Hello, anyone still alive here ? I decided to try rising this topic here with hopes of expanding knowledge on this topic. I should probably try to seek it in some other vintage racing enthusiasts forum too, would be nice to have some recomendations. Thank you. So, to begin with, recently I have had some discussions about how much exactly disc brakes were superior to drum brakes and how, eventually topic also expanding to engine braking which is another topic that no one in simracing knows anything about The only real comparative info I have found so far has been here: https://www.motorsportmagazine.com/archive/article/may-2000/53/disc-brakes/ It tells that in 1953 Ctypes had roughly half braking distance into Mulsanne corner against opposition. But it lacks providing any more details about it. On other sources it is said that Disc Brakes in terms of stopping power weren't much superior to big high performance drum brakes, at least aside brake fade. Brake fade is mentioned a lot, as well as some other interesting problems such as self-servo effect, but I never find information that goes more in detail about it. There is small docummentary of first Ctype run at Mille Miglia with Moss and Dewis. First run after true proper development stage where all disc brakes problems were solved, or solved almost (brakes fluid boiling, massive pads knockoff). According to Moss they were outbraking everyone and constantly cilmbing up in positions. In 1954 Dtypes (with Discs) didn't really have had significant edge against 375Plus (with Drums) in LeMans. Slight Dtypes deceleration and top speed advantage there was compensated by greater accelerations and better road holding of 375Plus, and only in wet weather Disc brakes became true advantage as well as greater power of 375Plus becoming lesser advantage. I also found little bit of Aston Martin documentary with Roy Salvadori sharing his memories about how he actually liked DB3s braking more than braking of Dtypes. Again lacking any ellaboration on the topic. Leaving lots of room to speculate as in context he was just talking about "Goodwood 9hours". Obviously Aston Martins must have used state of the art, best drum brakes of a time, while disc brakes were still in development, early for motorsport development. Could have been also a factor of being used to drum brakes, as I assume to some degree technique with discs was different, perhaps with much less fade some trail braking was starting to be needed, maybe on track with plenty of undulations and frequent fast turns pads knockoff was present in Dtype, who knows... It tells a lot how much better disc brakes were, that Mercedes needed to design futuristic active aero, aerodynamic brakes for 1955 LeMans, which were effective in making 300SLR capable to race Dtypes competitvely. Despite great Jaguar success with Dunlop disc brakes (later became Girling brakes), the technology didn't spread widely in motorsport till late 50s. Drum brakes were still in full development, better and better compounds of drum brakes shoes got developed, and they continued being competitive. Other manufacturers than Jaguar didn't have most advanced development of discs system. Supposedly Jaguar shared technology with Mercedes only after they withdrew from racing. Jaguar also was not very active in racing in later 50s. How much better disc brakes were by 1953-1954 is not known exactly to me. It is only known that they didn't have, or had greatly lesser problem of brakes fade. How bad exactly was brakes fade problem on other cars (most others were on Drum brakes) is not known very well to me. I am eager to find information about it.
About drum brakes and brakes fade. Brakes fade is an issue that happens in all brakes. Brakes don't brake optimaly when they are too cold or too hot. In racing extreme heat is particulary a big problem, or at least was years ago. Frequent braking, in long braking zones put great amounts of heat into the system, and eventually led to diminishing of braking power. Drum brakes had brakes fading issue highlighted. They had much worse cooling than disc brakes, so they reached undesired temperatures easier. Besides having bad effects of high temperatures at contact patch, if whole drum was not cooled efficiently and reached extreme temperatures the metal was expanding and warping, that with added vibrations and fast rotational speeds resulted in significant loosing of brake shoes contact area, or at least contact area pressure. While disc brakes also can fade due to extreme contact patch temperatures, they are mostly immune to disc deformations and loosing of contact patch size/pressure. Perhaps biggest issue for drum brakes was getting them wet and having losse bits of brake shoes lining trapped inside. Also they were heavier and bigger. And required exposure to air stream for best possible cooling, which obviously had a hit on overal drag of the cars. I think that for drivers back then it was normal to leave some reserve in braking distances, besides that lifting off and coasting early to loose initial chunk of speed only by aerodynamic drag and engine braking. Engine braking is different topic, how much can there even be, and how much is rational to have. Have to really admire how much far technology traveled since then. Now the only fade is desired one, where power has to fade in first braking zones when starting with cold brakes. After that, brakes fade is basically unhear, apart maybe due to brakes wear, which is less or more freqent now depending on brakes compounds. Brakes got so good, that there are usually too much of them for most of the braking. ABS systems working to deal with that, engine braking maps are there because engine braking is much less needed. I would even say that out of all developments in racing, and high performance cars - the brakes are most amazing all the time.
