2011 Ford Fiesta SES: Suspension Walkaround
We've finally tested the 2011 Ford Fiesta, and we like it a lot. To the surprise of no one, this fuel-efficient hatch isn't exactly a speed demon in a straight line. But the US-spec Fiesta, like its European counterpart, is very entertaining on back roads because it steers, handles (and rides) very well.
What's going on inside those wheel wells? We decided to have a quick look.
No magic here. The front end of the Fiesta is your basic MaPherson strut suspension.
Like nearly all front-drive cars with transverse-mounted engines, the Fiesta's steering linkage (white) works from behind the axle centerline. This in turn dictates that the brake calipers must be located in front.
The Fiesta's stabilizer bar link (black) is a direct-acting type, so named because it connects the stab bar end directly to the strut housing for an efficient 1:1 motion ratio that allows a smaller-diameter bar to get the job done.
So far everything we've seen is shared with the Euro-Fiesta, but this coil spring is about 10% stiffer. There are two possible reasons for this. The US car weighs just over 100 lbs more, and upping the spring rate helps keep the natural "ride frequency" of the body (the frequency at which the body wants to bounce when you push the bumper down repeatedly) the same as the EU version. At the same time, the US spec Fiesta gets all-season tires instead of summer tires. A firmer spring can help recover some of the difference if those summer tires had stiffer sidewalls.
From the front we can see the stamped steel L-shaped lower control arm (yellow). Oftentimes we'll see such arms welded into a closed-box cross-section, but the Fiesta is light enough that the cornering and impact loads can be handled by a simpler (and lighter, and cheaper) open design.
And because the Fiesta is light, single-piston sliding brake calipers (black) and ventilated rotors are more than up to the task.
Another look from behind at the lower control arm (white) and the stabilizer bar (yellow).
Here's another look at the single-piston sliding calipers and the 10.2-inch diameter ventilated rotors they squeeze.
Moving to the rear, we see a very simple twist beam axle. Think of it as a motorcycle swingarm, only car-spannigly wide with a wheel on the outside of each leg. The yellow arrow indicates the actual beam that does the twisting.
Like a swingarm, it's all welded together into one big piece. There is no additional stabilizer bar because, well, the whole dang thing behaves like a stabilizer bar. The beam itself is an open channel because it doesn't want to be very rigid in the torsional sense. Its cross-section is carefully designed to provide just the right amount of roll stiffness.
It ever a sporty version of the Fiesta were developed that called for more roll stiffness, a straight stabilizer bar could theoretically be run along the length of the open C and welded in place at each outboard end. It's a common way of adjusting the torsional stiffness of twist beam axles to suit various applications.
Another difference from the EU version is the rear shock absorber. The North American vendor that makes it uses a twin-tube internal valve design instead of the monotube type used at the European plant.
On a heavier car this might be seen as a step backwards. But the Fiesta is a light car and this is the lightly loaded back end of it, so the damping forces don't have to be terribly high.
Besides, the rear shock absorbers attach to the legs of the twist beam behind the rear axle centerline, so the motion ratio is greater than 1:1 and the shocks are more effective.
These slim 7.9-inch drum brakes do the job on this 2,557-lb car. The pedal feels firm, stopping distances are decent and we didn't experience any fade or smell. And the Fiesta has standard ESC and ABS, too.
So far we haven't seen anything really remarkable from an equipment standpoint. So why does the Fiesta feel so fun to drive when other small econoboxes with similar bits merely get by?
There are two answers: 1) success requires the will to make steering and handling a priority when development targets are set and big up-front design decisions are made, and; 2) it takes sound fundamentals and careful fine-tuning of all of the suspension bits you have, such as springs, shock valving, stabilizer bars (bar, in this case), bushings, steering assist curves, tire construction, and more. To be effective at that task you also need a rigid unibody that will allow the suspension tuning department free reign without fear of overstressing something or triggering some unwanted resonance in the structure. (Which brings us full circle back to #1).
And it's amazing what you can do when your car weighs 2,500 pounds instead of 3,500 pounds, 4,500 pounds, or more. As we all know, light weight and agility go hand-in-hand.