They’re laying it all on the line. But from a spectator standpoint, they might as well be at spinning class.

Leave it to this year’s Giro to throw in a diabolical wrinkle. Two days after the punishing climb of Monte Zoncolan, riders were cast back into the cauldron of oxygen debt and altitudinal nausea.

For the record, David Arroyo (ESP) held onto the pink jersey, although his lead shrank over rivals Ivan Basso (Liquigas) and Cadel Evans (BMC). Riding out of the saddle much of the route, Evans placed a surprising 28 seconds ahead of Basso, cutting Basso’s advantage almost in half.

Basso is now second overall, and Evans fourth.

The 13-kilometer profile of the Plan de Corones looked like the long side of a carpenter’s level. The final 1-kilometer kicker included a stretch of 24 percent grade, just how you like to finish a hard ride out of the saddle.

Plus much of the route is dirt and gravel, always a pace killer. And there was a headwind at the top. The only factor working in the riders’ favor today was the sunny weather, in the 70s at the start and the 50s at the top of the dirt climb.

Carlos Sastre, a strong climber, was riding a 34 X 28 gear, the only place outside Zoncolan and Angliru (Spain) where the bike gets fitted that low, according to his team mechanic (and VeloNews’ Andrew Hood).

Never in the Tour de France. This climb is that brutal.

34 X 28 … that’s our spinning gear! (Sastre, alas, was the day’s big disappointment, looking listless over most of the route and never challenging for the stage win.)

Alberto Contador, the winner of 2008′s Giro, finished fourth in this time trial at 40:48. The winner, Franco Pellizotti, averaged 19.14 kilometers an hour.

Most of the times in today’s stage, won by 2000 Giro overall champion Stefano Garzelli in 41:28, were well off the 2008 pace. It could be the result of the Giro’s difficulty level so far, and of Monte Zoncolan two days ago.

Also possible, in our view, is that the slower times are another pointer toward this year’s Giro as the true start of the post-doping era. The 2008 winner, Pellizotti, is under suspension for doping violations, and the No. 5 place, Riccardo Ricco, was suspended not long after the 2008 Giro for doping as well. The top six riders in 2008 were faster than today’s winning time over the same course.

On-road conditions also play a role, but today’s weather was perfect. Let’s hope it stays that way through the closing mountainous stages of the Giro.

The Giro d’Italia may be wearing the new mantle.

Ivan Basso, riding with his characteristic smile and/or grimace but with the methodical power and grace of a mountain lion on the attack, took the agonizingly steep but incomparably thrilling Monte Zoncolan, the 15th stage of the Giro — vaulting him into third place in the general classification and more than a minute ahead of his closest rival, Cadel Evans.

Spaniard David Arroyo maintained the leader’s pink jersey, but lost more than three minutes to Basso. Tomorrow’s rest day will prove a temporary respite from mountain pain over the final week of the Giro.

For a time Evans managed to duke it out with Basso. But Cadel was out of the saddle much of the time, expending precious upper-body strength while Basso simply ground out the gears in his saddle up the relentless grade.

The middle 6 kilometers of the climb — the day’s fourth — averaged 15 percent — which any cyclist who pays attention to such things knows is a world of hurt just over a few hundred feet. There were 22 percent pitches on the final 3 kilometers. To see world champion cyclists pedaling with the cadence and fatigue of weekend riders climbing was quite a sight. You don’t normally find that kind of suffering, even in the Tour de France.

It may be proof that the post-doping era has finally taken root in the Giro, because the slumped shoulders and saliva ropes and sunken cheeks and vacant expressions of the final climb testified to real sacrifice. During the height of the doping era riders would show hardly any signs of true suffering, and there was always the sense that their physical limits had less to do with god-given genetics than whether they were juiced that particular day.

Among the top three favorites of this year’s Giro, Evans is the only rider with unimpeachable credentials. Basso and Alexander Vinokourov both have been banned from the sport — and now returned — after testing positive. Evans has maintained from the beginning he was never part of the doping circle of cycling, and his results have never given any reason to doubt.

So far this year’s Giro has been “clean” (full testing cannot be completed till after the race is over), in contrast to the Landis-Lance eruptions going on over in the U.S. Let’s hope the Italian classic stays that way.

The champions of this year’s unbelievably exciting Giro — and the public who has followed them — deserve to have their victories and legacies unbesmirched in one of the most memorable Grand Tours of all time.