swim drafting affects the bike. Eight well-trained male triathletes swam 750 m at competition pace, in a wetsuit, either alone or in a drafting position, then cycled for 15 minutes at 75% of maximal aerobic power. Cycling efficiency was 4.8% higher after the drafting swim, which the authors linked to the lower relative intensity of the drafting swim. The authors highlighted "the advantage of drafting during the swimming portion of a sprint triathlon."

Eight men, a lab protocol and submaximal cycling isn't the same as a race. But the mechanism is clear. A cheaper swim leaves you fresher for the bike.

A real-world estimate

The most interesting age-group evidence comes from an unexpected source. A 2025 analysis by Reichel used Austrian triathlon results from 2010 to 2024, about 168,000 results from roughly 29,000 athletes, and inferred swim groups from athletes exiting the water within a few seconds of each other. In 2020, COVID rules introduced staggered starts that broke up swim packs, creating a natural experiment.

The analysis estimated an overall drafting benefit of about 24 seconds. That benefit became statistically insignificant in 2020, when packs were broken up, and partly returned afterwards. Important caveat: this is a preprint that hasn't been peer reviewed, and inferring groups from exit times is an approximation. But it's one of very few estimates of swim drafting's effect in real age-group races, and it points the same way as the lab studies.

Why swim fitness matters for drafting

Here's the link that's easy to miss. You can only draft off someone you can keep up with. If your swim fitness puts you at the back of a slower group, you'll be drafting a slow swimmer, or no one. If it lets you hang onto the feet of a stronger group, you get the drafting benefit and exit with athletes who are likely stronger on the bike too. That's an inference, not a tested finding, but it's why swim fitness and swim pack position compound.

Part 2: being "with" the group on the bike

This is the question many age-groupers ask from experience: once you're out of the water with stronger athletes, does riding legally among them help? There's no study of this in non-drafting triathlon. But there's a body of research on competitor effects in cycling that's directly relevant.

Competitors make you faster, sometimes

Williams and colleagues (2015) had 15 male competitive cyclists complete 16.1 km time trials on an ergometer under different conditions, including one where they raced an on-screen avatar they believed was a similar-ability rider (actually their own best previous performance). With the competitor present, they finished in 27.8 minutes, against 28.7 minutes racing their own avatar and 28.4 minutes with no display. Power output was higher, but perceived exertion was unchanged, and riders reported less attention on internal sensations. The authors concluded the competitor provided an external distraction that deterred perceived exertion.

Konings and colleagues (2016) had 12 cyclists complete 4 km time trials alone or against a virtual opponent who either started fast and faded, or started slow and finished fast. Both opponent conditions were faster than riding alone (about 385 seconds against 391 seconds), and riders started more aggressively when an opponent was present. A faster-starting opponent pulled their early power higher.

A 2018 review by Konings and Hettinga in Sports Medicine drew on 75 studies and concluded that the behaviour of opponents is "an essential determinant" of how athletes regulate effort. But it also found that the response depends on the competitive situation and the athlete's internal state.

There's an important limit. Wood and colleagues (2020) found that a virtual competitor had no effect on pacing or performance in 1 km time trials lasting about 90 seconds. Competitor effects seem to emerge in longer efforts, the kind of durations a triathlon bike involves, but they aren't universal.

What that suggests for a non-drafting bike

Now the logic, labelled clearly as TriForward's inference, not a finding:

• A reference pace. Riding legally among athletes of similar or slightly higher ability gives you a constant, external indication of what's possible, which can stop you drifting into a comfortable, slower effort over a long bike leg.
• Less attention on discomfort. The Williams finding, faster with unchanged perceived effort and less internal focus, suggests that having others to race against can make the same effort feel more manageable.
• Information. You see how others ride hills, wind and technical sections, which can help pacing decisions.
• Motivation. Being "in the race" with a group, rather than alone on an empty road, is motivating for many athletes. The Konings review suggests opponents shape effort regulation.

Passing and re-passing within draft rules effectively means a loose group of riders who keep each other honest. That's the "pull each other along" effect many age-groupers describe.

The cost: surges

This effect has a downside, and TriForward has covered it in detail in the bike articles. In "Smooth Beats Surgy" and "The W′ Bank," the evidence showed that variable power, with repeated surges above threshold, costs more energy than steady riding at the same average and can damage your run.

Passing within the rules often means a short, hard effort to get through the draft zone. If a group is passing and re-passing constantly, those surges add up. The Konings study also showed that a faster-starting opponent pulls your early power higher. That's exactly the overpacing risk in the first 20 minutes of a triathlon bike.

The practical balance:

• Use the group as a reference, not a target to match. If someone passes you, you don't need to pass back immediately.
• Pass decisively, then settle. Make the overtake efficient, then return to your planned power or effort.
• Watch your power or effort early. The first part of the bike is where competitor effects most easily turn into overpacing.
• Know when to let a group go. If staying with them requires repeated surges well above your plan, the run cost is likely to outweigh the bike gain.

Who benefits most?

This is inference, but it seems likely that the effect matters most for athletes whose bike is relatively strong compared with their swim. Those athletes usually exit the water among weaker cyclists, then spend the bike passing people alone. A better swim moves them into a group closer to their bike ability, where the competitor effect and reference pace are most useful.

Athletes whose swim is relatively strong compared with their bike may face the opposite problem: exiting with riders who are stronger on the bike and being tempted to overcook it trying to stay with them.

