Has anyone who has replaced their 18" stockers to 19" AND used stock 19" tire size seen any improvement in their speedometer accuracy?

My speedo was 7% fast (@50mph, GPS app on my phone), when I replaced the tires in October, I went with 255/45 in the rear and now the speedo is merely 5% fast. A 265/50-18 would theoretically bring the error to zero but I could only find one tire in that size and there wasn't a matching size for the front. Plus, I wasn't keen on the extra sidewall flex.

I'm guessing that the coupe speedos are more accurate than the sedans due to wheels and tires? I searched for the subject but only one thread dealt specifically with the topic and the responders had no interest in accuracy, they just rationalized it as a feature helping to prevent a speeding ticket.

 

I have a AWD sedan and I went from 17's to 19's my speedo is off by about 2-4 mph fast

 

Your original rear tire size should be accurate, the OEM 18" rear tires being
245/45/18. Are you seeing a 7% discrepancy w/ that tire size?
If so I would take that up w/ the dealer. Going from a 245 to a 255/45/18 will increase diameter about 1.3%, or make speedometer read 1.3% slower.

A 245/40/19 should only be 0.13% off from the 245/45/18.

 

Yes

I haven't yet investigated 19" tires but I would go with 245/45-19 to improve speedo accuracy. I did note in one of the threads that one sedan owner tested his speedo over a known distance and found it read fast but the odometer read correctly.

As an aside, I would have hoped someone would have the ability to reprogram the trans computer by now. I would like manual shift feel even if I'm not using the paddles in DS mode. Adjusting the speedo output would seem like an easy job.

 

Have you gone to the dealer about that 7% error? That would drive me crazy (as I'm sure it is w/ you too).

 

No. I did what I could myself. Then I searched for the problem here. Not many folks know or care about the issue and I'm positive all 2009+S sedans have this problem. I assume it's because the speedometer gearing was designed for the coupe and its 19" wheels, Infiniti cheaped out and did nothing to help the sedans when the wheels and tires were spec'd differently. I'm nearly due for an oil change, I'll bring it up to the dealer then.