I went from 195/55/16's to 205/40(5?)/16's and now my speedometer is off(faster) by approx. 6-8 mph. It also seems to be adding mileage quicker because of the smaller tires. Correct me if i'm wrong but I believe I'm gonna need to re-calibrate my speedometer. Is this something I can do on my own, Is there a shop I can take it to around So-Cal or do I have to take it to the stealership? As always, any help would be greatly appreciate it.

Eric

 

My r53 is the same way.. speedo read 7-8 mph vs GPS Speedo.. I have 205\45r17s on mine.. in for some info

 

There should be no speedo error with 205/45x17 tires on 7x17 wheels. Suggest you find a good stretch of Interstate with 1/10 mile markers and do an odo check for 10 miles. As for ericmakkar, to my knowledge, there's nothing you can do to re-calibrate your speedo to the smaller diameter tires.

 

No recalibration available. The 195/55/16's were the wrong size tires. They should have been 195/60/16's for accuracy. And NC is right 205/45/17's are the OEM size. Even with this size though there is about a 5% speedo error according to my dealer.
This is common on BMW's. The only way to get more accurate is to get tires with a greater circumference.

 

If you run 215/45/17 your speedo will be accurate as many of us have found out. I compare it daily against my GPS and it is accurate as compared to the 205/45/17 that were 2-3 mph off.

 

Will this issue make my odometer become inaccurate?

 

Technically yes..

 

So then what do I do to fix this?

 

Run tires the size it was designed for. 205/40-16 is way too small for everyday use. 205/50-16 is closer to it, but still a little small. 205/55-16 actually makes the speedo pretty accurate.

 

Here....Play with this to see the speedo error created by using the wrong size tires:
http://www.miata.net/garage/tirecalc.html

 

Speedo and Odo don't always agree.
My speedo is spot on per GPS but my Odo records about 3% low, less miles than actual.

 

I've got 215 45 18 (yes 18) on mine and my 2005 mcs still reads 60 when I'm going 58.5 - 59 but the mileage odo reads 200 miles when I've gone 210 miles.