Thanks to see5 for bringing this to our attention:



You can prove see5's point for yourself. I'm working on the assumption that Nissan speedos are calibrated for the stock GXE tire size of 215/55R16 and that the C&D test was conducted on an SE with 225/50R17 tires. Compare the GXE tire size with the SE tire size using the following tire size calculator:

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

As you can see, the speedometer reading with the 17" tire is 2.2% too slow. That means that when the speedometer reads 70 mph, you're actually traveling at a speed of 71.54 mph.

 

woohoo! that means, i shouldnt be too screwed when i upgrade to 17"ers.

 

No you won't. As a matter of fact, the perfect upgrade from your 215/55R16s would be 235/45R17s. The error is negligible . . . 0.1%. Just remember that to run 235/45R17 tires safely, you must upgrade to 17" rims that are AT LEAST 7.5" wide.

 

The 225/45R17 tire produces less of a speedo error than the 225/50R17 when compared to the 215/55R16. The error is only 1.3% for the 225/45 versus 2.2% for the 225/50. And there's a much broader selection of tires in 225/45R17 than in 225/50R17.

How 'bout that?

 

there are different ECU programs, like 5 of them, to account for 16 vs 17. Mine reads 2.5 mph fast, as does our pathfinder, at 70. tested with GPS, repeatedly, its a consistant 2.5 high. Most american cars I've been in are low, japanese high. dunno...

 

Sounds like a nice cluster ***k on Nissans part! How difficult would it have been for those idiots to mount 235/45R17s on 7.5 rims Just did not want to spend the extra $$$$ I guess!

 

That's what I was thinking, if they're so off why would Nissan have different ECUs for different stock tire sizes? Not saying you're wrong, but it seems like Nissan's just skiing uphill here.

 

I'm running 235/45 R17 Kumhos on my stock 17" SE wheels. They look a little odd and they seem to ride a little weird. But on the other side, I JUST put them on this morning so I didn't get a really good feel for them yet.

The reason I said they feel odd is because I was driving along and it seemed like the car was swaying side to side. This could have been due to the high wind today but I'm not sure. When looking at the tire, it seems to flare out from the rim to the outside of the tread - doesn't look normal.

The guy from TireRack said that 235/45R17 is what they recommend for our Maximas.

I guess I'll find out soon enough... I plan on running some AutoX events. Hopefully my tires won't come off the wheels!

 

Do you have photo's of your ride with the new wheel/rim?

 

I'm running the stock 17" SE Wheels with 235/45R17 rubber. I can put up some pictures...

 

In answer to posts I tried some GPS runs at various speeds to try and track speedo errors at various speeds. We know from cave hits in Afganistan GPS is dead (yes dead) accurate but lining up speedo needles with marks is the issue. Anyway the GPS reads out in .1 so @ various speeds 71.6,61.3,50.9 and 40.6 mph. I think it is safe to say the error is a %.
Mine is a 02 SE with 1100 miles and as tires wear and get smaller more error.
Here on Chevy I kept the circ. the same by increasing rim width from 9.5 to 10.5" and changed from 265 to 295 profile and kept the diameter.
Cheers

 

I've got an SE with stock size tires. My city occasionally sets up those radar machines that tell you your speed as you go by them. The other day when I saw one I turned around and went back by it with the cruise set dead on 55 and the radar said I was doing 54. I guess the cop's radar reading is the main one that matters!

 

The minimum acceptable rim width for 235/45R17 tires is 7.5", period. If you're foolish enough to mount 235/45R17 on 7" rims, you deserve what you get. For further info, see the discussion under RIM WIDTH in the following article from Dunlop:

http://www.dunloptire.com/tiretech/?...tire_width.txt

 

I'm curious why everyone seems to feel that their GPS are completely accurate. I vaguely recall Garmin quoting something like a 0.1 MPH accuracy but I don't recall the top speed for this accuracy. I would imagine they would use 55 as a reference speed. Its completely plausible that the error would increase as the speed increased.

 

thanks See5. So it looks like the error is not linear, it increases as the speed increases (which is what I would have expected). Of course that doesn't factor in your twitchy eyes trying to line up the speedo needle with the marks while reading the GPS

 

GPS is dead accurate! My eye is not. If we have a % error, which I am sure we do, then 1.02 works at any speed

 

I've been thinking about this for awhile, Tim. Yes, there are differences in ECU part numbers among the various Maxima models. But I'm not certain which parameters are affected from ECU to ECU. I assumed that one of the parameters is speedometer calibration. But that may not be the case, particularly given how closely see5's data correlates to the mathematical results and the fact that your speedometer reads fast as well.

