RAD Synth Review | Good for Short Runs and HYROX Sessions?

When RAD launched into the running shoe market, models like the Mallow and high-stack UFO runner captured a lot of initial attention. However, the RAD Synth has quietly risen through the ranks as a strong lightweight daily trainer available for athletes who love fast-paced running and hybrid conditioning workouts.

Positioned directly against high-tempo daily trainers like the Adidas Adizero Evo SL, the Synth brings a versatile, lively underfoot ride paired with a highly breathable upper and a sticky, full-coverage herringbone outsole.

After putting the RAD Synth through 5Ks, tempo runs, hill speed sessions, curve treadmill intervals, and HYROX-style workouts, here is the full breakdown of where this shoe excels and where it falls short.

Who Should Buy the R.A.D. Synth?

• Interval & Tempo Runners: If you prioritize a lightweight (8.2 oz), responsive shoe for 5Ks, interval speedwork, hill reps, and curve treadmill runs.
• Hybrid & HYROX Athletes: If you want a fast, grippy “cost-efficient” daily trainer that seamlessly transitions between running splits, sled pushes, and station work.
• Hot-Climate Runners: If you train in hot environments and need an ultra-breathable mesh upper that keeps your feet cool and breaks in instantly.

Who Shouldn’t Buy the R.A.D. Synth?

• Slow, High-Mileage Long Distance Runners: If you need an ultra-plush, highly cushioned max-stack shoe for slow 10+ mile recovery runs, options from RAD like the Mallow or UFO Runner will suit you better, or options like the Nike Vomero 18 or On Cloudmonster 3.
• Excessive Overpronators: If you require rigid medial post support or a heavy stability chassis, these may not give you the stability and support you want.
• Technical Trail Runners: If you regularly run on harsh, technical single-track trails that require heavy upper armor and rock-plate protection.

Sizing and Fit Suggestions

About My Feet: I have a normal arch/instep and my feet come in at an E/EE width. The length of my left and right foot are consistent with one another, and I size as a true US 10 for most companies’ sizing charts.

The R.A.D. Synth should fit true to size for most runners and lifters. I went with my standard US Size 10, which left just under a thumb’s width of space at the end of the toe box—the ideal sweet spot for running shoes.

• Standard D-Width & Medium Feet: Go true to size. You can expect a secure midfoot lockdown and an athletic, form-fitting feel.
• Slightly Wide Feet (2E Width): Stick true to size. While the forefoot has a slight athletic taper, the lightweight mesh upper stretches forgivingly without causing uncomfortable lateral pressure.
• Extra Wide Feet (3E+ Width): Consider going up a half-size to avoid feeling squeezed across the pinky toe, especially if you prefer ultra-wide toe boxes like those found in Altra or Topo Athletic

Performance Quick Hits

I’m going to do my best to separate personal preferences from this section, especially since midsole responsiveness, outsole bite, and upper volume handle very differently depending on your running style and training goals.

• Best For: Fast 5Ks, tempo runs, interval workouts (curve treadmills/hills), HYROX-style training sessions, and short-to-mid distance daily training (3–4 mile bouts).
• Running Paces: Thrives at faster clips (6:30–9:00/mile paces) and rapid interval pickups.
• Underfoot Feel: Lively, responsive SwellFoam midsole with a smooth bevel, natural toe spring, and a balanced 6mm drop.

High-Speed Interval Runs (8.8/10)

For fast interval sessions—especially on curved treadmills or slight-incline road hills—the R.A.D. Synth is absolute money. The combination of its 38mm heel / 32mm forefoot stack height and well-tuned toe spring gives forefoot and midfoot strikers a seamless, energetic roll-through.

When sprinting at top speed, the SwellFoam provides fantastic pop off the deck without feeling squishy or causing you to bottom out. It has quickly become one of my favorite interval-focused running shoes for curve treadmill work and hill reps where rapid foot turnover is key.

