Eryri by UTMB: What It Really Takes

Eryri by UTMB — known until 2026 as Ultra-Trail Snowdonia (UTS) — is one of the most technical and demanding trail races in the UK. Based in Llanberis over a long weekend each May, it combines steep climbing, rocky descents, unpredictable mountain weather and long periods of exposure.

With distances from a punchy 25K to a full 100 miles, this is not just a fitness test. It rewards pacing, fuelling, decision-making and the ability to move well on difficult ground when you're tired. Whether you're tackling your first mountain ultra or stepping up to the 100-miler, this guide covers what each race really demands — and how to prepare, race and finish strong.

The Races at a Glance

2026 edition (15–17 May). All races start in Llanberis except the 80K, which starts in Caernarfon. The 80K counts as a 100K-category race for UTMB purposes, which is why it earns three stones.

Eryri 100M (163km / ~9,200m+)

The full tour of Eryri is relentless, technical and exposed. It's not a longer version of the other races — it's a different challenge altogether, with multiple night sections, long isolated stretches and constant changes of terrain. Managing fatigue matters as much as fitness.

• Pacing: start conservatively — this race punishes early ambition.
• Strategy: have your nutrition, kit and pacing plan rehearsed before you arrive. Allow for short sleeps (even 10–20 minutes can reset you) and practise descending on tired legs.
• Terrain: expect bog, rock, scrambling and long technical descents.
• Reality: it becomes a problem-solving exercise — nutrition, movement and mindset all need managing continuously.

Eryri 100K (106km / ~5,400m+)

A true mountain ultra — long enough to demand respect, short enough that pacing errors still catch people out. The course is technical throughout, with little chance to settle into a rhythm, so you need to stay switched on all day.

• Climbing: climb strongly but don't overcommit early — fatigue compounds quickly.
• Descending: stay controlled — this is where most of the damage is done.
• Fuelling: get it right from the first hour (see how to fuel an ultra) — problems show up fast here.
• Night running: with a 05:30 start, many runners will finish in the dark, so be confident with your head torch.

Eryri 80K (78km / ~2,500m+)

This race is deceptive. It starts on Friday evening beneath Caernarfon Castle at sea level, and the fast, runnable opening can feel relaxed — but that changes quickly. You head inland into the dark through slate country, on old quarry tracks, before the climb to Yr Wyddfa (Snowdon) and a fast descent into Llanberis.

• Pacing: control your effort on the flatter start — it's easy to go too fast without realising.
• Transition: the switch to mountain terrain is sharp, and you'll meet it already tired and in the dark.
• Preparation: practise running at night and on tired legs — it pays off massively here.
• Reality: this is a race of two halves — manage the first well to survive the second.

Eryri 50K (56km / ~3,400m+)

This is not a “fast 50K”. With 3,400m of climbing, an ascent of Yr Wyddfa and rocky slabs and narrow ridgelines on the Snowdon massif, it's a compact mountain ultra that demands respect despite the shorter distance.

• Mindset: treat it as a big mountain day, not a race you can wing.
• Climbing: long, sustained efforts — efficiency matters more than speed.
• Descending: technical, and usually where time is lost or gained. Prioritise descending skill over raw fitness.
• Poles: a big advantage on the climbs, if you've trained with them.

Eryri 25K (22km / ~1,100m+)

Short, sharp and steep — but still very much a mountain race. It's usually raced hard, which makes pacing and control even more important.

• Control: start steady — the early climbs spike your effort quickly.
• Climbing: power hiking is often faster than running the steep gradients.
• Descending: fast but technical — confidence here is where places are won.
• Intensity: effort stays high throughout, so small mistakes add up quickly.

Entry, Qualification & Logistics

Eryri by UTMB is part of the UTMB World Series, so finishing earns Running Stones for the UTMB World Series Finals lottery in Chamonix — four for the 100M down to one for the 25K — plus a UTMB Index result. Our guide to qualifying for and training for the OCC explains how stones and the lottery work.

Required experience: the 100M requires a valid UTMB Index in the 100K or 100M category, and the organisers recommend an Index of at least 380 to make the cut-offs. For the 100K and 80K they recommend a valid Index in the 50K category or above. Above all, real mountain running experience matters more than previous race results — check the official requirements before you plan your season.

Mandatory Kit

Kit is strictly enforced, with random checks at the start and penalties up to disqualification. The core list for the 50K and longer races includes:

• Waterproof jacket with hood, and waterproof over-trousers.
• Long trousers or race leggings, warm and waterproof gloves, and a warm hat.
• Head or hand torch with spare batteries — two for the 100M and 100K.
• Survival bag or emergency bivvy bag (a foil blanket is not the same thing).
• Smartphone (switched on), map of the route, compass, whistle and a self-adhesive elasticated bandage.
• Reusable cup (150ml minimum), emergency food reserve, and capacity for at least 1 litre of fluid (1.5 litres for the 100M and 100K).

The 100M and 100K also need a warm second layer and a reusable plate or bowl and cutlery. The organisers can add hot- or cold-weather kit, or remove items, up to 24 hours before the start depending on the forecast. The list changes between editions, so always use the official mandatory kit page for your year.

Preparation & Gear

Terrain Training

Expect technical trails, rocky slabs and boggy ground. Focus your training on:

• Hiking steep gradients efficiently.
• Technical descending — often the deciding factor.
• Running on uneven ground while fatigued.
• Recceing sections of the course if you can.

