This helmet runs from XS to 3XL — 53 to 66 centimetres of head. That is a wider spread than almost anything else in the class, and for a rider at either end of it that single sentence outweighs every feature on the list.

Why "it will give" is wrong

A rider who measures 65 cm is routinely sold an XXL with the assurance that it stretches. It does not, and the reason is worth knowing.

A helmet has two layers inside: soft comfort padding, and behind it the EPS impact liner. The padding compresses two or three millimetres in the first hours of use and then stops. The EPS does not compress at all — not until it is crushing in a crash, which is its entire purpose. So a shell that is too small stays too small, and the pressure point it creates on the forehead or above the ears becomes a headache within the hour. A helmet that hurts is a helmet left at home, and that is a safety outcome rather than a comfort one.

Checking the fit properly

Two tests, both done with the strap fastened.

The rotation test: put a flat hand on the crown and turn. The skin of your forehead should move with the helmet. If the helmet turns and your scalp does not, it is too big. The roll-off test: take the rear edge in both hands and try to roll the helmet forward off your head. It should not come. This second one is the test most people skip and the one that matters — a helmet that leaves your head in the first tenth of a second protects nothing, and no strap setting compensates.

About the Fast C8 graphic

Gloss. The base is a saturated magenta pink, and over it runs the Fast pattern in deep violet: layered angular wedges following the shell's panel lines, with a scatter of smaller X and arrow forms breaking up the flat areas. The MT logo sits in white on the flank, and THUNDER 4 R is lettered small along the lower edge.

Pink and violet are neighbours on the colour wheel, so the pattern reads as texture at a distance and only resolves into shapes up close. That is the opposite of how the same graphic works on the red Fast C5, where the black shapes read hard from far away — same drawing, entirely different behaviour.

Speaker pockets, and why to check for them

The lining has recesses cut for the speakers of an MT-B01 Rider Sync intercom.

This is worth checking on any helmet you intend to fit an intercom to, and most product pages never mention it. Without pockets the speakers sit on top of the lining, pressed against the outside of your ear by the padding. It is uncomfortable within twenty minutes, it cannot be adjusted away, and on a long day it is genuinely painful. A helmet with pockets and one without are different objects the moment an intercom goes in.

The shell

HIRP — High Impact Resistant Polymer — MT's injection-moulded high-strength thermoplastic, at around 1,500 g.

A thermoplastic shell is heavier than carbon for the same strength and far more consistent unit to unit, because injection moulding is a repeatable industrial process where hand lay-up is not. At this price that consistency is worth more than the grams. It is also why a 3XL exists at all: a composite shell in that size would be a separate, expensive tool with low volume behind it.

The sun visor and the anti-fog insert

Two pieces of equipment cover the two ends of a riding day. An integrated shade drops from inside the shell for the light, and a Pinlock DKS435 Max Vision insert — supplied in the box, which is unusual at this price — keeps the clear screen from misting in the cold.

Together they are what lets one helmet handle a whole year without a second visor in a bag. Neither can be left at home, neither needs a stop to deploy, and the combination removes the two most common reasons a rider ends up looking through the wrong thing at the wrong time.

Purple and pink is also an unusual choice on a sport-touring shell, and it has an incidental practical effect. What a driver's peripheral vision resolves first is contrast against the background, not colour identity — and a saturated magenta against grey tarmac, hedgerow or a line of cars is high contrast in a way that black, grey and dark blue simply are not.

It is not a substitute for a fluorescent panel in flat overcast light, and it does nothing at all after dark. Reflective material on the jacket does the night-time work; a helmet colour does the daylight work.

The rest of the equipment

The MT-V-28C screen runs on the MT-M-28X mechanism, releases without tools through MT-QVSS, and carries a locking catch. Air enters through intakes MT enlarged for the R and leaves through an exhaust hidden under a reshaped spoiler. The strap closes on a micrometric ratchet.

ECE 22.06 · no DOT

Mandatory across Europe since January 2024. Compared with the 22.05: 18 impact points rather than five, several speeds, an oblique strike against an abrasive anvil measuring rotational loading, and a Brain Injury Criterion ceiling. No DOT marking is published for the Thunder 4 R.

On SHARP and the Thunder name

SHARP, the UK Department for Transport's programme, lists an "MT Thunder" and an "MT Thunder 3" at four stars. Those are earlier, different helmets. Neither the Thunder 4 SV nor the Thunder 4 R has been SHARP-tested, and it would be dishonest to let a shared name imply a rating this helmet does not hold.

The only MT model in our range with a genuine SHARP result is the Track SV. We say so on its page and nowhere else.

Buying a 3XL specifically

Two practical notes for the largest size. A bigger shell holds more lining, so wash it more often than you would a medium — there is simply more fabric doing the same job. And a larger shell has a larger frontal area, which means a little more wind pressure and a little more noise at speed than the same helmet in an M. That is geometry, not a fault, and it applies to every brand.

What it does not have

• No images of this colourway yet.
• No DOT marking published.
• No SHARP rating for the Thunder 4 R — see above.
• No tinted screen supplied.

In the box

• MT Thunder 4 R SV helmet — Fast C8, gloss, purple and pink
• Protective bag, user manual and MT Helmets stickers
• Pinlock DKS435 Max Vision insert included.

Size guide

Specification

• Model — MT-Helmets Thunder 4 R SV · Part number — 1375538C81 (XS–3XL: …03 to …09)
• Colour / finish — Fast C8 — gloss, purple and pink
• Homologation — ECE 22.06 · no DOT published
• Safety rating — none; SHARP's Thunder entries are earlier models
• Type — full-face, sport-touring
• Shell — HIRP (High Impact Resistant Polymer), approx. 1,500 g
• Sizes — XS to 3XL (53–66 cm)
• Visor — MT-V-28C on MT-M-28X, MT-QVSS release, locking catch
• Anti-fog — Pinlock DKS435 Max Vision supplied
• Sun visor — integrated drop-down
• Ventilation — enlarged intakes, reworked spoiler with exhaust
• Retention — micrometric ratchet
• Interior — removable and washable, speaker pockets for MT-B01
• Communication — MT-B01 Rider Sync prepared; no system supplied
• Manufacturer — MT Helmets, Spain
• Fitting — rotation test and roll-off test with the strap fastened, before the first ride
• Replacement — immediately after any impact, otherwise after about five years

• 1x MT Thunder 4 R SV helmet — Fast C8 — gloss, purple and pink
• 1x protective bag
• 1x user manual
• 1x sheet of MT Helmets stickers
• Pinlock DKS435 Max Vision insert supplied as standard — rare at this price