What does your speedo show

After fitting 265/75s on my standard rims,i thought that my speedo wouldnt be out,according to posts on here,but it is.
I just went to Little River for a shot today,and travelling on the freeway,sitting on a 100kms according to my speedo, i was passing everyone.
I made a call to my mate following behind me in a XR8 and i had to drop back to 95 kms to match his car doing 100 kms.
When i sat on 95 i was going the same pace as all the cars around me...
So im 5 kms out at a shown 100kms..
Any one else got the same readings?

Like many, with the stock wheels and tyres, mine reads about 9% low, i.e. when reading 100kmph I'm actually only going about 91kmph. Hard to believe a new car can be out this much.

thats a fair bit bit out....mine is now the opposite,im going faster than what it shows

My 3L reads 4km/h slow on 265/75/16 but on 265/70/16 it eads dead accurate and thats using 2 GPS's.

Dave.

heata said:

mine reads about 9% low... Hard to believe a new car can be out this much.

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ADRs require speedometers to be anywhere from 0% to +10% inaccurate.

You'll find that a GPS device is typically about 1% out at the most, which is also the margin of error for speed cameras and mobile radar/laser traps.

The short answer is "get a gps". Use its speed indicator. Forget your speedo, because it's just a needle reading a voltage and none of 'em read accurate for long. That guy in the XR8 probably had speedo error as well.

The closest you'll get is with a GPS. Making sure your odometer is accurate in one of those check length zones doesn't count - it proves your ECU knows how far and fast you're going, but it's still feeding that information to a needle's coils and THAT is the inaccurate bit.

Dion has given info from the ADR too and Nissan know it, and they won't touch your speedo if it's within ADR specs - which in short say that your vehicle is not allowed to display a lower speed than you are traveling at, but it can display up to 10% higher than you are actually traveling at.

With that size tyre you will be 5kms out.
For new cars they come standard now 5kms under.You know the saying drop 5 stay alive well they are making it like that on your speedo and not telling anyone.

Dion said:

ADRs require speedometers to be anywhere from 0% to +10% inaccurate.

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And with factory everything still installed my D40 mine is just within that figure at 9%. But I rarely use the speedo these days so I'm pretty much over another of Nissan's lovely features.

Check it against a gps mate, I'll bet your mares xr isn't spot on either.

Mine is out 5kms aswell with 265/75/16s when i had 245/75/16s it was about 5kms out the other way so i was never speeding

All cars will be out. Tyre wear/pressure/load comes into play.

The std car gps units are very accurate with there speed readings, except in hilly/trees covered roads where they may not have the required satelite coverage for accurate speed determination.

My 05' STR is 98 when speedo says 100. (BFG at's 265/70) but around 110ish with 285/75's

heata said:

Like many, with the stock wheels and tyres, mine reads about 9% low, i.e. when reading 100kmph I'm actually only going about 91kmph. Hard to believe a new car can be out this much.

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Mine is a 2010 and exactly the same. Legal by the law but a long way out in reality.

regards
Greg

A question i have on this obviously old issue is that if my speedo is out by around 9-10% with stock everything are there some more synister reasons. I do not normally partake in conspiracy theories but, since using my GPS as a speedo which inturn sits me on 109-110 on the car speedo my fuel consumption has increased (getting about 60-80k's less a tank) and i cant help but believe that my odo is also 10% out so inturn the i am actually getting 10% less fuel economy than the odo reads.
Correct me if i am wrong but when i get to 100,000 ks i have only actually done 90,000.
To me it allmost seems like a convenient error leading to better than actual fuel economy stats and more regular than required servicing.
any way theres my little rant that has been pissing me off with all the highway driving i have been doing over the last three weeks

Not sure if it's this thread or another but there has been some suggestion by people that even with their speedo out their odo isn't. Mine however is the same 9% as the speedo. I'd like to think that's taken into account come trade in time or anytime really but I also don't live in a dream world where such things come true.

You'll find that if you have stock tyres, your car knows exactly how far it's driving so the odometer is correct.

Test it at one of those check lengths. Stop at the first sign, reset your trip meter, stop and the last and look at how far out the thing is.

The inaccuracy in the speedo is actually in the needle itself. Using some numbers just to illustrate (they aren't accurate, but will give you an idea) ... assume the speedo shows max speed (220km/h) at 12V and zero speed at 0V. At 80km/h it sends 12*80/220 = 4.36V to the needle but this voltage makes the needle move MOST of the way to 80km/h, but not quite all the way, so it indicates 75km/h. Acceptable for ADR, okay as a rough guide and won't get you in trouble in a speed trap.

The car does actually know the speed quite well, if you get a scangauge and hook it up you'll see that it's not really far off at all - the bodgey bit is the needle.

Don't worry about your odometer unless you change the tyre sizes.

That's not entirely true Tony, my last three cars have been made the same, the speedo and odo are out uniformly and this is checked both by road side posts and Scangauge.

Here's the deal...

There's NO inaccuracy..

Nissan has the instrument clusters programmed that way and its the way they want it and WONT change it.

The speedo transducer and ECU read/calculate the correct speed/data.

I've proven this to myself with my laptop/software plugged into the OBD port.

End of story.



Happy Days...

Oops there is that raw nerve again.

Krankin said:

Here's the deal...

There's NO inaccuracy..

Nissan has the instrument clusters programmed that way and its the way they want it and WONT change it.

The speedo transducer and ECU read/calculate the correct speed/data.

I've proven this to myself with my laptop/software plugged into the OBD port.

End of story.



Happy Days...

Click to expand...

PS...but yes, changing things like tyre size, speedo driven gear or gear ratios will have an effect and so use your GPS to find out what the difference is when youv'e done any of these mods

I tested my 2010 year stock Navara D22 ST-R against the kilometer check length markers on the freeway and the odo seems correct, but the speedo shows 10Kph higher at 100Kph (according my sat nav and other car). At least I wont get a speeding ticket.