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I am thinking about putting a diffuser on the rear bumper for looks and to help pull the turbulent air out the back of the car. As you all know when its windy out the front end gets pushed around so this was my thought on fixing it.
Obviously I would have to use a heat gun to massage it but thats the general idea of what It would look like.
imho not needed....the car already has a .26 cd which is relatively low...plus the top speed is limited anyway where it would matter...
Yah but the front end is all over the place at 50 during windy conditions making it kinda dangerous to drive. The idea is to get the turbulent air to exit the rear of the car sucking it down to the road.
Also that means that any sudden disruption in the air stream stream will upset the car more than another vehicle with a different cd.
Last edited by 05ls430518; Jul 24, 2018 at 07:24 AM.
If you like the looks of the rear diffuser, then install one. Just don't be deceived into thinking that it will actually help in reducing the CD or improving stability. A diffuser with that steep of an angle just will not work!
If you like the looks of the rear diffuser, then install one. Just don't be deceived into thinking that it will actually help in reducing the CD or improving stability. A diffuser with that steep of an angle just will not work!
Thats why I am posting on here though if someone wants to help that would be awesome I am not an engineer by any means and have a basic understanding of aerodynamics.
The end result is to install a rear diffuser that looks good but also will help make the car more stable at higher speeds.
Basic engineering of aerodynamic starts by understanding the equation : Total pressure equals static pressure plus the velocity head (which is 1/2 air density multiplied by the velocity squared). Simple easy equation but in reality difficult for people to grasp. For example, weather forecasters talk a lot about a low pressure front moving in and displacing a high pressure area. Really? How can low pressure displace a higher pressure? Everyone knows that when you lose air from a tire (which is at a higher pressure than the ambient pressure) the high pressure air is flowing into the lower pressure area. The answer to the weather forcasters problem is because they are actually using pressure data that is static pressure and they don't realize it. Furthermore, we don't attempt to measure the ambient total pressure because it is so difficult to do. You have to have the pressure probe facing directly into the incoming velocity of the air. It would have to focus constantly into the air which may instantely change direction up, down, or sideways.
To apply simple engineering to a diffuser requires the ability to understand that a diffuser attempts to reduce the velocity head (static pressure component) which increases the static pressure. In order to do that the air flow must remain attached to the diffuser wall as it flows outward. If the angle is too steep, the airflow separates and the diffusion process ends, leaving the static pressure at the end of the vehicle at a much lower pressure than the total pressure at the front of the vehicle. The higher this pressure difference is, the higher the drag on the vehicle. The drag coefficient (CD) can only be determined in a wind tunnel. Very few cars for the general public are developed using a wind tunnel. The LS430 is one of those. All of the "diffusers" that are a current design feature on almost all cars are just for looks.
I am very surprised Nissan still puts spoilers on the trunk lid, that was en vogue in the 90's.
imho people always leave the frontal area out of the picture. The LS430 has a .26 cd, but it cheats the wind less than a 335i with .29 cd. I would even go as far to say that the 335i was never tested in a wind tunnel, yet the bottom of it is smoother than the LS430.
Keeping things in perspective, yes, much is for looks, the shape of the mirrors, etc. I think, rather I know, aerodynamics was one of the 4 principles on which Lexus was founded--top speed, quietness, fuel economy, and aerodynamics. If I got that wrong then it's just such an old story (1980-1989). I don't know that any of this even matters at 100 mph (it might).
Yah but the front end is all over the place at 50 during windy conditions making it kinda dangerous to drive. The idea is to get the turbulent air to exit the rear of the car sucking it down to the road.
Also that means that any sudden disruption in the air stream stream will upset the car more than another vehicle with a different cd.
If the front end is all over the place under ANY conditions something is wrong. Kinda dangerous = DANGEROUS !!!
I am very surprised Nissan still puts spoilers on the trunk lid, that was en vogue in the 90's.
imho people always leave the frontal area out of the picture. The LS430 has a .26 cd, but it cheats the wind less than a 335i with .29 cd. I would even go as far to say that the 335i was never tested in a wind tunnel, yet the bottom of it is smoother than the LS430.
Keeping things in perspective, yes, much is for looks, the shape of the mirrors, etc. I think, rather I know, aerodynamics was one of the 4 principles on which Lexus was founded--top speed, quietness, fuel economy, and aerodynamics. If I got that wrong then it's just such an old story (1980-1989). I don't know that any of this even matters at 100 mph (it might).
