Speedometer is 3mph fast, odo is off too. - Page 2

Redneckstone · #16 03-08-2010, 08:34 AM

Quote:

Originally Posted by ranger101

I have that. And it still puts it a couple mph off. I guess that's as close as it's going to get though.

it will change your MPH on the gauge but the OD still will be ticking away at the wrong amount

BigT8600 · #17 03-08-2010, 09:36 AM

Mine is actually 4 MPH slow. I guess due to higher tires? So now that I think about it, Im probably getting better MPG than I have been calculating.....hmm

Redneckstone · #18 03-08-2010, 11:05 AM

Quote:

Originally Posted by bigtt8600

Mine is actually 4 MPH slow. I guess due to higher tires? So now that I think about it, Im probably getting better MPG than I have been calculating.....hmm

yes you are need to always factor that in

richarddhoward · #19 03-08-2010, 11:13 AM

My speedo is of by about 3 mph too, I always attributed it to my tires being bigger than stock. I don't care enough though lol I don't speed generally (anymore at least lol) anyway

BigT8600 · #20 03-08-2010, 11:54 AM

Quote:

Originally Posted by Redneckstone

yes you are need to always factor that in

Someone care to help me with a useful equation to calculate my true MPG's?

I'm getting 220 Miles to a tank accroding to my odo.

So if my speed is actually 4mph faster than it thinks it is, I am covering more ground per tank.

But maybe its just because its monday, I can't think of a way to calculate this.

nismo2k6 · #21 03-19-2010, 07:30 AM

My 1987 Ranger is off by exactly 3mph also. I wonder if its because I am using bigger tires than the stock tires.

Tom · #22 03-19-2010, 01:57 PM

Quote:

Originally Posted by BigT8600

Someone care to help me with a useful equation to calculate my true MPG's?

I'm getting 220 Miles to a tank accroding to my odo.

So if my speed is actually 4mph faster than it thinks it is, I am covering more ground per tank.

But maybe its just because its monday, I can't think of a way to calculate this.

Use your trip meter to calculate your MPG, reset it to 0 on a fresh tank, then when you fill up divide the trip meter by the number of gallons you filled up (aka gallons that you used and are now replacing).

EX:
trip meter / gallons = MPG
250 miles / 15 gallons = 16.67 MPG

You're speedometer is not off by a flat rate due to larger tires. If you're going 0 MPH does it still say 4 MPH faster? If you're going 100 MPH does it say 104 MPH? It's off by a percentage. You need to figure the diameter of your old tires versus the diameter of your new tires and calculate the percentage difference.

For example, if you go from a 30" tire to a 33" tire, that is a 10% change, thus a 10% slower speedometer. So to calculate MPG you just add 10% (1.10) to your MPG figure, and there you ahve it.

Using our above equation:
trip meter / gallons = MPG x 1.10
250 miles / 15 gallons = 16.67 MPG x 1.10 = 18.33 MPG

Quote:

Originally Posted by nismo2k6

My 1987 Ranger is off by exactly 3mph also. I wonder if its because I am using bigger tires than the stock tires.

Yes, bigger tires throw off your speedometer.

BiggChris · #23 03-19-2010, 02:36 PM

According to my scan gauge i am also 3mph off

whfd930 · #24 03-19-2010, 03:47 PM

I think that it is a Gremlin in the Ford house that has done this, as mine is 3 mph off too. As for dead on balls accurate, there are places that calibrate the cruiser speedos and that is the only ones that I know of that can get it that close.

C Jizzle · #25 03-20-2010, 01:16 AM

its a relief to now know im not the only one with this problem lol

Coleosis · #26 03-20-2010, 01:41 AM

Quote:

Originally Posted by stephen

mines off by 2 or 3 when i drive by those signs on the side of the road that tell you how fast your going. i always thought it was the tires size but tom might have a point there with the liability.

That would have been my first thought too. hmph

Mine is right on...Ive only checked it by the speedo signs on the side of the road a few times...but everytime my speedo either says 55mph or 25mph and the sign says the same. (Ive only seen the signs in neighborhoods and highway construction zones.)

sgtsandman · #27 03-20-2010, 08:40 AM

It is not uncommon for the spedometer to read fast. Hondas read 3 mph fast as well. They are only required to be within a certain percentage of accuracy.