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Discussion Starter #1
In the fun days of my old 69 Mustang when I put some larger circumfrence than stock tires on the back I was able to compensate back to the correct speed and mileage on the speedometer by changing a little gear that sat on the end of the speedo cable going in to the transmission.

Is there something similar with the FX? Anyone know how it is done. I am toying with getting 275/45/20's that appear to effect the speed/mileage by 2% or so. Be nice to keep it correct if possible..
 

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I wonder with all the tech on our FXen if there's even any speedo gears; it wouldn't surprise me if the wheel-rotation sensors used by the ABS, VDC and ATTESA feed into the speedometer/odometer, Navigation and trip computers directly.
 

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is someone leasing their FX and going to go over the miles :lol: :lol: :lol:

i had a buddy who took out the fuse in his old durango so he could blow out 30K per year on it with a 12K lease....he just didnt have a speedo either :lol:
 

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My understanding is that the OBDll made that a thing of the past.Your ECU has the miles in it and without a cooperative tech with a tool for reclibration,replacing the ECU even requires the old mileage to be re installed.Someone I know :roll: had the gears in the speedo cluster removed(we no longer have those clusters).It is all done in the ECU

You have to find someone to do it(and the feds check for the abusers).He must have the piece of equipment.

Good Luck!
 

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Well someone I know very well has done such mods where you disable the VSS (vehicle speed sensor) input to the car's cluster or ecm etc. on many vehicles. That is if you are looking to "fit into your lease arrangement". Aren't there companies that make gizmos to recalibrate the odometer for such tire changes?
 

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brnjugfx45 said:
My understanding is that the OBDll made that a thing of the past.Your ECU has the miles in it and without a cooperative tech with a tool for reclibration,replacing the ECU even requires the old mileage to be re installed.Someone I know :roll: had the gears in the speedo cluster removed(we no longer have those clusters).It is all done in the ECU

You have to find someone to do it(and the feds check for the abusers).He must have the piece of equipment.

Good Luck!
If this is true on Nissan/Infiniti vehicles, then no-one at my dealership's service dept. knows about it. I specifically asked around about this one day and was told the ECM does not log the vehicle's milage. I heard from another source (but no-one at a couple of dealerships I checked with knew if it was true or not since they had never messed with it) that the car will not start if the gauge cluster is disconnected. My service manager gave me a copy of their procedures for replacing faulty instrument clusters; there is a regulated company that supplies them all and accurate milage is dialed into the new one before it is sent out.

Anyway, as far as the tires are concerned, a 2% variance in speedo reading is well within acceptable limits (anything within 5% is cool). Those speedos aren't nearly as accurate as you might think and you're likely off by a couple MPH with stock tires.
 

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Isn't tampering with a speedometer illegal?
 

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Discussion Starter #9
I am sure tampering, resetting, winding back etc the oddometer is illegal under some kind of law, what I am after is recalibrating it so that the one wheel turn represents the ground covered in that turn. It was quite easy to do in the days of manual take-offs from the gear box by replacing the gear used on the cable, and nothing illegal there.. One time when I did get a ticket in my old Mustang the cop asked me if my speedo read correctly as he noted the larger tires on the back! I had the correct gear in to show the correct speed so no excuse there! :)

The speed difference leaving it the way it is with the other tires isn't so big a deal (actually it will help keep you out of getting tickets as you are moving slower than you perceive from the speedo), it is the extra 1000 miles on the odometer when you hit 50000 that I am not too wild about, I don't have a lease vehicle but I kind of like to know that the mileage is correctly being totalled up over time. If re-calibration was something easy that the dealer could do I think I would do it and get the different tires, right now I just don't see it being worth the hassle and I will most likely get stock ( and pay more for them, even though they are smaller than the 275's - explain that!).

By the way, search on the internet for oddometer recalibration, there are devices and services out there, seems to me they are in that gray area, like radar detectors, able to help you something illegal. This should be a dealer only service in my books.
 

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I was only curious ForTheWife. Thanks
 

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Yes,and the federal penality is extreme,heavy fine and loss of license where applicable..Dealership called for me to pick up car(30Kservice) so I took the oppurtunity to talk to Hugh my tech.
-Currently the speedo holds the mileage and must be sent out to a certified company to be set(as stated)
-on 2005 the vin must be logged into any replacement of speedo/ECU
-my info was what the big three used to do

Manufacturers are regularly updating this process to foil the people changing the readings

ps my speedo is off 4-5mph at 80 so the larger tire may bring you dead on
 

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Discussion Starter #12
You know, I never thought of that! :)

It would be interesting to correctly check the accuracy of the speedometer etc before jumping in and getting the tires.

I wander how accurate my car is (Mazda RX-8), at a minimum I need a side by side run on the road to see now how much off they are from each other..

Anywhere where distances are correctly posted over a fair distance that could be used to check mileage? A GPS would be nice!
 

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Some Interstates have mile markers and you can cover 0ne mile in 60 seconds,or if you wear or borrow a chronograph ,you can check the accuracy at any speed.
I routinely check the speedo of a new car or a rental,better to know!
 

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MustGoFastR said:
Those speedos aren't nearly as accurate as you might think and you're likely off by a couple MPH with stock tires.
I dunno 'bout this- maybe back in the day, with gears and the way the old speedometers work (centrifugal magnets), but now that it's revolution pulses and electronic instrument clusters, I'm sure they read the speed accurately to at least .1 MPH .

My GPS and my FX always collaborate.
 

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Discussion Starter #15
I find this discrepency a little bit large also. The old type of speedo I think could be very off on the speed with the cetrifugal magnets but the cranked oddometer should be trustworthy with the correct gear in the takeoff from the transmission.

A weekend expirement is called for with the FX, need to find some mile markers (wish I had a GPS), compare both the oddometer reading and time the distance covered compared to the speedo speed, hopefully done at a constant trot with the cruise-control or something.

(Can't believe all this is over a set of tires :wink: )
 

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Speedo "off" by 10% - anyone else experience this?

All of a sudden i am passing a number of these radar checkpoints in my area and I am consistently about 10% off. If my speedo says 40, the radar says 35, if 28, radar says 25 ....

I replaced my worn-out Goodyears with Toyo Proxes, but I cannot imagine there is any discernable difference as they were the same size.

has anyone else experienced this? I guess Ill be visiting the dealer soon.
 

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Discussion Starter #17
I have ordered stock size Hankook's for the 35, I will try and do a before and after speed check with the worn out Goodyears and the new Hankooks for comparison. Still a week or more until the new tires are in.
 

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Been using my PDA GPS and looking at the local Speed Signs, the FX's speedo consistently shows 2-3mph faster(Stock 20's, only 2700miles). I guess I will have to set my cruise to 82-83 now :lol:
 

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As stated I was off 4mph at 80 a bit more now that I went to a shorter tire.
Somebod did a comparison on a "larger BFG tire" which turned out to be same height and width as stock

I really do not know how they determine speedo reading now,but I will try to rememer to ask
 
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