EDIT: Contacted by the son of the original photographer: Lee Hashbarger. This, I believe is just one in a series of excellent photos he took and my drawing honestly doesn’t do the original photo justice. Thanks to him for providing the information and my apology for not crediting it previously.
If you want to know about something, write about or draw it. For example, I’ve slowly been sucked into the BRM universe of the 1950’s. I believe in a self-controlled universal solipsism. Once you discover a topic, more information begins to appear. Maybe this is what the internet is best at. I’m pretty sure if I post this theory, there is someone willing to prove me wrong. The BRM P25 was an awful racing car, and part of that awfulness was it’s single disk rear brake.
Having just read Ken Gregory’s excellent memoir of his time with Stirling Moss, I was confused by his explanation of the accident: disk brake failure. I was confused until I recently found this photo posted at the ORMA BRM Facebook page.
Photographer Michael Pitkins, (reproduced here from the website atspeedimages.com)
The photo is actually the back of the 1960 BRM P48, but I understand the single disk brake on the back of the gearbox was also used on the P25. This explains the reason the BRP flipped when it’s rear disk brake failed. Probably, in the Avus accident the brake failed by locking up the main drive shaft, creating a force on the rear wheels capable of flipping the car. Am I right? I don’t know, I wasn’t there and I’m very capable of adding 2 and 2 and getting 5. It’s also possible Hermann lost control and the car didn’t start flipping until it hit the runoff area. As a rule of thumb, a change in forces on the tires is usually necessary to flip a car. This often happens when the surface changes dramatically.
I’m basically throwing this theory out to see if anyone who was there (or knows the history) can confirm or deny that this is what actually occurred. One argument in favor of my theory is that this is emphatically not how rear disk brakes were used in subsequent racing or street vehicles. A single disk brake makes sense as most of the braking force is applied to the front wheels. In general, front brakes are still sized larger than rears. Inboard braking was pioneered by Lotus to reduce unsprung wheel weight and was even present in the Alfa Romeo GTV6. But, not the single disk that I say, flipped Hans Hermann onto the tarmac at Avus.
Mystery solved? Probably not, I’m just curious what happened and if anyone can help me understand why the car flipped when the brake failed. There were other terrible things wrong with this design, oil and debris being thrown on the rear brake often caused failures, as did a lack of cooling and the solid pipe used for brake fluid, mounted to the gearbox, vibration often caused a union failure. Ultimately, right or wrong, the photo and drawing just remind me that we have come along way, and racing does improve the breed.
And, rereading this post, I was contacted that the rear single disk brake was not considered the problem in this case. The more I learn about the development of automotive technology through racing, the more respect I have for all of those involved. Thanks. (Update 08-21-2015)