"It certainly wasn't the start to the defence of our title that we hoped for," said Hartley. "Getting the win in Germany showed we can be as good as everyone else, but defending the title is almost out of reach now.
"In all the races so far, we have been one of the fastest in every qualifying session and even led the races at times. It's just been an unfortunate mixture of a few things that have caused us problems. Winning at the Nurburgring has given the team confidence that we are now back at our best."
The Mexican track is one of the highest encountered and, at 2250m above sea level, the air is a lot thinner. This will impact the engineers the most as they struggle to get the cars to breathe properly and understand how to get the most from the aero packages.
The thin air will also impact on driver fitness, as will arriving at the sharp right-left turn at the end of each lap as the track drops into a baseball stadium where an estimated 25,000 fans will be seated.
"It will be interesting to experience racing at high altitude, I arrived a couple of days early to acclimatise. I love to take on the challenge of learning a new circuit.
"It looks like a good circuit with a mix of street and road sections with a very long straight. Getting the downforce right will be a big challenge but we made progress with the new aero package at the Nurburgring. With the race being at such a high altitude, we'll have to wait and see how things go in practice.
"I have never been to Mexico, but from all I have seen the circuit looks great," said Hartley.
The 919 Hybrid is now clothed in its third iteration of aero design and it will be the last for 2016 as per the FIA rules to curb costs. There are adjustments that can be made for the remainder of the championship and, in a wise move by the organisers, teams have been allowed to fit extra cooling to cars.
The defending champions are a long way back from the leaders and will be focusing on collecting as many points as possible to keep Porsche in the hunt for the manufacturers' title.
"Car number one has been quick all year, but at the Nurburgring it finally all came together. Timo, Mark and myself will fight as hard as we can to stand on the middle step again in Mexico," said Hartley.
South of the border
• The six-hour race in Mexico City is the fifth out of nine rounds of the 2016 WEC.
• The circuit was remodelled and Formula One returned to it in 2015.
• One lap is 4.303km and has 17 corners.
• Race pace the 919 Hybrid is due for refuelling every 40 laps.
• Refuelling and changing tyres cannot happen at the same time.
• The drivers are normally changed only when new tyres are needed.
• Only four mechanics may work simultaneously when changing tyres and only use one wheel gun.
• A set of Michelin slick tyres should last two fuel tank fills.
