anybody else notice that the speedometers don't coralate with eachother. both duing acceleration and at a steady speed. I fist thought that maybe the dial could move as fast as the digital readout during acceleration but when cruising I noticed a differance of 2-4 mph. on top of that they would alternate as to which one was higher.

which do you think is more accurate, the dial or digital?

 

Same issue with mine, seemed to be 2 miles difference, digital always reads slower in mine than the analog speedo, except at 0 MPH. I'm wondering if they're measuring differently?

 

Digital consistantly 2 mph slower for me as well.

 

alright, atleast there is some consistancy. now we need a geer head to explain why and which is more accurate.

 

Could have anything to do with wheel size???

 

The reason for this (I read an article about the subject in C&D a while back), is that by law the spedo has to be calibrated so that the actual speed is never faster than the indicated speed. I think this may be a liability issue so that if you get a ticket you can't say "well the spedo said I was doing 55mph but the car was really going 60mph so it's not my fault" In other words every speedo has a built in error so that you are always traveling slower than indicated. This is a built in error and can not excees a certain percentage of the total speed, so the error will be less at slower speeds (say 2 mph at 40), but bigger difference at higher speed (say 6 mph error at 120).

Now the digital computer is not governed by this law so it is probably more accurate.

 

Wouldn't it be the other way around then. If the digital does not have to show =/ or faster than reality, then why is it reading slower than the needle?

 

The spedo HAS to read faster than actual speed, therefore if the digital readout is showing the real reading it will be slower than the spedo reading.

 

I see now, thanks

 

I would think the digital is more accurate since it has to calculate the MPG, miles to empty, etc. Someone will enventually test this with a radar gun I'm sure.

 

I'm sure some Z owner owns a handheld GPS unit that read out the car speed! That would be an easy way to check the accuracy of both speed indications.

 

I've done that with my BMW and found the On Board Computer's readout to be very close to actual speed while the speedo is 8-10% fast. I suspect other cars have similar behavior.

 

You could always try to find one of those police radar trucks that display your speed as you zoom past them.

 

Now that it was mentioned I remember reading about Miata owner's filing complaints years back. Apparently when the Miatas first came out, Mazda dialed the speedos to the highest percentage above the actual speed allowed by law to give the owners the feeling of driving faster! Apparently there is a small range in which manufacturers must calibrate speedos within. Anyone else remember this?

 

I don't know what the big deal is here; on the analog speedo, one MPH is about a millimeter in needle movement. Mine is usually within a MPH of the digital readout. Even two MPH is pretty damn close!

 

Anyone heard of GPS???? This is how I measured the speed of my boat @ 49.9mph.

 

Canadian meters read exactly the same all the time, in kms.

 

Feeling like typing, so........

Try this simple calculation: Time with a digital stopwatch, or a Timex IronMan, the time between mile markers (on all expressways), divide that number into 3600, walaha(SP?), the REAL speed. As an example, 48.6 seconds to cover a mile=74.07 MPH, not that I would EVER drive that fast

Doing the same over 10 miles is even more accurate.

Message being, NEVER trust factory calibrations!

As a side note, highway mile markers are a great way to verify a vehicles odometers. Most are off.

BTW, most speedo's errors are non-linier, the percentage of variance changes.

 

I have a GPS unit that connects to my laptop and I use it along with Street Atlas software on long trips. With the cruise set exactly on 90, I noticed that the GPS stated I was going 88. I have noticed a 2-3 MPH difference in 3 different cars.

-Plucky