Testing Speedometer Accuracy

[SlippinJoe]

So I got a speeding ticket the other night and my speedometer said 60 (and it was 55 zone) but the cop said I was doing 68. Which I think is BS, how do I go about figuring out if my speedometer is accurate? Other then driving next to another car and setting our cruise controls at the same speed

Does a dynometer also calculate speed, or does it just figure the horsepower and how much does something like that cost? like not a tune, just run the car on the machine quick to find out about the speedometer.

If my speedometer is messed up what would cause it to be inaccurate?

the car is a 1988 Mustang LX 5.0 5 speeed, with everything 100% stock. Even the stock plugs and wires


any ideas???

[SmithEvo]

Find someone with a GPS and borrow it.

Causes could be gearing, tire size, etc etc.

[ACRucrazy]

GPS ftw

My truck is over under by 3mph or so.

[SmithEvo]

GPS ftw

My truck is over under by 3mph or so.

my tahoe runs about 3 faster than what the speedo says.

My cummins runs about 5-10 faster than what the speedo says, depending on speed. Of course, the 35's and stock gearing may have something th do with that.

[AdamZ82]

Yep, GPS will work nicely. I've got a garmin trex or something like that, nothing too fancy, but it works great for checking speedometers and the speed of go-karts and such

[TRDon]

but it works great for checking the speed of go-karts

[2 beer]

or imagine this. You get a stop watch and you do 60 down the freeway. Going 60mph it should take you exactly one minute to from one mile marker to the next. . . . . . I know its old school and doesnt involve satellites and shit but really it does work.

[darkdan]

It's easy.

Step 1.) Drive 90 mph
Step 2.) Find a cop
Step 3.) When he pulls you over ask if you were doing 90 mph because you were testing the accuracy of your speedo.

[mousestang]

D & D Speedometer should be able to put it on their rollers and tell
how far off you are.

[SmithEvo]

or imagine this. You get a stop watch and you do 60 down the freeway. Going 60mph it should take you exactly one minute to from one mile marker to the next. . . . . . I know its old school and doesnt involve satellites and shit but really it does work.

You're starting to sound like Newbombturk or Maxpower

[2 beer]

You're starting to sound like Newbombturk or Maxpower

I'm just saying there is always an easier way to do things. How do you think they checked speedo's before they had GPS? I get this complaint all the time at every shop I have worked in. "My speed do is off can you fix it" Go drive it with a stop watch and its usually within about 3 percent. So I say "well thats just normal its within 3%" People who say their speedo is off by a certain MPH are full of shit. Its fucking linear, so if its off by 10 at sixty it wont be off by ten at twenty. It just takes some thinking sometimes people. Pretty easy to do.

[SmithEvo]

I'm just saying there is always an easier way to do things. How do you think they checked speedo's before they had GPS? I get this complaint all the time at every shop I have worked in. "My speed do is off can you fix it" Go drive it with a stop watch and its usually within about 3 percent. So I say "well thats just normal its within 3%" People who say their speedo is off by a certain MPH are full of shit. Its fucking linear, so if its off by 10 at sixty it wont be off by ten at twenty. It just takes some thinking sometimes people. Pretty easy to do.

I agree. Stopwatches are expensive though, so I just use GPS

[MisterCMK]

[PHRANQUY]

I'm just saying there is always an easier way to do things. How do you think they checked speedo's before they had GPS? I get this complaint all the time at every shop I have worked in. "My speed do is off can you fix it" Go drive it with a stop watch and its usually within about 3 percent. So I say "well thats just normal its within 3%" People who say their speedo is off by a certain MPH are full of shit. Its fucking linear, so if its off by 10 at sixty it wont be off by ten at twenty. It just takes some thinking sometimes people. Pretty easy to do.

Well, the speedo on the car has to be reading correctly to begin with too. My speedo doesn't start registering until 5mph. If the needle was ever taken off and not put back on correctly it could be off too.

[2 beer]

Well, the speedo on the car has to be reading correctly to begin with too. My speedo doesn't start registering until 5mph. If the needle was ever taken off and not put back on correctly it could be off too.

WTF thats how you figure it out, it will tell you if something is wrong it wont fucking pin point it it will just give you an idea that it is in fact off. From that point you need to trouble shoot and diagnose what is wrong.