HED has announced the Jet 180, a new rear wheel with a 180mm deep rim.
The Jet 180 is designed specifically for athletes competing in the Ironman World Championships in Kona, Hawaii. Full rear disc wheels are prohibited in Kona due to safety concerns in windy conditions.
The 180mm deep rim has a maximum external width of 32.5mm and an internal width of 21mm.
It is tubeless compatible and available in both rim and disc brake form. Claimed wheel weight is 1229g in disc brake form or 1258g in rim brake form.
HED has yet to announce pricing, but has indicated availability is currently four to six weeks from order, with a limited number of wheels available at the 2022 Ironman World Championships in Kona.
How fast is the HED Jet 180?
That said, the goal of the wheel seems to be to mimic the rim surface area of a disc wheel as much as possible, within the limits imposed by the Kona race organizers.
The vastly increased rim surface area of disc wheels and rims like this help improve aerodynamic efficiency in two ways, depending on how the wind hits them.
In a headwind or crosswind, the deep rim or surface of a solid disc helps keep the airflow attached to the wheel for as long as possible. This reduces turbulent airflow and lowers drag.
In a tailwind or crosswind, the rim surface acts like a sail, helping to push the rider forward more efficiently.
Could this tire be used on a front wheel?
In theory yes, although for now HED only offers it as a rear wheel.
Neither the ITU (International Triathlon Union) nor the UCI (Union Cycliste Internationale, cycling’s world governing body), impose a specific restriction on the depth of the front tire in individual time trials.
However, Britain’s time trial governing body, the CTT, puts a limit on the depth of the leading edge. Its rules state that a front wheel “must have at least 45 per cent of the surface area open”, although it is unclear how this would be measured in an event.
Regulations aside, though, the main issue holding people back is probably driving concerns.
A super deep rim may well theoretically be faster than a shallower one (all things being equal), but if it prevents you from confidently maintaining an optimal aero position on the bike because it keeps catching the wind, then it will probably be slower overall.
However, today’s wider and more sophisticated rim profiles generally offer vastly improved handling characteristics compared to the tires of the past.
As a result, time trial and triathlon specialists routinely strive for incremental gains.
Aerocoach’s AEOX Titan front wheel, which has a 100mm deep rim, has been widely used by some of the world’s top TT specialists in recent years, such as Filippo Ganna, Geraint Thomas and Wout van Aert.
Rumors have even circulated that at least one World Tour Team has tested a disc front wheel for road time trial use, and hasn’t ruled out the possibility of using it in a race scenario.
So if HED were to make this tire available for use as a front wheel, you can be sure it would spark some interest among fringe-profit hunters.