Giro Synthe II MIPS Helmet Review: A Fast All-Rounder for Race Day and Training

Overview

The Giro Synthe II MIPS is built to be a do-it-all road helmet rather than a pure aero shell — an aero-influenced shape with real ventilation, aimed at riders who don’t want to own a separate lid for hard training and race day. For triathletes splitting time between long turbo sessions and outdoor rides, that dual-purpose brief is exactly the point: one helmet, tested and comfortable, rather than switching between a heavily vented climbing helmet and a full aero TT shell.

Giro Synthe II MIPS Helmet
Giro Synthe II MIPS Road Helmet

Key Features

  • Weight — Around 270-280g in a size medium, competitive for the category without being the lightest helmet on the market.
  • Ventilation — 19 vent channels with internal air channelling and a large rear exhaust port, reviewers report it stays cool even in warm-weather riding and turbo sessions with a fan.
  • Mips integration — An integrated Mips Air Node system is paired with Giro’s “Roll Cage” — an internal structure moulded into the EPS liner — for added protection without a bulky look.
  • Fit system — The Roc Loc 5 Air retention system is consistently rated by reviewers as one of the helmet’s strongest features, holding a secure, stable fit through hard efforts.

Verdict

Testers consistently rate the Synthe II as a helmet that does everything well without excelling at any single discipline the way a dedicated aero or ultralight climbing helmet would. That’s the appeal for triathletes: you’re not buying two helmets to cover training and race day, you’re buying one that’s genuinely comfortable for a five-hour Ironman bike leg and cool enough for summer brick sessions. If you’re chasing outright aero numbers for a flat, fast 70.3 bike course, a dedicated TT helmet will still be faster — but for the other 90% of your training hours, the Synthe II is hard to fault.

Buying Tips

  • Try before you commit if possible — Roc Loc fit systems suit rounder head shapes better than some competitors’ retention systems.
  • Check for a MIPS colourway if you want the bright yellow liner as a visual reminder the system is fitted correctly.
  • Pair with a lightweight cycling cap or headband for cold early-morning rides — the vents are generous, which is great in summer but can feel draughty below 10°C.

Care and Maintenance

Rinse the padding after sweaty sessions to stop it degrading and holding odour, and avoid leaving the helmet in a hot car — UV and heat break down the EPS foam’s protective properties over time. Replace any helmet after a crash, even if there’s no visible damage.

Check price on Tredz — £189.99 at time of writing.

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