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12-06-2012, 06:56 PM | #45 |
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^ Yep. I totally agree with the fundamentals of driving skill on the track vs. pure HP. But these threads always end up at "Miatas passing Car X on the track" when the OP wasn't talking about that.
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12-06-2012, 07:15 PM | #47 | ||
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The OP did get a lot of solid input and options directly related to his core questions, so I guess I'm okay with a bit of trip into the forest as long as questions are addressed with solid and germane feedback/input. But I realize that's a personal preference not everyone will agree with (nor should they). I hope we get to hear what he decides to do (sounds like axle-back may be on the top of the list), as the results/changes folks make are always interesting and worth learning something from. |
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12-06-2012, 07:38 PM | #48 |
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So, I know we're taking this WAAAAAAAY off tangent here. But I would like to make one more point.
Even if I was to "live life from stop light to stop light," I would still know that half the time the result of these street racing "pulls," if the cars are even remotely comparable, that it comes down to the driver. And if I need to go pick on every Hyundai Accent driver with my MZ4 Coupe, well, I might as well just go kick myself in the @ss IF that's what stokes my ego. So really, what is the point? At the end of the day, you're still going to lose, even in drag racing, most of the time, to a guy that's more comfortable at launching his/her car and knows how to work the clutch to get the tires to hook up at maximum power as quickly as possible (or God forbid...Someone with an automatic because, frankly, they have their distinct advantages when it comes to launching from a stop)...If it's a car worth "challenging." And if you can't pull away from a stock last gen VW Beetle (non-turbo) in your MZ4 Coupe, do you REALLY think that extra 100 HP is going to be the deciding factor? C'mon. Really, if that is elitist attitude...Well, what can I say. I can't help but look down upon people that don't know what to do with the power they have. No offense. And really, if 300+ HP isn't enough for you to tool around town? Honestly you haven't been using all 300+ HP wisely, in my opinion. Having said all that. I fully support those who put on turbo-chargers or super-chargers or add headers and intakes or whatever power mods on their MZ4 Coupe without the pretense that the car doesn't make enough power, even though it's not my cup of tea. I understand the URGE to mod for mod sake. Or the urge to tinker. Or the urge to extract the maximum amount of power your wallet will allow. Heck there's no denying that I get that urge at times (already exploring a tune for the Veloster Turbo). There are those that need power, not for power sake, but just to know they can do it. But those that do, don't do it because 330HP at the crank is not enough. They do it because the lure for potential for speed is far too great. That is all.
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12-06-2012, 09:40 PM | #49 | |
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[OP here.] But this has been a fascinating read! Part of my challenge is that I seem to be having a hard time finding a BMW club around me, let alone AutoX. And the closest road track, I believe, is about 3 to 3 1/2 hours away. If I didn't have young kids to shuttle around, or a demanding job, or plenty of travel throughout North America, or a honey-do list at home...then I'd probably push myself a little harder in the direction many of you seem to enjoy - off the public roads fun. But as it is, I have to get my thrills taking off from a red light, or zipping around for an hour on a Sunday morning. So I don't know if it's elitist or not (this is the first Bimmer I've owned), but I will admit that I love the raw thrill of just hammering the accelerator and shifting gears while going straight. I'm sure hitting a road course is a heck of a lot more fun, but I'm an American male and I will admit I am a little addicted to raw horsepower. |
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12-06-2012, 10:03 PM | #50 | |
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12-06-2012, 11:21 PM | #51 |
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i remember reading somewhere, maybe even on this forum, a really simple example that goes a long way to explaining the difference in calculated car lengths from the algebra-style calculation to the real-world (empirical) data. It went something like this:
Q. If two cars were both rated at a 0-60 of 5 seconds exactly how come they don't pull off the line together and stay together all the way to 60? A. imagine the extreme of the two possible acceleration profiles, ie the first car, car A accelerates from 0-59mph in 1 seconds (remember this is theoretical) and then drives the next 4 seconds as near as damn it 60mph. Now take the second car, car B, whose acceleration profile is the exact opposite. Car B accelerates flat out and gets to 1 mph after 4 seconds, and then from 1 to 60 in the next 1 second. Both cars have a 0-60 time of 5 seconds but clearly car A will have travelled a much greater distance. I won't do the math here but you get the point. Hope that makes sense, but when I thought about it that way it made such obvious sense that the acceleration profile is so much more important than the 0-60 time. Now obviously no two cars will be as far apart in terms of acceleration profile, but theoretically it makes sense.
