My '06 came with 195/55-16's. I installed 205/45-17's.

Using the tire calculator, the difference in height was that the new tires were supposedly 4mm shorter.

According to the tire calculator, my speedo would have shown 60mph when I was really doing 59.6

That's great but I noticed on my last trip, I found out that instead of being less than .5 mph difference, I have 3-5 mph difference depending on going 60 or 75.

Not that it's an overly big deal but it's registering more than I'm really going. It's nice to have a built in safety factor but that also means the odometer is also off by at least 5%.... anotherwards, it's racking up 5% more miles than I'm really doing thus changing mpg, mph, oil changes, etc, etc...

I realize that not all tire manufacturer's tires come out the exact same height based on the same size but I want to correct this.

Anyone know how to go about this? Is it programmable in the ECM, can I remove the needle from the speedo and twist it over (of course, that would only help the speedometer, not the odometer)

Any suggestions on how to recalibrate the speedo/odo?

Thanks,

Mark

 

The speed display is a software output different that the mileage. Your mileage is still going to be accurate to within the % difference off of the stock wheel.

 

So is the software adjustable? Can the dealer or someone with the right equipment rewrite the ECM or that particular software?

Thanks Motor On... much appreciated.

Mark

 

I'd like to know, also. My speedo (with factory tires) is off 4mph at 70 indicated (actual measured speed 66mph). Odometer check on straight measured 4 mile stretch of interstate was dead on. That confirms Motor On's statement that the odo and speedo are not directly connected.

 

That's cool, I tried to check my odometer on the mile markers as I was going down the highway but I was having too much fun driving, I'd forget by the time a mile went by...lol.

Hopefully someone can tell us if there is a way to program/reprogram the speedo.

Mark

 

Mile markers are not precise and should not be used to measure odometer accuracy. If you can find the paint marks used for aerial speed checks those are set precisely.

 

I'm not so sure about that.... Over the years, I have checked mile markers and they've been right on the money. Now, exit signs are different but actually mile markers, I'd have to say if they're not perfect, they're pretty darn close.

However, what about speedometer adjustment.... still need to know.

Anyone?

Mark

 

I think the speedometer can be re-calibrated, but the dealer won't do it unless you're "out-of-spec". Problem is, the specifications are extremely wide. For instance, if you're actually traveling 70 MPH, the speedometer is allowed to read anywhere from 70-79 MPH and still be "in spec".

If you're willing to pay for the calibration yourself and the dealer still won't do it, you should be able to find a calibration facility in the Yellow Pages. Just make sure you let them know what kind of car you have, and that their calibration machine will probably need to drive *all four* wheels, not just the front or the rear. (If the computer isn't getting speed readings from all four wheels, I don't think it will display your speed.)

 

Thanks Scott, I'll check it out....


Mark

 

Agree. In this case, however, the odometer was in synch with the markers and that was backed up by a stopwatch.