Differences Between Brembo 380mm/380mm BBK and 365mm/345mm BBK

[swamp2]

Originally Posted by robc

Come on, I said discussion. The rudeness I experience when I post every five years makes me not post for another five years. Sheesh. Sorry I don't live up to your standards. I'll post my pics and go back into hiding and not share anything I learn here ever again.

Really not trying to be rude. My first correction of your statement was definitely not rude. However, even after the correction, you wanted to stick to your guns and called the terms interchangeable. Although I still would not call it rude, after that I did become firmer in my pointing out of your error. I'm simply a stickler for correct technical information and science in the discussions here. It really is not my standards, it is right or it is wrong on certain matters. Don't let anyone keep you away from the board, if you like reading and or posting keep doing do. Cheers.

[JAJ]

Originally Posted by lucid

These are all good points to consider, but without data, it's hard to tell. Regardless, I find it a bit hard to believe that BMW has tuned things to the extent that air flows from underneath the car and out through the wheels (and cools the rotors in the process) if that's what you mean.

Actually I meant the reverse - I think it's possible that cold air flows in through the wheel and gets sucked out of the wheelwell under the car. That would cool the brakes and evacuate the hot air.

Its all hypothetical until someone measures something, and that's the tricky bit.

[SenorFunkyPants]

Originally Posted by JAJ

Actually I meant the reverse - I think it's possible that cold air flows in through the wheel and gets sucked out of the wheelwell under the car. That would cool the brakes and evacuate the hot air.

Its all hypothetical until someone measures something, and that's the tricky bit.

If there is low pressure in the wheelwell area would it not get filled by the air flowing through the ducting in the bumper used to cool the oil/? radiators?

[SenorFunkyPants]

I came across this scoop, which looks promising:

More details here:
http://forums.vwvortex.com/zerothread?id=2001569

[lucid]

Originally Posted by JAJ

Actually I meant the reverse - I think it's possible that cold air flows in through the wheel and gets sucked out of the wheelwell under the car. That would cool the brakes and evacuate the hot air.

Its all hypothetical until someone measures something, and that's the tricky bit.

One of my friends is trying to design a wheel that does the opposite actually (not for the M3) since you don't want air flowing in to the underside of the car from the sides.

We are looking into ways of constructing an accurate mesh for the surfaces of the E92 M3 that affect flow. If anyone knows of such a representation, please let me know. We are planning to run a detailed CFD analysis, and perhaps redesign the front end to introduce downforce and brake cooling. The person I am collaborating with has done this kind of analysis for NASCAR teams, and thinks positive outcomes can be acheived.

[consolidated]

Originally Posted by lucid

One of my friends is trying to design a wheel that does the opposite actually (not for the M3) since you don't want air flowing in to the underside of the car from the sides.

We are looking into ways of constructing an accurate mesh for the surfaces of the E92 M3 that affect flow. If anyone knows of such a representation, please let me know. We are planning to run a detailed CFD analysis, and perhaps redesign the front end to introduce downforce and brake cooling. The person I am collaborating with has done this kind of analysis for NASCAR teams, and thinks positive outcomes can be acheived.

a body part that is more functional? your going against the grain here lucid. people will be confused.

[lucid]

Originally Posted by consolidated

a body part that is more functional? your going against the grain here lucid. people will be confused.

We'll just paint everything red, and it'll sell like pancakes!

[doba_s]

Originally Posted by lucid

Thanks for the pics. OK, that might partially explain why you are not running into major temperature issues with your rotors. I can't see the other end of the duct. How do they attach to the shield exactly? Did you cut a hole throught the shield?

+1


rob it would be great to see how you attached it to the shield. whenever you have time, please post some pictures.

thanks.

[doba_s]

I think it would be possible to cut either upper or lower part of the protection shield in marked red areas to attache the hose

[sparkyg]

If anyone is in Chicago why not go to Fall Line and see what they do, they build race cars, maybe take a look at what they have done.

[aus]

Originally Posted by robc

Come on, I said discussion. The rudeness I experience when I post every five years makes me not post for another five years. Sheesh. Sorry I don't live up to your standards. I'll post my pics and go back into hiding and not share anything I learn here ever again.

robc, don't let swamp get to you. He's just s stickler for the details. I don't think his response was rude (at least by internet standards), but I could see why you took offence by it.
Your contribution has been great and that set-up looks promising. Could you tell us how you connected it to the hub?

[lucid]

Originally Posted by doba_s

I think it would be possible to cut either upper or lower part of the protection shield in marked red areas to attache the hose

It seems like the rear facing part of the shield has a much broader gap. It wouldn't be that hard to bend some sheet metal to act as a cylindrical sleeve for the hose, and fasten the sleeve to the shield with 2-3 bolts. I don't have a sense of the relative dimensions yet, but it might not be necessary to cut the shield.

[lucid]

Originally Posted by SenorFunkyPants

I came across this scoop, which looks promising:

http://forums.vwvortex.com/zerothread?id=2001569[/URL]

This most likely would not work for our cars as the scoop is sitting too high in the wheel well. It needs to dip underneath the car to grab fresh air. Maybe in the VW car there is a vent through the bumper and thus fresh air behind it.

[JAJ]

Originally Posted by SenorFunkyPants

If there is low pressure in the wheelwell area would it not get filled by the air flowing through the ducting in the bumper used to cool the oil/? radiators?

Excellent question. I believe that the air from the oil cooler dumps into the smooth flow under the car, and that it doesn't increase turbulence by much.

As for the air in the wheel wells, my belief is that the rounded notch in the air dam under each headlight creates a vortex that acts as a barrier between the smooth flow under the engine and the turbulent flow around the wheel and tires.

