Against the clock: The Sella Ronda circuit offers cyclists the ultimate time trial

Anyone know the Italian word for "jelly-legs"? For 90 minutes, I'd been struggling to work it out – gambe gelatina perhaps? – while trying my best to keep up with Peter, my obscenely fit mountain bike guide. It had been around four hours since we'd started pedalling up into the backcountry of South Tyrol in northern Italy. It was getting on for lunchtime, and I'm not going to lie to you – my legs were a little on the wobbly side.

We'd cruised along gravel paths all morning, the only noise the thrum of our knobbly tyres crackling over small stones, and the heaving sound of my arrhythmic panting as I huffed and puffed my way ever upwards.

The route we were riding followed that of the Sella Ronda, the lap around the towering limestone peaks of the Sella group of mountains in the Dolomites that takes in some of South Tyrol's most celebrated passes. It's best known as a ski-touring trail – up there with the likes of France's Vallée Blanche and Switzerland's Haute Route – and until recently was something that could be tackled only in winter and on skis. Now, however, it's open to mountain bikers, and Peter and I were spending the day cycling the 55km loop.

The Sella group itself is an island of rock 9km wide, which tops out at a whopping 3,152m. Surrounding it are four deep valleys – Gardena, Badia, Fassa and Fodom – dotted with villages, and all threaded together by the ancient sheep tracks used by farmers for centuries to herd their livestock between the high pastures. It was this network of well-signposted trails that we were using to circumnavigate the mountains.

In my back pocket was a lift pass I'd bought from the local tourist board, which allowed me to take my bike on the gondolas and cable cars. Not only did this speed up progress substantially – indeed, to do the route without it would be impossible – but it gave me brief opportunities to sit back and soak up the scenery.

In contrast to the darker, fatter Alpine peaks with their more rounded tops, the Dolomites are lighter in colour and more jagged – vast, serrated fingers of rock rising out of nowhere, propping up the electric blue sky. On sunny evenings, these limestone crags are stained pink by the setting sun – something to look forward to later in the ride.

While a lift pass takes the sting out of most of the climbs, there are still plenty of uphill bits to get your teeth into. Tackling the route clockwise, as we were doing, meant that there was about 500m of climbing to do. In the opposite direction, there's a sweaty 1,150m of height to be gained. It's breathy stuff.

We'd begun our ride in the pretty town of Selva Gardena. If you were to imagine the Sella Ronda loop as a giant watch-face, Selva lies at roughly "11 o'clock"; it's a common start point for many cyclists, courtesy of the good rental facilities here. The town is about 190km north of Verona, the main Italian access point to South Tyrol, and, if you're looking to avoid the faff of hiring a car, there's a shuttle bus that whisks you from the airport to Selva, putting you in pole position for accessing the mountains.

I found Peter ready and waiting for me at the rental shop. We grabbed a couple of bikes equipped with suspension and the latest clipless pedals, and headed straight out onto the trails – bound for the first lift, Dantercepies.

By the time we got there, my legs were already feeling weak from the opening climb (a pitiful 100m of vertical). As the cable car arrived, I was relieved to hand my bike over to the lift operator so that he could deposit it in one of the bubble cars for the journey across the valley.

I've skied in South Tyrol several times, but the contrast between winter and summer is astounding. As we glided across the wide open valley towards the Passo Gardena, the thing that struck me most about this vast, vertiginous landscape was the colour. In contrast to the monochrome white of winter, the hillsides had erupted into lime green speckled with bright wild flowers. It was as if someone had come along with enormous felt-tip pens and coloured it all in.

Not that there was much time to sit back and admire it all; for much of the day I was too busy keeping my eye on Peter's back wheel. While most mountain-bike routes in the area are rideable without a guide, anyone tackling the Sella Ronda must be accompanied by one, to ensure that they stick to the prescribed route.

Throughout the day, Peter pointed out the sights – a family of mountain goats perched precariously on a cliff over here; a marmot scampering across the scrub over there – while I concentrated on making my wheels go round.

Nevertheless, there was plenty of time to pause and admire it all; indeed, by the time the cable car deposited us safely at the summit for the start of the Passo Gardena, I'd already used up most of my camera's memory card. This marked the "12 o'clock" spot on our loop: now was my chance to get stuck into the first downhill of the day.

Peter was in his element. All I saw was a Lycra-clad backside pointing skywards, nose skimming his handlebars as he streaked away from me at an impossible rate. "The trick to going fast down the hills is to keep your weight over the back wheel," he said, when I'd finally caught up with him at the bottom. "It makes your braking more efficient, and that will give you more confidence."

He was right. These days, rental bikes can be incredibly capable; you just need to relax while they soak up the bumps. At the next downward swoop, I made a conscious effort to let it all hang out – keeping a lighter touch on the handlebars. The bike floated satisfyingly over the trails, allowing me to maintain more speed. Away to my right the vast rock walls of the Sella massif rose out of the ground, shafts of sunlight beaming down to illuminate the grey limestone.

