Anybody know if there are any significant differences in aero drag at, say, 30 mph between a well designed aero frame or aero wheel when the item has a gloss finish vs the exact same item with a matte finish, all other things being equal?
I was thinking something similar a few days ago, with regard to textured clothing supposedly being more aerodynamic than smooth lycra. I presume the same would be true for textured material vs slick helmet and bike surfaces, so (durability aside) why not cover everything in fabric?
It’s a moot point for someone as slow as me, but an interesting thought nonetheless.
A matte finish isn’t a texture thing, its a sheen thing. However i don’t think a textured paint job would make any real difference. the dimples that are popular on other parts are engineered and very specifically sized to reduce drag. an orange peel paint job would just be bad painting and would probably hurt you aerodynamically more then it would help.
However, if you are looking to shave a half second off your IM time then it might be worth looking in to further.
A matte finish isn’t a texture thing, its a sheen thing.
You may be right, but what does this mean?
I thought that matte vs glossy was indeed a texture thing, in that glossy finishes have zero or many very very very tiny scratches. While matte finishes had lots more and much bigger scratches (still very small to the human eye, but hugely bigger than those on a glossy finish).
Or, is this not correct?
Not sure how (or if) it relates to aerodynamics, but years ago surfboard makers started sanding the gloss coat on some boards so that they had a matte (or semi-matte) finish to them, vs the previously-favoured high gloss. Supposedly it made them faster/more slippery by trapping a layer of water (boundary layer?) against the board that passing water would then “slip” over more readily.
Again, not sure if the same idea would apply to air as it was supposed to with water.
I think this, or a similar question, was asked of Chris @ Spec in the new Venge thread. My recollection was that they didn’t note a difference in testing.
Matte implies diffuse reflection, like most interior walls, whereas glossy surfaces create specular reflection, like mirrors. Pitting and scratches can create these differences, but the scale tends to be much smaller than that which affects aerodynamics. Internal refraction of translucent materials can also create a diffusion or matte look by letting light pass through the surface, while having many internal imperfections. Many “white” objects are actually composed of clear fibers that refract light to create a diffuse “white”. This is why paper and t-shirts look clear when wetted.
Roughness that can change the flow is larger than the laminar sublayer (search for Hydraulically Smooth). For bicycling Reynolds numbers, that roughness would have to exceed something like 0.02" or so, which would be much larger than most paint surface features (common lingo is morphology).
Roughness that can change the flow is larger than the laminar sublayer (search for Hydraulically Smooth). For bicycling Reynolds numbers, that roughness would have to exceed something like 0.02" or so, which would be much larger than most paint surface features (common lingo is morphology).
Not sure how (or if) it relates to aerodynamics, but years ago surfboard makers started sanding the gloss coat on some boards so that they had a matte (or semi-matte) finish to them, vs the previously-favoured high gloss. Supposedly it made them faster/more slippery by trapping a layer of water (boundary layer?) against the board that passing water would then “slip” over more readily.
Again, not sure if the same idea would apply to air as it was supposed to with water.
Textured surfaces initiate turbulence earlier than it would occur with a smooth surface. The trade-off is that the increased skin friction is offset by allowing the flow to stay attached longer, reducing the wake size. The effectiveness depends on how well the designers design the texture, surface, for the intended speeds and fluids.
For surfboards, I find it hard to believe that texture would help. The water is already impinging the high-pressure side of the board, not a “suction surface.” Here it only serves to add skin friction. The marine industry spends lots of money on anti-fouling - organic growth that increases skin friction on hulls; if anything, research is being done on superhydrophobic coatings, such as the food-safe research product from MIT. That may help surfers more than wax.
I recall some tests done back at the TA&M tunnel looking to see if rough paint (they added fine grain sand) improved aerodynamics; it did not.
The tests were done with round tubed steel frames, and if they did not see a benefit then it’s highly doubtful that aero section tubes (greater surface area, and inherently lower pressure drag) would improve with rough paint.
