2010 Honda Insight EX: Suspension Walkaround
July 22, 2009
Car-of-the-Week status means it's our 2010 Honda Insight's turn to be put in a compromising position so we can have a look at the suspension. This won't hurt a bit.
Seeing as how the Insight shares significant chucks of undercarraige with the Honda Fit, one would think that we wouldn't see any major surprises. That's partially true, but there are some differences and I've included a lot more detail this time.
Up front, the Insight shares a lot of parts with the Fit. It's your basic MacPherson strut set-up with a coil-over spring and a single lower ball-joint. The steering pivot axis is illustrated by the thin yellow line.
In case you've wondered, a MacPherson strut suspension has no upper control arm because the strut itself is very rigid in the lateral direction, and can therefore define the path along which the suspension moves. To do that it must be bolted firmly to the steering knuckle with two large bolts (yellow), making the whole affair one solid, albiet telescopic, piece all the way to the pivoting mounting point at the top.
Struts also act as dampers, of course, so they have all the internal valving and oil that a shock would have. But even though all the parts appear interchangeable, the spring and internal strut damping of this Insight will be different from the Fit because of differences in vehicle weight and weight distribution.
By comparison, shock absorbers are relatively flimsy because they are not asked to take the lateral loads that are necessary to actually locate and define the movement of a suspension. Of course they do just fine at "absorbing shocks" when subjected to pure compression and tension loads, and they can be smaller and lighter because supesnion arms and/or links does the suspension locating for them.
The lower end of the Insight's suspension is located by an L-shaped lower control arm with a single ball joint at it's outer end. The steering rack and steering arm (green) are located behind the ball-joint because it's generally not possible to mount the steering rack ahead when a tranverse engine and transmission mounting is used.
The front subframe bolts directly to the unibody, a move that saves money and weight while it improves steering feel and direct response. This isn't the path to ultimate road isolation and extreme cabin silence, but Honda has never prioritized such things to the extent that some of their home-market competition has done.
The Insight's front stabilizer bar is direct-acting, as evidenced by this long, slender link that connects directly to the strut housing.
In most cars the upper strut mount is obvious when you pop the hood, but the Insight's hood is so short that the sturt-top is actually hidden in a pocket under the base of the windshield.
The Honda Insight's brakes use a single-piston sliding caliper and a one-piece ventilated rotor. The term "regenerative braking" is associated with hybrids, but that's an independent electricfied version of engine braking that has nothing whatsoever to do with the standard brake system, which operates in an utterly normal way.
The unmoving rigid half of a sliding caliper bolts directly to the suspension knuckle (yellow) and holds the pads in place. The single hydraulic piston that does the work is implied by the single cylindrical bulge (green) in the caliper body. The moving half of the caliper follows a pin (green line) as it slides back and forth as the brakes are applied and released.
The Insight's rear suspension is a twist-beam axle, a semi-independent form of suspension that is very space efficient.
This axle pivots around two mounting bushings, represented here by the green circle and one like it on the other side. These are the only two mounting points to the body, in fact. OK, the shock absorbers have internal stops to prevent the wheels from extending down so far that the springs fall out if you jump the thing off a ramp -- I'll give you that. But the two forward pivots are the only points at which this type of axle is truly located.
It's basically like a very wide motorcyle swingarm with two wheels on the outside instead of one clamped in the middle.
The single c-shaped channel (white) spans between these arms, and it's designed to be twisty from one side to the other; hence, twist beam. It's categorized as semi-independent, however, because it's all one piece; what happens on one side has a limited effect on what happens on the other side.
Here's another look at the twisty cross beam and the rigid arms. A lot of times you won't see a rear stabilizer bar on one of these. But that's not really true because what you're looking at, in effect, is one giant stabilizer bar with wheels bolted directly on the ends.
The beauty of this suspension type is the packaging potential, because the slender cross beam (yellow) doesn't need much space. This leaves room for a huge well (green) between the tires of sufficient size to house the Insight's hybrid battery pack, spare tire, tools and a bit of storage.
Those arms need to be rigid, and that plays right into the hands of the spring and shock mounts (yellow and green, respectively) which consist of welded-on pieces that act as gussets for extra stiffness.
Did I say this suspension has no rear stabilizer bar? Well, that depends on how you look at it. The flexy c-channel itself amounts to a stabilzer bar, but it also houses a supplemental round torsion bar (yellow) that's there to fine-tune the torsional stiffness of the entire assembly. After all, the design engineers can't predict exactly how much stiffness will ultimately be needed and the suspension tuning engineers need a way to dial-in the appropriate amount of roll stiffness once they get their hands on a running prototype.
The rubber bush shown is slipped over the center of the bar to keep it from rattling around and making noise over bumps.
Here's where this supplemental torsion bar disappears into the side-arm where it is firmly welded in place (I think -- can't see in there).
The nub ends of the supplemental torsion bar (green), and the welds that hold it in place, are clearly visible. Honda's continued use of drum brakes in the rear speaks for itself.
Unlike a motorcycle swingarm, the two main pivot bushings are NOT oriented perpendicular to the direction of travel. Cocking them at an angle (looks like 30 degrees here) helps balance the need for high lateral stiffness when cornering against the need for a little fore-aft compliance to mitigate harsh road impacts.
All of this sits on 15" aluminum alloy rims and 175 / 65 R15 low roll-resistance tires that weigh 34 lbs mounted and ready to roll.
Dan Edmunds, Director of Vehicle Testing @ 2,235 miles