| Independent Rear Suspension, or "IRS" for short, can | | | | wheel in toward - and under the car, creating body roll |
| take turns, curves and throttle steering to a far higher | | | | and a possible roll-over. The way to correct for this |
| level. A quick Google of the subject will suggest it's not | | | | was to apply heavy torque to the wheel. The |
| a topic of insignificant interest to serious drivers. | | | | additional torque to the wheel would cause it to flatten |
| In my last article we reviewed the basics. We looked | | | | out and squat. If we applied forward torque, we called |
| at how IRS can introduce that Negative Camber thing | | | | it "powering through the curve." We were "pushing our |
| to our rear wheels, producing a much more stable | | | | leg out." |
| "squat". That's when the bottoms of those rear wheels | | | | The modern IRS system has sway bars and other |
| tilt out. | | | | good stuff so the wheel can't easily fold in under the |
| It's important to note that those rears don't just squat | | | | car any longer. As a result, "powering through the |
| all the time. At rest, or even on a straight of way, | | | | curve" still works -- but with far less risk of rollover. |
| they're going to act pretty much like any other system. | | | | The idea of speeding up on a curve to decrease your |
| In other words, they're going to rest or run with neutral | | | | rollover potential may go against natural instincts but |
| Camber. They're going to be running straight up and | | | | once you get used to it, it'll become quite natural - and |
| down. | | | | safe. |
| It's on curves, turns and bumpy roads that those IRS | | | | If you decide you want to slow down in the turn, letting |
| wheels just "wanna have fun". On the rough road, the | | | | off hard on the gas will create back force torque to |
| ability of one wheel to absorb shocks without jolting | | | | the wheel and also tend to squat it out. You want that |
| the entire car will contribute to a smoother ride and | | | | force to run through the drive train though, not the |
| more control. On curves the IRS really comes alive. It's | | | | brakes. |
| all about that squat - both recognizing it when it | | | | Letting off the gas or even a good downshift will do |
| happens, and creating it when you want some. | | | | the trick. You're making the rear wheels slow down |
| We can induce squat to those rear wheels by | | | | the car. If you brake, most of that stop force goes to |
| introducing torque (force) to them through the drive | | | | the front tires. The car will lean forward, reduce the |
| train. Torque is what converts the power from our | | | | weight on those rears, spring them back to neutral |
| engine to power that makes the wheels turn. Since this | | | | camber and introduce a very uncomfortable body roll. |
| torque must come through the drive system and since | | | | The bottom line, then, is applying either forward or |
| we're talking about "independent rear wheels here, | | | | back force directly to the rear wheels through the |
| control over squat is mostly about rear wheel, or to a | | | | drive train, will tend to squat the car and make it more |
| point, some all wheel drive vehicles. | | | | stable in the turn. But how do you do this with a front |
| We can increase "forward force", making the wheels | | | | wheel drive vehicle? |
| go faster, or what I'll call "back force", making the | | | | You really can't. Even without the ability to torque your |
| wheels slow down. Either will make the wheels squat | | | | rear wheels though, the IRS is still there in your front |
| to a degree. | | | | wheel drive. The rears will still move independently |
| Think of a hockey skater headed for the boards. In | | | | over rougher roads and they'll still squat on a harder |
| making a left turn to avoid hitting those boards, he'll | | | | turn. The response just won't be as controllable. |
| stick his right leg (his rear wheel) way out and pushes | | | | You won't find IRS on trucks or "go straight" drag |
| with it. This gives him the added stability and balance | | | | racing cars. IRS isn't as strong as the straight axel. IRS |
| he needs to complete the turn. To then make a right | | | | will also slide on slippery roads just as quickly as |
| turn, he'll straighten out and push off on his extended | | | | another system so all of this squat stuff assume a dry, |
| left leg. This is kind of similar to what we can do with | | | | sticky road surface. |
| our IRS rear wheels. | | | | Getting to know your IRS and what it can do for you, |
| So we're leaning into a right hand curve at about sixty. | | | | will allow you to safely approach turns and curves with |
| With the original IRS systems, that lateral force to the | | | | confidence. |
| rear wheel would have pushed the bottom of the | | | | |