Newbie Mile speed trap question.

[Chad M]

Hoping you guys can explain to me a question on the speed markers i don't understand. I searched to no avail on the answer. As I have seen many time slips posted on Instagram, id really like to know.

As I understand it right, on a 5 mile course, the first two miles are for getting up to speed, and the last three are for the run?  So after the first two miles starting, then we see marker mile 3 speed, mile 4 speed....but what is the "Exit" speed? and then we have the mile 5 speed.

And in the case of Poteets slip I saw, if the exit speed is before the 5 mile Mark, why isn't the 481 MPH counted?

And you guys were 100% right when I asked questions about going for the first time two years ago, it is addicting! I thought it would be a once in a lifetime trip, and it was, but I NEED to find a way to get back there again---and drink plenty of water this time so I don't cut it short from heat stroke---to much walking in the pits. Maybe next year.....

[trimmers]

Exit speed is the speed over the last 132 feet of the fifth mile.   While Poteet had a speed of 470 over the entire fifth mile, the 481 exit speed shows that he was still accelerating.  This might tell them to consider changing gears in the QC box, or making other adjustments.
There are lights at the following distances from the start (on a long course): 2.00, 2.25, 3.00, 4.00, 5.00 less 132 feet, and 5.00.

Jeff in Boise

[Chad M]

Awesome. Thank You for the explanation!

So in that instance did the vehicle loose speed at the end of the fifth mile? Or was it a case of letting off some?

[Elmo Rodge]

Chad, the 470 speed was the average over the entire 5th mile. The exit speed is just the last 132 feet. In this case (481mph) it indicates he was still accelerating. 
Wayno

[donpearsall]

Along the same lines, what does it mean when Jon says "in the quarter..."? None of the sensors are a quarter of anything. One-quarter of 5 miles is 1.25 miles. A quarter mile is 1320 feet. Whaaaa?

Don

[RidgeRunner]

     Mile 2 marker to the 2 1/4 trap, another tuning/setup info aid.  Good indication of rate of acceleration earlier in a run.

     Wish now they'd had it in '71.  I ran a '54 BSA BB34 and made multiple runs at 98-99 but couldn't crack the ton.  Held it wide open from the start every run and have wondered more than a few times since if it got heat soaked and was slowing a tad at the end........  Odds are I'll never know for sure now.

                 Ed

[Elmo Rodge]

Don, also to qualify for the long course you must exceed 175 in that quarter.
Wayno

[Chad M]

Interesting ways to calculate speed, but I guess it helps to subdued large anomalies in a single run.

It's a little different from my time spent drag racing, but I get it now for the most part. It's just different than I am used to in that respect.

[Saltfever]

Although it may be clear now here is a bit more.
The official surveyed timing lights start at the 1 and each mile thereafter. Another light has been added 1/4 mile after the 2 and is used for your tuning information only and is not part of the official time.  When we say "quarter" we mean your average speed in that 1st segment of the 2 mile trap. As Elmo mentioned you must have a minimum speed of 175 mph by that point to run on the long course. Remember any mph speed is an average of the time spent inside of a trap. You start the clock at the beginning and stop it at the end. If you have traveled 5,280 ft in 14.4006 seconds, that calculates to 250 mph. There is not a precise speed at any point inside a trap because there is no precise timing at discrete points.

Since it is difficult to sense a 2-4 mph speed increase over the course of an entire mile (or read a partial resolution on a bouncing tach) the 132 ft trap has been added at the end. It is a much shorter distance and therefore shrinks the "averaging" time giving a more accurate speed at the end of the five rather than the whole mile. As mentioned, it's not official but used as a tuning aid.

BTW: The 132 ft trap comes from the original Chrondek drag race clocks because it is exactly 1/10 of a 1/4 mile (1,320ft) making his calculations easier.

[salt27]

To be clear, the start of the timing is at the 1 mile marker.

[Saltfever]

. . .  my time spent drag racing, but I get it now for the most part. It's just different than I am used to in that respect.

Drag racing has always used a 132 ft trap. Originally it was after the end of the quarter. In order to get a top speed drivers had to drive through the quarter trap to the end of the 132 ft speed trap. In other words they were forced to stay WFO an additional 132ft past the end of the quarter! But speeds started to get too high so NHRA moved the 132 ft trap before the end.

[jl222]

. . .  my time spent drag racing, but I get it now for the most part. It's just different than I am used to in that respect.

Drag racing has always used a 132 ft trap. Originally it was after the end of the quarter. In order to get a top speed drivers had to drive through the quarter trap to the end of the 132 ft speed trap. In other words they were forced to stay WFO an additional 132ft past the end of the quarter! But speeds started to get too high so NHRA moved the 132 ft trap before the end.

 I thought it was split. 66 ft before finish line and 66 ft after.

                 JL222

[Saltfever]

To be clear, the start of the timing is at the 1 mile marker.

Opps,Thanks Salt. I edited that post.

[Saltfever]

I thought it was split. 66 ft before finish line and 66 ft after.
 JL22

Good point JL.  I haven't been to the drags in a long time. Could be you are right. Or maybe they shortened the trap to just 66ft because of much better clocks. Bandimer's 66ft clock stops at the 1/4 mile. But maybe it is track specific.
https://bandimere.com/racing-101/

[salt]

Saltfever says:
"If you have traveled 5,280 ft in 170.462 seconds, that calculates to 250mph."

In my world, if you need 170 seconds (almost 3 minutes) to travel 1 mile (5,280 ft), you're darn slow. But then, I'm old.
Willi