# Mechanical power transmission: Correlation Prices it moves with, and why Source page: https://www.materialinsights.org/energy/e_mechanical_transmission/correlation/ Gears, gearboxes, bearings, couplings and belts transmit power in machines from conveyors to wind turbines. Prices follow alloy steel, machining capacity and demand from industrial, mining and wind equipment makers, and are revised on price lists. Price index **US PPI: mechanical power transmission equipment** index · monthly, Jan 2006 to Sep 2026 #### What its price moves with Selected link ##### Mechanical power transmission and Steel Monthly changes 0.00 little or none correlation 12-month changes 0.12 little or none correlation Last 5 years -0.06 monthly changes Lead or lag +3 mo Steel tends to lead by 3 months (r 0.24) Price function, Jan 2006 to Sep 2026 Mechanical power transmission ≈ 11.8 × (Steel)^0.58 R² 0.58 On this fit, a 10% higher steel price goes with a 5.7% higher mechanical power transmission price over the long run. Units: index and index, BLS base period. Chart: Mechanical power transmission 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: Mechanical power transmission 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. Commodity [St Steel](https://www.materialinsights.org/commodities/steel/)Main material 0.00 Gears and shafts are machined from alloy steel. The index shows no monthly link to steel mill prices, correlating at 0.00, because machining, heat treatment and design dominate cost and list prices change only now and then. little or none co-movement month to month · 249 months Show charts Energy [Mot Electric motors and drives](https://www.materialinsights.org/energy/e_motors/)Paired equipment 0.27 Gearboxes are usually sold with electric motors to drive pumps, conveyors and machinery, and both follow industrial investment. Yearly moves correlate at 0.86 with the motors index, though monthly moves correlate only at 0.27. weak co-movement month to month · 249 months Show charts Energy [ICE Internal combustion engines and gensets](https://www.materialinsights.org/energy/e_engines/)Paired equipment 0.34 Engines drive generators, pumps and vehicles through gearboxes and couplings. The engines index correlates at 0.34 for monthly moves and 0.79 for yearly moves, as both are machinery priced by similar makers to similar buyers. weak co-movement month to month · 249 months Show charts Energy [WOn Onshore wind](https://www.materialinsights.org/energy/e_onshore_wind/)Demand driver 0.05 Most wind turbines use a large gearbox between rotor and generator, and gearbox failures are a major maintenance cost. The turbine proxy correlates at 0.53 for yearly moves, but monthly moves show almost nothing, at 0.05. little or none co-movement month to month · 184 months Show charts Commodity [Mo Molybdenum](https://www.materialinsights.org/commodities/molybdenum/)Alloy element Gear steels contain molybdenum, chromium and nickel for strength and hardenability. Spikes in these alloy metals add surcharges to steel bar prices, which can then pass through to gear and bearing makers. Not enough overlapping price history to measure. Chemical [Lub Lubricant additives](https://www.materialinsights.org/chemicals/lubricant_additives/)Gear oil Gearboxes run on oils blended with extreme pressure additives that stop gear teeth welding under load. Better additives extend gearbox life, which is why lubricant quality matters most in wind turbines and heavy machinery. Not enough overlapping price history to measure. How 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. ## Other sections - [Summary](https://www.materialinsights.org/energy/e_mechanical_transmission/index.md) - [Overview](https://www.materialinsights.org/energy/e_mechanical_transmission/overview/index.md) - [How it works](https://www.materialinsights.org/energy/e_mechanical_transmission/explain/index.md) - [Efficiency and losses](https://www.materialinsights.org/energy/e_mechanical_transmission/efficiency/index.md) - [Technology advances](https://www.materialinsights.org/energy/e_mechanical_transmission/advances/index.md) - [Value chain](https://www.materialinsights.org/energy/e_mechanical_transmission/valuechain/index.md) - [Geopolitics and regulation](https://www.materialinsights.org/energy/e_mechanical_transmission/geopolitics/index.md) - [Unit economics](https://www.materialinsights.org/energy/e_mechanical_transmission/economics/index.md) - [Impact on the biosphere](https://www.materialinsights.org/energy/e_mechanical_transmission/biosphere/index.md) - [Relationships](https://www.materialinsights.org/energy/e_mechanical_transmission/links/index.md)