There are no rear toe adjustments. How were the rear toe settings when the alignment was checked? If it's not tracking properly in the first place, you are going to have problems.
1 - 14 of 14 Posts
G
Prius Tek,
Thanks for your reply.
My rear axle toe settings turned out to be right on the money. However, now that I've spent a Saturday studying the rear suspension on my Prius I've come to the conclusion that rear toe measurements are meaningless. Why do I say this?
First keep in mind that each rear wheel is allowed to pivot around Trailing Arm Bushing No. 3. Imagine this scenario. Put the Prius on a lift, grab the rear of the right rear tire and pull it out away from the car, now pull the rear of the left rear tire and also pull it out away from the car. Lower the Prius back to the ground and make rear axle alignment measurments (don't move the car before taking the measurements). In this scenario you should get a toe in rear axle measurement.
Now lift the car and push in the rear of both rear tires and lower back to the gound. Repeat the rear axle alignment measurements. This time you should get toe out rear axle measurements.
Since each rear wheel is allowed to independently pivot around their No. 3 Trailing Arm Bushing it is my opinion that any rear axle toe measurement is a waste of time.
Keep in mind that the rear wheels do not pivot a great deal. This is because the No. 2 Trailing Arm Bushing limits how much the Toe Control Link can pivot around the No. 3 Trailing Arm Bushing.
********************************************************
Now I can talk about my experience with Prius handling. On smooth pavement with no crosswinds the Prius is the best handling car I've ever owned. However, I live in Idaho where it is unusual to find a stretch of smooth pavement and it is also unusual to have a day without significant crosswinds. It is indeed a special moment when the pavement is smooth and there are no crosswinds.
The Prius does not handle nicely above 55 mph on interstate pavement that is lumpy with 18 wheeler ruts. I now believe I understand the source of this problem and it has nothing to do with alignment. The issue is that the lumps in the pavement induce lateral forces to the trailing arm bushings in the rear suspension causing the rear wheels to "steer" the car in the direction of the lateral force.
In my first interstate freeway experience I had a tough time maintaining control of my Prius. Here was my problem. I would feel the rear of the car begin to pull the car to one side. I would compensate by steering the other direction. I would suddenly be veering way too far the other direction. Sounds like oversteer? Yes, it does. The issue was that no corrective steering whatsoever was needed and so even the slightest correction with the steering wheel gives a sense of oversteer.
I decided to test this theory. I went back out to the rutted interstate where the speed limit is 75 MPH. I convinced myself that I would not use the steering wheel to correct for any side to side movement. I would instead focus on holding the steering wheel steady and keep it aimed at a fixed point in the distance ahead. I off course would correct if it became obvious that I was going to drift out of my lane.
Here is what I found. In the deeper 18 wheeler ruts the tail of Prius "wags" as you cruise along at 75 MPH. I did not use the steering wheel to correct and focused on holding the steering wheel steady and straight ahead. As soon as you get to a smoother piece of pavement the wagging stops.
I've had my Prius a little over two months now and I think I've finally learned how to drive it. I think this "wagging" may take a little while to get used to. However, I believe there is no cure short of redesigning the rear suspension that will fix this problem. The rear wheels are merely pivoting on Trailing Arm Bushing No. 3 in response to lateral forces. They are doing exactly what they are designed to do.
When driving a Prius at highway speed focus on holding the steering wheel steady and don't try to correct for side to side motion that is caused by crosswinds or 18 wheeler ruts. The car is "self correcting" when these events occur. Any corrections that are implemented with the steering wheel will feel like oversteer because by the time you react to correct the car has also reacted to correct. If the driver and the car are both correcting you get overcorrection. A constant experience of overcorrection is worse than the "wagging" experience. From now on I'll just let the tail wag.
Ed
Thanks for your reply.
My rear axle toe settings turned out to be right on the money. However, now that I've spent a Saturday studying the rear suspension on my Prius I've come to the conclusion that rear toe measurements are meaningless. Why do I say this?
First keep in mind that each rear wheel is allowed to pivot around Trailing Arm Bushing No. 3. Imagine this scenario. Put the Prius on a lift, grab the rear of the right rear tire and pull it out away from the car, now pull the rear of the left rear tire and also pull it out away from the car. Lower the Prius back to the ground and make rear axle alignment measurments (don't move the car before taking the measurements). In this scenario you should get a toe in rear axle measurement.
Now lift the car and push in the rear of both rear tires and lower back to the gound. Repeat the rear axle alignment measurements. This time you should get toe out rear axle measurements.
Since each rear wheel is allowed to independently pivot around their No. 3 Trailing Arm Bushing it is my opinion that any rear axle toe measurement is a waste of time.
Keep in mind that the rear wheels do not pivot a great deal. This is because the No. 2 Trailing Arm Bushing limits how much the Toe Control Link can pivot around the No. 3 Trailing Arm Bushing.
