2016 Toyota Tacoma: Making Sense of Our Death Valley Results
by Dan Edmunds, Director of Vehicle Testing
The fact we blew out both rear Bilstein shocks on our 2016 Toyota Tacoma has created a lot of consternation among pickup enthusiasts in general and the Tacoma community in particular. Among other things, the refrain "Bilsteins are crap!" is something I've been reading and hearing.
Not so fast. I'm not jumping on the "Blame Bilstein" bandwagon, even though I was as surprised as anyone else as our own shocks sat there smoldering in Death Valley. There's more to the story than what you've seen and read so far, and after thinking it through I've got a good grasp of what happened.
And I know more than a little something of the backstory. After all, I was the engineer at the proving ground who was responsible for tuning the suspension of the very first TRD Off-Road Tacoma when I worked at Toyota in the 1990s. No, really. It was me.
We all know the Tacoma is a traditional body-on-frame pickup. Its rear end rides on leaf springs and a solid rear axle that's chock full of axle shafts, bearings and a locking differential. It also has brake assemblies and large all-terrain tires at either end. All of that stuff represents hundreds of pounds of below-the-frame unsprung mass that must be controlled and managed.
Now run that suspension across a washboard road, which, as we've all just seen, can be more punishing than it looks. When you drive on such a road, the truck itself stays level while the tires and suspension stroke up and down over and over again. This type of road excites unsprung mass like no other.
Shocks are there to control and regulate those motions and keep the wheels from bouncing off the road like a dribbled basketball. They do this by squeezing oil through a carefully tuned labyrinth of tiny passages and deflecting discs, a process that creates resistance (aka damping force) and heat.
Each washboard bump is only an inch or so high, and getting rid of that incremental amount of heat is no big deal when you consider just one. But our washboard path was a never-ending series of sinusoidal ripples that came at the rate of something like 3,500 to 4,000 bumps per mile. At that pace, heat builds up in a hurry if you can't get rid of it fast enough. And by the time we pulled over and gawked at the smoking remains, the trucks had rumbled over more than 40,000 of them with no letup.
Bilsteins are monotube shocks, a type that's especially good at shedding heat because the single-wall design allows the heat generated within a direct path to radiate out. It's one reason why you see them on many off-road package trucks. So what happened here?
This is where my insider knowledge comes in. When I tuned the first-generation Tacoma TRD Off-Road package back in the early '90s, Bilstein was the shock absorber vendor that was selected. A lot of the aftermarket brands we know today weren't in the business back then, and Bilstein was an obvious choice that tied in well with Ivan Stewart's Baja racing efforts, which were still going strong at that time.
Trouble is, I was only given clearance to use the 36mm Bilstein shocks on the rear of that Tacoma, the skinniest ones Bilstein makes. The front end used the larger 46mm version, but at the rear the design team worried about clearance with the fatter shock bodies when the rear suspension was fully articulated in off-road flex mode.
The truck went on to be a bigger success than any of us ever imagined. But later, when the Nissan Frontier Pro-4X was introduced, I quietly seethed because it had 46mm Bilsteins hooked to its rear axle. And Bilstein offered 46mm Tacoma shocks in its aftermarket catalog that I couldn't use either. Heck, the first Miata sport package used 46mm Bilsteins.
I left the company before the second-generation truck reached the prototype stage, so I never got the chance to raise the subject again. Two jobs later, fast-forward to our recent video with me marveling at the blown rear shocks on our 2016 Tacoma in Death Valley.
All of this came flooding back after the initial surprise wore off, and it finally dawned on me that Toyota is still using 36mm rear shocks. This despite the third-generation truck being much larger and significantly heavier — some 750 pounds or so — relative to the original truck I worked on. I hadn't thought about it for years, but part of me assumed I'd see 46mm Bilsteins under there.
How big a deal is this? I did the math. A 46mm shock body of the same overall length would contain about 63 percent more oil in which to absorb and distribute the same amount of heat. Its shock body would have 28 percent more surface area through which said heat can radiate. And it'd most likely have a larger-diameter rod and corresponding shaft seal (the part that blew out of ours), which would greatly reduce the stress on the seal itself.
In short, a pair of 46mm Bilstein rear shocks on the back of our Tacoma probably would have survived. The fronts certainly came through, but don't read too much into that because that end also features an independent suspension with far less unsprung mass.
And don't be distracted by our Nissan Titan XD, which had trouble despite 46mm Bilstein shocks all around. The Titan XD is a much larger and beefier heavy-duty full-size truck. There's much more unsprung mass pushing energy into its shocks. And don't forget that HD trucks usually have higher recommended tire pressures — 60 psi in the XD. It's a far more difficult problem.
In any case, auto manufacturers are caught in a pickle. They have to build to a price, and the line has to be drawn somewhere. They know the aftermarket for bolt-on parts such as tires and shocks is robust. They also know that the truly hardcore users not only will but want to upgrade their trucks no matter what the factory gave them. The internet is full of forum discussions and Instagram accounts that revel in this, and wheels, tires and suspension bits are among the first things to get swapped out.
But 36mm? Come on.
Dan Edmunds, director of vehicle testing @ 30,086 miles