odometer not right?

[jjarrett]

hi! on my 90 coupe the miles are coming up about 3 tenths to the mile too much. what can i do to correct this? the car is stock. thanks---john

 

[tonylong]

I believe this is a classical symptom of Newton's Law of Inaction. Try driving 33.33 MPH over the posted speed limit and you'll see some real changes.
BTW welcome to the board.
On the other hand -- do both indicators (digital and mechanical) read the same ? How do you know you're incorrectly indicating the mileage ?
Sometimes the roadside distance markers aren't right.

 

[John Robinson]

As stated the mile markers on the interstate are not exact. The best way to check the milage readout is to run twenty mile averages on the interstate. Also check the speedometer using a stop watch buy running at 60 for 5 miles. Usually if the odometer is off the speedometer is off also. If in fact you are running 3 tenths more then you actually travel just think how much less milage the car has then it shows.:cool

 

[bradfordsvettes]

you could also check it with a G.P.S Steve

 

[6speeder]

Are your tires the correct size?

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

 

[bradfordsvettes]

that is a very good point Steve

 

[jjarrett]

odometer reading

thanks for the input guys! i appreciate it! my tires are 275/75/17 bfgs,i run 40 lbs. pressure in them,when i became aware of the milage i checked it against a known 1.1 mile distance that i'm familiar with.that is how i came up with the 3 tenths over every mile. i don't know about gps.i guess i can go to a stealership as a last resort tho.---thanks--john

 

[LT4man]

Why are you running 40 lbs of air pressure?

I would check your air pressure sticker on the edge of the driver's door and run what Chevy recommends.

Running the recommended air pressure will probably allow your Vette to ride much better.

Just a suggestion.

SAVE THE

 

[6speeder]

.....my tires are 275/75/17 ......

Your vette ('90) came with 275/40-17 tires. Are you certain that your present tires are 275/75/17? If so, according to the calculations provided by the link, your speedometer would read 60 while your speed would be 77.

I would guess that the "75" should be "40", and that you are using the same size tires as the originals.

 

[jjarrett]

odometer

yes,my tires are stock 275/45/17.what is the correct pressure to inflate them to? thanks ---john

 

[6speeder]

yes,my tires are stock 275/45/17.what is the correct pressure to inflate them?....

The tire inflation pressures should be posted on the end of the door (or the sidewall of the tire), but 30lbs for convertibles, and 35lbs for coupes is usually the norm.

 

[ecss]

The 4 tires from the factory on a 90 Corvette (non ZR1) were 275 40 x17.
The rims were all 9.5 x 17.

 

[jjarrett]

odometer

well guys i really feel embarrassed about not knowing my tire size or inflation .when all else fails read the directions! the tire size on the vette now is 275/40/17 and the proper inflation posted on the door says 34 pounds per tire.thanks for a wake up!! but i still am puzzled about the odometer reading---thanks and i love this forum!---john

 

[HD2HVETTE]

Specs for the 90 (non-ZR1) were 245/40ZR17 with 35 PSI cold inflation pressure. You can add pressure up to the max recommended pressure found on the sidewall of the tire, but it is not necessary for every day driving. Car will ride much better at 35 psi. If you have 245/45ZR17's you would have the opposite effect-your odometer would show less mileage by a percentage instead of more.

 

[ecss]

well guys i really feel embarrassed about not knowing my tire size or inflation .when all else fails read the directions! the tire size on the vette now is 275/40/17 and the proper inflation posted on the door says 34 pounds per tire.thanks for a wake up!! but i still am puzzled about the odometer reading---thanks and i love this forum!---john

Here's how it works. Mounted on the transmission output shaft is a plastic drive gear. It drives a gear called the driven gear. The number of the teeth on each gear depends on what rear differential gear ratio you have.

As the output shaft turns, a AC sine wave signal is generated called Vehicle Speed Sensor (VSS). Its frequency is higher as the transmission output shaft spins faster.

The signal goes to the ECM (engine computer) where the signal is modified so that 4 thousand pules per mile is produced. The signal is used by the Cruise Control, Bose radio (increase volume at higher speeds) and FX3 adjustable shocks if you have that option.

The signal is also sent/processed by the CCM (Central Control Module) which displays on the Dash Cluster, the Speedometer and odometer reading.

Now you know how the circuit works so it's up to you to fix it.