What are the benefits of high-sided arm rests for triathlon?
What are the benefits of high-sided arm rests?
High-sided arm rests give your forearms a wall to brace against, so you hold the position you were fitted in for the whole bike leg. By AeroGain's in-house calculation for a rider at CdA 0.23 m² and 200 W on a flat 180 km course, losing that position costs between 8 and 17 minutes at the same fitness.
The arm rest does not make the position itself more aero. Its value is in what it protects. On flat arm cups or aero bar elbow pads, the forearm rests on top and the shoulders do the holding. As they tire, the forearms drift outwards, the shoulders widen and the head comes up. A high-sided arm rest gives the outside of the forearm a raised wall: the forearms rest into it rather than on it, the shoulders stay narrow, the head stays tucked, and the position you tested is the position you still ride at hour four.
How much time do you lose by sitting up?
On a flat 180 km course, sitting up one minute in every ten costs 9 to 11 minutes, and riding the second half on the base bar costs 17 minutes, at the same average power. This is AeroGain's in-house calculation from the guide 8 Ways to be Aero, for a rider at CdA 0.23 m² and 200 W with a 4 h 44 min baseline split; calculated, not measured.
Change only how well the position holds:
- Shoulder tension. Small posture changes every few minutes: the shoulders rise and widen, the head lifts, then the rider settles again. Over the ride that adds 8 to 10 minutes.
- Sitting up to recover. One minute in every ten sitting up, with power dropping to about 100 W while you do. Counting both the extra drag and the lost power, that adds 9 to 11 minutes.
- The position collapses at halfway. Aero for the first 90 km, on the base bar for the second 90 km, with the same average power throughout. That adds 17 minutes.
None of these riders is less fit than the one who holds the position. The time is lost to drag, not to the legs.
Why can't more power make up for it?
Because sitting up raises drag far more than training raises power. In AeroGain's in-house calculation, holding 38 km/h on the base bar takes 273 W instead of the 200 W the same rider needs in the aero position.
The rider is most of the drag on a triathlon bike; as a rule of thumb, about 80 % of it. So when the body changes shape, the whole bike-and-rider system changes with it. Sitting up on the base bar raises CdA from 0.23 m² to around 0.33 m².
The smaller losses work the same way. The 8 to 10 minutes of shoulder tension equal riding the whole 180 km with an average CdA of about 0.25 instead of 0.23: a position roughly 10 % less aero, without the rider ever leaving the extensions.
Do high-sided arm rests make you more aero?
Not on their own, and AeroGain claims no watt figure for them. They help you hold the aero position you already have, which in AeroGain's in-house calculation for a 180 km flat bike leg at 200 W is worth 17 minutes when the alternative is the base bar for the second half.
They also do not replace position training. A position that was never trained to last five hours will still fade. The arm rest takes load off a position that is already close to holding.
How wide should TT arm rests be?
Wide enough that you can tuck your shoulders in and stay in the aero position. If it becomes so uncomfortable that you have to come out of position, go wider.
Narrow is faster only if the shoulders can be held narrow; too narrow, and the shoulders tilt out, the head rises and the whole shape gets worse.
A slightly wider arm position with the head properly tucked between the shoulders is then faster. On the Aero Cockpit, the three standard sizes are set by arm pad width (S 20 cm, M 24 cm, L 28 cm), and our advice is the same: when in doubt, go a size wider.
Arm cups, arm pads or high-sided arm rests: what is the difference?
Arm cups (or arm rests) are the rigid shells that bolt to the aerobar; arm pads (aero bar elbow pads) are the foam or neoprene layer inside them; a high-sided arm rest is an arm cup with a raised outer wall. AeroGain claims no aero gain for any of the three; the difference is how well each lets you hold the position.
- Standard arm cups are shallow: the forearm rests on top, and the shoulders keep it in place.
- Arm pads are the replaceable layer. Our spare pads are neoprene, in TRI and UCI lengths, and fit the high-sided arm rests.
- High-sided arm rests add the wall the forearm braces against. The AeroGain High-Sided Armrest comes in a 124 mm UCI-compliant length and a 140 mm triathlon length.
A high-sided arm rest is the natural upgrade from standard arm cups: it gives some of the position-holding benefit of the Aero Cockpit without changing the cockpit. The full range, including the dual-sided arm rest, is in the arm rests collection.
How do you hold the aero position for a full bike leg?
Choose a position you can hold, train it, and remove the reasons to leave it. In AeroGain's in-house calculation, the difference between holding and losing the position on a flat 180 km course at 200 W is 8 to 17 minutes.
- Choose a position you can hold, not your fastest twenty minutes. Lower is not always faster in a long race. A slightly higher position you hold for 180 km beats a lower one you abandon at 90.
- Train it. Long rides on the extensions, all season, watching whether the position fades in the last third.
- Brace through the forearms. Give the forearms a wall to rest against, so the shoulders stabilise instead of carry.
- Drink without sitting up. A bottle between the arms is reachable from the position, and the mount itself made riders faster than no bottles: a median of 8 W at 45 km/h in AeroGain's 35-rider velodrome test. See the best bottle position on a triathlon bike.
- Check yourself late in the ride. Shoulders still, few adjustments, no posture change in the second half: then the position is working.
More on training the position: how to hold your aero position for a full Ironman bike leg.
How did we calculate the minutes?
The three scenarios come from AeroGain's guide 8 Ways to be Aero and were recalculated in-house for this article with a model of a flat course with no wind, a rider at CdA 0.23 m² and 200 W. They are back-of-the-envelope calculations, not measurements: drivetrain power × 0.97 = ½ × air density × CdA × speed³ + rolling resistance × mass × g × speed.
| Input | Value |
|---|---|
| CdA in the aero position | 0.23 m² |
| Average power | 200 W |
| Distance | 180 km, flat, no wind |
| Air density | 1.2 kg/m³ |
| Rider and bike | 85 kg |
| Drivetrain efficiency | 97 % |
| Rolling resistance (Crr) | 0.0036, set so the baseline split is 4 h 44 min (38.0 km/h) |
| CdA on the base bar or sitting up | 0.33 m² (assumption) |
Position collapses at halfway: 90 km at 38.0 km/h, then 90 km at 200 W with a base-bar CdA of 0.33 m² (33.9 km/h). Result: 17 minutes added. Sitting up one minute in ten: nine minutes at 200 W in position, one minute at 100 W sitting up, simulated second by second including slowing down and getting back up to speed. With a sitting-up CdA of 0.33 m² the result is about 9 minutes; the guide's figure of about 11 minutes corresponds to a more upright posture (CdA about 0.42 m², typical when sitting up to drink or stretch). Shoulder tension: 8 to 10 minutes is the guide's estimate; it equals an average CdA of 0.251 to 0.257 m² over the ride.
FAQ
What are the best arm rests for a triathlon bike?
The ones that let you hold your fitted position for the whole bike leg. Look for a raised outer wall to brace the forearm against, a length that suits your racing (124 mm for UCI events, 140 mm for triathlon) and a mount that fits your aerobar.
Are high-sided arm rests UCI legal?
The 124 mm version of the AeroGain High-Sided Armrest is the UCI-compliant length. The 140 mm version is made for triathlon and is not for UCI racing.
Will high-sided arm rests fit my aerobar?
They mount with two bolts in the standard two-bolt arm rest pattern used by most aerobars. If in doubt, ask us with your aerobar model before ordering.