Short and Mid-Range Tempo Runs (3–5 Mile Bouts): 8/10

Across 3-to-4 mile runs ranging anywhere from 6:30 fast clips to 8:30–9:00 average training paces, the Synth feels exceptionally balanced. The 6mm drop provides enough heel stack to catch you when decelerating, but stays low enough in the forefoot to offer a connected ground feel.

I tested these heavily on varied road inclines, declines, and gravel paths. Unlike the Adidas Adizero Evo SL—which can feel a bit flimsy and sparse underfoot—the Synth’s sticky herringbone rubber tread bites into concrete and loose gravel with complete confidence. The smooth heel bevel and toe geometry keep your knees feeling fresh across varied terrain.

HYROX-Style Conditioning Sessions: 9/10

For HYROX workouts, short interval runs mixed with sled pushes and wall balls, the R.A.D. Synth performs remarkably well. While it doesn’t offer the ultra-rigid, flat platform of a dedicated lifting trainer like the Adidas Adizero Dropset Pro, it provides more than enough base stability and sticky outsole bite to push sleds and tackle dynamic station work.

If you are a recreational hybrid athlete looking for a fast, non-plated running shoe that can comfortably handle both your running splits and station work in a HYROX race, the Synth is a top-tier contender.

The Performance Takeaway

If you stop reading this review here, here are your core takeaways.

The R.A.D. Synth is a stellar, foolproof lightweight daily trainer that punchily outperforms competitors like the Adidas Adizero Evo SL in traction and stability. Its SwellFoam midsole delivers incredible pop and responsiveness, while the full-coverage herringbone rubber outsole provides superior bite on concrete, gravel, and curve treadmills.

If you are a recreational runner or hybrid athlete looking for an energetic, $140 option for interval speedwork, tempo runs, 3-to-4 mile bouts, or fast HYROX workouts, the Synth is an absolute home run.

However, if you are a slow-paced, heavy-heel striker looking for an ultra-plush maximalist shoe for long marathon training miles, or if you require extreme medial pronation support, you will want to look toward more structured, plush daily trainers like the R.A.D. Malo or UFO Runner.

Construction Details

Upper

The upper features an ultra-lightweight, engineered mesh that runs from the forefoot through the heel, delivering maximum airflow and rapid heat dissipation in warm climates. Light synthetic overlays reinforce the midfoot and heel eyelets for structural lockdown without adding unnecessary weight.

Padding is strategically applied around the ankle collar and heel cup, though there is no external heel tab—so be sure to unlace them fully when putting them on to avoid crushing the heel counter. The lightweight mesh tongue features a subtle internal gusset and light padding; always pull up on the tongue using both hands to prevent tearing the lightweight mesh.

Midsole

The midsole consists of a full-length SwellFoam compound sitting at a 38mm heel and 32mm forefoot (6mm drop).

This midsole geometry features a noticeable heel bevel and aggressive forefoot toe spring, engineered to promote smooth transitions and rapid turnover for midfoot and forefoot strikers.

Outsole

The outsole features full rubber coverage across the forefoot and heel with strategic flex grooves to preserve foot articulation.

Utilizing a sticky herringbone tread pattern infused with R.A.D. branding elements, this outsole delivers exceptional bite on gym floors, asphalt, curve treadmills, and gravel trails.

Final Remarks: Is the R.A.D. Synth Worth It?

The R.A.D. Synth is an exceptional lightweight daily trainer that delivers high-end performance at an accessible $140 price point. By combining a lively SwellFoam midsole with outstanding herringbone outsole traction and a breathable mesh upper, R.A.D. has crafted a shoe that easily outshines many mainstream speed trainers.

Whether you’re bombing fast interval reps, tackling 3-to-4 mile tempo runs, or preparing for your next HYROX competition, the Synth offers a fast, comfortable, and reliable ride right out of the box.

If you have additional questions about how the R.A.D. Synth fits, how it compares to the Adizero Evo SL, or how it handles specific workouts, drop a comment down below!