Friday 13 October is Khunjerab day. The Security Force men, without transport, flag down a passing vehicle to deliver breakfast to their colleague on the pass. We thank them and inch our way up the dreaded switchbacks into thinner and thinner air, while buses and pantechnicons from China swoop down from the pass. At last the gradient eases in a snow-streaked field of moraine where yaks are nibbling sparse vegetation, and soon after midday we are at 4730m, on the Khunjerab Pass. The lonely KSF man checks our visas.

We no longer care whether this is the highest public road in the world. We're just glad we made it.

We coast down past grazing camels into China. At the border post an official in sparkling uniform checks our visas. More steep descent follows, into a bone-chilling wind. At the foot of the hill we stop to fix another puncture. Breakfast is a distant memory, but right here is a road maintenance depot; and where there are Chinese there's hot water! Chris goes in and returns with a full flask of kai shui. The men invite us in to warm ourselves by their stove, but they won't let us stay.

In the last daylight a cluster of mud and stone huts appears in the wide valley floor. It starts to snow. There are no trees so we collect yak dung and splinters from the hut-building. Chris lights a tiny fire on the doorstep, and Ann makes tea and soup before bed. We have crossed the Khunjerab.

In the night I am violently sick.

After many hours, sunshine creeps down the slope towards our hut, revealing a white world. In late morning when the road is clear of snow and traffic is passing, we continue, gliding gently downhill. Men in hats with ear flaps are watching yaks beside frozen streams. Back from the road are their yurts, with smoke rising and women with bright headgear who turn away, not returning our waves. Away to the left the long barricade of the Pamir Mountains marks the western border of this western province of China, Xinjiang. It's a brown, open land, utterly unlike the gorges and defiles of Pakistan, and with no company but the endless telephone poles marching beside the road.

A police post at Pirali holds hope of kai shui. An officer, wrestling to chain a huge labrador, does not want to know us. A perspex case displays tourist leaflets and pictures of modern industrial China.

At the police post in the next town we find our Mandarin phrasebook in the bottom of a pannier and point to the characters for "stove" and "broken". The man in charge motions us into a courtyard and then to a dining room where the remains of a meal are cleared away. Green tea, yoghurt, rice, vegetables and salad appear. No payment is allowed. Our spirits and faith in human nature revive mightily. Though my meal soon finds its way onto the road verge, I'm grateful to the policemen at that town whose name I cannot even remember.

We hurry on through mercifully gentle down-valley riding, Chris and Dave taking turns to pump Apollo's front tyre (I'm too weak) every few kilometres, to Dabdar, in the shadow of the Pamirs. The houses and businesses have walls and gates, and the peoples' minds seem walled and gated to the idea of welcoming tired, sick cyclists. There is no hotel. We wheel our punctured tandem from one faint prospect of rest to another. At length a man lets us camp among the donkey droppings by the village well and brings us a flask of kai shui. I go to bed as soon as the tent is up and sleep better than I have for a week.

And at the well in Dabdar, Providence sends us Mike from Vancouver and Reginald from Belgium. They're well and cheerful, and have ridden in two days the distance that took us four. Also they have stoves that work and are willing to share them.

We follow our new friends, rolling down a wide brown alluvial valley beside the Pamirs. A huge snow peak, Mustagh Ata, is suspended in the haze ahead, topped with a white plateau part-hidden in cloud. Willows soften the landscape as we approach Tashkurgan, a scatter of nondescript buildings 120 kilometres from the Khunjerab Pass and at a more lung- and head-friendly altitude. Tashkurgan is altogether dwarfed by its surroundings, as though its only function is to bring a little untidiness to the great valley. Here, two days from the border, we officially enter China. Delighted immigration officers swoop on Apollo and take turns riding round the yard. Their bleak town seems the acme of civilisation, and we revel in the modest comforts of the Ice Mountain Hotel and public showers. It's our first wash in five days.

In Tashkurgan's streets people hold conversations in mid-intersection. The traffic is mostly bicycles and the load-carrying variations on the theme of bicycle so common in China. China? Only just. Thirty kilometres to the west is Tajikstan, part of the USSR until its 1991 collapse. Smartly dressed Tajik women with red, flat-topped hats and high heels inspect flamboyant carpets and bedspreads and hideous children's clothes on sale in the open air.

Ann buys food for the last 300 km to Kashgar while Mike searches for a welder to repair his cracked bike frame, which has seen multiple adventures throughout Asia. On the way out of town we stop to refuel the Mike and Reginald stoves, and a traveller from Urumqi is so impressed with our journey that he pays for our petrol.

In a rising head wind we enter the Tagh Arma Basin. Grass (a novelty) appears briefly, then the desert reasserts itself. Rows of identical concrete houses line up in the dust in military formation, as if in response to a command from Beijing. The gale increases and fills the air with dust so we can see only fifty metres ahead. With dust in teeth and hair we ride into the storm in tight line astern, sharing pace like racing cyclists and grateful for the strength of our new friends. At length the wind eases and we come to a night's rest in a deserted hut under the snowy slopes of Mustagh Ata, vanishing upward into cloud.