Combustion road vehicles: Correlation
Prices it moves with, and why
Vehicle prices are set by carmakers' list prices and model cycles, and move slowly. Steel, aluminium, catalysts and tyres feed costs, while fuel prices shape what buyers choose. The index covers all US light vehicles, so it cannot separate engine types.
Proxy US PPI: automobiles, light trucks and utility vehicles index · monthly, Jan 2006 to Sep 2026There is no free public price for combustion road vehicles itself, so this tab uses the closest public series as a stand-in. Read the numbers as an indication, not as the price of this exact item.
What its price moves with
Selected linkCombustion road vehicles and Steel
Monthly changes -0.16 little or none correlation 12-month changes -0.01 little or none correlation Last 5 years -0.14 monthly changes Lead or lag +5 mo Steel tends to lead by 5 months (r 0.14) Price function, Jan 2006 to Sep 2026 Combustion road vehicles ≈ 42.9 × (Steel)0.23 R² 0.49 On this fit, a 10% higher steel price goes with a 2.2% higher combustion road vehicles price over the long run. Units: index and index, BLS base period.Chart: Combustion road vehicles and Steel prices rebased to 100 at Jan 2006, log scale
Both prices rebased to 100 at Jan 2006, on a log scale so equal percentage moves look the same size.Chart: Combustion road vehicles price against Steel price, monthly, log scales, with fitted line
Each dot is one month; paler dots are older (2006), darker dots recent (2026); the ringed dot is the latest month. The dashed line is the fitted price function. Both axes are logarithmic.Car bodies and frames are mostly steel, but the vehicle index does not follow it, with monthly moves correlating at -0.16. Carmakers buy steel on annual contracts and change prices with model years, so metal costs are hidden in margins.
little or none co-movement month to month · 249 months Show chartsCatalytic converters use platinum, palladium and rhodium to clean exhaust, and emission rules keep demand high. Monthly moves correlate at -0.15 with platinum, showing no pass-through: metal costs are absorbed by carmakers and suppliers rather than appearing in list prices.
little or none co-movement month to month · 249 months Show chartsPetrol and diesel prices shape running costs, so high oil prices push buyers toward smaller, hybrid or electric cars. The vehicle index barely reacts, with monthly moves correlating at -0.04, because vehicle prices respond to model plans, not fuel swings.
little or none co-movement month to month · 249 months Show chartsTyres use natural rubber alongside synthetic rubber and carbon black. Monthly moves correlate at -0.17 with rubber, so rubber prices do not show up in vehicle prices; tyres are a small part of the cost of a car.
little or none co-movement month to month · 249 months Show chartsCarbon black, made from heavy oil, reinforces tyre rubber and makes up a large part of each tyre's weight. Monthly moves correlate at 0.23 with the vehicle index, a weak link that mostly reflects shared US manufacturing cycles.
weak co-movement month to month · 249 months Show chartsThe engine is one of the costliest parts of a combustion car. Monthly moves hardly correlate, but yearly moves correlate at 0.43, showing that engine and vehicle prices share a slow US manufacturing cost trend.
little or none co-movement month to month · 249 months Show chartsHow to read these numbers
Correlation of monthly changes (the number in the coloured pill) compares how much each price moved, month by month, since 2006 or the first month both series exist. It runs from −1 to +1: near +1 the two usually rise and fall in the same months, near 0 there is no link, and a negative number means they tend to move in opposite directions. Above 0.7 is strong, 0.4 to 0.7 moderate, 0.2 to 0.4 weak.
12-month changes compare year-on-year moves, which shows whether two prices share the same cycles even when the month-to-month noise differs.
Price function is a straight-line fit of the two prices on logarithmic scales: price ≈ k × (partner price)β. β is how much this price moves, in per cent, for a 1% move in the partner over the whole period, and R² is the share of the variation the fit explains. Two prices that both drift up with inflation can fit well without any real link, so read it together with the monthly correlation.
Lead or lag checks whether the monthly correlation is clearly higher when one price is shifted by 1 to 6 months.
Correlation is not cause. The reasons on each card explain the economic link; the numbers show how strongly it has shown up in prices. Proxy series are US producer price indexes or related prices and can blur the real link.
Data: World Bank Commodity Price Data (Pink Sheet), October 2026; US Bureau of Labor Statistics producer price indexes, IMF primary commodity prices and US EIA prices via FRED, Federal Reserve Bank of St. Louis, retrieved November 2026. Calculations by this site.