SHIMANO RC903 vs. TR903 According to Kristian Blummenfelt and Gustav Iden
Photos: Santara Studios / Clara Hilger
When it comes to selecting the right SHIMANO shoe for triathlon, the question isn’t simply which is best, but rather which is best for you. The S-PHYRE RC903 road shoe and the S-PHYRE TR903 triathlon shoe represent the pinnacle of cycling footwear, each designed with unique features to match different athlete preferences and racing demands.
No two riders illustrate this better than Kristian Blummenfelt and Gustav Iden, two standout athletes from Bergen, Norway. Over the last decade, the pair have dominated professional triathlon – both winning IRONMAN and 70.3 World Championships – while building a reputation for their fierce on-course battles and their off-course camaraderie. Together, they’ve pushed the limits of the sport and shared insights into their training and racing approach, often through their engaging Norwegian Method podcast.
Yet even as training partners and rivals, their equipment choices reflect their individual racing styles. Both athletes trust SHIMANO to deliver the performance needed for world-class results, but each gravitates toward a different shoe: Blummenfelt favors the TR903 for triathlon-specific speed and transitions, while Iden prefers the RC903 for its road-focused stiffness and precision fit.
Like the athletes themselves, both shoes sit at the very top of their game. Each delivers distinct advantages, whether in pure power transfer or seamless transition efficiency, that can make the difference between a strong finish and a podium result.
Kristian’s Preferred IRONMAN Triathlon Shoe: The S-PHYRE TR903
For the 31-year-old Olympic and World Champion, the S-PHYRE TR903 triathlon shoe is his go-to footwear across every race distance. From sprint courses through full IRONMAN events, Blummenfelt relies on the performance, comfort, and transition efficiency of SHIMANO’s premium triathlon shoe.
“I use the tri shoes because I simply find them very easy to get in and out of. I like to use the same shoes for both short-course and long-distance, and in training as well. It’s good to train and race with the same equipment.”
That consistency is only part of the appeal. Blummenfelt points to the closure system – a combination of a single BOA dial and an oversize strap – as the ideal solution for quickly dialing in a precise fit.
“I really like the combination of the BOA and the strap because I can also tighten it up and get the exact tightness I want. I usually don’t touch that on race day. The Velcro is very easy to give it a tight fit around the foot. Half a second to tighten as much as I want.”
SHIMANO specifically engineered the closure of the TR903 to balance lightning-fast transitions with on-the-fly adjustability. The result: security, precision, and control in one seamless system.
“There’s a lot of technology going into the shoe that’s helped me in races. The bottom of the shoe is top of the line, very comfortable and stiff, which helps me put down the power that’s needed. It has good support too, not just a stiff bottom unit, it is very comfortable and supportive.”
What Blummenfelt describes is SHIMANO’s DYNALAST construction, a proprietary shaping that improves efficiency, reduces muscle fatigue, and enhances comfort mile after mile.
Key Highlights of the TR903
- Built for Triathlon, Excels in Transition – Oversized strap with reverse cinch design clears crank arms and allows pedaling with strap fully open.
- Single BOA Dial – Adds secure hold and volume control to reduce power loss on both short and long rides.
- Sock-Free Drainage and Ventilation – Mesh toe box, perforations, and sole drain holes keep feet cool and comfortable, even barefoot out of the swim.
- Transition-Optimized Heel Loop – Oversized, rubberized, and notched for easy grabs and rubber band setup in T1.
- Expanded Sizing – Available up to size 50 (US 15), offering a larger fit range than the RC903.
Gustav’s Preferred IRONMAN Triathlon Shoe: The S-PHYRE RC903
For the cycling leg of IRONMAN races, the 29-year-old three-time triathlon world champion favors the S-PHYRE RC903 road shoe. His reason is simple: fit and performance.
“For the IRONMAN, the cycling shoe is perfect. It has good stiffness and great comfort.”
The RC903 is SHIMANO’s stiffest cycling shoe, anchored by a carbon outsole and anti-twist heel cup. DYNALAST shaping locks the foot in place, reducing power loss and fatigue, while its optimized toe spring decreases tension in feet, calves, and hamstrings. The payoff is more efficient pedaling and more energy saved for the run.
Iden also points to the dual BOA closure system, which offers unmatched adjustability.
“Double BOA is very easy to adjust midway through. I can ride for some time without closing the straps, and that is good in the start. I like to ride with shoes open at first then tighten when I have better time later in the race about 10 minutes into the bike leg.”
For shorter races like sprints, Iden switches to the TR903, prioritizing faster transitions. Unlike Blummenfelt, he’s comfortable switching footwear between disciplines depending on the race demands.
Key Characteristics of the S-PHYRE RC903
- Dual BOA Closure – 360-degree surround wrapping fit proven across grand tours and one-day classics. Virtually eliminates foot movement for efficient power transfer.
- Enhanced Airflow and Drainage – Perforated synthetic leather upper and ventilated sole provide cooling and durability, with added drainage for wet rides.
- Exceptional Stiffness – SHIMANO’s stiffest sole (stiffness index 12) maximizes pedaling efficiency, delivering long-distance gains over the IRONMAN bike leg.
The Best of Both Worlds
From local triathlons to world championship races, both the RC903 and TR903 represent the very best in cycling footwear. Blummenfelt trusts the TR903 for its transition-ready triathlon design, while Iden relies on the RC903’s unmatched stiffness and all-day comfort.
Whether you’re chasing seconds in T1 or powering through an all-out bike leg, SHIMANO’s S-PHYRE shoes help you ride faster, run stronger, and reach the finish line at your best.