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12-07-2012, 01:57 AM | #52 | |
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12-07-2012, 07:15 AM | #53 | |
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While the exact distance in a race would be extremely difficult to predict I don't see why it's not possible to tell whether they should be closer to 7' or 29' apart with a calculation (unless the 29' is correct with the calculation shown). |
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12-07-2012, 12:42 PM | #54 | |
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In my math, I had to use the only available data, which is the elapsed time to hit 60. So, the acceleration rate in the formula is essentially a calculated net effective average over the run. I'd need to get telemetry data or something to show actual acceleration rate every 10th of a second or so to derive a more accurate #. I guess the question is, how bad is it really, to use such an average? At some points, the car is pulling harder than the average (ie: near redline in first), and at other points, it's accelerating much lower than the average (the moments in the middle of a shift). I have to say, it just seems subjectively less plausible that simply using the average causes the difference between them to drop from 40 ft to essentially zero. Keep in mind that the variances in acceleration affect BOTH cars, not just one, so if the calculated distance for car A is too high, then so is the distance number for car B. The delta between them may not change so much. The WRX example given earlier is a good one, in that it shows the penalty of gearing requiring a shift. But, it also points out the flaw of the blanket assertion that 2 cars, like the VW and the MZ4, will normally run neck and neck in a drag race. I'd guess if you filmed an STI and a regular WRX in a drag race to, say, 100mph, you would not see 2 cars whose bumpers are more or less aligned for most of the run. You would see the STI ahead most of the time, but due to gearing differences, you'd see the WRX momentarily "catch up" while the STI makes a shift that the WRX can delay, and then once the WRX finally does that same shift, he falls back to his natural position behind, until the next shift comes up (assuming equal drivers of course). Sadly for Subaru's marketing folks, one of those momentary points apparently happens right at the 60mph mark, which has arbitrarily become a universal measuring stick for performance. Adds weight to the idea that 1/4mile trap speed (not time) is a better indicator of cars ability than 0-60 time. Anyway, it's no different than seeing a backmarker "lead" an F1 race for a lap when the leaders all pit, but then order is restored when the slow guy finally pits too. Doesnt mean a Marussia can run neck and neck with a Red Bull. I'd bet there might be specific points during the run, right after 1 car makes a shift, when the gap might be closer to 7', but overall, most of the time, the gap would probably be closer to 29'. |
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12-07-2012, 01:59 PM | #55 |
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I dread the day the kids are gone to college, in about 6 years, but I am looking forward to being able to grab the wife and spending a weekend or two up at the track. So I'm a little jekyl and hyde right now...would love one thing, but can only really have another. Again, the RPI and short shifter might be all I need for a few years. And we do have plenty of winding, country roads around me and they are fun during the nice weekends. The car is tucked in for the winter now anyway. so it's all wishful thinking at present.
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12-07-2012, 03:48 PM | #56 | |
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12-07-2012, 03:51 PM | #57 |
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I agree but I could see a lot not wanting to read anymore.
After going through the equation you provided and then figuring it out another way I think it is correct. Like you said the number of times you have to shift affects the results as do a lot of other possible variables with two different cars but two cars that are exactly the same with one having more power I would expect the logic of the 29' to be correct (ending the race once one hits 60 and using the times in the equation). |
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12-08-2012, 02:02 AM | #58 |
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So, some calculations for the Z4M in terms of power and weight variations and distance covered:
When one stock Z4M reaches 100km/h (62mph) in 5 seconds, another with only 300bhp would be exactly one car length behind. In another scenario, a stock Z4M with a quarter tank of fuel reaching 100km/h in 5 seconds would be trailed by one car length by a stock Z4M with a full tank of fuel and a 100kg (220lb) passenger. In the quarter mile, assumed to be reached in 13 seconds, the Z4Ms would only need a 6bhp power difference to be separated by one car length, or a 30kg (3/4 tank of fuel) weight difference. |
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12-08-2012, 08:09 AM | #59 | |
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Ain't that the truth! I was an admin on a G35 forum. The stories I could tell .....
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