********************************************************
Now I can talk about my experience with Prius handling. On smooth pavement with no crosswinds the Prius is the best handling car I've ever owned. However, I live in Idaho where it is unusual to find a stretch of smooth pavement and it is also unusual to have a day without significant crosswinds. It is indeed a special moment when the pavement is smooth and there are no crosswinds.
The Prius does not handle nicely above 55 mph on interstate pavement that is lumpy with 18 wheeler ruts. I now believe I understand the source of this problem and it has nothing to do with alignment. The issue is that the lumps in the pavement induce lateral forces to the trailing arm bushings in the rear suspension causing the rear wheels to "steer" the car in the direction of the lateral force.
In my first interstate freeway experience I had a tough time maintaining control of my Prius. Here was my problem. I would feel the rear of the car begin to pull the car to one side. I would compensate by steering the other direction. I would suddenly be veering way too far the other direction. Sounds like oversteer? Yes, it does. The issue was that no corrective steering whatsoever was needed and so even the slightest correction with the steering wheel gives a sense of oversteer.
I decided to test this theory. I went back out to the rutted interstate where the speed limit is 75 MPH. I convinced myself that I would not use the steering wheel to correct for any side to side movement. I would instead focus on holding the steering wheel steady and keep it aimed at a fixed point in the distance ahead. I off course would correct if it became obvious that I was going to drift out of my lane.
Here is what I found. In the deeper 18 wheeler ruts the tail of Prius "wags" as you cruise along at 75 MPH. I did not use the steering wheel to correct and focused on holding the steering wheel steady and straight ahead. As soon as you get to a smoother piece of pavement the wagging stops.
I've had my Prius a little over two months now and I think I've finally learned how to drive it. I think this "wagging" may take a little while to get used to. However, I believe there is no cure short of redesigning the rear suspension that will fix this problem. The rear wheels are merely pivoting on Trailing Arm Bushing No. 3 in response to lateral forces. They are doing exactly what they are designed to do.
When driving a Prius at highway speed focus on holding the steering wheel steady and don't try to correct for side to side motion that is caused by crosswinds or 18 wheeler ruts. The car is "self correcting" when these events occur. Any corrections that are implemented with the steering wheel will feel like oversteer because by the time you react to correct the car has also reacted to correct. If the driver and the car are both correcting you get overcorrection. A constant experience of overcorrection is worse than the "wagging" experience. From now on I'll just let the tail wag.
Ed
G
I agree with the electric power steering. The steering wheel has no "play" and the car responds to even slight movements of the steering wheel.
I've also wondered about the tires. I've got Blizzak snow tires on my Prius right now. Ill be putting the factory Potenza's back on in a few weeks. I will pay close attention to any change in handling when I switch tires.
I've never paid much attention to rear suspension in the past. I think the Prius is the first car I've ever owned that has rear wheels mounted to a control link designed to pivot about a bushing. Have others driven cars with this type of rear suspension and noticed similar highway handling in crosswinds and ruts?
My new driving strategy is to focus on what I want the front wheels to do and ignore the side to side movement I feel from the back of the car. I'm starting to get the hang of it. I've finally figured out that there is no point trying to compensate for anything I feel from the back of the car. There is no way to correct for motion felt in the tail and attempts to control it with the steering wheel just seem to cause me nothing but grief.
I hope I don't sound like I don't like the Prius, because I really do like it. It's just taking me a little longer to "get the feel" than I thought it would. I spent my first couple months "fighting it" but I'm now starting to get the feel for it. Soon my Prius and I will zip down the rutted Idaho interstates and highways in harmony.
Ed
I've also wondered about the tires. I've got Blizzak snow tires on my Prius right now. Ill be putting the factory Potenza's back on in a few weeks. I will pay close attention to any change in handling when I switch tires.
I've never paid much attention to rear suspension in the past. I think the Prius is the first car I've ever owned that has rear wheels mounted to a control link designed to pivot about a bushing. Have others driven cars with this type of rear suspension and noticed similar highway handling in crosswinds and ruts?
My new driving strategy is to focus on what I want the front wheels to do and ignore the side to side movement I feel from the back of the car. I'm starting to get the hang of it. I've finally figured out that there is no point trying to compensate for anything I feel from the back of the car. There is no way to correct for motion felt in the tail and attempts to control it with the steering wheel just seem to cause me nothing but grief.
I hope I don't sound like I don't like the Prius, because I really do like it. It's just taking me a little longer to "get the feel" than I thought it would. I spent my first couple months "fighting it" but I'm now starting to get the feel for it. Soon my Prius and I will zip down the rutted Idaho interstates and highways in harmony.
Ed
G
Good point Doug.
The Toyota Prius was designed to navigate through downtown Tokyo rush hour traffic using a minimum of fuel and producing a minimum of pollution. When the Prius was on the drawing board the engineers were probably not thinking about stability and tracking while travelling 75 mph on a rutted interstate while being buffetted by the wind from the Suburban that passes you because you're only barely going the speed limit. I won't go complaining to Toyota about this.
