Why Isuzu PH didn't put rear diff lock on 2021 D-Max LS-E

And the story behind the 17-inch brakes on Isuzu mu-X

Isuzu Philippines is definitely having a better 2021, especially since both of their major nameplates are new generation models: the all-new Isuzu D-Max and the Isuzu mu-X.

The demand is so high that practically all units are spoken for as soon as they come out of the port. The pandemic, the parts shortage, and the tricky situation regarding unit allocation between Thailand, Australia, and the Philippines are proving to be complications. The demand is a “good” problem, but a problem nonetheless.

There are two things that we thought we'd revisit, the first being the 17-inch disc brakes on the Isuzu mu-X. Many viewers on our YouTube channel first spotted it during my preview video of the mu-X 2 months ago where I mentioned it had 17-inch discs.

On the spreadsheet for the specs, it did say 17-inch, but viewers were quick to point out that it looked far smaller than that. That's on me; I didn't measure at the time, and when I did for the full review where we really drive it, the brakes were about 12 inches in diameter. I say “about 12 inches” because it's hard to get a precise measurement unless you have a caliper that can go that big; the only caliper I had goes to 7 inches.

We informed Isuzu about the error last month and during the Philippine Rallycross Series that happened yesterday, we caught up with IPC executives and they confirmed the internal error. The funny bit is that no one is admitting that they made the error. In their words: "Walang umaamin". 

They have since edited their material (e.g. brochures) to reflect the proper measurement: the mu-X has 12.5-inch discs front and rear.

The other aspect that needs revisiting is the electronic locking rear differential or the lack of it. In the mu-X 4x4 LS-E it's understandable given that they're aiming for a family vehicle, but in the D-Max 4x4 LS-E it is very strange. A lot of 4x4 enthusiasts naturally gravitate towards the pick-up class, and that alone makes it odd. They do have the E-Differential Lock (EDL) fitted to the lower grade D-Max LS 4x4 MT, but if you want an automatic 4x4 with all the bells and whistles (and ADAS) then you won't get EDL. 

That is a strange choice made by Isuzu Philippines, and now we have the explanation. When Isuzu Philippines was planning for the local introduction of the Isuzu D-Max, they conducted a survey among D-Max customers, and over half of them said that they don't know what a locking rear differential does, and thus felt that it wasn't necessary. Isuzu took that customer feedback to heart and left it off of the LS-E.

We're wondering why customers answered that during the survey, but we understand because many customers don't really go off-road. So we thought we'd explain the benefit: a differential lock is one good feature to have and not need than to need and not have.

A normal “open” differential allows one wheel (either left or right) to spin at a different rate versus the opposite wheel; this makes cornering easier and quieter. The problem there is that the drive goes to the path of least resistance like how lightning finds the shortest or easiest path to the ground. If that is what happens, it means while you're going off-road and one wheel is suspended in the air, all your drive goes to that wheel which has minimal resistance because it's not in contact with anything. And you end up stuck.

A locked differential removes the path of least resistance principle. It'll make turning more difficult and louder, but even on tricky terrain, it's a godsend. If used properly you should be able to get through, without the need for advanced electronics with different off-road modes.

The lack of a locking rear diff isn't an easy upgrade for 4x4 enthusiasts because these kinds of parts are very specific to the model. And we asked Isuzu if a customer can opt for a locking rear diff in a D-Max LS-E or mu-X LS-E, and the answer is that it's not that simple even if you're willing to wait.

Given that both models are all-new, we expect Isuzu to start fitting those features to later updates or variants of the D-Max and mu-X. I have a feeling they'll save it for some kind of “Boondock” model which is usually targeted at 4x4 enthusiasts.