It matters. The drag on a vehicle at 100 mph is 4 times as much as at 50 mph, (100/50) squared.
It matters. The drag on a vehicle at 100 mph is 4 times as much as at 50 mph, (100/50) squared.
No doubt it's exponential, but I mean if one vehicle had no attention paid, the other every attention, at 100 mph, both cars would go down the highway just fine....on an aircraft, might be critical...
What if I put something on my LS430 for looks, like a huge wing? I could still probably go 100 mph despite the detrimental effects...160 mph (like an older LS) might be another story..
edit totally unrelated, but how fast can I go with 4 pieces of sheetrock on my roof (wth it's peeling again, the other side/drip rail) and my arm out the window, hand holding them?
Last edited by Johnhav430; Jul 24, 2018 at 09:53 AM.
Basic engineering of aerodynamic starts by understanding the equation : Total pressure equals static pressure plus the velocity head (which is 1/2 air density multiplied by the velocity squared). Simple easy equation but in reality difficult for people to grasp. For example, weather forecasters talk a lot about a low pressure front moving in and displacing a high pressure area. Really? How can low pressure displace a higher pressure? Everyone knows that when you lose air from a tire (which is at a higher pressure than the ambient pressure) the high pressure air is flowing into the lower pressure area. The answer to the weather forcasters problem is because they are actually using pressure data that is static pressure and they don't realize it. Furthermore, we don't attempt to measure the ambient total pressure because it is so difficult to do. You have to have the pressure probe facing directly into the incoming velocity of the air. It would have to focus constantly into the air which may instantely change direction up, down, or sideways.
To apply simple engineering to a diffuser requires the ability to understand that a diffuser attempts to reduce the velocity head (static pressure component) which increases the static pressure. In order to do that the air flow must remain attached to the diffuser wall as it flows outward. If the angle is too steep, the airflow separates and the diffusion process ends, leaving the static pressure at the end of the vehicle at a much lower pressure than the total pressure at the front of the vehicle. The higher this pressure difference is, the higher the drag on the vehicle. The drag coefficient (CD) can only be determined in a wind tunnel. Very few cars for the general public are developed using a wind tunnel. The LS430 is one of those. All of the "diffusers" that are a current design feature on almost all cars are just for looks.
Just saying.
I was not trying to be rude at all I am very happy you posted this. I sincerely appreciate you taking the time to type all that out. If you have an idea of the diffusers dimensions please share, you clearly have much more knowledge about this subject than I do
So your saying smaller fins less of an angle, so like this? That way the air gradually flows over it instead of abruptly going up.
Yah but the front end is all over the place at 50 during windy conditions making it kinda dangerous to drive.
Really? I only own mine maybe 2 months, and while have only driven her up to ~100 mph briefly, I have driven several hundred miles at 75-85 mph a few weeks ago (including on windy day). She was stable at up to 100 mph. I feel that she can go faster except I do not want to get a ticket.
I am thinking you have other problems if the front end is all over the place at 50. Even my Land Cruiser with aerodynamic like a square box feel stable at 50 mph. Tires and other suspension components can make a big difference how the car run at high speed, so maybe check them first before adding the diffuser? I am no expert at aerodynamics, but I doubt that rear diffuser is going to help at all (otherwise everyone would have been adding this to their cars).
https://www.caranddriver.com/feature...y-suck-feature
"A functional diffuser requires a flat underbody and a low ride height, attributes not often found on mainstream cars. The diffuser you get on, say, a Kia Forte Koup is just for looks."
Really? I only own mine maybe 2 months, and while have only driven her up to ~100 mph briefly, I have driven several hundred miles at 75-85 mph a few weeks ago (including on windy day). She was stable at up to 100 mph. I feel that she can go faster except I do not want to get a ticket.
I am thinking you have other problems if the front end is all over the place at 50. Even my Land Cruiser with aerodynamic like a square box feel stable at 50 mph. Tires and other suspension components can make a big difference how the car run at high speed, so maybe check them first before adding the diffuser? I am no expert at aerodynamics, but I doubt that rear diffuser is going to help at all (otherwise everyone would have been adding this to their cars).
Thoughts on rear diffuser?
