Does this rim desigh provide extra brake cooling effects??

[rsiwicki]

I have seen these a lot lately on the Benz's and have wondered if the fan blade like design creates an airflow pattern different than usual over the brakes keeping them cooler....

[jamesmost]

been seeing those on Benz as well

[Rex]

Well, I'll offer my "logic" (not facts based) thoughts.

It would take more the blades (that don't stick out past the tire/wheel assembly) to draw any air into the brake rotor for cooling, and the time when brakes need the most cooling the car would be at low speed or stopped (post use of brakes).

But I'm just an old redneck that never made it past high school??

[maxnix]

The blade design should be to evacuate air out when travelling forward and installed correctly.

[Rex]

The blade design should be to evacuate air out when travelling forward and installed correctly.

Ahh, air from under the car, pulled through the wheels. An guess to how fast the car would need to be moving (wheel/fan rotating) to be "effective"?

[AZhitman]

Brakes have a relatively low exposed surface area, and therefore probably benefit very little from any kind of convection cooling.

However, I have heard of some small benefit from wheel design, alleged by the manufacturer (see 84-87 Corvette for one example).

[maxnix]

Ahh, air from under the car, pulled through the wheels. An guess to how fast the car would need to be moving (wheel/fan rotating) to be "effective"?

Ferrari and others have done it from time to time. While the air extraction is negligible at sub triple digit speeds, the one thing you don't want to do is add air pressure under the car at > triple digit speeds.

Therefore, I think these are mounted on the wrong side of that Mercedes. Pity we cdn't have a picture of the otherside, because the wheels are definitely directional, so they should be blowing under also.

[Q45tech]

With a solid rotor [no isolated hat] wheel weight and conductance is critical in absorbing the excess heat to protect wheel bearings. Hot wheels are good.

[MinisterofDOOM]

With a solid rotor [no isolated hat] wheel weight and conductance is critical in absorbing the excess heat to protect wheel bearings. Hot wheels are good.

Ahh, that brings up an interesting point.Would wheels with more (comparative) surface area allow for more efficient cooling of brakes? Radiation does not *require* convection or even the presence of fluids for exchange. That would mean that any benefits of high-surface-area wheels would be present at a stop (as Rex said above, the most critical time for brake cooling).

[szh]

While present, radiation comes into play at higher temperatures - at normal brake temps, convection cooling has more of an effect.

More metal means more "heat capacity", so surface area is less important than total volume in this case.

Which why I think Dennis (Q45tech) always says that we should never get light-weight rotors for Q45's - certainly never less than OEM!

Z

[maxnix]

Actually, I think Q45tech was speaking of conduction of heat from the rotor, through its hat, then to the hub, and via the hub to the wheel.

While there will be some radiant heating from a hot rotor, conduction will account for most of the wheel's gain in temperature.
Modified by maxnix at 12:01 PM 8/1/2005

[Q45tech]

In theory, the 20 pound wheel and the 20 pound rotor means if the heat transfer was perfect the wheel would get as hot as the rotor........obviously there are problems in transfer between the rotor hat, the wheel studs and the inner surface of the wheel.........surface contamination [rotor hat rust and aluminum corrosion on the center section of wheel]...........heat conduction white grease after a detailed cleaning......like cpu are coupled to heat sinks in computer.

[szh]

Actually, I think Q45tech was speaking of conduction of heat from the rotor, through its hat, then to the hub, and via the hub to the wheel.

While there will be some radiant heating from a hot rotor, conduction will account for most of the wheel's gain in temperature.

Argh, I used the wrong term! I meant conduction ... but was sleepy enough (12:30am) that I wrote convection for some reason. Sorry about that!

I agree with your post ... that is exactly the point I was sleepily trying to make! Radiation effects do not matter as much as conduction. So volume (i.e., related to density and weight) of the rotor is far more important than surface area.

Z