The Giro peloton has been tested in rain and cold, on short, steep climbs, in time trials and on big mountains but everything until now could just be seen as a warm-up for what is still ahead. At the route presentation in October what caught most people's attention what the three extremely hard stages in the Dolomites towards the end of the race and the first of those crucial days is today. The 20,6km mountain time trial from Mori to Polsa has the potential to deliver a major shake-up of the general classification and is without any doubt one of the single most important days of the entire race. Starting at 14.15 you can follow the dramatic action on CyclingQuotes.com/live.

The 18th stage is the first of three crucial days which will determine the final winner of the 2013 Giro d'Italia. The 20,6km mountain time trial starts in the city of Mori and climbs to the top of the category 2 Polsa climb (20,6km, 4,9%, max. 10%). The stage starts off with 1,3km of almost flat roads before they start to climb all the way up to Polsa. The ascent is highly regular with a rather constant gradient averaging 6,6% in the early part but the monotony is broken at the midpoint where 4,7km of almost flat roads make up a piece for the time trial specialists to put their strength to good use. From then on it is back into climbing mode as the final 6,45km once again have an average gradient of 6,6% and the road points upwards all the way to the finish line.

While this is certainly a mountain time trial, it is not comparable to some of more extreme one which we saw in the 2008 and 2010 editions on the Plan de Corones climb. This climb is much more human and even has an easier section at the midpoint which should make take a little bit away from the pure climbers in favour of some of the stronger riders. It could be compared to the stage from Belluno to Nevegal won by Alberto Contador in 2011 which started off with a long, almost flat stretch before the climbing got serious. However, the ascent was steeper on that occasion which played into the hands of the climbers. The best comparison is probably the Col d'Eze time trial known from the Paris-Nice which is a little bit easier and much shorter though.

Nonetheless, this is a crucial day for the GC riders. Nobody knows what will happen to the next two stages in the Dolomites which are threatened by bad weather and so this stage has only grown in importance as news on the risk of alterations to the course continue to circulate. At 20,6km it is a very long mountain time trial and so we could very well see some rather huge time gaps. Furthermore, we are now deep into the third week of the race and we could very well see some of the GC contenders start to fade as fatigue plays a bigger and bigger role.

A mountain time trial is a much different thing from a "standard" time trial. The grand tour races against the clock often are often contested by a mix of GC riders and time trial specialists but this will certainly not be the case today. While the all-round GC riders will naturally still play a prominent role, they will have to battle with some of the pure climbers who are usually lose plenty of time in TTs but suddenly will be able to mix it up for the win on a stage like today's. John Gadret, Sylwester Szmyd, Rigoberto Uran and Jose Rujano are some of the riders who have excelled in the discipline in recent years despite their lack of time trial success.

The big favourite is of course Vincenzo Nibali. The race leader has not been troubled at all until now and has always appeared to have an extra gear to use if necessary. He has stated his intentions of taking a stage win in the Dolomites and while tactics will complicate affairs on Friday and Saturday, today's race will be determined by pure strength and ability to gauge your effort. Right now the Italian appears to be the strongest climber in the race and his hard work with Astana and Specialized to improve his time trial has paid off throughout the entire season. His 4th place in the long race against the clock to Saltara was arguably his best time trial ever, and when he can mix it up for the win in a flat time trial, he will be very hard to beat when it is almost all uphill. He finished 2nd behind Contador in 2011 and 4th on Plan de Corones in 2010 and knows how to handle time trials of this kind.

Cadel Evans hopes to start to take back some time on the Italian today and on paper the Australian is the strongest time triallist of the top 2 riders. However, the BMC leader was beaten in the flat one in the early part of the race, and that makes it hard to see him outgun Nibali today. The discipline is certainly one that he likes and he finished best of the GC riders in 2010 behind winner Stefano Garzelli but since he has struggled to keep up with Nibali in the mountains until now, it will probably be another day for the Australian to lose some time. Nonetheless, there is little doubt that he will mix it up with the best and it would be a big surprise not to see him end up in the top 5 today.

The surprise package today could be Carlos Betancur. Usually not a strong time triallist, the Colombian could be the man to break the usual TT hierarchy today. He has emerged as one of the best climbers in the race and he could use that ability to claw back time today. He needs to limit his losses on the two flatter parts but as soon as the road points upwards, he will probably one of the day's fastest riders.

Michele Scarponi used some solid climbing and a surprisingly strong time trial performance in the early part of the race but he suffered on Altopiano del Montasio and Jafferau to rule himself out of the battle for the overall win. Nonetheless, the Italian has bounced back in recent days and once again seems to be one of the strongest climbers in the race. He has had some solid mountain time trial performances in the past with a 5th place in 2010 and 3rd in 2011 and he could very well use today's stage to move a little closer to the final podium.

Tanel Kangert could very well take his second podium result in a time trial in this year's Giro. The Estonian has all the capabilities to perform strongly today and his immense strength has actually moved him into 12th on GC - despite his role as a domestique for Nibali. His leader has made nothing to hide that Kangert will be allowed to go all out today and that could very well make it two Astana riders in the top 3 today. He is a strong time triallist and a good climber and nobody knows how to set a strong, steady pace on a climb like the Estonian domestique. Expect Kangert to be right in the battle for the stage win once again.

It will be interesting to see what a rider like Samuel Sanchez can do today. He started the race slowly but as usual he gets stronger as the race goes on. The last two days have done nothing to remove the impression of the Spaniard's strength and he will find the rather long time trial to his liking. No one can gauge his effort on a climb like the Euskaltel leader and with good results in tough time trials already on his palmares, he could use today's stage to move a little closer to the GC.

Rigoberto Uran is one of the pure climbers who has performed strongly in the discipline in the past. His good result in the long time trial could indicate that another strong showing is in store but the Colombian has appeared to lack a little bit compared to his rivals in recent days. He hopes to gain time on Scarponi today but he could very well end up as the loser in that podium battle today.

Good performances can also be expected from Rafal Majka, Przemyslaw Niemiec and Benat Intxausti who is usually a very good time triallist. For Robert Kiserlovski and Mauro Santambrogio, today will be the test to find out whether their recent struggles were just a case of bad days or if they have started to fade in the third week of racing. However, if the latter is at his best, he could challenge Betancur for the position as the pure climber to gain the most from today's time trial.

There are fewer contenders among the time trial specialists than in a flat time trial, and the likes of Luke Durbridge, Svein Tuft, Alex Dowsett and Jesse Sergent can all be ruled out before the stage has even started. Nonetheless, there are a number of non-GC riders that could mix it up in the top 10. Stef Clement (Blanco) is not your usual specialist as he is also a rather strong climber who was 5th in the mountain time trial in the 2011 US Pro Challenge. His 5th place in the Saltara time trial is testament to his form and he has even appeared to go even stronger right now.

Sky is a formidable time trial team and the British team has a duo that could mix it up today. Dario Cataldo and Kanstantsin Siutsou are both strong time triallist and good climbers and they could be allowed to give it their all today. They have not appeared to be at their best in the race but the former has bounced back from an early bout of illness and will be eager to show off his Italian time trial jersey today. The steady, regular climb should suit both and they could be some of the riders to set some early good times.

Finally, Ramunas Navardauskas, Manuele Boaro and Nelson Oliveira are all climbing strongly these days and since all are good time triallists they could also deliver good performances on today's course.

CyclingQuotes' stage winner picks: Vincenzo Nibali, Cadel Evans, Carlos Betancur

Outsiders: Tanel Kangert, Michele Scarponi, Mauro Santambrogio