Part 3: getting into the right group

Practical steps that help you exit with a stronger group, reasoned from the evidence above:

• Improve swim fitness and efficiency. This is the foundation. See "Six Months, Same Pace" and "Critical Swim Speed."
• Start position. In mass starts, start where you can realistically hold position, rather than at the back out of caution or at the front out of optimism. If crowded starts make you anxious, a side position is a reasonable compromise.
• Rolling starts. Many age-group races now seed by predicted swim time. An honest, slightly ambitious seeding gives you the best chance of finding feet.
• Learn to draft legally. Practise swimming on someone's feet and at their hip in group swims. The lab data suggest staying within about 50 cm of the feet gives the biggest benefit.
• Sight efficiently. Efficient sighting keeps you on the group's line. TriForward's article on sighting covers the physiology.
• Don't burn matches to make the group. Peeling and colleagues (2005) found that swimming flat out made the following bike slower in nine male triathletes. Chasing a group beyond your means in the swim can cost more on the bike than the group gives back. See "Swim Easy, Bike Faster?"
• Fast, calm T1. Groups break up in transition. A smooth T1 keeps you with yours.

Rolling starts change the picture

Many age-group races have moved from mass starts to rolling or wave starts, often seeded by predicted swim time. That changes how groups form, and the Reichel preprint gives a hint of how much. When 2020 staggered starts broke up swim packs, the estimated drafting benefit largely disappeared, then partly returned once racing normalised.

TriForward's inference from that: in a rolling start, the group you exit with is shaped more by where you seed yourself than by your swim ability alone. If you seed too far back, you'll spend the swim passing slower swimmers with no feet to follow, and exit among athletes slower than you on the bike. If you seed much too far forward, you'll be swum over and may overcook the first few hundred metres trying to hold on. An honest seed, perhaps slightly ambitious if your swim has improved, gives you the best chance of finding feet and exiting with athletes of a similar level.

In wave starts by age group, your group is fixed in advance, so swim fitness and positioning within your wave matter more.

Practising the pack effect in training

You can rehearse most of this before race day:

• Group swims. Practise swimming on feet and at the hip in open-water group sessions with appropriate safety cover. Getting comfortable with contact and close proximity is half the skill.
• Swim-to-bike bricks. A hard-ish swim followed straight away by a bike lets you learn what your legs feel like coming out of the water and how quickly you can settle to your planned effort.
• Legal-distance group riding. On a safe, quiet route, practise riding with a training partner at legal draft distances, taking turns to pass and settle. This builds the habit of passing decisively and then returning to your own effort, rather than surging repeatedly.
• Pacing discipline drills. In some rides, deliberately let a faster partner go early and hold your planned power. Learning to ignore a competitor when you need to is as useful as learning to use one.

What we don't know

No study has tested whether exiting with a stronger group improves age-group bike or overall performance in non-drafting racing. The competitor-effect research used small samples of mostly male cyclists in laboratory time trials lasting minutes, not hours. Draft-legal group dynamics in real races, including how often passing surges happen and what they cost, haven't been measured. The real-world swim drafting estimate comes from a preprint. This article's conclusions are best read as well-reasoned hypotheses, consistent with the evidence available, rather than tested facts.

References

• Chatard JC, Wilson B. Drafting distance in swimming. Medicine & Science in Sports & Exercise, 2003;35(7):1176–1181. PubMed 12840639
• Silva AJ, Rouboa A, Moreira A, Reis VM, Alves F, Vilas-Boas JP, Marinho DA. Analysis of drafting effects in swimming using computational fluid dynamics. Journal of Sports Science and Medicine, 2008;7:60–66. Journal of Sports Science and Medicine record
• Delextrat A, Tricot V, Bernard T, Vercruyssen F, Hausswirth C, Brisswalter J. Drafting during swimming improves efficiency during subsequent cycling. Medicine & Science in Sports & Exercise, 2003. doi:10.1249/01.MSS.0000084422.49491.2C
• Reichel F. Using Covid-19 response policy to estimate open water swim drafting effects in triathlon. arXiv preprint 2502.09277, 2025 (not peer reviewed). arXiv record
• Williams EL, Jones HS, Sparks A, Marchant D, Midgley A, McNaughton L. Competitor presence reduces internal attentional focus and improves 16.1 km cycling time trial performance. Journal of Science and Medicine in Sport, 2015. doi:10.1016/j.jsams.2014.07.003
• Konings MJ, Schoenmakers PPJM, Walker AJ, Hettinga FJ. The behavior of an opponent alters pacing decisions in 4-km cycling time trials. Physiology & Behavior, 2016. doi:10.1016/j.physbeh.2016.02.023
• Konings MJ, Hettinga FJ. Pacing decision making in sport and the effects of interpersonal competition: a critical review. Sports Medicine, 2018. doi:10.1007/s40279-018-0937-x
• Wood T, Bui CTL, Lubbock C, Wilson J, Jeffrey S, Lawrence M, Leung C, Mashar D, Sims N, Konings MJ, Hettinga FJ. Head-to-head competition does not affect pacing or performance in 1 km cycling time trials. Journal of Sports Sciences, 2020. doi:10.1080/02640414.2019.1674525
• Peeling P, Bishop D, Landers GJ. Effect of swimming intensity on subsequent cycling and overall triathlon performance. British Journal of Sports Medicine, 2005;39(12):960–964. doi:10.1136/bjsm.2005.020370