speedo after bigger tyres

Thought I'd share my observation, now that I have put 265/75 R16 BFGoodrich All Terrains on my Nav, my odometer and speedometer read low.

To get the best reading for a comparison I reset my odometer and my GPS trip log at the same place whilst stationary then before driving anywhere i ensured i had GPS fix. you can see from the photo after driving 100.4 kms (gps measurement) my odometer had read 94.5kms.

Therefore my speedo reads 94.12kms @ 100 kph. out by 5.87 kph.

This needs to be considered for service intervals, fuel consumption calculations etc. it might seem like nothing but after my odometer clicks over 5000 kms it is a real world 5276.56kms.

Thoughts anyone?

Great info, Will.

The speedometer will never be accurate, because it's really just a voltmeter reading a voltage supplied by the ECU. It only has to be close but (legally) "never reading under the actual speed". It's allowed to read over by up to 10% but higher margins are sometimes ignored anyway.

Jaycar sell a kit that alters the impulse rate from the sender on the gearbox, which is where speed is measured. You could adjust this with the kit, but it's the odometer that really needs the adjustment for all of the reasons you outline.

This is where I hit the limit of my knowledge. I know for certain measurements, the ABS sensor (on the front left wheel, I believe) is used by the ECU. Is that for calculating distance travelled? I don't know, but I suspect it might, which means the Jaycar box can't be used to adjust your odometer. If the ECU gets its distance measurement from the rotation sensor on the gearbox output shaft, then the Jaycar box will work to adjust that.

Does anyone else know where the ECU gets its odometer reading from?

I have the same size tyres basically on my D40 and the speedo is almost correct. Odometer is out but I go by the scangauge for economy anyway.
As to where the ECU gets its readings from. I am lead to believe that on the D40 it actually an average reading from all ABS sensors. The guys in the UK and the US are where I get my info from and to the best of my knowledge there isnt anything that really will adjust the readings.
If you put the dash into diag mode and check the readings from the speedo you will find the speedo reading and the Gauge reading are different.
The Frontier gets a different dash to ours but they basically get the top of the range Pathy dash to get DTE etc .Many of the guys in the US get bad readings from their dash so its an indication not an accurate reading.
I use my Scangauge and so far if it says I have 16 litres of fuel left then the tank will fill with 74 litres from the pumps.
I drive by the scangauge for speed and economy and so far its not let me down.

Oh yeah my fuel gauge is a waste of space on the cluster. When it reads just under 1/4 tank it actually has over 30 litres left. When the low fuel light comes on I only have about 18 litres left in the tank.

On the D22,
and every other vehicle i know of, wether using mechanical or electrical transducer the signal is taken from the output shaft of the gearbox which has a 'Drive' gear that drives the 'Driven' gear mounted on the extension housing, which then via cable or electrical transducer feeds the signal to the speedo cluster or to the ecu.
The D22 actually knows/reads the 'correct' speed, though the speedo is set at the factory to read the lower speed that we all know about 'love or hate'.
similarily my mitsi work van shows a lower actual speed on the speedo and when i connect my pc via the obd port it shows the true speed on the pc software program confirmed by my gps.

As for the abs sensors, have'nt looked on the d22,
but on the territory and falcons the abs has sensors on all 4 wheels and works by reading what speeds all 4 wheels are doing, eg when you lock the fronts up, the rear are still moving then the abs takes over and releases/brakes the fronts so that you still have steering.

I should have read the bloody manual.

From DI.PDF, Page 4

Speedometer:
*ABS actuator and electric unit (control unit) reads a pulse signal from wheel sensor, and transmits vehicle
speed signal to combination meter with CAN communication.
* Combination meter indicates the vehicle speed according to vehicle speed signal.

Click to expand...

And from page 5:

ODO/TRIP METER
With ABS
* ABS actuator and electric unit (control unit) reads a pulse signal from wheel sensor, and transmits vehicle
speed signal to combination meter with CAN communication.
* Combination meter uses the vehicle speed signal to calculate the mileage, and it displays.

Click to expand...

It does say for models that don't have ABS:

Without ABS
* Combination meter reads a pulse signal from vehicle speed sensor.
Signal is supplied
– from vehicle speed sensor terminal 1 and 2.
– to combination meter terminals 47 and 48
* Combination meter converts a pulse signal to vehicle speed signal.
* And indicates the vehicle speed according to vehicle speed signal.

Click to expand...

So that Jaycar unit is pretty much useless. There's no way I'm messing with my ABS.

