Brake Cooling - Cheap DIY method

[Ewazix]

The Great British tinkerer is alive and well, ingenious

Does it work? It would be interesting to see some laps then checking the disc temp with a probe, both with/without the vents being blocked.

My DIY brake ducts on my Z3 M Coupe work very well on track and therefore I every reason to expect that they'll work just as well on the Z4MC with this very similar set up. The hottest that I've ever seen the brakes on my Z3 M Coupe with brake cooling is 270 degs C, which is well below the boiling point of DOT 5.1 brake fluid that I use. Whilst experimenting with different routing on side-to-side of my Z4MC, I did some comparative temperature testing after doing multiple braking events with short intervals for cooling, and the routing and siting of the outlets I've described consistently produced the lowest brake disc temperatures.

If you use the calculator here: http://www.1728.org/flowrate.htm you can estimate the flow rate of air at different speeds of the vehicle. If we assume the diameter of the brake ducting is 1.75" (being conservative) then at 50mph over 34 litres/sec of air passes into the centres of the brakes and at 80mph it is 55.47 litres/per second, all that air MUST have more cooling effect on the brakes than with no ducting.

Brilliant work, a mod with a purpose I like it a lot

[exdos]

I've achieved temperatures in excess of 625 degrees on track and had the brake discs glowing but I only know that from the heat paint and photos taken from outside the car. The cooling rate will be exponential so the greatest cooling rate will be when the temperature is at its highest. I have no doubt that your cooling ducts will be of considerable benefit in cooling th brake discs but it's a dangerous assumption to make that peak temperatures don't exceed the boiling temp of th brake fluid by measuring temps after the car as stopped.

As an aside, there will be very little airflow through the drilled holes in the discs. The holes are there to allow gas build up under the pads to escape rather than aid cooling.

I am aware that a hot mass will lose heat exponentially in accordance with Newton's Law of Cooling. As we both know, braking converts kinetic energy into heat energy, and if the brakes are used with short duty cycles between hard braking events, they will progressively get hotter and hotter, eventually leading to brake fade. Likewise, as we both know, providing an additional supply of cool air to the brakes will partially resist the progressive increase in temperature rise of the braking mass in accordance with Newton's Law of Cooling, thus delaying, or preventing, brake fade.

I am sure that if your brakes were visibly glowing red hot in daylight (i.e. 625 degs C) as your car came to a complete stop and you immediately took the brake disc temperature, they would still be glowing red hot in accordance to the colour temperature scale, which is irrespective of metal type as below:
400 degs C Red heat, visible in the dark
474 degs C Red heat, visible in the twilight
525 degs C Red heat, visible in the daylight
581 degs C Red heat, visible in the sunlight
700 degs C Dark red
800 degs C Dull cherry-red
900 degs C Cherry-red
1000 degs C Bright cherry-red
1100 degs C Orange-red

[Lower]

On a trackday, which is the only situation that a road car needs additonal brake cooling, you don't get to come to a complete halt after you think your brakes might have got as hot as they are going to. As you have stated, you build up the heat in the brakes through a series of duty cycles as you drive round the track.

What you can't do (nor should you for that matter!) on a trackday is stop the car after each braking zone and hop out to measure the disc temperature. The will inevitably be a significant amount of cooling before being able to measure the temperature. That is why heat paint is the accepted and best method for measuring brake temperature.

When my brakes got as hot as they did i had no idea as by the time i'd got to the pits they had cooled significantly from their peak and certainly weren't glowing hot. The reason i was using the heat paint was that i was measuring the effect of various different designs of internal cooling vanes on the discs. This was as a result of what can be seen in the photo below at Rockingham. The disc was a Spoon disc with curved cooling vanes and had been used for approx 1000 miles:

[ga41]

Yikes!

[BMWZ4MC]

Yikes!

As above!

[exdos]

Yikes! and thrice yikes! I would say that that Spoon Disc design needs some auxiliary brake ducts. Did those brakes (and pads) not produce a funny smell whilst you were driving? It appears to me that there's a lot to be said for BMW's floating disc design.

I acknowledge all of the shortcomings of my methods and fully recognise that auxiliary brake cooling is totally unnecessary on the road. My only point in developing an auxiliary brake cooling method for the Z4MC was to be able to do so and to do it cheaply when others have reported that there was nothing commercially available for the Z4MC. Now there IS a DIY method

[Lower]

The brakes stank, but then the aroma of hot brakes is just what you get over the pits on a track day

Your brake cooling ducts look really good and i'm sure will be very effective. My only point is that peak temperatures will be a lot higher than you're measuring.

I could write a load more about why my disc cracked (it was actually the result of the pad compound i was using rather than a disc fault) but its probably not for this thread.

[ga41]

I could write a load more about why my disc cracked (it was actually the result of the pad compound i was using rather than a disc fault) but its probably not for this thread.

Do it. More material to read through.

[exdos]

Do it. More material to read through.

+1.

