It always fascinates me. When someone is talking about the "go fast" attributes of their car, I'll ask them, "What kind of rear suspension do you have?" Inevitably, I'll get a blank stare.
If you're a "go fast" -- and don't really understand your car's suspension, something's kinda' suspect.
There have been volumes written on IRS and suspension issues but for the sake of brevity we're going to cut right to the chase.
Independent Rear Suspension, or IRS for short, is about how a vehicle handles curves and turns. Among many other things, it's about Camber. "Okay, so what's Camber"? Camber is basically the "tilt" or lack of tilt, of the wheels - in this case, the rear wheels. How rear wheels tilt or don't tilt significantly impacts the ability of the vehicle to handle (or not handle) curves and turns at speed. Do the wheels remain straight up and down, vertical to the road at a ninety degree angle? If so, our camber is neutral. If they begin to tilt in or out as our car leans into or out of a curve, we're going to be experiencing positive or negative camber.
While there are many variations, today's Rear Suspensions basically break down into two versions. First, there is the Straight Axel or Live Axel. Then there is IRS.
With a Straight Axel or Live Axel, each of the rear wheels are directly connected to each other. The Straight Axel will be found in front wheel drive cars. It reaches directly from one rear wheel to the other, connecting the two wheels together. The Live Axel is basically the same thing with a differential stuffed in the middle. This will be found on Rear Wheel or Four Wheel Drive vehicles.
With either of these configurations, what ever happens to one of the wheels, will directly affect the wheel on the other side because of that direct connection. If you hit a bump with the left wheel, it will jump up and cause the right wheel to tilt in the opposite direction. If the car or truck leans into a turn, the wheels will still be straight up and down. Not a bad thing, but not especially great, either.
With IRS, the rear axel is, in effect, two separate axels. Each side of the axel can flex up or down on its own. This allows each of the rear wheels to act independently of the other. By definition then, it also allows each wheel, individual camber or tilt flexibility. This is good.
Why would we care about all this? It makes a big difference. If those tires lean bottom-in toward the car, Positive Camber, will make the car unstable. It can get loose or even roll over. That's called Body Roll and it's not good. If on the other hand they squat - that is, if the bottom of the tires tilt out, it will increase stability and allow the car to glide effortlessly through curves you may never have thought possible.
Let's talk about the Positive Camber body roll problem first because this was definitely a bad thing. "Was," -- because the problem's been pretty much fixed.
Back in 1960, Chevrolet was one of the first American Cars to introduce IRS with their Corvair model. The Foreign makers already had plenty of them but then, they were more willing to spend the money and their customers were more demanding.
The Corvair was a pure delight if you knew how drive it and if it had a stick shift. But the IRS concept was sort of new to most American Drivers and they soon began rolling over the Corvairs in rather significant numbers. Those independent wheels would go positive camber with a hard emergency turn. Basically, they would just fold up under the frame and roll the car right over. Ruined a lot of door handles. Ralph Nader jumped all over the Corvair in his 1965 book "Unsafe at Any Speed" in 1965. Anyway, it didn't take too long (about five years) for Chevrolet (and the foreigners) to come up with solutions to the problem.
Today IRS vehicles have sway bars, multi links and other good stuff which basically eliminates the Positive Camber problem, leaving IRS equipped vehicles with only positive attributes - or more specifically, Negative Camber. This leaves most Independent Rear Suspension cars of today, with nothing but positive characteristics.
You can safely drive IRS today without ever even knowing you have it. But if you do, it's kinda' nice to know how it can keep you safer and more confident on the road.
If you're a "go fast" -- and don't really understand your car's suspension, something's kinda' suspect.
There have been volumes written on IRS and suspension issues but for the sake of brevity we're going to cut right to the chase.
Independent Rear Suspension, or IRS for short, is about how a vehicle handles curves and turns. Among many other things, it's about Camber. "Okay, so what's Camber"? Camber is basically the "tilt" or lack of tilt, of the wheels - in this case, the rear wheels. How rear wheels tilt or don't tilt significantly impacts the ability of the vehicle to handle (or not handle) curves and turns at speed. Do the wheels remain straight up and down, vertical to the road at a ninety degree angle? If so, our camber is neutral. If they begin to tilt in or out as our car leans into or out of a curve, we're going to be experiencing positive or negative camber.
While there are many variations, today's Rear Suspensions basically break down into two versions. First, there is the Straight Axel or Live Axel. Then there is IRS.
With a Straight Axel or Live Axel, each of the rear wheels are directly connected to each other. The Straight Axel will be found in front wheel drive cars. It reaches directly from one rear wheel to the other, connecting the two wheels together. The Live Axel is basically the same thing with a differential stuffed in the middle. This will be found on Rear Wheel or Four Wheel Drive vehicles.
With either of these configurations, what ever happens to one of the wheels, will directly affect the wheel on the other side because of that direct connection. If you hit a bump with the left wheel, it will jump up and cause the right wheel to tilt in the opposite direction. If the car or truck leans into a turn, the wheels will still be straight up and down. Not a bad thing, but not especially great, either.
With IRS, the rear axel is, in effect, two separate axels. Each side of the axel can flex up or down on its own. This allows each of the rear wheels to act independently of the other. By definition then, it also allows each wheel, individual camber or tilt flexibility. This is good.
Why would we care about all this? It makes a big difference. If those tires lean bottom-in toward the car, Positive Camber, will make the car unstable. It can get loose or even roll over. That's called Body Roll and it's not good. If on the other hand they squat - that is, if the bottom of the tires tilt out, it will increase stability and allow the car to glide effortlessly through curves you may never have thought possible.
Let's talk about the Positive Camber body roll problem first because this was definitely a bad thing. "Was," -- because the problem's been pretty much fixed.
Back in 1960, Chevrolet was one of the first American Cars to introduce IRS with their Corvair model. The Foreign makers already had plenty of them but then, they were more willing to spend the money and their customers were more demanding.
The Corvair was a pure delight if you knew how drive it and if it had a stick shift. But the IRS concept was sort of new to most American Drivers and they soon began rolling over the Corvairs in rather significant numbers. Those independent wheels would go positive camber with a hard emergency turn. Basically, they would just fold up under the frame and roll the car right over. Ruined a lot of door handles. Ralph Nader jumped all over the Corvair in his 1965 book "Unsafe at Any Speed" in 1965. Anyway, it didn't take too long (about five years) for Chevrolet (and the foreigners) to come up with solutions to the problem.
Today IRS vehicles have sway bars, multi links and other good stuff which basically eliminates the Positive Camber problem, leaving IRS equipped vehicles with only positive attributes - or more specifically, Negative Camber. This leaves most Independent Rear Suspension cars of today, with nothing but positive characteristics.
You can safely drive IRS today without ever even knowing you have it. But if you do, it's kinda' nice to know how it can keep you safer and more confident on the road.
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