Have you looked at your roof???????

[Flatcoat]

Reminds me many years ago reading the late great muttering wrotter ‘Steady Barker’ writing in Car magazine about economy savings. As he said, if you added up all the alleged percentages of fuel saved by this design change or that product use we would need a fuel tanker to follow us to take all the surplus fuel generated…. 

[Lawnmowerman]

2 hours ago, Flatcoat said:

Reminds me many years ago reading the late great muttering wrotter ‘Steady Barker’ writing in Car magazine about economy savings. As he said, if you added up all the alleged percentages of fuel saved by this design change or that product use we would need a fuel tanker to follow us to take all the surplus fuel generated…. 

Steady Barker - great journalist - sadly missed. Also the eccentric LJK Setright..........

[Lawnmowerman]

5 hours ago, Mike2222 said:

Generally speaking, in aerodynamics, perfectly smooth surfaces are best, but in reality manufacturing this at scale to perfection is not possible. The golf ball logic is that its easier to reliably manufacture a balanced design of dimples, which (as said above) create microeddies of air, making a choice to sacrifice a small amount of drag in order to buffer the solid matter of the ball and allow it to pass thru the air in a consistent fashion. If was smooth, tiny imperfections in the surface (and considering the game involves repeatedly slapping the ball with a piece of iron/wood, a perfectly smooth surface wouldn't stay that way for long 😂) would cause unpredictable patterns of drag, leading to wildly unpredictable movement in flight. 

 

There is an argument that roof channels on cars are designed to smooth airflow over the back of the car, so you don't get unpredictable/variable turbulence/eddying at the rear, which increases drag at higher speeds. But in a 2 ton SUV with a fairly blunt frontal area, I think this is like the cyclist who proudly boasts about their £5000+ worlds lightest carbon-graphite frame that Sir Broderick Wigglesworth rode to victory up L'Alp d'Huddersfield, yet themselves is 6ft6 and 18st. 

 

The most likely answer is that in a big car that's expected to go at highway speeds on a regular basis, a smooth/flat sheet of metal could vibrate/buffet in the wind, so adding ridges adds rigidity/strength, without having to increase thickness/weight/efficiency, thus improving headroom and keeping centre of gravity lower. 

 

That's my 2 cents, at least. 

That's a great 2 cents worth - makes a lot of sense.

Now, golf ball logic............my logic is that I get better value from my round of golf because I get to hit the ball more than my friends. Seems that is not what it's about - ah well, back to the drawing board 🙂.

[Flatcoat]

59 minutes ago, Lawnmowerman said:

Steady Barker - great journalist - sadly missed. Also the eccentric LJK Setright..........

I really liked Car magazine in those days and had piles of them bought from mid 70’s to late 90’s, politically incorrect and so not in thrall to the car industry. They loved tweaking noses. Sorry for topic drift! 
Back on topic, the alternative to forming stiffening ridges is to create a curve or dome shape, think Beetle or Audi A2 (just about my all time greatest car). However if flatter profile is required, ridges are the better solution. 

[Lawnmowerman]

32 minutes ago, Flatcoat said:

I really liked Car magazine in those days and had piles of them bought from mid 70’s to late 90’s, politically incorrect and so not in thrall to the car industry. They loved tweaking noses. Sorry for topic drift! 
Back on topic, the alternative to forming stiffening ridges is to create a curve or dome shape, think Beetle or Audi A2 (just about my all time greatest car). However if flatter profile is required, ridges are the better solution. 

A2, yup - the one that got away. Never did get one. 

Strongest shape? An egg of course 😄

[Bernard Foy]

7 hours ago, Mike2222 said:

Generally speaking, in aerodynamics, perfectly smooth surfaces are best, but in reality manufacturing this at scale to perfection is not possible. The golf ball logic is that its easier to reliably manufacture a balanced design of dimples, which (as said above) create microeddies of air, making a choice to sacrifice a small amount of drag in order to buffer the solid matter of the ball and allow it to pass thru the air in a consistent fashion. If was smooth, tiny imperfections in the surface (and considering the game involves repeatedly slapping the ball with a piece of iron/wood, a perfectly smooth surface wouldn't stay that way for long 😂) would cause unpredictable patterns of drag, leading to wildly unpredictable movement in flight. 