There are several reasons why they could have observed those results:
Texture too small for regimeDrag improvements too small for tunnel sensitivityPaint thickness increased frontal area simultaneouslyFreestream turbulence intensity artificially high (poor maintenance, screens, fan pitch, etc.)Maybe other specifics that I’m not privy to
I’m not really advocating textured paint for bicycles. My post was more of an explanation of when initiating turbulence would be beneficial, and how I doubt it works well for surfboards.
That said, I don’t think the argument of airfoils not benefiting due to higher surface area and lower “pressure drag” is sound. Everything in aerodynamics is scale and regime dependent. Consider an airfoil which has just stalled: it will have a large wake and associated drag. Adding vortex generators upstream of the separation will likely reattach the flow and reduce drag significantly.
Under normal cruise conditions (low angles of attack) a designer would not want to depend on vortex generators to attach flow, but it may be necessary for take-off and landing.
I think that a skilled aerodynamicist should be able to reduce drag on a round-cylinder tubed bicycle, though by how much I wouldn’t guess at the moment. It would never be the ideal solution unless weight was a primary concern.
We can certainly agree that the skilled aerodynamicist wouldn’t opt for a homogeneous coating (ex. rougher paint). I bring this up in the context of the OP’s question about matte vs. gloss finishes (ignoring for the moment that the imperfections in the matte finish are not aerodynamically significant).
I’ve wondered about this as well (and may have even started a post on this topic a few months back???) but I don’t think its about matte vs glossy. I think you’d need an actual texture like what Pearl Izumi has on the Octane sleeves or perhaps grooves similar to the face of a golf club (to act as a trip wire at yaw).
With that said, I really doubt there’s much left on the table in terms of aero gains for the frame itself (over the Speed Concept/P5/etc). IMO, from here on out it will be mostly about integration, comfort, and serviceability (making the bike easier to wrench on). One thing on my wish list is clearance for bigger rear tires. I doubt there would be much of an aero penalty (maybe even a benefit?) but you could pick up some noticeable comfort (just imagine 28s or even 30s…on a purpose built disc of course).
Some years ago the original ridley noah and Dean had a special textured paint that was supposed to initiate turbulence and slow boundary layer separation. I’m not sure if it still has this.
“To improve the air flow in areas of high resistance, our engineers developed and patented F-Surface aerodynamic paint which re-establishes the laminar flow. F-Surface reduces the drag on the frame by up to 4,1%, as measured in our wind tunnel tests.”
I’ve wondered about this as well (and may have even started a post on this topic a few months back???) but I don’t think its about matte vs glossy. I think you’d need an actual texture like what Pearl Izumi has on the Octane sleeves or perhaps grooves similar to the face of a golf club (to act as a trip wire at yaw).
Yes, this was my line of thinking. Nonetheless, I think the gains to be made on paint on bike frames is miniscule compared to clothing and helmets. I look at the big, bluff faces on aero helmets/visors and can’t help but think that there’s scope for improvement there.
I presume dimpled helmets like the Louis Garneau Vortice simply don’t test any faster than alternatives, otherwise everyone would be doing it?
The old Cervelo P3sl had a “shot peened” finish that was very rough to the touch. Lots of folks put in really, really fast times on this bike. Fastest 10 mile TT I ever did was on a P3sl and I’ve owned a lot of “superbikes” since. But I’m also getting old. Regardless, that P3sl was a fast little bike!
Did you ever reach a conclusion? I have been looking up and reading over F1 threads, but maybe you can save me some time.
Seems like matte vs gloss paint really is no different.
From my reading here and on other places on the interwebs, I think the bottom lines are:
It is not clear if gloss paint is faster or slower than matte paint at cycling speeds. {Remember that in some cases a smooth surface ends up being overall faster than a rough/dimpled surface, in other cases it is the other way around. This is because, while a rough surface always creates more local drag than a smooth surface (via skin or surface drag), in some cases, this additional skin drag can affect and lower ‘form drag’ (or induced drag) by a lot more than the minor increase in skin friction, this all relates to the boundary layer of air, much like in the case of dimpled balls or dimpled rims being sometimes faster than their smooth equivalents.}
That said, any difference in drag between gloss paint and matte paint (at cycling speeds), if one exists, appears to be so low as to be well below the threshold of measurement of most wind tunnels.
( But gloss paint is sure is easier to keep clean ! )