There is loads of confusion regarding this at the minute, i will try and simplify it.
Cars Registered before March 1st, 2001, there is only two bands-
Up to 1549cc = £115 12 months, £63.25 6 months
Over 1549cc = £180 12 Months, £99 6 months
Cars Registered on or after March 1st 2001 are put into bands (A to G) CO2 emissions and fuel type would determine which band the car is placed, the number of wheels driven is not a factor.
CO2 emission figures (g/km) = its carbon dioxide emissions level in terms of grams per kilometre driven.
Petrol car 12 months rate, 6 months rate in (brackets)
A up to 100 (g/km) £0.00
B 101-120 (g/km) £35.00
C 121-150 (g/km) £115.00 (63.25)
D 151-165 (g/km) £140.00 (£77.00)
E 166-185 (g/km) £165.00 (£90.75)
F Over 185 (g/km) £205.00 (112.75)
So basicly, pay it once a year else you will be paying £225.50 for a £1*2
Cars registered on or after 23 March 2006
G Over 225 (g/km) £300.00 (£165) going up to £400 next year, this band only applies to cars made on or after 23/03/06.