We’re now at the business end of the Giro, with the next few days set to determine all the major classifications. With that in mind, let’s have a look at what we can expect to happen tactically over the trio of high mountain stages which will be tackled on Thursday, Friday and Saturday (assuming this afternoon’s relatively straightforward run to Vicenza doesn’t spring any surprises).

Let’s start by examining the top ten of the general classification as of the end of yesterday’s stage 16, and then examine the three upcoming stages in turn to understand what each of the top riders will be aiming for.

1. Vincenzo Nibali (Astana)

2. Cadel Evans (BMC) +1:26

3. Rigoberto Uran (Sky) +2:46

4. Michele Scarponi (Lampre-Merida) +3:53

5. Przemyslaw Niemiec (Lampre-Merida) +4:13

6. Mauro Santambrogio (Vini Fantini-Selle Italia) +4:57

7. Carlos Betancur (Ag2r La Mondiale) +5:15

8. Rafal Majka (Saxo-Tinkoff) +5:20

9. Benat Intxausti (Movistar) +5:47

10. Domenico Pozzovivo (Ag2r La Mondiale) +7:34

Stage 18: 20.6km individual time trial

The time trial will produce a concertina effect on the top ten, with some gaps closing up, others widening, and some riders potentially swapping places – for instance, just 50 seconds separate Mauro Santambrogio in sixth from Benat Intxausti in ninth. Whereas the stage eight time trial was long – approaching 80 minutes – and contained a mix of technical sections, descents and punchy climbs, this one is shorter – the fastest riders should dip under 40 minutes – but uphill all the way. So the pure climbers will be breathing a sigh of relief, as the vertical nature of the course ironically levels the playing field.

Who can we expect to go well? We can take pointers from the earlier ITT but only cautious ones, as the nature of the two courses is quite different, and of course a time trial in the third week of a tiring grand tour is always a different beast. But examining the time gaps provides some indication of likely form, although we can expect the gaps between the TT specialists and the pure climbers to be smaller. Of the top ten, Vincenzo Nibali had the best time, finishing fourth. Cadel Evans (18 seconds slower than Nibali) and Michele Scarponi (32 seconds) were the only two to finish within a minute of the Sicilian. So we can expect all three to be targeting gains of 30 seconds or more on the rest of the top ten here.

Third-placed Rigoberto Uran (+1:27 versus Nibali) will primarily look to keep Scarponi behind him while limiting his losses to Evans and Nibali. Meanwhile fifth-placed Przemyslaw Niemiec (+1:52) will be hoping to extend his 44-second advantage over Santambrogio (+2:35), who in turn would expect to take time back on him on the following two stages.

In the white jersey competition, only five seconds separate Carlos Betancur from Rafal Majka, but the latter is a vastly superior time-trialist, having taken 1:52 out of Betancur (the worst performer against the clock in the top ten) in the first time trial. Majka will be looking to finish the day with a handy cushion in this head-to-head battle. Conversely, Domenico Pozzovivo (tenth overall) trails Benat Intxausti by nearly two minutes on GC but was 1:28 faster in the initial time trial, so he will be looking to close the deficit.

The time trial route itself will test riders’ pace management as much as their climbing ability. It’s relatively steep near the bottom before a couple of false-flats either side of the intermediate time-check. Riders must avoid pushing too hard early on and aim to keep a little in reserve to tackle the steep, twisty sections near the summit where large chunks of time could easily be lost.

How the riders perform relative to one another will dictate individual race tactics over the following two days.

Stage 19: Passo di Gavia – Passo dello Stelvio – Val Martello, 139km

Riders will face a choice heading into this concluding pair of stages. They can attack hard on one or the other, but probably not both. So which do you go for? Most of the top GC men will take the conservative option and try to save their energy for Saturday’s final battle.

That means we will probably see a breakaway go on the Gavia which the leaders won’t be overly concerned with chasing down. Look out for mountains classification leader Stefano Pirazzi to lead that charge in search of the points which will secure the jersey, but  also a gaggle of opportunists desperate to win a stage. I’d expect Pirazzi to attack on the Gavia and Stelvio for maximum points, then drift gradually back to the peloton to save energy for Saturday.

There are plenty of opportunities for a brave GC rider to make an attack – possibly even an early one – stick on what is a short stage at just 139km. The Gavia descent is technical, narrow and on well-worn surfaces while the road down from the Stelvio is highly technical and very long at 25km. But the likelihood is that the main contenders will stay together until the last 5km of the concluding Val Martello climb, where the steepest gradients are. Then we will see attacks, and Nibali (and to a lesser extent Evans) will have the luxury of picking and choosing who he goes after, assuming he himself doesn’t attack.

One final variable is the weather. Reports this morning suggest that weather conditions may render the Gavia and Stelvio impassable, in which case the tactical complexity is greatly reduced, with the likelihood being that we would see a straightforward break-and-chase  with the GC contenders slugging it out on the climb to the Val Martello summit. Such a scenario would also greatly favour Pirazzi by removing opportunities for his rivals to gain mountains points.

Stage 20: Passo Giau – Tre Cime di Lavaredo, 203km

The final mountain stage is long – at 203km it will be at least 6½ hours in the saddle at the end of three weeks of racing – and extremely tough, but as it is the last climbing day riders won’t hold anything back here as they face their final opportunity to improve their GC position.

Again, expect a break to go early with a similar combination of mountain classification riders and stage-hunters to the previous day, while the GC big guns keep their powder dry over the opening two cat 2 climbs. We might see a contender pop off the front on the second of those climbs, but it’s more likely that if anyone is going to try a long-range attack they will do so on the 9% stretch at the top of the Passo Giau, whose summit is nearly 40km from the finish. A skilled descender who can find a few seconds of clear air over the summit could easily build a useful advantage on the long descent to the final climb, but it’s a big risk to take given the severity of what is to come.

The final climb of the Giro, the Tre Cime di Lavaredo, is essentially a three-part climb: a steady grind, a short, sharp kick-up and then a final section of 3.9km which averages a brutal 12.2%. A rider who’s suffering could easily lose 2-3 minutes on the final section alone.

As to who will attack where, it depends on each rider’s ambitions and the time gaps to those ahead of them. Some will ride defensively, while others will target a sharp attack on the last climb. But anyone looking to gain a larger chunk of time on those in front may choose to accelerate on the rise to the second peak, possibly even the first. The earlier the attack, the bigger the potential gain – but also the greater the potential loss.

Again, the weather may throw a spanner in the works, with question marks hanging over the Giau and Tre Cime. The removal of either or both climbs would again reduce riders’ tactical options, and the threat of doing so may also encourage a less conservative approach to the previous day’s stage for those desperate to make up time.

One thing’s for sure. If anyone has ambitions to jump up the GC – and some will be happy to defend their current position rather than take a risk – this is the last real chance to make time up, so it’s now or never.

So there you have it. In summary, expect the time trial to shape the GC contenders’ tactics on the two stages to follow. Don’t be surprised if a big breakaway goes early on both days. Their best chance of success is probably on the first day, while on the second expect the big names to be fighting it out for the win and precious seconds at the summit of Tre Cime. We should be guaranteed an exciting and explosive end to the Giro, and one in which we will see tired riders both making and responding to multiple attacks. How this chess game plays out will determine the outcome of the race.