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 |   |   |  R&D Done Right - Tein USA's Coilover Development Process
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R&D Done Right - Tein USA's Coilover Development Process

A look at TEIN USA's coilover development process and why it's different from everyone else's.

Aaron Bonk
Oct 13, 2016

Those adjustable coilovers you've got bolted up underneath that Integra of yours didn't wind up there by accident. Before you monkeyed them into place, somebody a whole lot smarter than you went through all sorts of research and development to make sure they wouldn't just fit but would also make your car ride and handle better than before.

At least that's what you hope. As it turns out, not every suspension maker goes to the trouble of making sure every coilover's specifically suited for every application it'll bolt up to. Pseudo suspension makers that are famous for farming out manufacturing to places like China are just as famous for not giving a lick about things like damping characteristics, valving, and whether or not your 240 will handle worse than it did before you started.

And then there's TEIN, the renowned Japanese suspension maker who defines what research and development ought to mean, and who lays out the whole process of new-application development for us—no plane ticket to the People's Republic required.


Every TEIN coilover application bound for North American vehicles starts with test driving an unmodified version of whatever car they're aimed at. Here, TEIN USA's lead engineer, Nakai-san, makes use of one of the company's most accurate instruments—the seat of his pants. A half-hour's worth of him mobbing up and down the residential byways that circle around TEIN's Southern California headquarters is all he needs to determine things like starting points for the application's recommended ride height and reworked damping characteristics. What you don't know, though, is that all of this happens after the Japanese-bound version of the very coilovers that TEIN USA plans on selling to you already underwent the same process.

Tein rd tein rd stock acura tl suspension Photo 2/13   |   Preparing one of TEIN Japan's existing coilover applications for North American-bound vehicles starts with the engineers at TEIN USA test driving and collecting as much data as they can about the vehicle's original suspension.
Tein rd acura tl japanese coilover test Photo 3/13   |   Once TEIN's engineers understand the car's natural shortcomings, the Japanese version of whatever coilovers are being tested are installed and then subjected to a test drive and data-collection process.

Right about now you're wondering why in the world TEIN would go to the trouble of manufacturing and signing off on a perfectly good set of coilovers that are already being sold in Japan and then shipping them overseas only to have its U.S. arm test them again. The answer is asphalt, or, the dramatic difference between that which covers the street of, say, Tokyo, and that of Los Angeles. Differences like pot holes the size of toilet bowls and ruts the girth of cocker spaniels all mean that what's fit for Japan probably isn't suitable for, say, San Diego. And besides, for TEIN, a one-size-fits-all coilover just isn't an option.


But before Nakai-san can go on and implement the sort of valving characteristics he thinks whatever car he's experimenting with needs, he and fellow technician Chris Acevedo have got to bolt something of theirs up and go for another one of those test drives where Nakai-san's ability to pick up the sort of handling nuances you'd never notice begin to take shape. In most instances, the fitment varies little between Japanese and North American versions of the same car, which means the brunt of TEIN USA's job is left to the dampers' internals.

Tein rd tein shock body Photo 4/13   |   Initial coilover research and development takes place back home in Japan where TEIN's engineers ensure proper fitment. Since Japanese and North American versions of the same model typically share identical suspensions, TEIN USA's engineers are left to focus solely on ride quality and the dampers' internals.
Tein rd tein suspension springs Photo 5/13   |   TEIN's Japanese branch is also responsible for selecting the appropriate spring rates and spring types. Here, a more cost-effective tapered spring replaces the original OEM version and was designed to accept the original top mount, which also keeps costs down.


Right about now is when the Chinese-outsourcing coilover seller puts his stamp of approval on those shocks that China says most likely, probably, should work before slapping their own label on them and boxing them up. And right about now is when—for TEIN at least—the real work's just begun.

Tein rd tein coilover assembly pieces Photo 6/13   |   Here's where the real work begins for TEIN's U.S. engineers. Based upon engineer Nakai-san's recommendations, the dampers' compression and rebound valving is adjusted to what he thinks will best suit American roads. Here, a series of specific washers are placed in a strategic order and then slid onto each damper's piston.

The seat of Nakai-san's pants and his intuitiveness are what lead to the dampers' compression and rebound characteristics that he and Acevedo implement and that may or may not reap success their first time around. TEIN understands that American roads aren't always as well maintained as those in Japan, which means that this suspension maker isn't afraid to put in the work and offer two different part numbers for what may otherwise appear to be the same set of shocks—one for the U.S., and one for just about everywhere else. According to Acevedo, TEIN is the only suspension maker that goes to all this trouble, offering two different versions of what are, essentially, the same coilovers.