A speedometer error of 3% or less is generally considered acceptable. If that's the case, is it possible that ALL 5th Gen Maxima speedometers are calibrated for the 215/55R16 regardless of ECU part number?

 

Excuse me, the standard size on GXE is 205x65R15, thats what was on my car...

 

Yes, I believe you're correct. Let's do the math on that tire geometry as well.

If you have 205/65R15s and exchange them for 215/55R16, your speedometer will read 0.7% too fast. In other words, when your speedo reads 60 mph, you'll actually be traveling 59.6 mph. That's well within the standard deviation for speedometer accuracy.

If you have 205/65R15s and exchange them for 225/50R17, your speedometer will read 1.4% too slow. In other words, when your speedo reads 60 mph, you'll actually be traveling 60.9 mph. That's also within the standard deviation for speedometer accuracy. Interpolating for 70 mph on the speedo, you'd actually be traveling at 70.98 mph.

Interesinger and interestinger!

I suppose one test would be to compare your ECU part number with the ECU part number of another GXE from the same dealer running 215/55R16 tires. Whether the ECU part numbers are the same or different might tell us a lot. Determining the ECU part numbers is easy. Just have your dealer's service department hook up their Consult to both cars. They can then read the part numbers directly from the Consult's display.

 

After reading though this thread, it seems like the importance of variations of the tire is being overemphasized. After all, vehicles with stock wheels and tires were examined. Frank Marcus, the author of the article, admits that inflation level, vehicle load and wear all contribute to inaccuracy, but the standards to which automakers conform to are the source of the error. Even though the speedometer may be reading high, the trip computer may still be accurate (it was in the case of the BMW X5 cited in the article). Because the specifications of the speedometer are dictated as a percentage of vehicle speed, larger errors are permitted as speed increass. Aren't the automakers just trying to get us to slow down?

 

Good points, beaglemax. And they tend to argue in favor of a single speedometer setting for all Maximas regardless of wheel and tire configurations. But I wonder if anyone on this forum knows that for sure?

 

So, to summarize, if all 5th gens are really calibrated for 215/55/16 (not hard to believe, we are speaking of Nissan after all), here are some numbers:

Stock 225/50/17 --> your speedo reads 2.2% too slow -- this can cost you in a delicate cop situation

235/45/17 --> your speedo reads 0.1% too slow -- almost a perfect match

235/40/18 --> your speedo reads 0.4% too slow -- still pretty good (0.2 miles off at 60 mph)

 

That's about right, naidd, although I'd suspect that all the tires are calibrated to the GXE base tire size of 205/65R15 rather than 215/55R16. But that's sheer speculation on my part.

 

It would be nice to know for sure what size Nissan based the calibration on. If they based it on 215/55/16 that would be nice, because the margin of error on 225/45/17 would be 1.3% too fast. If it is based on 205/65/15 it would be 2.0 too fast. Maybe too much???

Does anyone run 225/45/17's?? I need to rubber and as you know there is a larger selection in this size.

 

I believe the general recommendation is not to run more than 3% out of spec. 225/45R17s should be just fine.

 

I doubt that the service dept. has an explanation. Next time I go for an oil change, however, I'll ask them a question..and try to compare ECU for Maximas with different tire sizes.

 

I have a 2001 SE AE, with the 225/50R17's and was wondering, on the anniversary edition, is that a 7" or a 7.5" wide rim?

 

To the best of my knowledge, all 5th Gen Maxima 17" rims are 7" wide.

 

Did you guys happen to see this yet??

http://www.nissandriven.com/owning/R...Maxima,00.html

 

Did not know you could get there from ND.com.
Thanks!

 

I have a 2K with 215 55 16 and mine reads 2.5 to 3mph faster than I'm going at all speeds too, but the odometer is dead on! I'm old fashioned - stopwatch and mile markers, 1,5,10 miles. I suspect there's a deliberate offset by Nissan - they might be liable if you got tickets because the speedo read low.

 

So once again, it appears that all Maxima speedos may be calibrated the same regardless of OEM tire geometry. That certainly wouldn't surprise me.