by Jim Kerr
If you are an average Canadian driver, your vehicle will be seven to eight years old. Test drive any new car – and I mean any new car regardless of price range – and it will undoubtedly provide far superior ride and handling than your current car. That is one reason I often tell friends to drive as many new vehicles as they can when shopping, so they can compare them to other new cars; not just their existing vehicle. So what makes the new cars handle so much better?
Part of the answer is in the stiffness of the body construction. Car and truck bodies, just like any other structure will have a natural frequency at which they flex. If you could compare two almost identical bodies where one has a natural frequency of 20 HZ (cycles per second) compared to one with a natural frequency of 22 HZ, the latter would provide a much more stable platform and could potentially be a much better handling vehicle. This small change in body stiffness doesn’t sound like much but plays a major part in vehicle handling. Computer simulation of body flexing enables the designers to add material only where necessary to stiffen the body yet keep total vehicle weight down. For example, the high performance MazdaSpeed Protegé was only offered as a sedan although the Protegé5 hatchback was extremely popular. The sedan had bracing behind the rear seat to stiffen the body that would be impractical when placing cargo in the Protegé5 hatchback.
With a stiff body, the suspension can now be softened. Many enthusiasts think that strong springs and heavily damped shock absorbers are necessary to make a vehicle handle, but actually the opposite is true. Yes, you need a spring strong enough to support the vehicle but too strong a spring will create a rough ride over bumps and cause the tire to bounce on the road surface. Traction is only available when the tires are on the ground, so a bouncing tire will detract from handling, acceleration and braking. Keep the springs as soft as possible.
Shock absorbers also need to be calibrated for smooth soft action. When a tire hits a bump, the shock must let the tire rise quickly to avoid disturbing the vehicle. The shock must then control the release rate of the tire going back down so the tire doesn’t bounce on the rebound. Many performance shocks are pressurized with nitrogen gas. This prevents the oil from foaming as it passes through the shock valves and keeps the shock action constant, so that the tire is controlled accurately even over a long series of bumps such as washboard roads.
When I look at some vehicles with greatly improved ride and handling characteristics, such as Ford’s F150 pickup, the new Mustang, or Nissan’s Titan truck, I see that they have moved the shock absorbers out as far as possible to the ends of the axle to help control wheel and axle movement. Positioning these shock absorbers out a few extra inches has made a dramatic difference. Over the years, manufacturers have also staggered the shocks, placing one at an angle in front of the axle and the other side at an angle behind the axle. This design helps reduce sudden changes in the angle of a solid rear axle during acceleration or braking for improved axle control.
Sway bars are another area that the manufacturers have improved. A sway bar (sometimes called an anti-roll bar) keeps the vehicle level when it is cornering. Without a sway bar, the car would roll around its centre of gravity and lean sharply on every corner. Not only is this disconcerting for the driver, but it also changes the angle the tire contacts the road so traction is decreased. Modern vehicles use sway bars at both the front and back of the vehicle and each is sized to provide balanced handling on corners. Change the size or position of one bar only and your car will handle much differently, not necessarily for the better.
Off road handling has its own requirements. Rough terrain requires each side of the suspension to move up and down large amounts independently, but sway bars tend to reduce this. Porsche offers a feature on the Cayenne SUV to overcome this. They have hydraulically activated front and rear anti-roll bars with built in “claw clutches” that can be deactivated with a console switch when in low range. By uncoupling the roll bars, front and rear axle articulation is increased by 60 mm to decrease body lean on rough surfaces and increase tire contact on the
Of course, tires play a significant part in vehicle handling characteristics. Low profile sidewalls improve steering response but also stiffen the ride, so for optimum handling, the tires, springs, sways bars and shock absorbers must all work together as a package. Attention to vehicle design in these areas is why new vehicles handle so much better.