Introduction: Why This Blog Exists
The Atomic Redster STI 150 is not designed to be comfortable out of the box. It is designed to win races.
With an extremely narrow last, aggressive stance, and a high flex rating, this boot demands a precise, methodical fitting process. For most skiers—even experienced ones—putting an STI 150 on for the first time is a shock. For me, it was clear within seconds that these boots were nowhere close to fitting my feet out of the box.
As a boot fitter and aspiring ski racer, I decided to make these boots my project for the ski season. I am used to generous fitting mid-volume boots that need to be modified to fit my wide feet. The Atomic STI 150 at a 26.5 has a 93 mm last, much more narrow than my 108 mm right foot...
This blog is a living journal documenting every step of the fitting process required to turn a raw World Cup–level race boot into a functional, high-performance tool. Nothing is skipped. Nothing is sugar-coated.
I’ll be sharing:
-
Initial fit analysis
-
Pain points and movement limitations
-
Punching, grinding, and shell shaping
-
Liner work and modifications
-
Stance and alignment adjustments
-
On-snow testing and feedback
-
What worked, what didn’t, and what changed
Photos and videos will be added throughout the process.
This is not a guide for beginners. It’s an honest look at what it actually takes to fit an elite-level ski boot—and why professional boot fitting matters more than any spec sheet.
Boot Fit Update #1 - Unboxing
Date: January 2, 2026 | Location: The Pro Ski and Ride | Time Spent: .25 hours
The first step was to unbox the ski boots and take a look at all of he optional accessories. The Atomic Redster STI 150 comes with laceup WC liners, laces, volume reduction shims, spoilers, and additional bolts. Out of the box, I removed the spoilers to allow for room for my calves and added the laces to the liners to promote more shin contact in the front of the boot. The boot is already tight and stiff so there is no need for shims or additional bolts at this time.
Boot Fit Update #2 - Footbed Modification
Date: January 2, 2026 | Location: The Pro Ski and Ride | Time Spent: .25 hours (.5 hours total)
For these boots, I decided I would use a pair of Sidas carbon fiber footbeds I had a colleague previously cast for me. These were used for testing in a previous pair of boots. Although they were made for a narrow race boot, they needed to be ground significantly more narrow and have the heel cup reduced to fit properly in these boots.
Boot Fit Update #3 - Routering
Date: January 2, 2026 | Location: The Pro Ski and Ride | Time Spent: .25 hours (.75 hours total)
VIDEO COMING SOON!
The Atomic Redster STI 150 ski boots come with a solid sole that has a built in 5 mm lifter. Out of the box, these boots cannot be used in a ski binding without modification. To prepare these for use, the heels and toes must be routed to confirm with DIN height standards to proper safely in an alpine ski binding.
After some setup, I flattened the sole of the ski boot on a belt sander since there was some rock in the sole out of the box. With the soles flat, I routed both heels and toes. After confirming the heights were correct, I used a Foredom flapper to lightly sand the bevel on the heels and toes to take away the sharp edge, making it less likely to get damaged by bindings.
Boot Fit Update #4 - Initial Try On
Date: January 2, 2026 | Location: The Pro Ski and Ride | Time Spent: .25 hours (1 hour total)
Boot Fit Update #5 - Heat Molding and Buckles Moved
Date: January 2, 2026 | Location: The Pro Ski and Ride | Time Spent: .25 hours (1.25 hours total)
Last items on the agenda for the night were to heat mold the liners and the ladders over on the cuff. Although this ski boot has a thin liner, there is still some heat moldable material that will help things feel slightly better than the boot out of the box.
Standing in a skiing position during the cooling process produces the best results.