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Differentials ratio experiment -

  / stacjakontrolitrakcji     / 4x4.tests.on.rollers   We didn't describe well the purpose of our last experiment, where one side of the car was on asphalt and the other on rollers, and we counted the revolutions of the front and rear wheels and observed their precise position relative to each other (markers on the wheels). The goal was to check whether the rear differential and power transfer unit ratios were the same or different, meaning whether one axle (in this case, the rear) was spinning faster than the other. Obviously, there already were experts who argued that the ratios had to be equal, otherwise everything would grind to pieces and fall apart, so why even ask such a meaningless and pointless question? ;) So, what's the point? Manufacturers sometimes use a very small difference in gear ratios to achieve faster coupling response. This eliminates backlash in the system while driving, allowing to switch to full 2WD without maintaining minimum coupling engagement at all times. Nothing falls apart, firstly because the gear ratio differences hover around 1%, and secondly, in such cases, the coupling never goes 100% compressed. An example - Mazda 3 AWD, where the output ratio of power transfer unit is 0.390, and the rear differential is 2.533 (~0.395). In other words, with coupling fully compressed, 0.39 front axle rotation = 1 driveshaft rotation = 0.395 rear axle rotation (2.533 driveshaft rotation = 1 rear axle rotation). The same trick is used in Toyota GR Corolla, GR Yaris or Ford Focus RS but there the task is much more demanding (hence the extended coupling) – generating oversteering characteristics. Returning to the experiment – at launch, due to backlash, the marker on the front wheel slightly slipped, but after several dozen rotations, the marker on the rear wheel began to catch up with the one on the front. Unfortunately, the difference was so minimal that it is very difficult to say whether there was a deliberate difference in gear ratios or whether we are dealing with a measurement error. #duszaniespokojna #allgrip #suzukivitara