how fast am I driving?

SDE · Jun 26, 2016

After driving 20 miles on freeway, my trip meter showed that I had driven 21. That is an error of about 5%. If I want to drive at 55, what do I need to set my cruise control at to get a true 55 mph? I think 57.5 should be close, but I was hoping for a more definitive answer.
I can't be wrong all the time, or am I wrong about that too?
Thank you
STEVE

old popper · Jun 26, 2016

the speedometer in my '03 Ranger pickup is off by a good margin, so I keep my GPS in it to use for a speedometer. To me that is the simple way to keep track without constant adjustments.

JF in MI · Jun 26, 2016

Modern GPS units are pretty darn accurate and should tell you your speed.

showcrop · Jun 26, 2016

Where would you drive 55? That could be pretty dangerous.

Royse · Jun 26, 2016

60 miles per hour is a mile a minute.
Check it by the mile markers or with a GPS unit.
Or, you can play Sammy Hagar and let the nice
police officer tell and how fast you were going.

Sammy Hagar on Youtube

4wdtom · Jun 26, 2016

Now I see where some of the fools I see on the road get their ideas.

Bob NY · Jun 26, 2016

I agree with your math.

RogerinIowa · Jun 26, 2016

There may be no connection between your "mileage" and your "speed" of your speedometer. Need to check given mileage (mile markers) and time. Does it take you 10 minutes to go 10 miles when your speedometer says you are doing 60?

notjustair · Jun 26, 2016

Use the speedometer app. There are a couple of big trucks around here with unreliable speedos so that's what I do. Works slick.

Southern Ray · Jun 26, 2016

Are you running the recommended tires for this truck?
Smaller tires means more wheel revolutions to the mile.

Steve in VA · Jun 26, 2016

I trust that the 20 mile basis is just an example since that is a really, really small value to be statistically reliable. Others have cited GPS and that would definitely be the way to go.

fixerupper · Jun 26, 2016

If your speedometer is off the same as the odometer your math is about right. Your phone should have a stopwatch (I know, messing with the phone while driving) you could find out the accuracy IF you can find a stretch of road where you can run a constant 60 for ten or fifteen miles or more. I have done it with all of my vehicles except for one just for kicks on a certain stretch of road that I know is accurately marked. There is a bunch of GPS apps that show MPH for smart phones but some of them are easier to use than others and not all are free.

I made a liar out do a neighbor once when I used the stop watch feature. I was driving my dually down the road and he was following me. Next time he saw me he kidded me for being in a hurry because his speedometer showed a few MPH faster than mine did and he is the kind of person who is ALWAYS right. Next time I had a chance I checked it with a stop watch and proved HIM wrong. Sweet revenge!

Greg1959 · Jun 26, 2016

sde= Quit driving up and down mountain ranges. LOL! You are driving more vertical (up and down0 than horizontal.

massey333 · Jun 27, 2016

Because that is still the speed limit in a lot of places,even on the Interstate system.Ran into that Sat.,open Interstate road(15-20 Mi.between exits)55Limit and it WAS being enforced. NO,I didn't get stopped.

Determined · Jun 27, 2016

(quoted from post at 19:41:35 06/26/16) After driving 20 miles on freeway, my trip meter showed that I had driven 21. That is an error of about 5%. If I want to drive at 55, what do I need to set my cruise control at to get a true 55 mph? I think 57.5 should be close, but I was hoping for a more definitive answer.
I can't be wrong all the time, or am I wrong about that too?
Thank you
STEVE

Simplify, multiply x 3 to figure your MPH travelled
20 miles travelled x 3 = 60 miles
odometer 21 miles x 3 =63 miles

63 divided by 60 = 1.05

1.05 x your target speed of 55 MPH = 57.75
Were you using an accurate reference to determine you had travelled 20 miles?
GPS
Property markers
I would not trust road signs or a hilly or curvy road.

oldtanker · Jun 27, 2016

(quoted from post at 17:57:09 06/26/16)
Where would you drive 55? That could be pretty dangerous.

How about on roads where the speed limit is 55?

Rick

Ferd · Jun 27, 2016

55.75

showcrop · Jun 27, 2016

(quoted from post at 08:05:51 06/27/16)

(quoted from post at 17:57:09 06/26/16)
Where would you drive 55? That could be pretty dangerous.

Click to expand...

How about on roads where the speed limit is 55?

Rick

Again, driving 55 on a road where the speed limit is 55 would be unsafe and dangerous. Perhaps on a road where the speed limit is forty.

Ferd · Jun 27, 2016

Should have posted 57.75.

Old Scovy · Jun 27, 2016

Do like we did with the old B models, Pull the hand throttle all the way out and bend it over as those old 673 engines didn't have power enough to get you a speeding ticket.

SDE · Jun 27, 2016

I divided 20 by 21 and then subtracted that from 100 to get a percentage. I multiplied 55 by that percentage and then added 55 and got 57.64. That is why I asked this question, because I did not know if this was the correct way to calculate this problem. Either way I am close enough to the correct speed.
Thank you everyone. I do intend to try a stopwatch and see if I can do a mile in a minute.
SDE

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