Why is there a huge bulge in 2021 Lexus IS 300 AWD’s driver footwell? We explain

Following an initial convert a few months back for the 2021 Lexus IS initial drive assessment, the revised luxurious sedan has returned to the Autoblog garage for a 2nd look. This center-of-the-road IS 300 AWD pairs a 260-horsepower V6 with a 6-velocity computerized transmission and 4 driven wheels, and frankly it really is the the very least exciting way to spec out the redesigned sedan. Although there are cars in this phase intended to get a general performance boost from their all-wheel-drive units even in dry disorders, the IS is just not one particular of them. Incorporating insult to injuries, you get trapped with a cramped driver-aspect footwell care of the engineering shenanigans that went into producing this program doable. 

Although we have mentioned this certain compromise just before, we seldom contact on the good reasons why it exists in the initial location. The fundamentals are relatively clear the standard IS utilizes a longitudinal, rear-wheel-drive powertrain. As is regular with this configuration, the transmission sits in a tunnel beneath the center console. This arrangement functions just great, furnished you never need to energy the front wheels. 

To do so in a conventional car like the IS calls for a literal close-all over maneuver involving the engine and transmission, which we have diagrammed for you beneath care of MSPaint. This is a little bit simplified for the sake of this write-up, and it need to be observed that this is not the only way to put into practice AWD in an inherently RWD system, but it illustrates how the energy for the front axle (pink) and rear axle (blue) flows from the transmission to the drive wheels.

To get juice flowing to the front axle, Lexus had to incorporate a parallel output shaft, exiting the transmission from the front with adequate clearance for the bell housing and engine, which sits amongst the transmission and the front differential. This calls for pretty a little bit of lateral access, meaning the housing has to extend considerably farther out than typical to accommodate it (yellow arrow). As a end result, the all-wheel-drive transmission appears to be like a great deal like a sci-fi gun with a chunky drum journal hanging off the aspect of it. The hump (over ideal) in the footwell is there to apparent this protrusion.

This fundamental configuration is just not one of a kind to Lexus. In actuality, if you look at a BMW xDrive cutaway, it really is equivalent. So, why no “hump” in other cars? There are multiple things, but to boil it down to what is most applicable, it really is a combination of the ensuing form of the Lexus transmission housing and the dimensions of the IS chassis. This compact, slender car simply has much less area to accommodate a large, vast transmission tunnel. Compounding this, the protrusion sits really considerably forward on the transmission, which is why the “hump” is in the footwell. In a BMW, the place of the protrusion would in all probability be beneath the driver’s seat, exactly where any related physique modifications would be much less clear. 

And why the driver’s aspect? Nicely, in Japan, it really is not the driver’s aspect. Presented the option amongst re-engineering the transmission for world wide marketplaces or simply acquiring the ideal way to skin the compromise, Lexus erred on the aspect of preserving some coin. And we recommend you do the similar. If you never need all-wheel drive in the IS, skip it. Not only do you get more fat, much less legroom and no dynamic benefit, you’re also shelling out $two,000 more for the privilege. 

There are a lot of good reasons to like — appreciate, even — the 2021 Lexus IS the all-wheel-drive program just is just not one particular of them. In any other case, this is an athletic, cozy car that retains some of the analog sense that so endeared us to compact activity sedans in the initial location, and a lot of of us here at Autoblog are hyped to the ceiling about the upcoming IS five hundred F Sport General performance product and its accompanying V8. By all implies, keep the little Lexus on your searching list just skip the AWD.