The 100% S3 Photochromic sunglasses are the closest I have found to one pair of riding glasses for the whole year. They work on bright open trails, in deep woodland and through the awkward patches where sunlight and shadow alternate every few metres.
The photochromic lens changes quickly and, more importantly, gets the useful part of the transition right. It stays clear enough to read roots and ruts beneath the trees, then adds enough tint when the trail opens up and the sun appears.
Comfort and stability are just as convincing. The S3 sits securely behind the ears, stays in place on rough ground and provides the broad field of view expected from a modern shield-style lens. After riding them across changing UK conditions, I cannot find a meaningful performance weakness.
They are now my first choice for year-round mountain biking and deserve a place alongside the strongest options in our best MTB sunglasses guide.
100% S3 Photochromic sunglasses
From £114.99
Pros
Excellent photochromic response across sunlight and deep woodland
A genuine one-lens option for year-round MTB riding
Comfortable and secure behind the ears
Wide, clear field of view
Good coverage from wind, dust and trail debris
Cons
No significant performance fault found during testing
Premium price compared with basic clear or fixed-tint riding glasses
Specifications
Frame: Polished Translucent Grey TR90
Lens: Rose Gold Mirror Photochromic polycarbonate shield
Light transmission: 84–26%
UV protection: UV400
Lens design: 5.5-base cylindrical shield with 360-degree field of view
Lens treatment: Hydrophobic and oleophobic coating
Fit: Ultra-grip rubber nose and temple tips
Ventilation: Lower lens air scoops
Included: Hard case, microfibre cleaning bag and alternative nose pads
100% S3 Photochromic sunglasses review
The version tested here is the 100% S3 in Polished Translucent Grey with a Rose Gold Mirror Photochromic lens. The S3 uses a large single shield, a lightly framed upper edge and open lower section, with intake vents influenced by the 100% Speedcraft.
On paper, that gives it the ingredients expected from premium performance eyewear: a flexible TR90 frame, impact-resistant polycarbonate lens, full UV protection and coatings intended to shed water, dirt and oil. The reason to buy this particular version, however, is the photochromic lens.
Photochromic lens performance
The S3 handles rapidly changing light exceptionally well. Riding from an exposed section into dense woodland can make a heavily tinted lens feel too dark, while a clear lens can leave you squinting when the trail breaks back into sunlight. The Rose Gold Photochromic lens manages both situations without demanding a stop or a lens change.
The transition feels quick enough that I never found myself waiting for the lens to catch up. It cuts through bright sunlight and shadow while preserving the trail detail needed to spot roots, braking bumps and changes in surface texture.
That matters on an eMTB because speed can build quickly between shaded and exposed sections. The S3 reduces the visual interruption, allowing attention to remain on line choice rather than whether the lens is too light or too dark.
Comfort and secure fit
The S3 is comfortable from the start. The nosepiece sits cleanly without creating an obvious pressure point, while the rubberised temple tips grip securely behind the ears.
That hold is one of the strongest parts of the glasses. They stay settled when the trail becomes rough and do not need to be pushed back into position after repeated hits, braking bumps or faster descents.
Secure does not mean tight. The frame has enough flexibility to feel natural rather than clamped, and the temple shape worked well with an MTB helmet during testing.
Coverage and trail visibility
The large cylindrical shield provides a broad, uninterrupted view. There is very little frame in the rider’s eyeline, which helps when looking through corners or scanning further down a technical section.
Coverage is generous across the front and sides. That keeps wind away from the eyes at speed and adds useful protection from dust, insects and small pieces of trail debris without moving all the way to an MTB goggle.
The lower vents help air move across the lens. I would still judge fogging by temperature, effort and helmet fit, but the physical ventilation is sensibly placed for trail riding.
One pair for the whole year
The main advantage of the 100% S3 Photochromic is simplicity. There is no need to choose a dark lens before a bright ride, carry a clear spare for the woods or accept a compromise when the weather changes halfway round.
For UK mountain biking, where one ride can move from open sunshine to heavy tree cover and flat grey light, that makes the S3 unusually easy to recommend. The lens range is useful enough that these can remain the default riding glasses across the seasons.
What is not so good?
I did not find a meaningful performance problem with the 100% S3 Photochromic during testing. The lens, comfort and stability all did exactly what I wanted from year-round MTB glasses.
The price is the only obvious barrier. There are cheaper photochromic glasses that work well, and riders who only go out in one predictable light condition may not need to spend this much. The large race-style shield is also a matter of taste, while face and helmet fit are always personal with eyewear.
Final verdict
The 100% S3 Photochromic sunglasses are the best one-lens solution I have used for year-round mountain biking. They adapt quickly, make it easier to read the trail through alternating sunlight and shadow, remain comfortable and grip securely behind the ears.
I went into the test looking for the usual compromise between a lens that works in the woods and one that works in bright sun. I did not find it. For my riding, the S3 gets both sides right and is as close to perfect as MTB glasses currently come.
100% S3 Photochromic sunglasses
From £114.99
100% S3 Photochromic alternatives
Tifosi Moab Clarion Fototec
£89.99 (RRP £109.99)
The Tifosi Moab Clarion Fototec is the strongest lower-priced photochromic alternative. Its adaptive shield, adjustable nose and ear pieces make it easy to tune the fit, while the current price leaves a useful saving against the S3.
Choose the Moab when value and adjustability matter most. The S3 feels more premium and was more convincing as a single year-round lens in this test, but the Tifosi remains one of the best ways to get a broad photochromic shield for less.
Smith Syncline
£129.99 (RRP £160)
The Smith Syncline has an even more goggle-like shape and excellent coverage. Its ChromaPop lens provides strong contrast, and the included clear lens gives it genuine versatility when conditions become very dark.
Choose the Smith if maximum coverage and interchangeable lenses appeal. The S3 is the simpler option for riders who want one lens to manage the change from open sunlight to shaded woodland automatically.
Julbo Fury REACTIV 1–3
£163.99 (RRP £205)
The Julbo Fury REACTIV 1–3 is the premium photochromic competitor. It combines a lightweight, vented frame with a broad adaptive lens range and is particularly attractive to riders who want minimal weight and a more open frame around the lower edge.
Choose the Julbo if low weight and REACTIV lens technology take priority. The S3 costs less at current prices, grips exceptionally well behind the ears and has the stronger all-round verdict from our own testing.
100% S3 Photochromic sunglasses FAQs
Are the 100% S3 Photochromic sunglasses good for mountain biking?
Yes. They provide a broad field of view, secure fit, useful protection and a lens that adapts well as an MTB trail moves between sunlight and shade.
How quickly does the S3 photochromic lens change?
In use, the change is quick enough that the lens does not feel behind the conditions. It responds effectively when moving between exposed trails and darker woodland, although every photochromic lens changes progressively rather than like an electronic switch.
Can the 100% S3 Photochromic be used all year?
Yes. That is its strongest quality. The 84–26% light-transmission range covers dark and overcast riding as well as much brighter conditions, making it a convincing one-pair option for UK MTB riding.
Do the 100% S3 sunglasses stay secure on rough trails?
They stayed securely in place during testing. The rubber temple tips grip well behind the ears, while the flexible frame remains comfortable rather than feeling excessively tight.
Do the 100% S3 Photochromic sunglasses come with a case?
Yes. This version is supplied with a hard case, microfibre cleaning bag and alternative nose pads. Package contents can vary between lens and model-year options, so check the retailer listing before ordering.
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