Audi R8 copies Lotus braking system

[jah29]

Apparently Audi uses the same rotor on both front corners of the R8. One side has the vanes pointing the wrong way just like the elise/exige. I can understand lotus needing to save money, but I'm surprised audi did this.

[RoadDad]

The direction of the vanes has no effect on the actual cooling of the rotors.

[jah29]

Originally Posted by RoadDad

The direction of the vanes has no effect on the actual cooling of the rotors.

really!? I would expect it to help a little bit, just along the lines of barely measurable. Don't most high performance and racing cars have front rotors with both sets of vanes pointing the same way? Are Audi and Lotus the only two companies to figure out this braking secret?

The last thing I want to do is argue on the internet. Please share more info, because now I'm curious. I just posted the R8 info because I thought it was funny. It's rare for people too complain about the braking ability of the R8 or the lotus.

justin

[waydui]

Originally Posted by RoadDad

The direction of the vanes has no effect on the actual cooling of the rotors.

According to Racing Brake and AP Racing, vanes DO have an effect on rotor cooling: "Angled vanes must sweep rearwards to evacuate heat from the rotor, and slots must angle rearward to evacuate brake pad dust."

Diagram below shows the correct vane positioning and reasoning.

Regards,
Wayne

[Murix]

Why is everything always copied from Lotus like they invented the car? That's a lame statement.

[jah29]

Originally Posted by Murix

Why is everything always copied from Lotus like they invented the car? That's a lame statement.

Lame? I wrote the title that way because I thought it was funny. I like my lotus, but I don't brag about the company's ability to save a buck.

[andykeck]

Somebody here posted years ago the formulas for a ducted fan with curved vanes that showed a near-zero difference in efficiency. You can also measure the temperature after a track session and see very little side-to-side difference. I think Nick Adams at Lotus pointed this out once from their own testing.

The vanes are curved not to help airflow, but so a disc doesn't develop radial ridges and pedal pulsation due to differential expansion and contraction.

[waydui]

Back to the original assertion that vanes have no effect on cooling, here is an extract from the US Patent Office relating to the scientific characteristics of vented brake rotors:

Automotive vehicle disk brakes with vented rotors are distinguished by having a single ring of air passages or cooling vents separated by annularly spaced cooling vanes.

The vanes act as impellers that force air through the passages by centrifugal action during rotation of the brake rotor when the vehicle is moving. The vanes also connect the two cheeks of the rotor together and so affect the stiffness of the rotor by their structural characteristics.

The air passing through the passages cools the brake rotor and the associated brake pads and thereby extends the life of the pads and improves the braking action of the pads against the rotor.

A vented brake rotor has greater surface area per unit of mass of the rotor than an unvented rotor and has higher cooling rates due to both increased air velocity and increased surface area.


It seems a safe bet that vanes do, in fact, aid in cooling along with providing other benefits such as structural performance.

Regards,
Wayne

[andykeck]

Originally Posted by waydui

It seems a safe bet that vanes do, in fact, aid in cooling along with providing other benefits such as structural performance.

Regards,
Wayne

I wish I could find the original post. The math is pretty clear that it doesn't matter. More to the point, borrow a non-contact thermometer and see for yourself.

eta: This is the best I could find. I remember a longer discussion with formulas and ****, but good luck searching on "brakes" here...

I don't suppose anyone here has actually done any mechanical engineering with regard to centrifugal blade fans. If you had, you would have known that while a backwards blade fan (the way you say you want your brake rotors) is more efficient as the static pressure at the output of the fan goes up, if the output has no static pressure (as is the case with our brake rotors), a forward blade fan (the ones you are complaining about) move just as much air at the same RPM.

xtn

[RoadDad]

Originally Posted by waydui

Back to the original assertion that vanes have no effect on cooling, here is an extract from the US Patent Office relating to the scientific characteristics of vented brake rotors:

Automotive vehicle disk brakes with vented rotors are distinguished by having a single ring of air passages or cooling vents separated by annularly spaced cooling vanes.

