When you think power reserve, you thought that the 7-day IWC’s or the 8-day Panerai’s were already massively powerful – and obviously, they have more power than 99% of the mechanical watches produced. Well, if power is your thing and if you simply hate to wind a watch, you might have to consider the cheap A. Lange & Söhne Lange 31… and 31 here is nothing about the diameter of the watch, but it is about the length of the power reserve, in days. Yes, this watch can run for 31 days, coming from one single barrel, when fully wound. Impressive, right. This powerful watch comes in a new version for the SIHH 2017, in white gold with a grey dial.
The A. Lange & Söhne Lange 31, when introduced in 2007, was the wristwatch with the longest power reserve available, and the first watch to have 31-day / 744h energy stored in a single movement. If some others achieved to reach a 50-day / 1,200h power reserve (Hublot with their MP-05 LaFerrari) it was only because the movement stacked 11 mainspring barrels. In the case of the Lange 31, everything comes directly from one single barrel, with a two mainsprings that each measures no less than 185 centimeters (approximately the length of average Joe). These two springs are actually so long and so rigid that you couldn’t wind them classically, by rotating the crown. Thus, winding is done via the caseback, with a separate key that inserts in a square socket in a recess of the sapphire crystal back. Its technical features include an integrated backstop ratchet for smooth and easy winding as well as a torque limiter that prevents unintentional overwinding of the springs.
Still, as impressive a 744 hours / 31 days power reserve movement can be, if this comes from one single barrel, it will immediately create a huge issue, an issue that will drastically affect the precision of the watch. The two mainsprings that are featured in the Lange 31 are so strong that, when fully wound, they will deliver an enormous amount of torque to the movement, a torque that could simply damage the escapement. Yet, the torque will gradually decline toward the end of the power-reserve period – and that mean that the power sent to the escapement won’t be linear at all and that the amplitude of the balance will be greatly affected, meaning poor accuracy of the watch over the length of the power reserve. The solution found by cheap fake A. Lange & Söhne UK is constant-force escapement, which aims in smoothening the torque of the mainsprings over the length of the power reserve. A remontoire between the twin mainspring barrel and the going train delivers a constant amount of energy to the escapement every ten seconds, so consequently, the balance always oscillates with the same ideal amplitude (a same device can be found in the Lange TerraLuna).
For the SIHH 2017, this best replica A. Lange & Söhne Lange 31 (which was previously available in platinum with rhodium dial or in rose gold with silver dial) will now be offered in a limited run of 100 watches, in white gold with a grey dial and brown leather strap. The case still measures a large 45.9mm diameter and 15.9mm height, dimensions that are simply explained by the massive size of the barrel. Lots of power requires lots of space. Price: 142,300 Euro.