Tein rd tein coilover washers Photo 7/13   |   The specially shaped washer in the center and its precise grooves allow a specific amount of oil to pass by, determining things like compression and rebound characteristics. Nakai-san has a pretty good idea of where to start following the initial test drive, but it isn't uncommon for him to redo the process multiple times before getting exactly what he wants.
Tein rd tein needle valves Photo 8/13   |   Similar to the washers, a number of differently sized needle valves can be used to obtain the exact characteristics Nakai-san's looking for.

The whole process starts with implementing Nakai-san's recommendations that include a series of specific washers, shims, and needle valves that control things like how hard it'll be to compress or rebound those shock as well as how much fluid gets displaced while doing it. There's a whole lot more to it than just trial and error, though. According to Acevedo, shim selection is critical. "The Piston valve shims and base Valve shims have got to work together," he says, "otherwise a vacuum can occur inside, which can lead to all sorts of damping problems."

Tein rd tein shock body internals Photo 9/13   |   Before the dampers are reassembled, the washers are slid into place in the exact order that Nakai-san's determined will work best.
Tein rd tein twin tube display Photo 10/13   |   A specialized tool made by TEIN is used to fill each shock with its oil before being sealed up. This twin-tube display shock shows the oil-filled shock body and its piston that, when compressed, will displace the fluid in proportion to whatever washers, shims, and needle valves have been used.


At this point both Nakai-san and Acevedo expect the sort of ride and handling characteristics Nakai-san was aiming for but are fully prepared to undergo the whole process all over again, which, according to Acevedo, happens more often than not. "Experience and feel is what determines the changes we make," he says, which means that his and Nakai-san's spending as many as two days fine-tuning an application that the Chinese coilover hucksters would've passed off as acceptable 48 hours ago isn't uncommon at all. And make no mistake, it's those sort of things that, if you ask the people at TEIN, separate them from just about everybody else.

Tein rd tein engineer torque specs Photo 11/13   |   Nakai-san performs the final steps of assembly using a carefully calibrated torque wrench before installing the reworked coilovers onto the test car.
Tein rd tein engineer height recording Photo 12/13   |   Here, engineer Chris Acevedo dials in Nakai-san's recommended ride height before embarking on the first of what may be several road tests with the reworked dampers.
Tein rd tein edfc test fit Photo 13/13   |   TEIN's R&D process is nothing if not extensive. Here, mock-up EDFC stepping motors are installed to confirm hood clearance.

On the Road
By Rodrez

The stock suspension being removed in this article actually belonged to my personal car - a 2012 Acura TL SH-AWD that I picked up earlier this year as a daily driver. I reached out to TEIN about coilovers that they already offer for the vehicle and the timing was right, as they were on the hunt for my particular year/make/model to do some R&D testing for the Street Advance system.

The first thing I noticed about the TL when I was searching for a solid used car is that for a stock vehicle, the ride was remarkably stiff. Being that it's an SH-AWD model with a focus on performance handling, slow cruising on the freeway, something I experience weekly while commuting through Los Angeles traffic, produced a fairly bumpy ride. The trade-off: great handling for a little rougher ride is something I accepted wholeheartedly when purchasing the car. Still, I was hopeful that the right spring or coilover set up would help remedy some of the jolting rebound. Speaking with TEIN, I wasn't alone in my assessment, as the crew there commented that the factory TL SH-AWD suspension was one of the stiffest they'd come across - surprising when you think about all of the various models they deal with day in and day out.

When I headed back to TEIN to pick up the car, it sat fairly low, with less than an inch of wheel gap all around. Driving out onto the surface streets that run past the TEIN facility, the ride was noticeably more comfortable which, at first, was a concern. Was it so comfortable that the highly touted precision handling from the factory had been compromised? That concern was quickly stripped away about halfway through the sharp, snake-like freeway on-ramp that I entered. The crisp feel was certainly still there but with noticeably less body roll.

Entering the freeway around 5pm in Los Angeles is comical, but it was a good chance to feel the stark contrast that the new coilovers offered during the painful crawl down the 405. Thanks to the R&D efforts of TEIN, that rather annoying "freeway bounce" had been smoothed and was all but nonexistent.

I've never been a fan of the look of a vehicle lowered on stock wheels and the fact that this suspension will only increase the fun factor further with a more capable wheel and tire combo, well, my new wheels can't get here soon enough.

If I had to take a guess, I'd say this is somewhere around my 35th suspension set up since the automotive bug back in high school first bit me. In those early days, it was a nice, comfortable ride or sharp handling, but rarely both. These days, things have advanced considerably, and the best of both worlds is a tangible thing for those groups that are willing to go the extra mile - groups like TEIN.


Tein USA
Downey, CA 90241
By Aaron Bonk
416 Articles



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