Mountain-biking: Spectators' guide to thrills and spills of white-knuckle, two-wheel racing

There are 17 much-coveted, UCI rainbow jerseys ready to be handed out to 17 new world champions at this week's world mountainbike championships. The jerseys, and accompanying gold medals, will be at stake in four separate disciplines in Rotorua.

The first titles will be decided on Wednesday - cross country for junior women and women under-23, and the last four on Sunday.

THE FOUR DISCIPLINES:

4x

Similar to BMX racing in that four riders break out of the starting gate at the same time. The 4X course drops 70m over the 500m track on which riders have to negotiate obstacles and some huge drops. Average time expected is between 45sec-1 minute.

Two classes, elite men and women with Americans Brian Lopes and Jill Kintner back to defend their titles.

Best NZ hope: Cameron Cole.

Trials

For the technical buffs. Ridden over a series of tricky and demanding obstacles in a variety of zones [eight]. Riders have to go the distance as points are lost when a rider's foot or other part of their body touches the ground. The zones will be placed at different points on the mountain making it spectator-friendly. For the women it will be a straight ride-off, for the rest semifinals to find the top eight. Up to 80 riders are expected. The lowest points score wins.

Five classes, men's elite 20in and 26in (size of wheel); junior men 20in/26in; women's elite (one class).

* Elite men (20in): Current champion Benito Ros Charral (Spain) back to defend his title.

* Elite men (26in): Current champion Kenny Belaey (Belgium) back to defend.

* Junior men: Current champion Ben Slinger (GB) back to defend both 20in/26in titles.

* Elite women: Current champion Karin Moor (Switzerland) back to defend her title.

Downhill

A 2.2km scurry from a starting gate close to the top of Mt Ngongotaha to the base of the mountain near the gondola station. A variety of terrain including an "outback garden" and a "boardwalk" provides the challenge for the riders who are expected to take between 3-3 1/2min to get down the mountain. After a seeding run (on Thursday), the medals are decided with one-off timed runs in the four classes on Saturday.

Elite men: Current champion Fabien Barel (France) injured, not defending. Best NZ hopes: Nathan Rankin, Justin Leov.

Elite women: Current champion Anne-Caroline Chausson (France) retired. Best NZ hopes, Vanessa Quin, Scarlett Hagen (who won elite/junior titles in France 2004 the only New Zealanders to win world mountainbike championships).

Junior men: Current champion Amiel Cavalier (Austria) has moved up to elite.

Junior women: Current champion Rachel Atherton (England) has moved up to elite.

Cross-country

The showpiece Olympic/Commonwealth Games discipline.

Contested over a 6km circuit the number of circuits for each class will be decided on the day when weather conditions are taken into account. The aim is for each race to be close to the two-hour time limit.

Organisers have come up with a spectator-friendly but testing course featuring a steep uphill and vertical drop with a technical rock garden tossed in. Unlike other disciplines, competitors start and finish at the same point. Massed start for the six classes.

* Elite men: Current champion Julien Absalon (France), the two-time world champion and Olympic champion is back to defend. Best NZ hope: Kashi Leuchs.

* Elite women: Current champion Gunn-Rita Dahle Flesjaa (Norway), also the Olympic champion, back to defend.

* Best NZ hopes: Rosara Joseph, Annika Smail.

* Under-23 men: Current champion Yury Trofimov (Russia) back to defend but faces tough challenge from Nino Schurter (Switzerland).

* Best NZ hope: Clinton Avery.

* Under-23 women: New class. Best NZ hope: Michelle Hyland.

* Junior men: Current champion Robert Gehbauer (Australia) who has moved up to under-23.

* Junior women: Current champion Tereza Hurikova (Czech Republic) who has moved up to under-23.

* Best NZ hope: Monique Avery.