Some of us love techy stuff!

[BMWZ4MC]

+2

[Tommo Two]

Missed this thread untill talking to BMWZ4MC about brakes at Abingdon track day.

I've got a slightly more bodged setup on my track 328 same principal but doesn't fit to the caliper area or hub just aims air at the brake disc area, i've removed the backing plates aswell to decrease airflow obstruction.



I've run the brake set up on this track twice once with cooling once without cooling. The tracks were both dry and warm same brake fluid (ate super racing blue).

1st outing was in the Z4 3.0 231bhp 1290kgs (both book figures) no cooling lasted 10-15mins before brake fade. As most people, I was disapointed. (removed the caliper, pads & disc and upgraded to E46 330 set up)

2nd outing was in the E36 328 193bhp (book figures) 1180kgs. Fitted the Z4 caliper same old discs and pads, standard M3 cooling ducts and 3" additional ducting. Really impressed with them no brake fade after 20mins, and I was giving 100% in the 328 and about 80% in the Z4, the limiting factor was driver concentration started cocking up after about 20mins!

In conclusion Z4's need brake cooling!

[Lower]

By popular demand...sorry for the delay.

As i've said elsewhere, brake temperature is heavily influenced by the friction coefficient of the pad and the pad's initial bite. Whilst the amount of kinetic energy being converted into heat remains the same, the lower the pedal pressure applied to the pad and the shorter the period of time that the brakes are applied the lower the brake temperatures will be. The exact physics mechanism for this i do not understand but is the generally accepted rule. I have been in extended dialogue with a brake pad manufacturer, but they were not able to explain it in a way i understand.

My mistake was finding a pad that worked well at all temperatures, specifically the Ferodo DS2500. This pad has a higher coefficient of friction than OEM which allows a lower pedal pressure and improved braking, but it isn't quite good enough. Its friction coefficient remains constant even when the pad temperature has increased way beyond what would cause other pads to fade. The net result of that is you have no idea that your brakes, specifically the discs, are overheating as there just isn't any fade and braking performance remains strong. This is why i was driving round the track with my discs glowing under braking but having no idea. If you get cast iron brake discs hotter than 600 degrees for any length of time you risk the disc cracking, which is exactly what happened in my case on a number of occasions. Floating type discs, as per the Z4m, are much less prone to cracking because they are more able to expand and contract freely whereas a solid bell type disc is constrained by the hub.

My initial mistake was to try to compensate for the heat problems with better discs and better cooling when i should have looked more at the pad itself.

I ended up using a Dixcel pad which had an even higher coefficient of friction than the DS2500. This meant that you had to be very gentle with the brake pedal as the pedal pressures for normal braking were very low. But even with extreme on track braking over an extended period of time the discs were running somewhere around the 450 degrees Celcius mark at their peak. Braking performance was phenomenal and on the S2000 this is the pad that the racers and serious trackday drivers use. No upgrade to the brake cooling or to the single pot caliper is required. Just upgraded pads, a slightly better disc and higher boiling point Dot4 brake fluid and the brakes provide exceptional and fade free performance.

The downside was the price. They were roughly double the price of the Ferodo's and very hard on the discs. You'd need to replace the discs for every other set of pads.

I'd love to know the details of the Dixcel compound as they don't make pads for the Z4M.

For those people who's pads are wearing out excessively quickly on trackdays, one of two things are happening.

Firstly, the pad may just not be able to cope with the temperatures it is experiencing. That's where brake cooling helps if you can't change to a better pad.

Secondly, the pads may not have been bedded in and heat cycled properly.

The pad compound is held together with resin binders and when these get hot they produce a gas which has to work its way out of the pad. If the pad gets too hot too quickly the gases cannot diffuse out of the pad quickly enough and it has the effect of separating the grains of the pad compound and in extreme cases blowing the pad apart. You can often see this because the pad will be crumbly and will fall apart to the touch.

Decent pads will either be heat cycled in an oven as part of the manufacture process and don't need heat cycling or will have specific bedding instructions which normally involve a fixed number of braking cycles from one speed to another followed by a cooling period followed by the process being repeated again.

Exdos's brake duct cooling mod will only help with all of the above.

[exdos]

As i've said elsewhere, brake temperature is heavily influenced by the friction coefficient of the pad and the pad's initial bite. Whilst the amount of kinetic energy being converted into heat remains the same, the lower the pedal pressure applied to the pad and the shorter the period of time that the brakes are applied the lower the brake temperatures will be. The exact physics mechanism for this i do not understand but is the generally accepted rule. I have been in extended dialogue with a brake pad manufacturer, but they were not able to explain it in a way i understand.

Thanks for the information. I would like to hear the explanation even if it might be beyond my comprehension.

[ChawenHalo]

Proof that there you are a smarty pants and it works:

You have to go to the 6.20 mins of video.

[exdos]

Proof that there you are a smarty pants and it works:

You have to go to the 6.20 mins of video.

Is there a link to a video missing?