December 2012 Fastrack

[Chip42]

and even if it were, 10mm of diameter isn't going to be worth much.

all the 16V VWs stay in ITA, the entries and weights were simply corrected and run to process.

[jjjanos]

Not a process consideration...

K

IIRC, bigger brakes is in the process.... they just chose to ignore it.

[Andy Bettencourt]

IIRC, bigger brakes is in the process.... they just chose to ignore it.

Which they should in this case. As written - and as intended - the brake 'adder' is to 'reward' cars with brake sizes that are anomalous to the class. A 10mm difference does not a penalty make.

The problem is that people view this the wrong way. They only focus on when the same chassis has different brake sizes, ignoring 100% when two different cars have different sizes.

[Knestis]

IIRC, bigger brakes is in the process.... they just chose to ignore it.

What Andy said. I should have been more precise with my response. The advantage has got to be pretty substantial and relative to the entire class. The conversation came up after we listed the Golf IV at the same weight as the Golf III - since they have the same stock power - and later determined that the brakes are even larger than they are on the MkIII.

I shared the opinion with the committee that bigger brakes wouldn't be any kind of practical advantage. In fact, if I were building a 100%-build, sprint-specific MkIII today, I'd backdate it to drum rears.

K

[Chip42]

another "smaller might be better" consideration is inertia - lighter brakes means less unsprung mass and lower rotating inertia of the "wheel assembly". IF the larger brakes aren't helping you in braking or brake life, they are hurting you in acceleration and damping. again, though, 10mm is likely to be immeasurable either way.

and it's rare that a brake adder is applied at all, though it has been and can be. to me, it has to be for brakes that are larger with respect to the default weight of the car than the norm for the class. we are in the process of actually calculating the statistics for such things to make it even more objective in the future, should we choose to do so.

[JeffYoung]

another "smaller might be better" consideration is inertia - lighter brakes means less unsprung mass and lower rotating inertia of the "wheel assembly". IF the larger brakes aren't helping you in braking or brake life, they are hurting you in acceleration and damping. again, though, 10mm is likely to be immeasurable either way.

and it's rare that a brake adder is applied at all, though it has been and can be. to me, it has to be for brakes that are larger with respect to the default weight of the car than the norm for the class. we are in the process of actually calculating the statistics for such things to make it even more objective in the future, should we choose to do so.

Good lord I hope not. We've too many chances to screw things up as is with teh adders and "objective" formulas we already have.

No more adders/subtractors until we get the basics sorted out and right and even thn, let's not think we are smarter than we are. There is NO WAY we can calculate the different 10 mm difference in rotor size makes. Zero. Zilch. None.

[Chip42]

exactly the point, Jeff. when we have the data, we can point to it and say "yeah, those brakes do 'look' small but that car's weight vs. brake size fits within the normal distribution for the class." and NOT apply an adder. no doubt 10mm on an otherwise identical specline will fall here.

conversely, we have the option of saying, "hey, look, this thing has normal looking brakes but is a featherweight, and the ratio is outside of the normal range. it might need the adder."

my intent is not to granularize the process nor to make it overly automatic, it's more to have data to support decisions or rebuke them, which requires a little bit of number crunching.

[Andy Bettencourt]

Another one of the reasons the codifying of the Process took so long. If you say there can be a 'adder' for abnormally sized brakes, you really need to define that in the manual. That would really require calculating an 'average' sized rotor for each class, then determining a % over or under that average to apply the adder. You could even go so far as to make the argument that a core race weight/rotor size would be more accurate.

See how fun this minutia is?

[Knestis]

Better off simply waving the "it's lost in the noise" flag and ignoring additional detail adders, etc. by policy. You don't HAVE to "prove" that the brakes are not too big (good luck with that, by the way) if policy says it's not even on the drawing board. And you'll burn up massive time trying to get the data organized, which won't help ANYWAY.

K

[Ron Earp]

See how fun this minutia is?

And it gets worse.

The size of the disc or drum is just one part of sorting out the brakes. To do it properly you must consider the pad size, calculate swept area, then determine the piston or wheel cylinder area to get a clamping force.

If you want to do the brake modifier correctly you have to go to this level of detail as there are examples of tiny rotors that get it done with large pads, good calipers, and examples with large rotors that have poor brake components.

Screw all that noise. We should not go to that level of detail for the process.

[Chip42]

I more want to have the data to fight OFF the attempts to arbitrarily add weight to cars for seemingly advantageous characteristics. If a car is getting a PCA, call it what it is.

Ron is, of course, correct. theres just so many inputs to the real equation that we don't even try to capture, and in many cases, couldn't anyway.

ITR has some "big brake" cars. I'm very curious how the numbers will support that.

[jjjanos]

Good lord I hope not. We've too many chances to screw things up as is with teh adders and "objective" formulas we already have.

As opposed to the many chances to screw things up using a straight weight to HP ratio?

No more adders/subtractors until we get the basics sorted out and right and even thn, let's not think we are smarter than we are. There is NO WAY we can calculate the different 10 mm difference in rotor size makes. Zero. Zilch. None.

1. It is difficult, but not impossible, to calculate the exact impact of the difference in rotor size. The exact impact, however, does not need to be known.
2. It is considerably less difficult to estimate an approximate impact of such a difference. I.e. Not allowing the pursuit of perfection to forestall the pursuit of improvement.

If such a difference in brakes matters (for identically prepped cars driven by the melding of the genetic material of Clark, Senna and Andretti), then the two cars should not have identical weights. One can argue that too much of an adder runs the risk disadvantaging one chassis relative to the other, but the converse actually is true -- not adjusting for it actual does put one chassis at a disadvantage.

