Lotus technical director Nick Chester says the E23 Hybrid's predictability in cornering has been the major step forward from Formula 1 pre-season testing.

Chester has be thoroughly impressed by the Mercedes power unit, stating the Lotus team has only used a single Mercedes PU106B Hybrid engine all winter and the consistency has enabled the drivers to extract better performances from the car.

The technical director added Romain Grosjean and Pastor Maldonado have been able to find the limits of the car much easier compared to last season's car. In the case of the Venezuelan driver, he unfortunately discovered the full limit of the E23 when he crashed heavily on the final afternoon of the last day of testing at the Circuit de Catalunya.

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"This year is looking a lot better, the power unit is a big step forward," Chester said. "The chassis is also a step forward, the drivers can get a lot more from it and it's easier to drive on the limit as well as being more predictable.

"We spent some of the test exploring the E23's suspension geometry and it has a lot of effect on the balance of the car in the middle of the slow speed corners. We're also making the car less sensitive for the drivers so it's easier to extract performance."

Chester also says the car has developed since the first pre-season test in Jerez with "bigger upgrades" expected after the season-opening race in Australia.

Explaining the current evolution of the Mercedes power unit, Chester says the team has adapted its cooling system around it but is happy with the progress made.

"The response of the power unit in addition to peak power does play a significant role and we have found that tuning our control systems has been made easier with a very responsive power unit," he added. "I don't think our approach changes as we're always aiming to make the car better.

"The area where we didn't take too many risks was the engine installation. We wanted to be reasonably comfortable with cooling and we've been quite conservative ahead of Melbourne.

"It's been a challenge to fit the engine as the rear surface of the chassis is quite different and we had to do a lot of work to have a neat installation. We've gone back to air to air charge air cooling because the packaging switch to Mercedes power on a short timeline meant we had to find a simple solution."

Reflecting on the 2015 pre-season testing programme, Chester is thankful for the consistent running which has helped banished the painful memories of last year.

"It's massively different in 2015 compared to 2014, straight out of the box we're running over 100 laps a day without problems. Given the number of changes, I'm pleased with the running and limited problems we've had."