Old.Tony said:

So that Jaycar unit is pretty much useless. There's no way I'm messing with my ABS.

Click to expand...

Have a look in your service manual, in the auto trans section and check for the transducer in the rear of the trans.
If you have one, this is where you speed is read from and thus you can use the jaycar gizmo without touching the abs.

The manual says it has a speed sensor there as well, but it's tied into the auto gearbox control unit. It's certainly different to the usual way of doing things.

Revolution sensor detects the revolution of the idler gear parking pawl lock gear and emits a pulse signal. The
pulse signal is sent to TCM which converts it into vehicle speed.

Click to expand...

In the manual, "ECM" = "Engine Control Module" and "TCM" = "Transmission Control Module".

The CONSULT-II reference value is "VHCL/S SE-A/T" and its description is "Approximately matches the speedometer reading." If it only approximately matches the reading, is it used to create the reading or is it just another source?

Could the combination of the ABS sensor readings and the gearbox sensor reading be used not only for speed determination, but also wheelspin (for models with traction control) and brake lockup?

Interestingly, the wiring diagram for the automatic transmission has the revolution sensor feeding data into the "A/T Fluid Temperature Sensor-1" unit with output going to the TCM on pins 11, 12, 13, 14, 16, 17, 18, 19 and 20. ECM pins 87 and 95 are connected to pins 1 and 2 of the TCM.

More curious is that there are a bunch of other sensors I'd not expect to be used in the transmission contrl. Turbine revolution sensors 1 and 2 both feed into the TCM, not the ECM, which might mean the TCM is simply passing data through to the ECM. Further, the front brake solenoid valve and ABS control unit both feed data into the TCM.

Understandably, the starter control relay, several pressure sensors and temperature sensors also feed data into the TCM.

There's an output directly from the TCM to the instrument cluster, appears to control a light for "A/T OIL TEMP" and "O/D OFF".

Bloody thing is a maze, Krankin. I feel like a rat, I think I'll jump out and get my cheese at Woolies.

Yep,
like my old EF Falcon,
the six cyl auto model sent all its sensor output signals to the ecu,
while the V8 auto model had its own module for the trans together with the ecu, like your auto truck..
This way gives the trans a dedicated processor module/ less work for the engine/main ecu.

I suspect the correct way to get the speedo to read correct is to reprogram the cluster,
but I'm not aware of anyone having the gear to do this apart from nissan japan/ or the cluster manufacturer.

Untill such time, the gps will have to suffice.

Yep any tyre change will affect your speedo, mine brought it almost back to correct, The D40' are way out from factory. I would stress over an extra 200 odd kms between services though.

I'd just take the simple thought approach, when you finally come to sell the Navara (heaven forbid) it will have less mileage on the clock than actually travelled - and you can say with all honesty that you have NOT wound back the odometer !!!

WoodyD40 said:

I'd just take the simple thought approach, when you finally come to sell the Navara (heaven forbid) it will have less mileage on the clock than actually travelled - and you can say with all honesty that you have NOT wound back the odometer !!!

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The problem with that is that it would only work for second hand car salesman. You tell a dealer that your car has less than the counted k's on it and they will laugh at you and say it makes no difference to the price because the new owner will only see the figures in front of them. However if the second hand dealer is shrewd enough he will be able to convince the buyer that the car had a speedo problem up until the previous owner sold it and the actual speedo reading should be 10K less than it shows but they have fixed the problem and it's all true and honest because he's Honest Sam's Secondhand Cars.

But of course even with a 10% error there has to be a lot of k's on the clock before it would make a difference to the sell or buy price of the car. Even after 500K it's unlikely the error making the actual k's about 450K would be a big selling point.

In reality, do they care about km, or is it just "Car Make/Model and year of manufacture" ?

They only care about the k's if it's a selling point. eg. "This 1980 model has only 2000ks on the clock and was only driven to church on a Sunday" you don't often hear them say "This car has done 700,000ks but they were all nice calm granny k's on her way to church."

Similarly on a trade in the k's only come into it if they think they can wipe some dollars of the trade in price. "400,000 ks in 18 months, well thats alot of driving most of the cars of this age only have 40,000 ks that's going to drop the price a bit." If you go in with a 18 month old car that's done 2000ks and ask them if it's worth more because of it's lack of k's they will come back with something along the lines of the price is governed by the car and it's age not the k's.

It's a double edged sword no two salesman are alike and no two sales pitches are alike but like everything else about the car when it comes to sales day each feature or problem can be twisted each way in the hope of convincing a person to fork out the dollars.

