Speedometer reading questions
 

Hi

Just wanted to know two things about the speedo reading.

1. The speed is taken off the front tyres right?
2. How much does the Z speedo overestimate the actual speed?

thanks

It's taken from the transmission.

Mine seems accurate within 1-2 mpg when I pass some of those signs. 30-60mph range when I see them depending on where.

You sure it's from the transmission? Because wouldn't that mean that when you get rear wheel spin the speedo should fly up?

As I've never done a burnout i dont know if this happens or not. But thought the most accurate reading would be off the non-powered wheel.

Yea i am pretty sure when you get wheel spin the speedo should fly up

hmm ok...

hmm... damn...

:icon18:

According to my GPS, my speedo is 1 mph fast.

So where is the reading taken from?

I'm considering putting tyres with a larger RR on my rear to give it the effect of higher gearing but won't do so if it'll change teh speedo... doing to be doing some sydney to melbourne trips soon.

um as far as I know this was true with my megane

when it was spinning its front wheels on the ice the speedo flew up in the air

OK Guys...This is a legit question for those that might change tire sizes.
Also can the speedo be re-calibrated and if so how.

I've never heard of a car that uses an individual wheel for the speedo sending unit. Not saying it doesn't exist, but I've never heard of it.

Ok so it's taken from the trans. Now can the speedo be re-calibrated and if so how.

I'm sure it's computer controlled. In older transmissions there was a gear/sprocket you would change to get as close as possible, but I bet it's a little more exact now.

Maybe this:

Universal Speedometer Signal Interface

That's great thanks Vipor. There are even some on ebay for a little less money and free shipping.

i thought it was taken off the a/c blower speed.

I would trust my car's speed reading before i trust a GPS, thats for sure

In my vehicle, my GPS (I use my Passport as a "primary" spedo) indicates the exact same thing...per GPS I'm going 70 while my Z's spedo shows 71 or so.

Then again, those highway readout radar sets I occasionally will usually show something different than what my GPS or the car's spedo is showing!

but then if your tires are over/under inflated...

oh wait, doesnt matter cause it's not connected to the tires...

I am quite sure that it IS connected to the wheels since I had it happen in two cars.

speed flew up on the ice while i was pretty much standing still

Any car with ABS has wheel spin sensors. It is very easy to use this source of the speedo. In fact, I believe it is Subaru that uses the wheel spin sensors as their "flat tire detection system". It monitors all the wheels and if one is spinning more than the others, then the tire is low on air...hence smaller.

If I were Nissan, I would use the front wheels for the speedo. The car is already monitoring the tire rotation, so why not feed the rotation into a calculator.

As a follow-up...In the service manuals. The Vehicle Speed Signal is in the Wheels and Tire section. So I would bet against the tranny.

Bump from the dead

Any difinitive answer?