With winter testing set to begin on Monday, ESPN looks at the biggest issue facing each team on the grid ahead of the 2016 season.

Mercedes

Driver disharmony

AP Photo/Eric Gay

Team boss Toto Wolff issued a stark warning for Lewis Hamilton and Nico Rosberg at the end of 2015 -- play nice, or one of you is out. Though it lacked the intensity of their 2014 title fight, in 2015 Hamilton and Rosberg had publicised rows on several occasions (notably China and the U.S.) and exchanged veiled (and some not-so-veiled) criticisms of each other in the final few races of the year. Wolff recently suggested "unleashing" both drivers by giving them free reign over strategy might be best for the team and F1, but with Ferrari likely to be even closer this year that does not seem to be a sensible or likely option for a team hoping to win both championships for a third consecutive year. Rosberg's strong finish to the 2015 season adds to the intriguing narrative going into the new campaign, though a reset championship fight and a new Mercedes car should level the playing field again. Either way, the likelihood of a Ferrari challenge this year means driver harmony (or the lack of) could be giving Wolff a headache for much of 2016. Mercedes' policy of giving the lead driver the optimum strategy looks likely to continue. With two men more determined than ever to beat the other to a world championship, there might be a diplomatic incident waiting to happen.

Ferrari

Fulfilling expectations

If you had any doubt about what Ferrari expects from 2016, you need to look no further than chairman Sergio Marchionne: "We have a strong team and while our opponents also are, we want to be the team to beat in Australia, because we are the most successful squad in history." The Canadian-Italian also issued a warning to everyone involved in the team: there can be no excuses for not challenging for the title this year. Marchionne went as far as to say not winning the title in the next few years would be "a tragedy", making pointed reference to Ferrari's barren spell which stretches back to 2008. The problem now is delivering. With Sebastian Vettel at the helm Ferrari has one of the most gifted drivers in a generation and one who has been given a new lease of life at Maranello. But they are not chasing a standing target -- Mercedes' development will be relentless. The world champions were testing new 2016 car concepts in Brazil last year and brought a development engine from Monza onwards, proving how seriously it is taking the threat of Ferrari. The success of Ferrari's work over the winter -- such as its reportedly innovative work on the combustion chamber of its new engine and the aggressive design of the SF16-H -- will go a long way to determining the team's chances.

AP Photo/Antonio Calanni

Williams

Avoiding recent mistakes and weaknesses

It's a measure of how good Williams' 2014 campaign was that it could be disappointed by the 2015 season and the team's failure to take the fight to Mercedes or Ferrari. It ended 2014 the best of the rest behind Mercedes but finished last season fending off the likes of Red Bull as the two lead manufacturers opened up a gap to the chasing pack. Ron Dennis justified McLaren's switch to Honda by saying a customer team could never win a world championship. The tweaked rules for 2016 prevent factory outfits giving a lower-spec engine to its customers, so Williams will have no excuse this coming year as it did in the final races of 2015 that it is not receiving the same package as Mercedes. But other things need to change. Williams has produced successive cars which struggled in low speed corners and have been poor on tyre management. Conservative calls from the pit wall have hurt Williams in recent times; its decision not to implement team orders when Valtteri Bottas was quickest during last year's British Grand Prix saw them fail to seize initiative at a vital part of the race. It may not have had any bearing on a race eventually settled by a late rain storm, but demonstrated a mindset on the pitwall which cannot continue into 2016 if it wants to return to the top step.

Red Bull

In engine limbo

Red Bull approaches 2016 in a strange situation. After months of quit threats and posturing in 2015 and a rather embarrassing about-face to Renault, it will line up with engines branded as TAG Heuer. However, before a wheel has even turned on the RB12 or any of its rivals, the team has been on the losing side of two major battles which could shape its future in Formula One. The agreement between F1's four manufacturers to cut the cost of customer engines was a blow for Red Bull. Doing so effectively killed off the 'budget' engine Jean Todt and Bernie Ecclestone had threatened to forcibly introduce to the sport. If it had known a cheaper and, crucially, independent engine supplier was joining in 2017 it could have gone into this year knowing it was simply an interim season with what will likely be another uncompetitive power unit. The budget engine would have likely been equalised in some way -- explaining why manufacturers were resolutely set against it -- thus giving Red Bull a chance to return to competitiveness next year. Alas, that option for post-2016 is now off the table.