 

There is an argument that roof channels on cars are designed to smooth airflow over the back of the car, so you don't get unpredictable/variable turbulence/eddying at the rear, which increases drag at higher speeds. But in a 2 ton SUV with a fairly blunt frontal area, I think this is like the cyclist who proudly boasts about their £5000+ worlds lightest carbon-graphite frame that Sir Broderick Wigglesworth rode to victory up L'Alp d'Huddersfield, yet themselves is 6ft6 and 18st. 

 

The most likely answer is that in a big car that's expected to go at highway speeds on a regular basis, a smooth/flat sheet of metal could vibrate/buffet in the wind, so adding ridges adds rigidity/strength, without having to increase thickness/weight/efficiency, thus improving headroom and keeping centre of gravity lower. 

 

That's my 2 cents, at least. 

That post is sensible and well worth the two cents 👏👏

[TonyHSD]

6 minutes ago, Bernard Foy said:

That post is sensible and well worth the two cents 👏👏

That’s right, on the rav4 looks like is there to increase hardness of the roof than anything else, maybe play some role to reduce air drag but the shape in general is a flat roof, nothing like Prius, my mistake not to look properly first 🫣. 👍 

[davidif]

8 hours ago, Mike2222 said:

Generally speaking, in aerodynamics, perfectly smooth surfaces are best, but in reality manufacturing this at scale to perfection is not possible. The golf ball logic is that its easier to reliably manufacture a balanced design of dimples, which (as said above) create microeddies of air, making a choice to sacrifice a small amount of drag in order to buffer the solid matter of the ball and allow it to pass thru the air in a consistent fashion. If was smooth, tiny imperfections in the surface (and considering the game involves repeatedly slapping the ball with a piece of iron/wood, a perfectly smooth surface wouldn't stay that way for long 😂) would cause unpredictable patterns of drag, leading to wildly unpredictable movement in flight. 

 

There is an argument that roof channels on cars are designed to smooth airflow over the back of the car, so you don't get unpredictable/variable turbulence/eddying at the rear, which increases drag at higher speeds. But in a 2 ton SUV with a fairly blunt frontal area, I think this is like the cyclist who proudly boasts about their £5000+ worlds lightest carbon-graphite frame that Sir Broderick Wigglesworth rode to victory up L'Alp d'Huddersfield, yet themselves is 6ft6 and 18st. 

 

The most likely answer is that in a big car that's expected to go at highway speeds on a regular basis, a smooth/flat sheet of metal could vibrate/buffet in the wind, so adding ridges adds rigidity/strength, without having to increase thickness/weight/efficiency, thus improving headroom and keeping centre of gravity lower. 

 

That's my 2 cents, at least. 

Very nearly spat my coffee out reading the 2nd paragraph😂

[TonyHSD]

5 minutes ago, davidif said:

Very nearly spat my coffee out reading the 2nd paragraph😂

Hahah, funny indeed 😁 , but the air drag actually can have a huge effect on efficiency. Airplanes weights tons but they have small spoilers at the rear of the wings and once open they slow down the plane a lot, even some sports cars has that active spoilers. Prius just because of its shape has better mpg than Corolla by 5-8mpg more. 👍

[Firecycle]

9 hours ago, TonyHSD said:

Hahah, funny indeed 😁 , but the air drag actually can have a huge effect on efficiency. Airplanes weights tons but they have small spoilers at the rear of the wings and once open they slow down the plane a lot, even some sports cars has that active spoilers. Prius just because of its shape has better mpg than Corolla by 5-8mpg more. 👍

Does this mean my wife will move faster when doing the house work now she has lost a couple of stone 🤔 🤣🤣

[TonyHSD]

1 minute ago, Firecycle said:

Does this mean my wife will move faster when doing the house work now she has lost a couple of stone 🤔 🤣🤣

Definitely 👌👍

[Cyker]

Careful, with comments like that it's more likely you will move faster while doing the house work!!  

[Big_D]

Or you might even have to do the housework 😁

[Lawnmowerman]

18 hours ago, Firecycle said:

Does this mean my wife will move faster when doing the house work now she has lost a couple of stone 🤔 🤣🤣

Just add dimples - it works for golf balls 🤣

[ernieb]

10 hours ago, Lawnmowerman said:

Just add dimples - it works for golf balls 🤣

Sorry sir but dimples can not be ordered on that model…..