The vanes act as impellers that force air through the passages by centrifugal action during rotation of the brake rotor when the vehicle is moving. The vanes also connect the two cheeks of the rotor together and so affect the stiffness of the rotor by their structural characteristics.

The air passing through the passages cools the brake rotor and the associated brake pads and thereby extends the life of the pads and improves the braking action of the pads against the rotor.

A vented brake rotor has greater surface area per unit of mass of the rotor than an unvented rotor and has higher cooling rates due to both increased air velocity and increased surface area.


It seems a safe bet that vanes do, in fact, aid in cooling along with providing other benefits such as structural performance.

Regards,
Wayne

Wayne,

With all due respect, my original assertion was that the direction of the vanes has no effect on the actual cooling of the Lotus rotors, not that the presence of vanes has no effect on the cooling.

[waydui]

Originally Posted by RoadDad

Wayne,

With all due respect, my original assertion was that the direction of the vanes has no effect on the actual cooling of the Lotus rotors, not that the presence of vanes has no effect on the cooling.

Hi RoadDad,
Point taken. I'm not trying to beat anyone up on this, it's an interesting technical topic on a slow afternoon...

I did run across an explanation as to why our car's vanes are unidirectional, again from the US Patent Office technical section:

It is generally believed that a curved vane profile is inherently more efficient than a straight vane profile for cooling air flow purposes. However, the use of curved vanes is often undesirable because it entails the use of oppositely curved vanes on opposite sides of the vehicle leading to a proliferation of component part numbers.

Regards,
Wayne

[RoadDad]

Originally Posted by andykeck

I wish I could find the original post. The math is pretty clear that it doesn't matter. More to the point, borrow a non-contact thermometer and see for yourself.

eta: This is the best I could find. I remember a longer discussion with formulas and ****, but good luck searching on "brakes" here...

Are you thinking of the, IIRC, "Best Brake Pads" (or something like that) thread? Somewhere in the middle of that xtn and someone else got into a formula 1 race about brake pad heat generation.

EDIT: it was elptex, xtn and DreamCar Best Brake Pads?

[jah29]

So what's the norm? Anyone know of other cars that use the same rotors on both sides so that the vanes are going opposite directions? How do porsche and ferrari do their systems?

[Vulcan Grey]

I bought a set of Brembo Racing calipers and rotors (full race, not their Gran Turismo)

The calipers are pretty much corner specific, i.e. can only be mounted leading the axle on the front right or trailing on the left front. This is due to differential piston diameters to minimize pad taper, and also due to fluid pipe orientation.

The rotors are also directional and can olny be used in one location.

Most AP Racing Brake Discs feature Curved Vanes. The brake discs are handed and should be installed with the cooling vanes running back from the inside to outside diameters in the direction of rotation as indicated in the sketch.

http://www.apracing.com/info/info.as...ntification_41

Brembo specifies the same.

[Monsi]

the big brake kit uses symmetrical rotors in the front so the veins rotate the same way and identical rotors in the back

[Noel]

Proper competition brake systems will no doubt state, left and right clearly. If they don't have specific directions, it's more a cost saving measure vs. real true performance.

Wayne is right. There is no argument to this application.

[Keeper]

http://www.dba.com.au/Forum/slot_direction.JPG

[lotusbrakes]

Originally Posted by Keeper

http://www.dba.com.au/Forum/slot_direction.JPG

The image you linked to is talking about the slots, not the vanes inside the rotor.

-G

[Keeper]

Originally Posted by lotusbrakes

The image you linked to is talking about the slots, not the vanes inside the rotor.

-G

Check again. It talks about both and clarifies why the slots go the "wrong" way on rotors with curved vanes.

[apk919]

Hmm... there is such a thing as a centrifugal fan... Centrifugal fan - Wikipedia, the free encyclopedia

The direction of rotation has a definite effect on airflow... look at the discussion of forward curved vs. reverse curved vs. radial flow vanes.

Now whether the effect is important when it comes to venting brake rotors...