Difference Between What Your Speedo Says, And Your Actual Speed. Anyone Have This?

[puddlejumper]

I've been told that all cars, in particular Japanese cars, overestimate your speed, so that the speed shown on your speedometer is actually off by a bit. I tested mine using a phone app called Ulysses Speedometer which uses GPS tracking to measure your speed exactly. I discovered that my speedometer is off by a ridiculously huge 8.3%. Which means when my speedo reads 100, I am actually only driving 91.7. And that to reach 110kmph which is the top speed on some highways, my speedo actually has to read 120kmph. I dislike having to estimate the speed I am driving at and never quite sure if I am now speeding or not, and am annoyed that I must be the frustrating person on the road driving unecessarily under the limit.

Have you guys measured the difference on your car? Is it similar to mine? Can it be adjusted?

Edited December 25, 2012 by puddlejumper

[Sklyn]

my old car had speed on the turbo timer which was usually about 2 kph less than the speedo at about 100km. the timer was calibrated at 60kph from the speedo though...

Comparing speedo to satnav in other cars usually had about 2-3k difference also (but they weren't jap)

So i think usually a speedo is only a cpl k over actual speed.. things such as tire size and wear can have an affect on the precise accuracy...

[Nightcrawler]

As per above, unless you are running the stock tyre sizes (which almost no-one ever does - even on stockies), then you will affect your speedo's accuracy. My tyre width/profile is WAY off - my speedo is out by about 15%, but I compensate for it and normally use my GPS digital speedo instead of the oem cluster.

[scotty nm35]

You will find all the V35's and M35 Stageas have this discrepancy, but the ecu gets a good speed signal and you can display this actual speed via the obd2 port. (it is much more accurate.)

I agree, it is very annoying and can cause frustration, 10k's out at 100 is a joke.

[PN-Mad]

The tacho is over ambitious too. Its about 400-500 rpm out by the redline.

Again - ECU gets the clean feed of RPM.

[sonicii]

My V35 is fairly close. About 2% last time I checked with GPS. And I am running stock size tyres.

But our J31 maxima is out by about 8%. Again with stock size tyres.

[puddlejumper]

Good to know I'm not the only one. Still frustrated by it though. Will try and hook up the ecu to display.

[GeeDog]

My V35 Coupe seems to almost spot on - I've tested at 80 & 110 against the GPS in my phone, and the difference is no more than 1 - 2 kph. I've got 18s with stock rear tyres - 245/45R18.

[Frosty]

depends on rolling diamater etc

what size are standard wheels/tyres?

what size are your current wheels/tyres?

this can be worked out their are also calculators on the net if you use google

[81gSKy]

I got 2km/h difference between the fronts and rears because of the tire sizes (width and profile) that came with the wheels, I'm not sure how much it is in relation to the speedometer. Use this tire size calculator (http://www.1010tires...ecalculator.asp) to help you choose the tires within the closest possible tolerances for your set of wheels. There may be other factors as well...

Edited December 26, 2012 by 81gSKy

[Commsman]

Here's the results of a test I did a while ago. As per above, the Informeter (display from OBD2 data) is accurate, thus confirming Nissan deliberately engineered our cars to show the incorrect speed on the dash.

[bigdr33gtst]

i am out by 10% due to rim and tyre size also, i just add 10% to my speed and know how fast im going.

[vee35]

So, are we saying that the GPS is connected to the engine control (ie fuel)? and the traction control as well? What happens when the GPS loses a signal?

[scotty nm35]

If you look at the graph above you will see it isn't 10% across the board.

[sonicii]

So, are we saying that the GPS is connected to the engine control (ie fuel)? and the traction control as well? What happens when the GPS loses a signal?

?? GPS is only used for Navi. If you don't have Navi, your car doesn't even have a GPS receiver. the ECU uses wheel speed sensors to determine vehicle speed (as well as using them for ABS, TC and VDC). If you are running stock size tyres, the ECU speed derived from these sensors is quite accurite.. however, the speedo doesn't display exactly what the ECU reads, the speedo almost always reads faster.

[sonicii]

If you look at the graph above you will see it isn't 10% across the board.

I corrected the speedo on my J30 years ago, there was an adjustment on the back of the speedo cluster which adjusted a % of speed, however, the speedo was also out by an absolute figure, there was no adjustment for this, but fortunatly I was able to elongate the mounting holes where the speedo mechanism attached to the face, that allowed me to make an absolute adjustment and I was able to get the speedo to read accurite at 60, 80 and 100km/h.

I had a look at the back of the speedo cluster on the J31 Maxima, but there is no physical adjustment.

[Deep Dish V35]

at least puddles speedo is out in the negative direction. years ago i found out the hard way that my car was showing 100 on the speedo but was actually doing 111 on the road... *flash*

[t5iv]

at least puddles speedo is out in the negative direction. years ago i found out the hard way that my car was showing 100 on the speedo but was actually doing 111 on the road... *flash*

You should've been able to contest that... Right?

[sonicii]

^^ Lol.. and end up with a defect notice too...

[t5iv]

Not if you take it to court and can prove that you were made aware of this issue and rectified it straight away.