Not what I am looking for but interesting to read. https://medium.com/formula-one-fore...history-of-how-f1-cars-slow-down-5e7491e333d6 It is about F1. Vanwall apparently used discs since 1954, but only started winning in 1957. Maserati 250F was also winning a lot in 1957, it had very good drum brakes, and also Fangio. Makes sense for F1 cars to catch up later to disc brakes, these cars are lighter, so they generate less heat. Because of being open wheelers, their brakes cooling is better. By 1960 or 1961 almost no one were using drum brakes anymore. I wonder what was last F1 car to use drum brakes.
I've got some period articles to share, but I have to dig them out. Where I come up short is what friction compounds were available... I think the decent Ferodo compounds were available about 1952 or '53, but have no proof.
July, August, & September 1959 issues of Sports Car Illustrated has a 3-part series by Karl Ludvigsen on racing brakes. Will scan them soon...
Here are the articles. I intended to scan them into a single file, but then goofed with Part 2... it says continued on pg 76 and I skipped it, instead scanning Part 3. The second file is the missing pages. Note that Part 1 also has a "continued on pg 76" and that is complete in the first file. https://drive.google.com/file/d/1v5lOQWIFlGSzOLe7N5-HuiYnAdHlvAXu/view?usp=sharing https://drive.google.com/file/d/1gEAOIgBC0QLK9vQr8YPWNh07xl5qJvwQ/view?usp=sharing
Wonderful ! Big thanks to you, will enjoy reading these non-internet articles a lot, first thing in the morning tomorrow.
Fantastic article @Emery . Thank you again for sharing. It is so packed with details, that reading one time is not enough. Clearly disc brakes only truly won battle of likes by the end of 50s. GP cars held for quite some time. Unfortunately there was still no direct comparison, even mentioned in the article that Maserati could have given great comparison in 1955, but used superior cars with drum brakes. It is amazing to read about how much effort was being given trying to perfect drum brakes, interesting to read about all these technical problems in detail. I think part of the reason why drum brakes were holding on for so long was because because of all that sunken cost into developingthem already, and I guess for engineers it was great sport trying to see how much they could perfect them, and at the same time racing against different technology of discs must have been making it more interesting. Some nice info about exact temperatures figures. Pretty much what I expected. I suppose in rF2 we are getting the brake contact point temperatures, obviously higher than temperatures of drum or disc iteslf. However, speaking of temperatures of drum vs disc, very interesting nuances about how mass of them affects heat storage and cooling. I did not think about before, how drums could have taken longer time to heat up, as well as to cool down. On the other hand, apparently they were fighting to make drums as light as possible. Question still remains for how much could drums actually keep up with discs in races. I think it likely didn't take long. But how long. Obviously it would have been different in every track. Cars being wildly different also doesn't make comparing easy. Would be nice too to find some similar read, but steming up from GT racing. As cars were heavier, also often racing in higher speed tracks with harder braking zones.
