It makes me curious, the stock sport 275/35 diameter is 26.6 inches and the Nismo 285/35 is 26.9 inches, does Nissan calibrate the difference or do they just accept the slight difference in speedo accuracy between the two (1mph @ 90mph difference)?

Well after much thought and research thanks to many of you, I've decided to go with the Contis in 255/40/19s front and 295/35/19s rear. I have the stock 2013 sport rims still, so these sizes are better suited for my rim width of 19x9 f and 19x10 r. This setup will stay well within 3% of each other at +0.4% also.

According to this site www.tiresize.com/calculator my speedo would be pretty accurate in these specs.

RESULTS:
Speedo Reading / Actual Speed
20mph / Actual Speed 20.1
30mph / Actual Speed 30.1
40mph / Actual Speed 40.1
50mph / Actual Speed 50.2
60mph / Actual Speed 60.2
70mph / Actual Speed 70.3
80mph / Actual Speed 80.3
90mph / Actual Speed 90.3


Thoughts? Does everything look right?

Your feedback has been invaluable gents. :tiphat:

Different ECU so I'm guessing it's programmed accordingly but what the fuk do I know lol

I don't know why I thought you had Nismo wheels. The OEM rear tire size for the sport wheels is 275/35/19. That is 26.6 inch diameter. So when calculating the speedo differentials, make sure that's the comparison you used and not the 26.9 Nismo diameter I cited earlier (I didn't bother to check your math). Edit- I checked your math and it looks off to me. Compare sizes 275/35/19 with whatever size you're looking at. The speed differential calculation is done for you on that website.

If you go 265/35/19 and 305/30/19, the tire diameter is reduced the same in the front and the rear (-1.5%) and gives you a 1 mph difference at 70 mph. Very reasonable.
If you use the 295/40/19 rear tires, the diameter increases by 1.9% which gives you a 1.3 mph difference at 70 mph. Still plenty reasonable.

Also, I like the benefit of going down in tire diameter makes you think you're going faster than you are, which helps me cut down on those speeding tickets lol. I've had cops tell me it's easy to recalibrate the speedometer, but I've never bothered to look into it.

I'm going to go out on a limb and say they're talking out of their a$$. Anyone who's looked into the Z's electronics knows that most of the data is communicated over CAN, and likely requires the consult device.

The first time I heard that, in my head I was thinking, "yeah, maybe 50 years ago in the first car you got as a kid. Now only the dealer can do it and they'll charge an astronomical fee."

I changed mine out a little over a year ago and went with Conti Extreme Contact DWS06 tires. I'd have preferred the Conti Extreme Contact Sport tires but because I'm in New York I was concerned about the seasonal changes, especially the winter. I avoid driving my Z below certain temperatures anyway but in the event I have to I didn't/don't want any issues. I'm satisfied with their performance but not thrilled. At some point in the future when I relocate to a warmer state I'll definitely switch them out again for something more to my liking. So I'd definitely give some serious consideration to the Conti Extreme Contact Sport.

Update
 

Well, I put the tires on yesterday. (Will update with some photos later hopefully)
Got to try them out in the rain last night..

Holy Shiz! The amount of grip these tires have in the wet is borderline supernatural. :eek: WOT from a DIG in the wet felt like it was in the dry. Couldn't believe it, no spinning at all :confused:

Need more power now obviously. :stirthepot:
Dry grip is equally fantastic.

I got some Continentals a few weeks back... I agree, solid riding tires!

I've always loved Continental ExtremeContacts. This is one of the best all-season tires to take into consideration for your vehicle. I bought mine at 4wheelonline two years ago, it was referred by my friend. If you are in search of ultra-high performance tires that can provide great grip and traction, then this tire is the one.

What's crazy is the tires I got aren't the ExtremeContact A/S ones. I got the Sport Summer tire variant for maximum dry grip.
Still, its wet traction is just incredible.

And to think Michelin tires are even better, I wonder what that feels like. :yum:

You must take into account ABS sensor readings between the front and rear and if they're off by too much it will illuminate the ABS error light.

I run 255/45/19 & 305/35/19 without issue and 1 mph speedo/gps error.