Rep Power: 0

Hi, I was wondering about my time at the drag strip.
I did 16.685 @ 86 MPH and sometimes i see people posting times like this on

Best ET: 16.18@83.5
Best MPH 16.20@85.4
(for a ford probe)

I noticed that the MPH is lower but the time is faster. Do you think my time is slower because of a bad launch? or the probe has a lower MPH because of a bad launch?

thank you for your opinions

BTW I have a 2002 Coupe VTEC.

 
Rep Power: 340

that is WRONG think about it.. if ur going faster... the time is always less....
i forget what the speed/time calculations are

 
Rep Power: 0

You're wrong, dude. You can attain higher MPH and run slower times, and have lower trap speeds and run higher times. If you have more wheel spin, you will have a higher time.

Case in point:

My 2 best 1/4 times:

14.8 @ 94.3, 2.173 60'

14.9 @ 95.4, 2.201 60'

I had a HIGHER trap speed on my SLOWER run, because I spun my wheels a tiny bit off the line, which is also why my 60' was a little slower.

 
Rep Power: 0

There is also no such thing as a formula for calculating speed from time, or time from speed, because the accelleration is not linear. Your simple high school algebra won't work here son.

It depends on the amount of work done by your engine from point a to point b- point a being the starting line and point b being a quarter mile away. The total work is approximately the sum of the work done in each gear, which will vary depending on the shift points and the gearing- essentially derived from the area under the horsepower curve between the engagement point/disengagement point in each gear (this assumes perfect, instant shifts, and no powershifting, but it's close enough).

As a result, depending on the shape of your power curve, you may run better times than another car but get slower trap speeds. A car like a 5.0 mustang with GREAT low-end torque and power will accellerate much faster off the line than a car that has great high-end power like my IS300. I ran a 5.0 that ran a 14.4, at 90mph, and I was nearly a half second slower, but my trap speed was 5 miles an hour faster. Why? because of my top end power and gearing. But, he was able to do MUCh more work in 1st gear off the line before he shifted to second, giving him a huge lead right away. The rest of the race was me catching up to him.

Which is why some cars you can beat on the highway, but never in a stoplight race. 2 cars that come to mind with my car are the WRX and 5.0 mustangs. I would lose to both consistantly in stoplight races, but on the highway will walk them both no problem. (Coefficient of drag also comes into play here, but lets not get into that)

Make sense?

Hope this helps.

-C

 
Rep Power: 401

FYI.

Your fastest trap speed will almost NEVER also be on the same run as your fastest ET.

Example, my best ET is 13.79 @100.2mph.
Best TRAP, is 14.0@101.84mph

 
Rep Power: 0

13.79 all motor 4 banger..............GOD DAMN I LOVE HONDA!

 
Rep Power: 0

FYI, it will:

Average velocity: R=D/T

Average acceleration: s=(vo)t + 1/2at^2 Where s (Distance in meters - 1.0 meter = 3.281 feet) is equal to vo (Initial Velocity - for CO2 cars this is 0) multiplied by t (time in seconds) plus one-half a (Average Acceleration - what we are looking for) multiplied by t squared (time in seconds again).

 
Rep Power: 401

oh yah, as DRJ pointed out. You CAN graph speed and acceleration, however, it does not account for human error or shifting. YOu have to add variables for that.

and that was stock.

 
Rep Power: 0

Dude, I double majored in mechanical engineering/comp sci. Trust me, I know my mechanics, particularly my calculus. But the simple distance equation you provided won't work for REAL cars. CO2 cars have a relatively constant accelleration, for the most part. We don't care about AVERAGE acceleration in this case, because so much of your run depends on your launch and shift points. Your accelleration will not only be variable throughout your rpm range, but it will be different in each gear. Throw in rolling resistance, wind resistance, etc, and it's not a simple algebra problem.

R=D/T is too simple of a formula to even consider using here. My entire point is that if it worked like that, then yes, you could never run a slower time with a faster trap. But, in the real world, you in fact CAN, because of the complexity of the problem and the huge number of variables. See my point? You can't oversimplify this problem. 10th grade math doesn't work here buddy.

 
Rep Power: 0

I wish our cars had linear acceleration... then they'd be fast...

But seriously, I totally understand what you're saying doublins (thank god there are actually some engineers on this site), I've never actually drag raced my car, BUT, I have played the hell out of Gran Turismo 3 (and yes, i know video games aren't the same as real life) and several times, i've come up with a MUCH lower trap speed, and yet a great time, and likewise, i've had very high trap speeds, and horrible times. Also think if you had a reall great run, then slammed on the breaks before the end of it, you'd have a really low trap speed, but your time would still be pretty high up.

-Mark

 
Rep Power: 0

EXACTLY! I'm glad some people understand. It's also why you can still win a head-to-head by braking at the end to prevent "breaking out" of your dial-in. You will have a faster time, but a lower trap than your opponent.


If you're going to use the mechanics equations, then you will be calculating the AVERAGE ACCELLERATION. But, then you cannot use your trap speed. You actually have to calculate your "adjusted trap speed", by using v= .5at^2, which will ALWAYS work out to be lower for slower e/ts and higher for faster e/ts.

Get it, folks???

 
Rep Power: 0

I see you point now. I'm a comp sci major too, but math obviously isn't my strong point. Thanks for the explaination.