Nothing is settled in this wild and wacky Tour de France. With one mountain stage to go, six riders are still within four minutes of each other: two Spaniards (Oscar Pereiro and Carlos Sastre), a German (Andréas Klöden), a Frenchman (Cyril Dessel), an Australian (Cadel Evans) and a Russian (Denis Menchov).

Thursday’s 200.5km stage 17 from St. Jean-de-Maurienne to Morzine is not the hardest mountain stage of the Tour, but coming after almost three weeks of relentless racing, mostly in heat-wave conditions, it will be a terrible test of perseverance and stamina.

More than half the peloton is totally fatigued. That was confirmed on Wednesday’s epic stage up the Galibier, Télégraphe, Glandon, Croix-de-Fer and Mollard passes before the death march to the 5595-foot summit of La Toussuire. If the normal time cut of 12 percent had been applied, only 67 riders would be left in the race. The other 80 finishers were outside the 40:20 time limit, so the race officials again used a little-known UCI rule to increase the time cut by 2 percent to 47:03.

Even the team leaders are suffering. That was clear at La Toussuire, where not only Floyd Landis was in trouble at the end of stage 16. Several riders who made strong attacks ended up conceding time, including Yaroslav Popovych, who attacked on the descent of the Galibier (and finished 51st at 28:56); Levi Leipheimer, who attacked halfway up the Glandon (ninth at 3:24); and Denis Menchov, who twice accelerated on the La Toussuire climb (11th at 3:42).

Both Menchov and Leipheimer could come back on Thursday, while Pereiro (who lost almost half an hour on the big Pyrenean stage) will need to nurse his form to hold off Sastre, Klöden and Evans on a stage that features five more alpine climbs — including the savage Col de Joux-Plane just 10km from the finish.

“The Joux-Plane is one of the hardest climbs, and the descent is dangerous,” said T-Mobile’s Michael Rogers, who is in seventh overall and riding shotgun for Klöden. “With a lot of guys who are tired, a lot could happen.”

Wednesday’s winner, Michael Rasmussen, now that he has won his stage and secured the polka-dot climbers’ jersey, will return to domestique duties for Rabobank leader Menchov, along with a still-solid Michael Boogerd. Caisse d’Épargne’s Pereiro will be hoping that his Spanish teammate Xabier Zandio will again be strong, while Davitamon’s Evans will be relying on revived American Chris Horner to help him over the Cat. 1 Col des Saisies, Cat. 2 Col des Aravis, Cat. 1 Col de la Colombière and Cat. 3 Côte de Châtillon before reaching the foot of the hors-cat Joux-Plane.

With long stretches at 10 percent, and an average of 8.5 percent for its 11.7km length, the narrow Joux-Plane climb should witness yet another “final showdown” in this dramatic Tour. Lance Armstrong fans will remember that the seven-time champion bonked on the Joux-Plane in the 2000 Tour and conceded more than 90 seconds to rival Jan Ullrich.

It’s also the climb where, in 1987, Irishman Stephen Roche took many risks on the descent to take back vital seconds in his duel with Spaniard Pedro Delgado. That Tour went down to the wire in the final time trial a couple of days later, with Roche emerging as the overall winner by just 40 seconds.

This year’s Tour will also come down to the 57km time trial from Le Creusot to Montceau-les-Mines. If the leaders are still separated by a couple of minutes, then the advantage would be with Klöden and Evans, rather than Pereiro and Sastre. But that could all change after Thursday’s stage 17. Nothing in this Tour thriller can be taken for granted.