I've now dug far more into brakes than I ever wanted! Brake parameters in rF2 seem entirely intended for disc brakes, but most of them can be replicated for drum brakes. BrakeDiscInertia can be calculated for a brake drum using density and volume of the material(s). It's a little more complicated for the AlFin style of brake drum, where you have two materials and voids. BrakeResponseCurve is a simplified description of the friction material's coefficient of friction vs. temperature. You can use one of the physics spreadsheet's brake pads as examples or take it from an existing car or make your own from a chart offered by the likes of Wilwood. Ideally, for a racing car, we're looking for a Ferodo DS11 curve which has a max Cf=0.35 (but I don't know the temperature range) and probably a lower Cf prior to 1960. Looking up friction compounds from the '50s is... difficult. Can find their names, but the properties are annoyingly not published on the web. Modern street pad compounds (skip over the semi-metallic & carbon compounds) are possibly representative of the earlier drum brake compounds. BrakeTorque requires us to make some calculations using the drum radius, shoe radius, shoe/drum width, max Cf, and the line pressure(*). Line pressure is the hardest to obtain because we usually don't know the sizes of the hydraulic system, mechanical advantage of the brake pedal, or how much a brake booster affects it. However, at least there's a starting point with an online calculator, even if you'll need to do unit conversions afterwards: Disk and Shoe Brake Equations and Calculators (engineersedge.com) BrakeTorqueAI gets the usual reduction since AI are not affected by cold or faded brakes. BrakeGlow temperature range is just like it is for disc brakes. The AlFin style of brake drums should not use it (don't assign the graphics as a brake disc), but if you have an exposed steel/iron drum, then it should. And now we get to where the parameters are fuzzier... BrakeHeating and BrakeCooling are going to rely on mass and material properties of the brake drums. It should be possible to use the physics spreadsheet as a model for what these calculations should look like. However, the dual materials of the AlFin style complicate things. I'm inclined to make the simplification that the alloy fins are all that matters, maybe with an arbitrary reduction in heat transfer. BrakeDuctCooling I don't believe will be any different from the physics spreadsheet. Even more difficult... BrakeDiscRange, BrakeWearRate, & BrakeFailure are described as dealing with the disc thickness, which is counter intuitive and confusing to me, since I think of pad/shoe wear as what would cause brake failure. Well, I suppose we can substitute brake drum thickness for disc thickness (though we aren't going to see 20cm to 25cm drum thickness!) and scale BrakeWearRate and BrakeFailure accordingly. Digging into how the physics spreadsheet calculates this would help my understanding. Or just use the values we commonly see for disc brakes. (*) I'll see if I've got enough info to calculate line pressure for a specific car, maybe an MGA, which could be used as an estimate for other cars. And that gets me to thinking about making a spreadsheet to do the other calculations... stay tuned... maybe someone will beat me to it!
Trying to find information on early brake linings led me to this: Continuation of the 1922 Report on Brake-Lining Tests (jstor.org) In that period, they're not yet measuring coefficient of friction vs. temperature, rather they're measuring it vs. time for a specific pressure.
I see Emery did quite a dive deep into details of drum brakes. Great that rF2 even offers that much variables, even though there could probably be even more of them for drum brakes specifically. As in my case, at first I am just looking for principally correct base performance, temps curve for torque and overall torque, rate of cooling. I think 90% of authenticity can be achieved without going ultra scientific on stuff, but just have to know proper references and by following them rationally. But every detail adds up to research, of course.
Trying to build the spreadsheet to copy Disk and Shoe Brake Equations and Calculators (engineersedge.com), but I'm having trouble getting the same values for the intermediate steps. First step, calculating X, is fine following their equations, but calculating Mr and Y hasn't worked so far. Either they lost something or I'm misinterpreting something.
Found my errors! After an overnight rest and reflection, I correctly reasoned that I misassigned a named range. Then it became clear that I missed converting degrees to radians in another spot. Today I finished out the steps and the spreadsheet math is working correctly. One can obviously just double the leading shoe BrakeTorque that is currently calculated and use it for twin leading shoe brakes that were often (not always!) used for the front brakes. However, there's a difference between the leading shoe and trailing shoe (as usually used on rear brakes) as far as pressure required to attain the same braking torque, so I need to research that (and a few other items) before releasing this spreadsheet for public consumption. My intent is to make the spreadsheet as easy to use as possible by providing guidelines for the dimensions & pressures. Typically we know the diameter & width, but the other parameters are going to be estimates at best because accurate measurements are nigh impossible to find.
Those braking torques should be rather decent judging by all the information. Good luck with all this maths and physics stuff, this is very complex problem with drum brakes.
Getting closer to finishing the spreadsheet! According to Double-Shoe Brake - Frictional brake with two pivoted shoes diametrically positioned about a rotating drum with triggered faulting - MATLAB (mathworks.com), BrakeTorque is the same for both leading and trailing symmetrical brake shoes when they have no difference in coefficient of friction and pressure. Usually there is no difference, but sometimes in racing a harder brake lining was used for the leading shoe and/or sometimes the trailing shoe was given more pressure to compensate for lack of self-actualization. Next up is taking some measurements of drum brakes and then tinkering with the parameters to see how much effect they have, what sort of tolerances are acceptable.
It's a looooong time ago but ISTR one of the single leading shoes on my Mini used to wear more quickly. But weren't racing cars fitted with twin leading shoes (twin cylinders)? Ah, probably not allowed under the draconian homologation rules at the time unless originally fitted to production cars.
