mph question?
 

hey
i was wondering if anyone knows how if possible i can measur the speed in mph of my cars and trucks with a stopwatch.if not a stopwatch how can i with simple household items? thanks

RE: mph question?
 

You could measure the amount of time the vehicle takes to cover a certain distance at full throttle. With a running start (i.e. max speed throughout) you should be able to roughly calculate your speed - although judging when the car is passing a certain point at some distance away can be difficult, making the results inaccurate.

RE: mph question?
 

You will need help of two other persons. (flag men) lets say you have 50 yards of distance(example only). #1 will be at 25 yrds and indicate start of timer, #2 will be at the 50 yrds and indicate stop. The car build's up speed from 0 - 25 yard and likely to be full speed by this time already. Driver could be somewhere close to the 50 yrd marker.

Offcourse everything will be a rough estimate, due to the reaction time for the person to raise their flag, and reaction time to start and stop the timer. But you'll have a good idea how fast you are going.

RE: mph question?
 

ok now that i now i can use a stopwatch to measure mph. how do i do the calculations to find out the speed?

RE: mph question?
 

Excerpts from an old threat by a member named Stablok. As he said take several readings at full speed in both directions and use an average. You'll end up with a pretty good idea (if not completely accurate) of how fast you're going.

"There is an easy way to figure how fast your truck is at top speed.

Draw two lines 100 feet apart. You'll need room on either side of the lines for braking and to reach your top speed . Do it on a nice level road. Then you'll need a stop watch and someone to time you. Get your truck up to operating temperature and do a run. You want your truck to be at top speed when you hit the first line and continue until you hit the second line. Get that someone to start the timer as soon as your truck starts to cross the first line. That someone will have to stop the timer as soon as your truck starts to cross the second line. Do it a few time. This will allow the time keeper to get some practice on the timing. Then, do it several time in both direction and record each time. Now, with your calculator, take 100 divide by your average time and multiply that by .68 and it will give you your speed in mph. So if your average time between lines is 1.8 seconds then it's 100/1.8x.68=37.77 mph."


His calculations.

1 mile = 5280 feet.

If it takes you 1 hour to drive 5280 feet, then you drove 1 mph.

1 hour = 60 minutes = 3600 seconds

3600 seconds / 5280 feet = .68181818181818

So, however many feet divided by however many seconds times .68 will give you MPH.

I suggest you do it over 100 feet for several reasons. The accuracy on the person timing the run for one thing. Anything less then 100 feet will be hard to time accurately. And anything over 100 feet, well, I would want to hold my throttle wide open that long."

And some other intresting info.

"1 tank holds 160 cc of fuel
1 Gallon = 3785.4118 cc
1 Gallon = 23.658823 tanks of fuel
1 Gallon = $26.00 (canadian)
$.90 = 1 tank of fuel
1 tank = 15 to 20 minutes
each minute = $.04 to $.06 of fuel."