If I'm right, then the hot air in the wheel well will get sucked under the car, but through the big hole at the back of the wheel arch. Basically, there's smooth flow along the center of the car and turbulent flow at the sides. The diff cooler hangs down into the smooth flow.

If you look at the post with the drawing of the rotor and backing plate, notice that for air to go out through the cooling vanes in the rotor, it HAS to come from the wheel-side, not from the backing plate side. Air from the backing plate side cools the wheel bearing. Air from the wheel side cools the rotor. This design detail of the rotor is part of the reason I think BMW intended to cool the brakes from the wheel side and draw hot air out of the wheel well into the airflow under the car.

If you study a BBK rotor, the rotor hat is set up so that cooling air from the backing plate side flows into the cooling vanes in the rotor, the reverse to the factory setup.

Now, I'm not sure that this is how it all really works, but if I'm right, the reason for doing it this way is actually to improve "general" performance and fuel economy. It's a good aero solution that meets a lot of goals, but doesn't optimize any of them. Brake cooling will be "ok" but not great. Fuel economy will be good "for a performance car". And so on.

The CFD results will reveal a lot about what's really going on down there. I'm looking forward to it!

[SenorFunkyPants]

A slightly different question...given that a decent push of the brake pedal can trigger the ABS at 75mph, how much more of a push would be required at 150mph to trigger the ABS?

[AP Racing - Chris_B]

Originally Posted by SenorFunkyPants

A slightly different question...given that a decent push of the brake pedal can trigger the ABS at 75mph, how much more of a push would be required at 150mph to trigger the ABS?

Theoretically, 4 times what was required at 75 mph, since there is four times as much energy at that speed (Energy = 1/2 * mass * velocity^2). In reality, it could be somewhat different due to many variables other than speed. Nearly all street cars produce aerodynamic lift, so there is less weight on the tires at higher speeds, reducing the amount of pedal effort required to lock one or more of them. How much depends on the car and any mods that have been done to it.

Thousands of pounds of aero downforce (and slicks) is why you can stand on the brake pedal with both feet, exerting about 350-400 lbs., in a racing car at 200mph and not lock the brakes. Those can generate braking forces of over 4g at the higher speeds. As they slow down, the driver has to modulate the pedal to keep from flat spotting the tires.

[SenorFunkyPants]

Originally Posted by AP Racing - Chris_B

Theoretically, 4 times what was required at 75 mph, since there is four times as much energy at that speed (Energy = 1/2 * mass * velocity^2). In reality, it could be somewhat different due to many variables other than speed. Nearly all street cars produce aerodynamic lift, so there is less weight on the tires at higher speeds, reducing the amount of pedal effort required to lock one or more of them. How much depends on the car and any mods that have been done to it.

Putting aside all the complications like drag lift etc...to trigger the ABS you have to overcome the grip of the tyre on the tarmac...is it no so that the tyre grip at 75 mph is not that dissimilar to its grip at 150mph? So do you actually need that much more pedal pressure at 150 than 75mph?
I have tried hard braking from 100mph, maintaining a constant pedal pressure and noting the rate of deceleration and it did feel to be roughly constant.
I can see how kenetic energy fits in with the thermal aspects of braking but is it relevant to braking force and rate of deceleration?

[sparkyg]

I measured the weights of the kit

365 mm slotted rotor 24.5 lbs

6 pot monobloc front caliper 12 lbs

front caliper bracket 2.0 lbs



345 mm slotted rotor 15 lbs

4 pot rear monobloc caliper 8 lbs

Rear caliper bracket 1.5 lbs

All weights measured on digital scale used for shipping so prob +- 0.5 lbs

[lucid]

Originally Posted by sparkyg

I measured the weights of the kit

365 mm slotted rotor 24.5 lbs

6 pot front caliper 12 lbs

345 mm slotted rotor 15 lbs

4 pot rear caliper 8 lbs

All weights measured on digital scale used for shipping so prob +- 0.5 lbs

Great info!

Do the caliper weights include the mounting bracket?

[sparkyg]

Originally Posted by lucid

Great info!

Do the caliper weights include the mounting bracket?

No, do you want me to weigh them?

Can prob do that too.

I just thought all the other weights from other kits did not include the bracket.

I'll weigh it and break it out.

[lucid]

Originally Posted by sparkyg

No, do you want me to weigh them?

Can prob do that too.

I just thought all the other weights from other kits did not include the bracket.

I'll weigh it and break it out.

Yes, please weigh them as well. I would like to know what the net weight reduction/increase would be. (As you know, I am also considering this kit along with the Stoptech Trophy system). Some of the other reported numbers include the stock brackets. Thanks.

[AP Racing - Chris_B]

Originally Posted by SenorFunkyPants

Putting aside all the complications like drag lift etc...to trigger the ABS you have to overcome the grip of the tyre on the tarmac...is it no so that the tyre grip at 75 mph is not that dissimilar to its grip at 150mph? So do you actually need that much more pedal pressure at 150 than 75mph?
I have tried hard braking from 100mph, maintaining a constant pedal pressure and noting the rate of deceleration and it did feel to be roughly constant.
I can see how kenetic energy fits in with the thermal aspects of braking but is it relevant to braking force and rate of deceleration?

If you assume tire grip is the same, the brake system still needs to overcome the rotational inertia of each wheel/tire. This gets substantially more difficult at the higher speed since the rotational kinetic energy is also 4x higher. You can maintain a relatively constant deceleration rate, but to lock up a tire at 150mph will usually take more effort than at 75mph.