For the 2001 Maxima line, there were three available tires of slightly different sizes, dimensions, and revolutions per mile (205/65-15, 215/55-16, and 225/50-17).

Does anybody know whether Nissan developed specific speedometer calibrations for each tire size or if they simply used one calibration across the entire model line? I realize that differences between any such separate calibrations would be small, I just want to know if they even exist.

I don't have access to a FSM or any sort of flash tuning documentation that might answer this question, nor am I having much luck with the (slow) search feature.


Norm

 

I have a feeling if you measured the diameter of each wheel and tire combination, they would measure out pretty much the same. Therefore they can use a single calibration method regardless of the stock tire/wheel combo they use.

 

Indeed, they're all pretty close (close enough, anyway):
205-65-15: 25.5"
215-55-16: 25.3"
225-50-17: 25.9"

Plus or minus a tenth for wear, inflation, etc.

 

I'm aware that they are all close (from as low as 795 revs/mile to perhaps as many as 838 from a little research at TireRack.com). That would suggest that with a single mean/median calibration that the 16" tires (generally the "little" ones) would make the speedometer read a little higher than actual, and that the "big" 17's would cause a slightly lower than actual reading.

I don't myself particularly care about ± a percent or two, but somebody else needs to know.


Norm

 

According to my nav, my speedometer reads a bit slow, at 75, I am actually going 77 mph.

 

That's funny. My nav reads slower than my speedo.

 

Interesting.

What make/model/size tires are you guys running?


Norm

 

Toyo Proxes4 235/45/17. So I expect to have some error (2.5% approx.?).

Navi is Pioneer Avic D2. Come to think of it, it may be connected to the VSS, but I'm not sure.

 

i have a feeling that many of these speedo inaccuracies come from slight differences in how the needle was put on the speedo. I pulled my needle and fine tuned its placement and now its dead on thru the entire spectrum

 

Your NAV is very likely accurate. Your tires are undersized in comparison to the factory spec. Therefore your car thinks it is going faster than it actually is. Smaller diameter tire = covering less ground. The Speedo is expecting a larger diameter tire and is calibrated as such.

The NAV calculates your speed from several satellite positions. Completely independent from car information with regard to speed.

 

I had the same discrepancy running my winter tires, Bridgestone Blizzak WS-50 225/50/17.

 

Assuming tire pressure is the same in both cases, I would refer to manufacturer reported runout on each brand\model. A 225/50/17 does not have the same runout for all manufacturers\models.

 

I'm not saying I'm getting the same error. I'm saying I'm getting the same discrepancy between speedo and nav.

 

?

Help me with the difference. Is one set of tires reading positive while the other set reads negative? You're not explaining yourself clearly.

 

Regardless of the set, the speedometer readout on the navi reads lower than the speedometer proper of the car. I cannot comment on the actual error. All I'm saying is that the navi and the speedo are different regardless of the tire size. Whether that's because the navi is getting it's speed from the GPS or the VSS I don't know. Does that make sense?

 

I see your point. Despite an assumed difference in tire diameter, the descrepency between the speedometer and nav remains constant, leading one to believe the nav may be taking input from the car.

Correct?

I doubt very seriously the nav is taking speed input from the car. This would require the nav manufacturer to write code to take and factor the input, when nav units are already built to calculate speed from sattelite information.

 

Falken ZE-912s, stock size, 225/50/17

Similar slightly slow speedo compared to nav with the Michelin Pilot HX MXM4s.

 

Yes. I do remember reading (on avic411.com) that disconnecting (or not connecting) the nav to the VSS results in less accurate speed readings.

 

Ahhhh. Then maybe I stand corrected. Unusual. Not me, the nav.

 

Found this on Crutchfield.com. Not the same Avic unit as yours, but Pioneer probably addresses your unit in a similar fashion.

"As far as the AVIC-N1 goes, I've installed an in-dash navigation system in my car before, and I didn't find this one any more difficult than the first one.

The essential connection is the one you make from the navigation unit to your vehicle's speed sensor (VSS). The VSS sends critical information about the speed at which you're traveling, which the AVIC-N1 uses to perform its functions and monitor your position. The position of this sensor lead varies from vehicle to vehicle; I found it easiest to tap in under the hood, then run the lead through the firewall.

In order for the system to know when you're going backwards, you also have to connect a lead to your reverse light, but that's not so difficult. I simply ran a lead back to the car's trunk, tapped in right at the reverse light, and was ready to go.

Finally, a lead has to be run from the AVIC-N1 to the vehicle's emergency, or parking, brake. Watching videos in the car is illegal when the vehicle is in motion; the connection to the parking brake lets the system know when the brake is engaged and the vehicle isn't in motion, which unlocks video playback capability.

Pioneer provides wires for connecting to the VSS wire, parking brake, and reverse light. They've got plenty of length, which made the wiring go that much more smoothly, cutting down on total installation time."

So I do stand corrected.

 

So do you have a calibration procedure for the VSS to nav system connection?

In another car I have a very simple calibration procedure for an aftermarket electronic speedometer, and I suspect there might be something similar involved here.



Norm