Inacurate Speedometer

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Sep 15, 2003 | 09:01 AM

00Expo&73Bronco

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Inacurate Speedometer

I was wondering if anybody thought that their speedometers may be somewhat inaccurate ? I am curious because no matter how easy I drive the expo (4x4, 4.6, 3.55) I only get 11-12mpg in town and 14+ on the road. I originally had the 16" rim (255x75x16) and went to the 17" rim (275x70x17) and thought maybe this threw it off. Is their a way to check accuracy without taking it somewhere to recalibrate ?

Sep 15, 2003 | 09:40 AM

buzzard

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From: All over Texas

Inacurate Speedometer

I can think of a few ways:

1. Have a buddy drive beside you in his car/truck without modifications.

2. Use the test mile markers highway depts. install and time with a stopwatch.

3. Find a nice cop with a radar gun or use one of those radar machines that posts your speed that are usually found in a shcool zone or some other low speed limit area.

Based on your tire and wheel size, you're off by about 7%.

Sep 15, 2003 | 09:44 AM

00Expo&73Bronco

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Inacurate Speedometer

Thanks for the good ideas buzzard ? I have not seen the mileage markers along the side of the road in awhile but I will keep looking. Our office actually has several of those radar speed boards that we put out on the roadways.

Sep 15, 2003 | 10:34 AM

nickalbu

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From: Detroit

Inacurate Speedometer

My 00 Expy came with 17s and the speedo was dead accurate with my handheld GPS. Have not checked my 03 yet.

Sep 15, 2003 | 03:59 PM

BigMan69

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From: Long Island, NY

Inacurate Speedometer

With your changeout of the rims and tires, when your speedo reads 60mph, you are actually traveling 62.1mph. Check out this link to compare tire sizes.

http://www.miata.net/garage/tirecalc.html

BigMan69

Sep 15, 2003 | 07:49 PM

buzzard

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From: All over Texas

Inacurate Speedometer

Quote:

Originally posted by BigMan69
With your changeout of the rims and tires, when your speedo reads 60mph, you are actually traveling 62.1mph. Check out this link to compare tire sizes.

http://www.miata.net/garage/tirecalc.html

BigMan69

That's only 3.5%, but there's a 7% difference in height between a 255/70/16 and a 275/70/17. I come up with 64.2 mph when it says 60.

Sep 16, 2003 | 03:57 AM

philrush

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Joined: Sep 2003

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From: Virginia

Inacurate Speedometer

a nice little tool to have is a hand held GPS unit. There is absolutely no guessing....

MPH reading is dead on accurate.

So is distance traveled.

Also, there are several calculators on the internet that can help calculate mph, rpm, distance.