Shoes (Often the Deciding Factor)

This is not the place to guess with footwear. Grip, stability and confidence on technical ground matter far more than outright speed. Different brands approach this terrain differently:

• Inov-8: aggressive grip and precision — ideal for muddy, technical, fell-style ground.
• La Sportiva: built for technical mountain terrain, with a precise fit and excellent grip on rock.
• Salomon: a balance of grip, protection and durability — a solid all-rounder.
• Scarpa: durable and secure, well suited to rugged, alpine-style ground.
• Hoka: maximum cushioning for long distances — helps with fatigue on runnable sections, at the cost of some ground feel.

What actually matters: grip over cushioning, confidence on descents over comfort on climbs, a secure fit on uneven ground, and deep lugs for mud. More cushioning means less ground feel and stability. If you're less experienced on technical terrain, lean towards grippier, more stable shoes; experienced runners can trade some grip for comfort over distance. There's no perfect shoe — only the best compromise for you and the course. Non-negotiable: train in the exact shoes you'll race in.

Disclosure: Kat is an Inov-8 ambassador, and Inov-8 is one of our discount partners.

Weather

Eryri weather is unpredictable — prepare for heat, wind and rain, sometimes all in one day. Train in poor weather on purpose so nothing on race day comes as a shock.

Kit Tips

• Poles for the climbs, if you've trained with them.
• Spare socks for wet conditions — a mid-race change can be a huge boost late on.
• Foot care: tape or lubricate early — blisters end races faster than fatigue.
• Don't overpack: carry the mandatory kit and what you need, nothing more. A medium-volume vest discourages overpacking, and pairing it with a running belt spreads the load.
• Train fully loaded: practise running, hiking and descending with your full race kit.

For more on packing for a long day, see our guide to The Lap — tips for first timers.

Race Strategy

Aid Stations & Logistics

Treat aid stations as pit stops, not rest breaks: refill, grab food, check your kit and move on. On the 100K and 100M, a drop bag and a well-briefed crew are a big advantage.

Nutrition

This race exposes poor fuelling quickly. Aim for 60–90g of carbohydrate per hour, start early, mix sweet and savoury to avoid taste fatigue, and drink before you feel thirsty. Our guide on how to fuel an ultra covers targets and an hour-by-hour plan, and do ultra runners really need gels? compares gels with real food.

Coping When Fatigue Hits

At some point it will feel hard, physically and mentally. That's part of the race — the key is to respond, not react.

• Slow down before you fall apart. A short hike or easing off early can prevent a full collapse later.
• Fuel first, decide later. If things feel off, eat and drink before making any big decisions.
• Race to the next checkpoint, not the finish.
• Change something: pace, food, a layer, your posture.
• Keep moving forward. The low points almost always pass.

The runners who do well here aren't the ones who avoid fatigue — they're the ones who manage it best.

Top 5 Mistakes

1. Starting Too Fast

The early miles feel controlled, but effort creeps up and early descents do damage you feel hours later. Fix: start easier than you think you need to.

2. Underestimating the Terrain

This is a technical mountain event, not a runnable trail race — rocky descents destroy legs and bogs drain energy. Fix: train specifically for technical ground.

3. Fuelling Too Late

Waiting until you feel low is too late. Fix: fuel early and consistently from the first hour.

4. Getting Kit Wrong

Too much, too little or untested kit all create problems — and missing mandatory kit can end your race. Fix: test everything in training and check it against the official list.

5. Letting a Low Point Decide Your Race

Bad patches happen. Fix: slow down, fuel, reset — and keep moving.

Final Week

Prioritise sleep and arrive fresh, not overtrained. Check the latest kit and weather updates from the organisers, and plan your post-race transport — you may not be fit to drive.

This race rewards patience, preparation and good decisions far more than raw fitness. If you can move efficiently, fuel consistently and stay composed when it gets tough, you're exactly where you need to be.

Frequently Asked Questions

Is Eryri by UTMB the same race as Ultra-Trail Snowdonia?

Yes. Ultra-Trail Snowdonia (UTS) becomes Eryri by UTMB from 2027 — Eryri is the Welsh name for Snowdonia. The 2026 races were already branded Eryri 100M, 100K, 80K, 50K and 25K.

When is Eryri by UTMB?

Over a long weekend in May, based in Llanberis. The 2026 edition ran from 15 to 17 May; check the official site for 2027 dates.

How many Running Stones does Eryri by UTMB award?

Four for the 100M, three for the 100K and the 80K, two for the 50K and one for the 25K.

Is Eryri by UTMB beginner friendly?

Not really — even the shorter races are technical and steep, and need experience on uneven mountain ground and good pacing discipline. The 25K is the most accessible starting point.

What shoes are best for Eryri by UTMB?

Shoes with strong grip and stability. Brands such as Inov-8, La Sportiva and Salomon are popular for this kind of technical terrain — but the right shoe is the one you've trained in and trust on descents.

How should I fuel during the race?

Aim for 60–90g of carbohydrate per hour and start early. A mix of gels and real food tends to work best over the longer distances.

Sources

• Eryri by UTMB race list and race pages: eryri.utmb.world/races
• Name change: eryri.utmb.world
• Required experience: eryri.utmb.world — required experience
• Mandatory kit: snowdonia.utmb.world — mandatory kit
• UTMB World Series Running Stones: utmb.world/sports-system