different kind of question

A guy ask me a question today that I really couldn't answer honestly.He wanted to know if there was an equation for elapsed time (et) and car lengths.In other words, if 2 cars left the line at exactly the same time and the winner was 1 car length ahead at the finish, would he be 1/10 quicker more or less.And would it be different whether it be 1/4 or 1/8 mi.

I wouldn't think so, look at it like this. If you are driving behind someone at 45mph and you stay 3 sec back. Then speed up to 70mph and stay 3 sec back and the gap would widen.

So no.

Or are you trying to say you are dividing the 1/4 or 1/8 mile into 1/10's?

I'm sure there is a technical term for what your asking but I can't remember it. I'm more of a tangible knowledge guy.

You could figure out his et based off you mph / et and length of his car. Thats only if you was door to door with the exact same rt.

Somewhere, I have a spreadsheet that I did based on MPH... Feet per second...that would equate distance between the cars at the stripe, based on et difference.
Was pretty basic, even with rusty math skills.
Now, I let Crew Chief Pro figure all of that with a mouse click.

Car lengths would be different times based on how fast the cars were going at the stripe. Really fast cars one length apart would be much closer in times vs. a street race.

I would have to offer No, there are too many variables and not enough constants for it to remain consistent. If the car that is 2-car lengths behind spun the tires or slept it could be out MPH-ing the winning car making the closing rate inconsistent as an example. Would be reasonable for indexed cars given the index +/- would remain close to the same... except throttle stops etc will move where and when the power is applied throwing the numbers off again.

rmcomprandy wrote:Exactly how long is a car length equated to be ...??

The length of the car your racing...

...and factored for MPH

In my thinking,which is scary in its self,it really shouldn't matter how good of a pass either car made.The answer would be when the first car hit the stripe and the race was over.The ets and the car lenghts at that point should be the answer.mph shouldn't make a difference when the still shot is frozen at the stripe.jmt

bbf-falcon wrote:In my thinking,which is scary in its self,it really shouldn't matter how good of a pass either car made.The answer would be when the first car hit the stripe and the race was over.The ets and the car lenghts at that point should be the answer.mph shouldn't make a difference when the still shot is frozen at the stripe.jmt

You time is still based on a fixed point (finish line) not the distance between the two cars. If he is running 200mph and puts a car length on you at the stripe with you running doing 100mph is not going to be the same as you both doing 100mph with him a car length in front of you.

Wheelie58 wrote:...and factored for MPH

rmcomprandy wrote:

bbf-falcon wrote:In my thinking,which is scary in its self,it really shouldn't matter how good of a pass either car made.The answer would be when the first car hit the stripe and the race was over.The ets and the car lenghts at that point should be the answer.mph shouldn't make a difference when the still shot is frozen at the stripe.jmt

YES ... it is all about time and the space.

jones wrote:

bbf-falcon wrote:In my thinking,which is scary in its self,it really shouldn't matter how good of a pass either car made.The answer would be when the first car hit the stripe and the race was over.The ets and the car lenghts at that point should be the answer.mph shouldn't make a difference when the still shot is frozen at the stripe.jmt

You time is still based on a fixed point (finish line) not the distance between the two cars. If he is running 200mph and puts a car length on you at the stripe with you running doing 100mph is not going to be the same as you both doing 100mph with him a car length in front of you.

^^^^^^^^^^^^^^^^This

ET is just that Elapsed Time, in order to predict the "ET" of the distance in car lengths you need to measure the Feet/Second which is measuring the time it takes to cover the distance given... in this case we want to use 10th's of a second. So for argument sake if we use 120MPH - 176 FPS and 160MPH 234.67 FPS if the car length is 35' then it will take 2tenths to cover the distance at 120MPH and 1.5 tenths to cover at 160MPH FPS of the MPH will remain constant at that MPH.

If that's the case,then 35' would be equal 2 normal racecar lengths.correct?

Essentially it would be the distance from the front tires or wing(whatever breaks the beams) of the second place car to the finish line beam. Yes I would probably call that 2-car lengths, the first car from the front tires back plus the gap to the second cars front tires.

I think your probably fairly close with those calculations. Thx