Mileage Report

[82vdub]

The odometer is directly driven from the rotation of the speedo cable through gears in the speedometer head. According to Tylernt, it's a magnetic interface between the rotation of the speedo cable to the speedometer - ie: no direct gear interface. Afterall, if it was gear driven, the speedo would keep spinning just as fast as the speedo cable is spinning and wouldn't indicate anything.

[JRM]

checked it again on my way home, yup odo 100% correct, Speedo is 4mph fast at 60MPH and 5 mph fast at 70.
I am going to have to return my pump timeing and fuel screw back to stock as its way to gutless for onramp signals

[Asymtave]

The speedo on my caddy was way off when I got it. The odo was also broke with the classic stripped nylon gear. This type of speedo is indeed a magnetic coupled type - so there's always slippage.

Not knowing any better how to fix it, I actually pulled the needle off the shaft and pushed it back on a couple notches over. I know that since then it's read silly fast at lower speeds (like reading 15 when I'm going 5.) But since getting my GPS I have learned that I did pretty good at cruising speed - 57.5 mph at an indicated 60.

With my current tires my odo reads 5% low. So when it says I've gone 100 miles I've actually gone 105. Tire wear will change the odo calibration over time. If you lose 1/4" tread, that 1/2" on the circumference of the tire. I think the odo calibration can easily change 5% over the life of your tires.

[Vdub-bub]

Maybe the speedo is calibrated to be 4 MPH off, if it was reading 10 MPH off then your odo would be off, just an opinion.

[be158]

those gears crack on every one i took appart..

i just had to take apart 4 and put them together to get one working one which had 0-85mph with the diesel only face plate

appears was already answered but ya what i found

the odo is direct gear driven.

it appears the speedo is more of a mag/centrifugal design not direct driven.

slight rust caused one to be low
one was oiled up was high.. so i guess depends how it wears

[Caerbannog]

If you lose 1/4" tread, that 1/2" on the circumference of the tire. I think the odo calibration can easily change 5% over the life of your tires.

Actually, if you lose 1/4" of tread (that's 1/2" in diameter) on a 23" tire (approximate diameter of 185/70R13), you'd lose about 2.2% in diameter. That also means a loss of 2.2% in circumference, so your odometer would over-read by 2.2%.

To get 5% change in 1/4" of tread, you'd have to be running 10" tires! I looked at some truck tires with 1/2" tread, but they were 38". So, even they would only change 2.6% in their tread life.

[jolotter]

The circumference of the tread is calculated C=pi D. The circumference will shrink by 1.5" over the life of the tire, as the tread diameter wears from 23" to 22.5" That's nearly two percent.

The odometer is going to run 2% faster by the time you change your tires. The speedometer will behave the same way.

The easiest, cheapest and probably the most accurate way to recalibrate your speedo is to get an accurate reading at key speeds and then make new marks on the back plate.

Johann

[jolotter]

My AAZ Golf, for the first two tanks, (my first diesel,) got only 30mpg and 31 mpg. I was really disappointed. It was about 3/4 highway averaging 120 to 130kph. That's 75-80mph. Kinda fast to be getting smileage but still seems pretty poor.

Is this what I should be expecting? Does the 1.9 use that much more fuel? Or do I have tweaking to do?

Johann

[JRM]

thats about right for your AWY tranny, its a .89 5th gear and at those speeds with a 1.9L engine spinning 4,000 RPM hurts, id swap your tranny rations to match the 1986-1989 .75 or even a .71 5th gear as your engine can handle the tall rations as seen below
http://scirocco.org/gears/