How much difference can 5g/km of CO2 make to a car?
In the case of the Volvo C30 DRIVe, quite a lot if you travel into and out of Londons Congestion Charge zone. It now emits just 99g/km of CO2 down from 104g/km and under new regulations cars emitting less than 100g/km are exempt from paying the charge saving owners up to £2500 a year.
You dont have to live in London to save money, either. As well as being VED road tax free, the C30 with the 113bhp 1.6-litre diesel engine averages 74.3mpg and has a decent 199lb ft of torque.
In order to achieve the 99g/km CO2 figure, Volvo has lowered the standard C30 by 10mm and fitted a different wheel design to reduce drag. Other aerodynamic improvements come from an altered radiator grille, reworked rear bumper, underbody panels and wind deflectors around the front wheels.
The car also uses engine stop-start technology, low-rolling-resistance tyres, longer gear ratios and low-friction engine oil. It also uses engine management, cooling and power-steering settings that have been optimised for maximum efficiency.
Youd expect such a long list of changes to have a dramatic impact on the performance of the car, but in reality the changes are only slight. The economy improvements are the result of each individual tweak delivering fractional improvements that add up to that magic cut of 5g/km.
That means there are no glaring shortcomings as a result of performance being traded in the pursuit of economy. At no point does the C30 DRIVe feel like it is struggling to pick up speed, and theres plenty of performance for the car to excel in its natural town habitat and even flow nicely on A-roads. Its not thrilling, but it is effective.
The only minor quibbles are the intrusion of some road noise on rough country lanes, numb steering and slightly long gearing if you want rapid acceleration. The ride is also slightly jiggly, especially at low speeds, but its not overly harsh.
On top of this, you get all the standard C30 benefits: composed handling, stylish looks and a well-built interior.
All that stands between this car and a higher rating are its cramped rear space and boot, which many people wont be able to live with. However, if you can make the compromise the C30 DRIVe offers something a little different.
Prices start from £18,905.
What Car? says