[jjjanos]

Better off simply waving the "it's lost in the noise" flag

There is no such thing. The noise is the standard deviation.

Car A is capable of running an average lap time of A. It's actual lap time is A +/- SD.
Car B is capable of running an average lap time of B. It's actual lap time is B +/- SD.

A<B.

Which car is expected to turn a faster lap?
Which car is expected to complete 30-laps quickest?

[Chip42]

JJ-we aren't going there. ever.

the process was never intended to get cars that close - it isn't designed to, and lap times are not an input. it CAN, however, add or subtract some arbitrary weight for meeting certain threshold conditions. brake size is one of those indicated in the Ops manual, along with torque, displacement, suspension design, engine placement, etc... the ops manual details the maximum adder/subtractor for each category, but the thresholds are NOT well codified.

when we have stats on the class in general, we can then make statements about what X±σ or 2σ (or whatever) are and how car C relates to the class in that way. from there, should there be a need, we can modify weights in a way I would be willing to accept, though I am not looking to change anything that doesn't seem to be broken. I'm personally much more interested in stopping these additions where they are not warranted than finding places to put them.

[Knestis]

The amount of difference the brake size makes is lost in the noise of the factors that we don't try to control - budget, tires, driver skill, and a dozen other major variables. Unless we have a dependent measure that isolates it, there's no way to know if the multiplier/adder/subtractor/whatever is "right." Lap times are NOT that measure. We will NEVER know what lap time any car is truly capable of. We only know what they do - and from gawdawful small samples - with those myriad factors wobbling all the hell over the place.

K

[jjjanos]

The amount of difference the brake size makes is lost in the noise of the factors that we don't try to control - budget, tires, driver skill, and a dozen other major variables.

Budget, tires and driver skill are all irrelevant factors.
Budget = when setting weights, prep always is assumed to be 100%.
Tires = when setting weights, prep always is assumed to be 100%.
Driver skill = when setting weights, maximum performance out of the car always is assumed.

Unless we have a dependent measure that isolates it, there's no way to know if the multiplier/adder/subtractor/whatever is "right."

You mean like the mid-engine adder? The FWD adder? The DW adder? Y'all built RWD versions of the classified FWD cars and did statistical testing under identical conditions? Same for cars with DWs? You moved the engine of an MR2 to the front to see what happens?

You are arguing that because we can not achieve perfection, we should not strive towards betterment. We've already got a situation where the weights are not "right" because we've ignored those factors.

Other ignored factors do impact the theoretical best lap time of the vehicle, but you are suggesting the cumulative errors of the ignored factors net to zero. That's not the case.

These things are going to need to be considered if IT gets to go to the big show, because if they aren't, people will look for the "unfair advantage" created by the gaps in weight classification (and lots of people will throw gobs of money at building 100% prepped versions of those cars) and all of IT will start looking like ITA -- one car to rule them all, one car to beat them.

Lap times are NOT that measure. We will NEVER know what lap time any car is truly capable of.

You'll note that I've spoken of theoretical lap times. But I will guarantee you if 10mm larger brakes is a positive factor, then, when prepped identically (per the process) and driven by identically skilled drivers (per the implication of the process), the car with the bigger brakes will beat the other car more often. That's simply the way the math works.

[Knestis]

I've never argued that that bigger brakes make NO difference. However, there's a huge difference between knowing THAT they make a difference and knowing how MUCH difference they make, which is necessary if it's going to be part of the process.

If you're going to do a regression analysis, you've got to have a dependent measure on which the predictors bear. All of those factors that you criticize as theoretically irrelevant are hugely relevant to the only outcome measure available - and the worst one available. Lap times.

But you know what? I'm the guy who thinks we already have too many considerations into the process. My biggest concern forever has been that we'll give people the false impression that we can really manage all of the factors that we DO take into consideration, encourage people to get more mired in the line-item math BS, and discourage them from the reality that for damn near EVERY SINGLE CLUB RACING CAR in the SCCA, 10mm of brake diameter is not making more of a difference than other factors that many drivers gladly ignore - like new tires. For 90% or more of us, that difference is less than the lap-to-lap variance that we can maintain on an empty track.

Spending ANY time trying to account for it is silly and counterproductive.

K

[jjjanos]

I've never argued that that bigger brakes make NO difference.

Which is it noise or not noise?

However, there's a huge difference between knowing THAT they make a difference and knowing how MUCH difference they make, which is necessary if it's going to be part of the process.

You've side-stepped the question... the FWD, the DW, the ITR with FWD and struts, the life axle ITR, the mid-engine adders are all known EXACTLY or via statistical analysis of real-world (i.e. not the output of some software program) data?

Because if they were not, then using these and not taking a stab at the other things that matter is the equivalent of saying it doesn't count because she meant nothing.

For 90% or more of us, that difference is less than the lap-to-lap variance that we can maintain on an empty track.

That's sloppy statistics and you know better.

[Flyinglizard]

SCCA races are less than 1hr. The smallest brakes that can stop the car at the same points for that duration, will usually yield the most distance for that time frame . IT allows very nice brake ducts, >wearing out the pads or over heating the fluid is not a common issue. The Fiesta and the MR 2 may have some issues, but they can work around it at these short races, with pads, ducts, fluid.
The RWD cars stop the best, but not due to brakes, due to balance.
There is already correction for FWD/RWD, that should cover the braking differences also, due to balance.
If the Aero is tossed out , than why worry about the very minor brake differences?

[Chip42]

Mike, I generally agree with your statement but then... how do you figure the MR2 and fiesta "have issues?" where do these 'facts' of yours come from??? I'm almost afraid to ask.