Hub Color: silver or black ?

LewTwo

1 MW
Joined
Apr 8, 2014
Messages
2,119
Location
Houston, Texas
Here is a question I have never seen: which dissipates heat better a silver or black hub ?

Given most hubs are cast aluminum and or machined cast aluminum, one would assume that there is no surface treatment applied to silver hub. A black hub on the other hand is likely anodized. I believe that thin anodized layer is an insulator (both electrically and thermally). Black also absorbs radiant heat from the sun (something we have a lot of in southern Texas). They paint the tops of school buses here white to help reflect the sun's heat. On the other hand I have heard people claim that black heat sinks radiate heat better than those without any surface treatment.

Does anyone know the correct answer?
 
LewTwo said:
Here is a question I have never seen: which dissipates heat better a silver or black hub ?

Given most hubs are cast aluminum and or machined cast aluminum, one would assume that there is no surface treatment applied to silver hub. A black hub on the other hand is likely anodized. I believe that thin anodized layer is an insulator (both electrically and thermally). Black also absorbs radiant heat from the sun (something we have a lot of in southern Texas). They paint the tops of school buses here white to help reflect the sun's heat. On the other hand I have heard people claim that black heat sinks radiate heat better than those without any surface treatment.

Does anyone know the correct answer?

I know that if I leave my iPhone on the dash in the sun, even with the AC on in the car, it will overheat and start glitching. I'm pretty sure it's because it's black.
 
Yeah darker colors absorb heat and lighter colors reflect heat.
Having the hub motor blend in with the rest of the bike looks better, having a black hub motor against a black rim, and black spokes, black tire and black frame makes it harder for people to detect if you are riding an electric bike or not. I can actually tell more often then not from a head-on point of view if another bicyclist is electric or not, the harder ones to pinpoint are usually the Lycra roadies.

E-HP said:
LewTwo said:
Here is a question I have never seen: which dissipates heat better a silver or black hub ?

Given most hubs are cast aluminum and or machined cast aluminum, one would assume that there is no surface treatment applied to silver hub. A black hub on the other hand is likely anodized. I believe that thin anodized layer is an insulator (both electrically and thermally). Black also absorbs radiant heat from the sun (something we have a lot of in southern Texas). They paint the tops of school buses here white to help reflect the sun's heat. On the other hand I have heard people claim that black heat sinks radiate heat better than those without any surface treatment.

Does anyone know the correct answer?

I know that if I leave my iPhone on the dash in the sun, even with the AC on in the car, it will overheat and start glitching. I'm pretty sure it's because it's black.
 
Reflectivity and emissivity are opposites. The more reflective a surface, the less it will radiate heat when it's hot. A black surface absorbs more radiated heat from the sun, but also radiates accumulated heat much more effectively.

Surface coloration won't change convective cooling (from air flow) much either way.
 
Doesn't matter. What matters is that the load on the motor is not so excessive, that the hub cannot dissipate the heat as fast as its made. The hub should not be making so much heat, unless its overloaded.

Get that part right, and you can climb a mountain in the desert, when its 110F out there. Or, get it wrong, and you can melt a motor in 30 min on a cold winter day.

In case that wasn't so clear,,, cooling the hub is not the problem, or solution to the problem of overheating. Not building a bike that overheats carrying the load you give it is the solution. lighten up, or get stronger motors with more copper and bigger magnets if you must overload a hub motor.

typical bike kit hubmotors in the 500-1000w range can take loads up to 300 pounds total, for bike, rider, batteries and motor, and any cargo.

The smaller the wheel size the better, if overloaded. In 20" size, the weight limit is closer to 400 pounds.
 
Chalo said:
Reflectivity and emissivity are opposites. The more reflective a surface, the less it will radiate heat when it's hot. A black surface absorbs more radiated heat from the sun, but also radiates accumulated heat much more effectively.
Thank you. I was thinking that might be the case.

One of my thoughts was when the bike is parked here in Houston in the summer (in the sun because that is what is available). I put a white terry cloth over the seat (sometimes wet cloth) so I can sit on it when I get back. I was thinking a black hub would absorb the sun's radiated heat and start off hotter than the ambient air to begin with ... that can not be a good thing.

As an aside: I just looked at Grin's motor selection. I think all but two (maybe three if I missed one) come with a black hub .... but those people live in the frozen north country.

markz said:
Having the hub motor blend in with the rest of the bike looks better, having a black hub motor against a black rim, and black spokes, black tire and black frame makes it harder for people to detect if you are riding an electric bike or not.
I will have to take exception to that. Once you have a 7-12 inch diameter hub aesthetics and stealth have gone completely out the window anyway. As far as "looks better" that is is in the eye of the beholder. Personally (I am old fart) silver hub/spokes/rim looks much better to me than black ... and do NOT get me started on tires that are red, pink, blue, yellow, white (how do you keep a white tire clean), etc.

And as far as spokes are concerned: my preference will always be for stainless steel spokes with brass nipples. Long term anything else corrodes, rusts or flakes.

OH ... just to be clear: my opinion is worth a little less than you paid for it (i.e. nothing). :|
 
The ability of a motor to dissipate the heat has little to do with its color. The larger its surface, the heavier its weight, and the faster it is moving, the better it does shed heat.
 
MadRhino said:
The ability of a motor to dissipate the heat has little to do with its color. The larger its surface, the heavier its weight, and the faster it is moving, the better it does shed heat.
I was just trying to see if there was a logical reason so many hub motors are black these days. I thought heat dissipation might enter into the equation. I just got a new EbikeLing front Hub/Wheel kit: black hub, black spokes, black rim ... ugly as the original sin. :(

Good news is that it was delivered in less than 48 hours (thank you Amazon).
 
Well I’d say black is less obvious.

Then, if you want to find a relationship with motor paint and heat shedding, look more at the texture than color. Remember the larger surface and note that matte, rougher finish does create larger surface while even, polished, shiny finish does reduce the surface to a minimum.
 
Back
Top