Gasturbine

I’ve noticed, when on a hard surface, at full turn lock, it feels like I’m getting some binding in the front, and tire scuff. It reminds me exactly like a having a 4wd truck (in 4w lock) and making tight turns on asphalt.

So do our cars have a conventional “transfer case” and front diff, IE; everything hard locked together? If so, I’m going to deem it normal, and adjust my driving style, but if not?

arentz07

Naturally, there's a transfer case, but it isn't like a truck 4WD system. There's no front diff, for instance. I believe what you are experiencing is just thanks to the suspension geometry of the AWD cars. I had the same thing happening on my 2016 IS 300 AWD if I turned the wheel to full lock. Doesn't happen on my 2021 RWD car, and a friend with a 2015 RWD said he didn't have it either. There have been posts about this topic on ClubLexus before, but I haven't tracked them down yet.

Sasnuke

I get the same thing you mentioned...file it under normal.
Yes it has a transfer case, but unlike a truck, the mode is not driver selectable...the ECU does the magic in the background.
The front diff. is just your regular old diff.
i chalk it up to 4WD axle windup or binding that naturally occurs when making tight turns.

Gasturbine

Yup, as I suspected. I remember the early Subaru "AWD", the "transfer case" was actually a 3rd diff so it wouldnt bind, and the power was equal to all wheels, BUT, if you lost traction to any one wheel, that wheel would take all the power. Im sure it has been refined currently tho.

Thanks Sasnuke!

SonarSpeed

Our AWD system isn't a pure mechanical AWD system like those Subarus and Audi torsen AWD system. It's bassicaly a knockoff version of Nissan ATTESA system found in the R32/33/34 GTR in the 90s where the front and rear are mechanical but the 3rd diff is replaced by the TCU and it decides wether to go 30:70 or 50:50 bias based on what triggers the VSC or TC. Also our AWD and 99% of AWD systems out there will do exactly what you mentioned. If you lose traction to any one wheel then it will take all the hp that is diverted to the front or rear differential. This is only fixed by installing a LSD in the front and rear however no one makes them except for people who have Subarus and old Audis

Gasturbine

I would love to see a schematic or diagram of our system, but have search far and wide, no luck.

So I presume the 70% is to the rear...

Again, Id like to know how this all works. Im also curious what my "Snow" button does...maybe put it in 50/50 all the time?

Answer

70 rear, 30 front, you are correct. And yes, snow mode is supposed to make it 50/50 and will allow less slippage.

SonarSpeed

There's no official Schematic or diagram on how our system work but like I said above, how our system work is how the Nissan ATTESA system works (like 99% the same) and there's some diagram on those. The difference between the two is how the TCU controls the system.

For your question about snow mode, it decreases throttle and brake response and shifts slower. Supposedly (not confirmed) the car ECU will cut power and the TCU will also kick in VSC and TC sooner. Personally never experienced that but quite a few IS AWD owners have said it does happen. It also does NOT make the AWD system 50:50 like someone said above. 50:50 only kicks in whenever TC and/or VSC kicks in. Which is unfortunate but whatever you gotta live with it. >.>

Pretty good article on the ATTESA system and how it works: https://dsportmag.com/the-tech/educa...it-technology/

arentz07

Subjectively, I found that my former 2016 IS 300 AWD was less likely to oversteer when Snow mode was enabled. It was much easier to slide/do donuts with Snow mode off.