The only thing I’m worse at than predicting car values is predicting tractor values.

But a relatively safe bet for the biggest sale at Mecum’s Spring 2011 Gone Farmin’ auction, scheduled for March 26, is Lot S33, a 1966 International 1206 Tractor from Tom Geyman’s unbelievable collection.

The 1206 is a milestone in IH history because it was the first 100-plus horsepower row crop tractor built by the company – a factory turbo-diesel hot rod, if you will, that saw plenty of action at tractor pulls when the work day was finished.

Beneath the 1206′s long red hood was a 361-cu.in. inline turbo diesel six-cylinder. The tractor was specially built to handle boost, with oil-cooled pistons, a hardened crankshaft, a large-capacity radiator and high-volume cooling fan, as well as a hefty engine oil cooler.

After some of the disastrous drivetrain and engine failures in late-1950s and early 1960s Farmalls, IH engineers overbuilt the 1206 with hardened transmission gears and stouter rear-axle components, as well as a larger PTO drive.

One of the problems IH engineers faced during testing of the 1206 was keeping it from tearing up rear tires. With more than 100hp on tap, conventional tractor rubber was no match, so heavy-duty meats had to be commissioned.

For more about the 1206 and other tractors in Geyman’s collection, check out Mecum’s auction catalog.