On top of that, the aerodynamic changes initially proposed for 2017 could be watered down due to fears initially raised by Mercedes about tyre pressures. Pirelli agreed with the world champions and that means F1 is likely to remain heavily slanted in favour of engine performance over aero under the new 2017 rules -- a bitter blow to the designers at Milton Keynes. Tempting another manufacturer into F1 is something Red Bull tried last year with Volkswagen but, as Honda's horrid first season proved, that is no magic solution either. Whether 2016 is another of Red Bull playing the pantomime role of pram-toy-ejector again remains to be seen, but at the moment it is hard to see how and when it can get back to the top of the pecking order under the current regulations.

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Force India

Making the next step

Force India was one of the most impressive teams in the second half of 2015. Spurred on by the introduction of the B-Spec VJM08 at Silverstone, it only failed to register a point at one race after the British Grand Prix. Sergio Perez's superb drive to a podium in Russia was just reward for the team after that improvement but now the key is building on that into 2016. It is clear no Aston Martin deal will happen in 2016 but there is no indication the team is behind schedule on delivering this year's car to the first test this time around. The aim must be to build on the successes of last year and perhaps challenge fellow Mercedes customer Williams higher up the grid. The team has limited resources compared to most of its rivals, but, in the last two seasons especially, has demonstrated the uncanny ability to do more with less. With the talented pairing of Perez and Nico Hulkenberg Force India has to be targeting a third consecutive year with at least one podium finish to its name.

Renault

Be competitive as a manufacturer

Renault faces a big task in its return to the grid. Wounded and humiliated in the last two years, the French manufacturer has been on the back foot since the beginning of the current turbo era. Even last year, a late engine upgrade at the Brazilian Grand Prix was met with criticism from Red Bull and it finished the year a distant third to Mercedes and Ferrari. It is easy to forget Renault powered four of the last six drivers' and constructors' champions. Red Bull's failure to give recognition to its French engine partner became a point of contention when the former world champions then laid the blame for 2014 and 2015's failures squarely at Renault's doorstep. From a PR perspective Renault's return as a manufacturer is a chance to fix the damage done by the breakdown of that relationship and its poor performances in the V6 turbo era, to prove Viry-Chatillon has not forgotten how to make winning engines.

The benefit of being a factory team is the control of everything in-house, everything moving towards a similar goal. The negatives are not being able to deflect blame to a customer team -- failure to eventually deliver a competitive package will be laid squarely (and fairly) at Renault's doorstep. Winning another championship will be a huge challenge, especially with Mercedes enjoying such a strong start, but one Renault must be praised for taking up when walking away from F1 looked like the easier choice at the end of last year. The goal this year must be simple: at the very least stay in front of Honda and claw back the gap to the front. Its first issue will be recovering from last year's deficit and the delay in development which came from its protracted takeover of Lotus.

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Toro Rosso

Treading water with Ferrari

There's good news and bad news for Toro Rosso going into 2016. The good -- it has retained one of the most exciting driver pairings on the grid in Max Verstappen and Carlos Sainz while securing Ferrari power units which kept it on the grid. The bad -- those engines will be a year old. It's not fair to look at Manor bringing up the rear in 2015 with a year-old Ferrari engine as a comparison; Ferrari took a huge step between 2014 and 2015 and Manor was a team with limited resources and zero upgrades through the year. However, the drawbacks of the delayed engine deal are already clear -- the team will run with a temporary testing livery in the opening Barcelona test because it is behind schedule. The team is also likely to see a drop off in performance as its rivals receive upgraded power units through the year but the big question is whether the 2015-spec Ferrari is better than the new Renault power unit in Australia. However, as evidenced by its lock out of the third row in Spain last year, Toro Rosso has a very gifted design team and will start the new season with an engine some said was level with Mercedes on power output by Abu Dhabi.