By the way, I find myself with both hands on the steering wheel all the time. Since the Prius does not have a convenient place to rest an arm I just leave both hands on the steering wheel all the time. I wonder if this is some kind of subliminal safety feature.
Ed
The Toyota Prius was designed to navigate through downtown Tokyo rush hour traffic using a minimum of fuel and producing a minimum of pollution. When the Prius was on the drawing board the engineers were probably not thinking about stability and tracking while travelling 75 mph on a rutted interstate while being buffetted by the wind from the Suburban that passes you because you're only barely going the speed limit. I won't go complaining to Toyota about this.
By the way, I find myself with both hands on the steering wheel all the time. Since the Prius does not have a convenient place to rest an arm I just leave both hands on the steering wheel all the time. I wonder if this is some kind of subliminal safety feature.
Ed
G
Steve,
I'll be curious what you learn. You mentioned the possibility of adding a heavier sway bar. I don't think the Prius has any true sway bars. I think a true sway bar has one end that mounts to the frame or unibody. The Prius does have front and rear stabilizer bars and also stabilizer links on the front. If you feel the need to modify the suspension to give the car a "stiffer" sports car feel be sure to let us know how it goes. The rear end of the Prius does feel "loosy goosy" to me but I'm getting used to it. So far I think I'm happy with the feel and control of the front wheels.
Make sure you get good advice before starting on your endeavor. The Prius is a unibody car. This means that the Prius does not really have a frame upon which the body mounts. Unibody cars are more like a skeleton. One way to describe a unibody car is that in a unibody car the roof holds up the floor (or at least keeps the floor from sagging down). In a car with traditional frame construction the body is mounted on the frame and the frame carries all the weight.
Unibody cars are very popular because they do quite well in crash tests. They protect the occupants much more than a flimsy body mounted to a solid frame. I've read that the vast majority of new cars and about 1/3 of new minivans have unibody construction.
One problem with upgrading the suspension on a unibody car with stiffer components is that stresses that would have been absorbed in the suspension are now passed on to the unibody. These stresses may be too much for the unibody which will result in the car body bending and twisting instead of the suspension components absorbing those stresses. In the cases where people want to upgrade the suspension of a unibody car for racing purposes they sometimes find they must mount the unibody onto some sort of subframe support in order to get the handling they desire.
My guess is that the Prius pivoting rear wheels were a way to reduce stress on the unibody and allowed Toyota to make the unibody lighter. In order to reduce unibody weight without sacrificing crash test safety Toyota may have decided to take weight out of the floor and underbody. The downside is that now you don't have anything solid on the bottom of the car to mount a stiff high performance type suspension.
Be sure to have the race car drivers take a look at the interesting rear axle and the manner in which the rear wheels are mounted on toe control links that are allowed to both pivot and deform (bend). I would be interested in hearing their thoughts.
Ed
PS. Remember, the Prius was designed to be happiest in stop and go urban traffic. The Prius is a bit out of its element on the race track.
I'll be curious what you learn. You mentioned the possibility of adding a heavier sway bar. I don't think the Prius has any true sway bars. I think a true sway bar has one end that mounts to the frame or unibody. The Prius does have front and rear stabilizer bars and also stabilizer links on the front. If you feel the need to modify the suspension to give the car a "stiffer" sports car feel be sure to let us know how it goes. The rear end of the Prius does feel "loosy goosy" to me but I'm getting used to it. So far I think I'm happy with the feel and control of the front wheels.
Make sure you get good advice before starting on your endeavor. The Prius is a unibody car. This means that the Prius does not really have a frame upon which the body mounts. Unibody cars are more like a skeleton. One way to describe a unibody car is that in a unibody car the roof holds up the floor (or at least keeps the floor from sagging down). In a car with traditional frame construction the body is mounted on the frame and the frame carries all the weight.
Unibody cars are very popular because they do quite well in crash tests. They protect the occupants much more than a flimsy body mounted to a solid frame. I've read that the vast majority of new cars and about 1/3 of new minivans have unibody construction.
One problem with upgrading the suspension on a unibody car with stiffer components is that stresses that would have been absorbed in the suspension are now passed on to the unibody. These stresses may be too much for the unibody which will result in the car body bending and twisting instead of the suspension components absorbing those stresses. In the cases where people want to upgrade the suspension of a unibody car for racing purposes they sometimes find they must mount the unibody onto some sort of subframe support in order to get the handling they desire.
My guess is that the Prius pivoting rear wheels were a way to reduce stress on the unibody and allowed Toyota to make the unibody lighter. In order to reduce unibody weight without sacrificing crash test safety Toyota may have decided to take weight out of the floor and underbody. The downside is that now you don't have anything solid on the bottom of the car to mount a stiff high performance type suspension.
Be sure to have the race car drivers take a look at the interesting rear axle and the manner in which the rear wheels are mounted on toe control links that are allowed to both pivot and deform (bend). I would be interested in hearing their thoughts.
Ed
PS. Remember, the Prius was designed to be happiest in stop and go urban traffic. The Prius is a bit out of its element on the race track.
1 - 14 of 14 Posts