Quite apart from being a Unesco World Heritage Site, this whole area is one big adventure playground. In summer, you'll see climbers scaling the cliffs, and it's not unusual to spot base-jumpers flinging themselves off mountaintops. Away in the distance, the sky was speckled with brightly coloured canopies: paragliders circling on the thermals like vultures. These are all things you might miss if you simply tear around the route as fast as possible.

Happily, for me, riding the Sella Ronda is as much about enjoying the scenery as it is about speed. It's also about eating. South Tyrol may only be the size of Devon but it has one of the highest concentrations of Michelin-starred restaurants in the world – a rather tasty 18 stars, shared by 15 eateries. And throughout the course of our ride, Peter and I were never far from the next (admittedly not Michelin-starred) mountain hut, providing plenty of excuses to stop and refuel.

Having descended the Passo Gardena via a series of switchbacks and cruised through the village of Colfosco, pedalling on to Corvara, it turned out that we'd notched up just 11km since leaving Selva. It was at this point (about "1pm" on our route, and, indeed, in real life) that my case of jelly legs began – coinciding with our arrival at the Col Alt hut.

Perched above Corvara at just under 2,000m, it formed the perfect pit stop, with much of the food – including the prosciutto and cheese that we munched on while catching rays on the terrace – coming from farms in the surrounding valleys.

Suitably refuelled, we stepped out into the sunshine to continue our journey. Carrying on past the Rifugio Pralongia (excellent puddings), we reached a stretch of single track running parallel with the Campolongo Pass, which took us in and out of the trees – the dappled sunlight causing the scenery to strobe as we picked up speed.

Much of the day was spent under the watchful eye of the Sella group's highest peak, Piz Boe, which snagged the odd puffy cloud that drifted too close. During the First World War, this area witnessed heavy fighting between Italian and Austro-Hungarian soldiers. The result was 900,000 young men killed and wounded in battles that earned only 30km of territory – and saw vast chunks of mountain blown to smithereens.

"You see that section over there with the flat top?" asked Peter, pointing to a rocky outcrop with a peak like a horse's saddle. "It used to be pointed like a triangle." These battle-weary peaks – gnarled and weathered like old grey teeth – remained a constant orientation point throughout our ride.

Everything else, though, varied considerably from one valley to the next. Since leaving Selva, Peter and I had tackled rocky sheep trails, wide open farm tracks, shady forested sections and switchbacks that looked like lengths of string dangled over the hillside. Now, as we made our way down into Arabba (passing "four" on the giant Sella Ronda clock face) and caught yet another cable car, up to Porta Vescovo, the landscape changed again.

Up here at nearly 2,500m, the views are almost lunar: a clutch of vast boulders were left strewn about as if by some prehistoric giant. Scenery on this scale restores your sense of perspective; as we clicked through the gears, accelerating downhill, I spied a couple of fellow bikers in the distance who looked like ants scuttling about among small stones.

A loose dirt road took us down past enormous fields of scree – before a lung-busting climb up to the Passo Pordoi, with our reward the 7km downhill run into the village of Canazei. It was now coming up to "eight" on our metaphorical clock-face, and there was just one more lift between here and our return to Selva. Although we were still some 16km from the finish, it was mostly downhill from here.

My thoughts were already turning to a long, hot soak in the bath back at my hotel – a chance to revive my jellified limbs. Maybe I'd try one of those Michelin-starred restaurants, too; after all, I deserved it.

Matt Carroll is the author of Escape Routes (Punk Publishing, £16.95), a hand-picked selection of cycle rides around England: escape-routes.co.uk

Getting there

* The region can be accessed from Verona, served by Ryanair (0871 246 0000; ryanair.com), British Airways (0844 493 0787; ba.com), easyJet (0843 104 5000; easyJet.com) and Bmibaby (0871 224 0224; bmibaby.com). Bus transfers to South Tyrol cost €25 each way ( suedtirol.info/fly).

Cycling there

* Dolomite Biking (00 39 34 5843 0374; dolomitebiking.com) offers one-day guided rides along the Sella Ronda from June to September for €50 per person.

* A map of the Sella Ronda Bike route can be viewed at sellaronda-mtb.com.

* For more details on cycling holidays in South Tyrol, visit bikehotels.it.

* The Sella Ronda Bike Day, where the roads surrounding the Sella range are closed to vehicles, allowing 18,000 cyclists to tackle all four passes – is held in July. This year, a second instalment will take place on 18 September, as part of a weekend-long festival (sellarondabikeday.com).

* South Tyrol Tourist Board: 00 39 0471 999 999; suedtirol.info

Staying there

* Piccolo Hotel, Selva di Val Gardena (00 39 0471 795186; hotel-piccolo.com). Double rooms start at €105, half board.