I have a 2011 prius gen3, which has 180k kilometers. I found that when it rains, the mpg will decrease. The acceleration obtained by the same accelerator pedal position is different. There may be a certain resistance when the tires discharge water. However, the road surface is only water, not very thick. I am not sure about it. Will have a big impact. I measured the toes of the front and rear tires and found that the toes of the rear wheels seem to have some relationship with the temperature. When it rains, the temperature is generally lower. At that time, the toes of the rear wheels are 5mm, which is +5mm, and when the sun is shining, It was because the temperature was relatively high. At that time, the toe was -1mm, and the driving was very brisk. When the toe leaves 0, the rolling resistance of course increases. I don’t know if my toes are an exception or a common fact. What do you think? It is very simple for me to measure the toes. I use a tape measure to measure the distance between the tire treads (fixed tread position), and measure the same height above the ground before and after the tire.
there's more friction loss with rain than yoy think, even though there's less friction. and keep n mind, the entire car is trying to plow through it, not just the tires
Of course. This would be true with any vehicle. You should see the effect on miles/kWh on a Prime. No puddles required. As for the toe, did you verify that your tape measure was absolutely horizontal for each measurement, that it didn't sag, and that the tires were in the same rotational position? IE: valve stems both at 180° for example. Not 181° or 179°? I can't imagine any way that the temperature would change the angles of the wheels.
I would think of all that water that has to be shoved out of the way, as a major energy vampire, continually sucking energy from the car's motion. It takes extra fuel to maintain speed, thus reducing mpg. The tires plow a lot of water out of the way, accelerating it to at least the same speed as the vehicle, and some of it to even faster speeds as it gets cast aside. Some of the water that adheres to the tires, then gets thrown off over the top, even reaches double the vehicle speed. Accelerating all this mass (water is heavy) up to various speeds inherently requires energy. And it is all extra energy, not needed in dry conditions.
A good analogy is when driving in rain and you encounter a relatively deep puddle. The vehicle suddenly wants to slow down as you are traversing the deep water. The same thing is happening on rain soaked roadway. The tires are pushing the water out of the way. Water does not compress so the tires are essentially working like a squeegee…pushing against a liquid barrier.
This is how I measure the toes of the rear wheels. The car is parked as level as possible. At the place where the height of the rear tires is the same, use a tape measure to measure the distance between the fixed patterns of the tires. The different lengths will be obtained. If the rear distance is r , The front distance is f, then f-r= toe. This measurement cannot be measured at the diameter position, only the approximate toe can be obtained. If you want to estimate accurately, you need to use functions such as sin cos tan to calculate. I think if the toe is 0, then at different heights The measurement should all be 0. When I tested the resistance, the speed was not high. I was not sure that the thin water on the road would produce sensible resistance, and the wind resistance would be weakened due to the reduced speed. I think the influence of the toes would be greater than the resistance of the water. My back toe is corrected with gaskets, which are processed with aluminum. There are no finished modified parts sold locally. I added a piece on the front top of the bearing plate. The purpose is to change the inclination and toe angle at the same time, and the temperature of aluminum is stretched. The rate is greater than that of steel, and there are 4 screws in total. I only raise the position of one screw. It may also cause uneven force on the bearing plate and produce complex deformations related to temperature. I am not sure about this. Maybe there are other ways to do it. Change the rear wheel toe angle, such as rear torsion beam correction, but that seems to require special tools, I am not sure. What do you think.
Hi James- your car sounds like a labor of love! Any chance you can attach some photos of this mod to the rear suspension?
I used to own a Honda car. Its front and rear are independent suspension, so its front and rear wheel inclination and toe angle are adjustable. I tried to change the inclination and toe angle values. I found that if the inclination angle is 0, the toe angle 0, the tire tread temperature is the lowest at that time, and the rolling resistance should be the lowest. When the inclination angle is negative, the toe angle must have a little negative value to make the tire temperature the lowest. On the contrary, when the inclination angle is positive (normal vehicle Rarely), there must be a positive toe angle to cooperate. My purpose is not to drive intensely, but to reduce driving resistance and make the vehicle run briskly. It turns out that a toe angle of 0 will not stabilize straight driving. The premise is that there is no problem with the suspended ball joints, rubber sleeves and other moving parts. Because the rear spring of that Honda car is a little aging and shortened, the car sinks slightly, and the rear wheel inclination is negative. I use a little negative beam. The horns are matched, and the effect is very good. It's just that the temperature on the inside of the tire is slightly higher than the temperature on the outside, which is caused by the inclination.
How thin of a water layer are you considering? Some quick calculations indicate that a 1 mm water layer in the path of standard Prius tires has a mass of about 390 kg per km. That is a lot of water to shove out of the way. Or for Americans, a 1/10th inch water layer represents 3500 lbs of water, which is heaver than the Prius itself. And the faster the car is moving, the more energy is wastefully put into accelerating and plowing that water out of the way.
Yes, brother. I admit that the water on the road will bring resistance to driving. The tires must discharge this water to move forward. Otherwise, they will lose control. I just don’t know how much the resistance will be. I haven’t found a suitable method to calculate it. it. I only have some experience. Before driving this prius, I have never had this feeling. When I used to drive a Honda car, it was also a hybrid car. On the contrary, I felt that the driving resistance would be less when it rained. It might be water. Play the role of lubrication between the road and the tires, it's just afeeling, and there is nothing digital, Move the 390kg horizontally instead of raising it. If you translate a distance of 195-215mm, do you think it will require a lot of energy? It may be the same as what you said, but also consider therotation of the tire to bring water to a high place. This doesrequire some energy, but the water is falling in the forward direction of the tire, and there may be a lot of water leaving the tire due to centrifugal force. It will be very difficult to calculate, anyway I am still at a loss,maybe you are right. this is just my point of view.
For a first estimate, given a tire width, water depth, and vehicle speed, calculate the mass flow rate of water that is being displaced. Then calculate how much power is needed to accelerate that mass to the same speed as the vehicle. All my previous non-hybrids suffered the same problem, losing MPG in rainy weather. Though lacking MPG displays, the indicators of it were much more coarse, just MPG computations when refueling. Lubrication between tires and road is a very bad thing for traction and control and staying on the road. Even giving it horizontal speed to push it out of the way, without raising it at all, is very costly. Clearing a wider tire path means moving even more water at the same speed, thus requiring more energy
Yes, brother, I agree with all of your points. Maybe this is the tire factory to design low-wear tires to meet the needs of some customers. Different patterns may have different drainage efficiency. What I can do is to solve the toe problem of the car first. , Next time I change the tires, I will considerchoosing the right tires. This is what I can plan for now. If I think too much, I will be tired. I will start working soon. It is estimated that there will be no more time to solve this icing on the cake. Thank you all.
This is the photo of me adding spacers. The work is not perfect. Limited by materials and tools, it is good to achieve the purpose. The bearing discs of some cars may not be easy to remove. I made tools and used angle grinders to make them easily. It turned out that there was only a spacer in the front-up direction. Today, in order to take a picture, I added very thin spacers in the front-down direction and the back-up direction after disassembling. I hope that the bearing plate's fixed plane will be more evenly stressed.