Sauber

Anywhere but the back

Two teams finished behind Sauber in 2015 -- McLaren and Manor. Events in the last few months about both will have caught the Hinwil team's attention. Manor's acquisition of Mercedes engines for 2016 will have been a concern, while Honda will not expect another year so far off the pace as it targets improvements in its engine this year. Though Sauber enjoyed a strong start at last year's Australian Grand Prix it then dropped down the order, with its lack of resources meaning it struggled to keep up with those around it. The team will benefit from its Ferrari power unit but will also face competition closer to home in the form of Haas. The American debutants join the grid on the back of a highly-publicised technical partnership Ferrari which has included extensive use of the Maranello wind tunnel. Sauber will not want to be beaten by Haas, nor Toro Rosso, which will compete this season with a year-old Ferrari engine. Staying away from the back of the field is an unfortunate but realistic aim for the team this year.

McLaren

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The only way is up

It was painful to watch the McLaren MP4-30 drive in a straight line in 2015. Both drivers put on a brave face through the team's worst season since 1980, optimistic about what 2016 would bring. Honda knows where it went wrong last year, failing to deliver on the Energy Recovery System (ERS) and encountering performance problems from the slim packaging of its power unit in McLaren's 'size-zero' concept. There were glimmers of strength through corners in the final races of the season but this was often lost in the fact the McLaren was a sitting duck in a straight line. Honda has responded with significant changes to its engine for 2016, including a bigger turbocharger. Mercedes is not taking the threat of Honda lightly this year and it seems both the manufacturer and McLaren learned valuable lessons through their struggles in 2015. Hanging over everything is the fact the team has two former world champions, Jenson Button and Fernando Alonso, waiting for the team to deliver a competitive car. Alonso is considered by some to be the most complete driver of the current era and he will surely not tolerate another season so far off the pace. Rumours of a sabbatical were immediately quashed last year but you can bet the first question to Alonso after sampling the MP4-31 in Barcelona will be whether he plans to see out the 2016 season with McLaren. A tongue-in-cheek question, maybe, but a fair one given the fact time is running out on his bid for a third world championship.

Manor

Cracking the midfield

Manor enters an exciting season in 2016, equipped with new Mercedes engines, a technical partnership with Williams and a raft of big-name recruitments. The team spent much of 2015 treading water with year-old Ferrari engines after a remarkable comeback from administration. The team's new name and logo suggests a break from the past, which included the departure of key figures John Booth and Graeme Lowden. In their place come figures such as Dave Ryan, Pat Fry and Nikolas Tombazis and they have been immediately tasked with a step up the grip. Mercedes boss Toto Wolff thinks his newest customer team can challenge the midfield this season and the onus will be on the perennial backmarkers to live up to those expectations early on. Joining the team's ranks is the exciting Pascal Wehrlein, DTM's youngest ever champion, and he has the talent to help spearhead Manor's challenge this year, while Indonesia's Rio Haryanto brings valuable resources to the team. Former sporting director Lowden memorably said the team will have "nowhere to hide" this year with Mercedes engines and the same gearbox and rear suspension as Williams. That assessment is correct and it is now down to Manor to prove what it can do with arguably the most even playing field it has had with its closest rivals since joining the grid as Virgin in 2010.

Haas

Avoiding new team syndrome

It's always risky when a team boss or owner of a new team makes predictions about the debut season. Haas' strong links to Ferrari have already set tongues wagging about immediately challenging the midfield in its first season. Wisely, team boss Guenther Steiner has been at pains to temper expectations around the American outfit. But this is not just another new team joining the grid. Haas' extensive use of Ferrari's facilities at Maranello last year will have been an enormous benefit. Couple that with the fact Gene Haas has considerable resources to throw behind his F1 team and it is easy to back up the expectations some have about the Kannapolis team. Haas arrives with racing acumen from NASCAR and, in Romain Grosjean, one of the most talented drivers on the grid.

Haas' debut season feels somewhat bigger than just another team joining the grid. F1 is currently facing an important moment in its relationship with the United States. The U.S. Grand Prix has become a re-established, popular venue on the calendar at Austin's Circuit of the Americas but financial doubts continue to linger about its future. With talk of another West Coast grand prix joining the calendar in future, plus F1's failure to attract new teams to the grid in recent years, the success or failure of the Haas team this year and beyond will not be insignificant.