Yup, i agree. Salemen will always put the spin to suit their own purposes. Either way, they will spin it to suit themselves - less money for trade ins if kms are high, or higher sale price if kms are low.

You can only work it in your favour if selling privately.

I think Kms clocked only have a impact at significant milestone intervals.

Eg, less than 50,000 - like new
less than 100,000 - low kms
around 150,000 - average and most would expect to be around there
under 200,000 - getting high, what needs doing, whats still standard
over 200,000 - might need work soon, make sure you get it cheap
300,000 - nope! forget it and keep looking (unless it is dirt cheap)

thats my thinking / approach. different strokes for different folks, my Mrs wont buy unless it has less than 50,000 but then she is looking for a murano or similar.

And the dealer looks at it like

Under 50,000: I can rip this off as a near new car despite the 40,000 of the k's being done with just the back wheels moving
Under 100,000: This is still close enough to new that if the right patsy comes in I'll tell them it's got dealer warranty, but lets hope they don't see the bald tyres.
Under 150,000: It's done a few more k's than most it's age but they were done by a granny who only drove it on country roads to church on a Sunday, it's never been over 80ks in it's life.
Up to 200,000: Granny only drive it to church but she went three days a week, it's only hit 90k's once when her grandson drove it and it's been serviced every other week to make sure it's in tip top shape.
Over 200,000: Our expert mechanics replaced all the important bits so it drives like new, you wont need to do anything other than service this car for atleast 100,000ks.
Over 300,000: It's only just out of factory warranty but we are so confident this car is the best on our lot that we will give you 6 months warranty if you buy it today.
Over 400,000: Sure we give you a warranty on this superb piece of motoring history. Then the whisper than can be heard is, "it's a concrete warranty, once it's off our concrete the warranty expires."

I'm sensing that KraftyPg has been ripped off by a dealer.

whenever I'm buying a car (or anything for that matter) i approach it as though I'm buying it from myself. *Caveat Emptor* or *Buyer beware* Sure if you ask me a question you will get a version of the truth, it's then up to you to come with enough knowledge that you dont get burnt. I expect inteligent questions and relevant answers. thats it.

Oh and you can use high Kms to your advantage... "it's going to need tyres soon, shockers, maybe wheel barings / clutch / brakes etc; i'm interested, just not at that price".

will said:

I'm sensing that KraftyPg has been ripped off by a dealer.

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I'm sure we've all been ripped off by a salesman in some form or another but no I've never been blatantly ripped off by a car dealer. I'm sure there have been some that got over me in some areas just like I got over some in other areas, it's the rules of the game. It's the attitude of salesman and reps that bug me, selling ice to eskimos is one thing but selling them the freezer as well is something many salesmen see as their prime goal. There is very few markets out there where profit has to be made at the expensive of pissing off the buyer yet car salesmen seem to be one area where bullshit reigns supreme.

will said:

Oh and you can use high Kms to your advantage... "it's going to need tyres soon, shockers, maybe wheel barings / clutch / brakes etc; i'm interested, just not at that price".

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We will stick another (never use the word new unless you mean it) set of tyres on it for you, the shocks were replaced at the start of winter and we've still got the receipt. The wheel bearings were done as a part of our inspection and the brakes passed the road worthy. I'll talk to the boss but I really can't see us getting you a better price for you're trade in because the k's are so high and the margins on second hand cars these days just aren't enough.

10 minutes later the salesman returns from his chat with the boss where they discussed the footy results pointed a lot at the car in the yard and shook their heads generally played the role of arsehole boss and "trying to earn your love" salesman.

Look the best we can do is maybe knock $500 off it for you because we've had another guy come in and he wants it for the price on the window, he doesn't have a trade in like you do where we can cut the profit on the sale a bit so you really need to make up your mind quick. This is a remarkable car and you wont find better on a lot anywhere.

A few minutes later the salesman comes back with. Look I'll tell you what I'll do, I knock $800 off the price if you sign today but you have to be sure not to tell my boss because he'll tear me a new one for cutting the price down so far.

The smart person still walks away but the person who's suckered by salesmen crap has just brought themselves a car and is rushing home to tell the missues how he talked the guy down $800 and got some new tyres thrown in.

it's always the desperate and the ones who don't see through the crap that get lumbered with the stuff noone else wants it's not always their fault it's quite often the fault of the mongrel selling the vehicle who knows is not fit to be on the road in the first place.