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Old 08-30-2020, 01:10 PM   #1 (permalink)
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Bedliner paint job effects on wind

I bought an old suzuki samurai and it has what I call a "high school paint job." Where someone just rolled bedliner over the entire thing. With the rough surface everywhere it got me thinking about how much that would potentially effect the wind resistance. I know some studies that say putting golf ball dimples on a car can help but I assume a rough and inconsistent pattern of which a bedliner paint job I think could really hurt your drag and not help. Any guesses by how much?

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Old 08-30-2020, 02:51 PM   #2 (permalink)
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Assuming "rough" does not mean 10,000 one inch protruberances from the body panels, the answer is most likely "not much or virtually not at all." Most drag is pressure drag, not body friction, from what I have read. I am no expert, just an interested reader.
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Old 08-30-2020, 02:57 PM   #3 (permalink)
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+1 for California98Civic's response. The air immediately touching the body panels is stagnant. As you get farther away from the panel the air speed increases until you get to freestream which is the air speed of the air that is not close to the car. That should be equal to the car's forward speed.

See attached pic for maybe a better explanation. The bottom black line is the surface of the car. The longer the arrow the faster the air is moving along the surface. There aren't any units because it's not something to be set in stone (I think) and is partially dependent on the situation (car in question, speed, etc.). It's called viscous drag. This is also why clay barring a car doesn't really do much (if anything) because the air is stagnant anyway.


My brothers motorcycle was bedlined before he got it. It's an interesting thing to do, but it's held up really well including spilled gas and a few drops. Conversation starter for sure though
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Old 08-30-2020, 06:32 PM   #4 (permalink)
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Quote:
Originally Posted by eou_edu View Post
I bought an old suzuki samurai and it has what I call a "high school paint job." Where someone just rolled bedliner over the entire thing. With the rough surface everywhere it got me thinking about how much that would potentially effect the wind resistance. I know some studies that say putting golf ball dimples on a car can help but I assume a rough and inconsistent pattern of which a bedliner paint job I think could really hurt your drag and not help. Any guesses by how much?
Ford in 'proper' testing found dimples increased drag.

As people have said, I don't think the bedliner coating will make any measurable difference - especially on that vehicle.

That said, on some specific parts (eg exterior mirror housings) a rough coating has been used to trip the airflow (changing it from laminar to turbulent in boundary layer), so reducing noise. (P 235 of my book, for people who have it.)
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Old 09-09-2020, 05:32 PM   #5 (permalink)
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Quote:
Originally Posted by JulianEdgar View Post
Ford in 'proper' testing found dimples increased drag.

As people have said, I don't think the bedliner coating will make any measurable difference - especially on that vehicle.

That said, on some specific parts (eg exterior mirror housings) a rough coating has been used to trip the airflow (changing it from laminar to turbulent in boundary layer), so reducing noise. (P 235 of my book, for people who have it.)
mythbusters tested it but they made a small error by not removing the spoiler

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