The Volkswagen Golf rival is set to be offered in three variants: a five-door hatch, an estate, and a four-door coupé targeted at the European market, but the three-door shape will be dropped because of poor sales figures.
The latest test mule was spotted towing a trailer as part of its development. Previous mules have been seen winter testing in the Arctic and Swiss Alps, as well as undergoing performance tests at the Nürburgring - where Hyundai has a dedicated development centre.
While the camouflage of the early-stage mules covers up most of their styling features, we can see the new i30 will come with a revised grille similar to that used by the facelifted car and the updated i40.
i30 N performance model
Key to the success of the next i30 will be a range-topping performance version, which will be the first road-going model to come from Hyundai's N Performance sub-brand. That model has already been spotted testing at the Nürburgring and will compete with the likes of Volkswagen's Golf GTI when it goes on sale.
It will get a 2.0-litre turbocharged engine and could have a top speed of around 155mph.
Hyundai officials have also confirmed the i30 N will use technology derived from Hyundai's i20-based WRC car, which is also built by the N Performance division. The Korean firm's current rally car runs a 1.6-litre four-cylinder turbocharged petrol engine producing 296bhp.
i30 engines and tech
Further down the range, the recently launched i30 Turbo will continue to be powered by its current 183bhp 1.6-litre Gamma GDI petrol engine, while the rest of the i30's petrol and diesel engine range will be carried over with minor changes.
A hybrid version of the next i30 - using technology garnered from Hyundai's Ioniq hybrid model - can't be ruled out. The Ioniq mates the i30's 1.6-litre petrol engine with an electric motor to offer a claimed 79mpg.
Clues to the look of the next i30's interior could come from a preview picture for the US-market Elantra, which sports a minimalist, buttonless design and a redesigned centre console. The i30 hatch is sold as the Elantra GT in the US.
Darren Moss and Sam Sheehan