Speedo accuracy

[fuel miser]

Here are a couple of pics showing the info from the sat nav and a slightly blurry speedo.

You will notice the sat nav says 59 mph or 96 kph where the speedo is smack on the 100 kph line.

I also checked this with a gps and also my iphone and the results were similar. 96 kph when the speedo said 100 kph.

It would appear that maybe the speedo is setup for 60 mph as our American friends would require (the market is a little bigger there than here). The kph numbers have just been placed in the required positions.

[King Young]

Or maybe the error exists because they don't want you to get caught on a speed camera?

God help you if you are more than 4km/hr over though...

[SirNed]

Yep will agree with that. Checked mine on run today from Brissy to syd today. Gps was about 5 k out from the speedo and also one of those radars on the side of the road. Radar was showing exactly the same as the GPS but out to the speedo.

Edited June 2, 2010 by SirNed

[Buff Hamster]

If you stick to the speed on the speedo you will NEVER get a fine unless the speed camera is totally F***ed up.

Using my GPS at 60kph on the speedo i am actually traveling at 55-56kmh.

At 100kmh on the speedo i am actually traveling at 94-96kmh.

So you can say the the average speed difference is 4-6kmh less than it really is in real life when reading off the speedo.

I was confused when i got the car i was traveling at 60kmh and people were speeding paste me. In actual fact i was the slow one :D

Edited June 2, 2010 by Hamster

[stedyedy]

get a 3rd speed reading by timing how long it takes to travel exactly 1KM or 2Km etc, as long as your on a flat road and the speedo is constant, should be the best way of testing it

[DJKOR]

Or maybe the error exists because they don't want you to get caught on a speed camera?

On that topic of things, you have to look at it from the manufacturers point of view.

If you are going to be building a large amount of speedo clusters and there are particular budgets that need to be applied, you can't exactly afford to make a precision gauge for every single car out there.

So in the end, they can get a gauge that reads pretty damn close, but there is always going to be the possibility that it will be off by a small amount. Now when factoring in fact that you may end up with some error in your gauges, to prevent legal issues, you would have to adjust your bias so that if you're going to have error, it better be in the safer direction (ie. showing a speed faster than what you are really doing).

If you then make all your gauges read slightly higher than your actual speed, then this can factor in most potential cases where a gauge may be produced and read lower than your actual speed.

[Silver-Aurion]

Why would you want it to read the same? If you want a fine go right ahead make it exactly perfect. I've nicely tricked myself that when I sit on 60, that I AM doing 60. It's a good way for me to never get a fine.

[DJKOR]

I've nicely tricked myself that when I sit on 60, that I AM doing 60. It's a good way for me to never get a fine.

If only it were that easy for me to do. Though, that said, I found just trying to take my mind off my surroundings seems to help.

It's quite crazy. If you sit on the speed limit (as shown on your speedo), just count the many many cars that speed by you.

[Silver-Aurion]

I've nicely tricked myself that when I sit on 60, that I AM doing 60. It's a good way for me to never get a fine.

If only it were that easy for me to do. Though, that said, I found just trying to take my mind off my surroundings seems to help.

It's quite crazy. If you sit on the speed limit (as shown on your speedo), just count the many many cars that speed by you.

Yeah mate, I'm not really into "speeding" so sticking to the speedo speed limit is easy. But for sure when I do I have a lot of car's overtaking me.

There are those odd occasions that I will also stay above the speedo limit if I want to get somewhere "faster" by driving the real speed limit.

[fuel miser]

I am not overly concerned about being just under the speed limit.

The info supplied was only to confirm what others have made comment on earlier. (60 mph is 96.561 kph).

Although I have been in a car crossing the Nulabor with two others and the guy driving was sitting on 180+ kph for 3hrs heading west from Eucla to the next town.

The interesting part about doing that speed is when you stop and fill up, have a stretch, drink etc the cars you passed within the last 10 - 20 minutes drive past or are not far behind you by the time you resume your journey. (Not to mention the extra cost in fuel and wear and tear on your car and the effort needed to perform at those speeds for that long).

[boxerboy]

In my experience, most manufacturers set speedos to optimism. From memory, I think Germany may even legislate this?

Eg, any BMW I have had has always shown a speed higher than actual, around 5% give or take....car or bike.

[50Sport16]

mine is out by 5%. found if you tweak your tyre sizes you can get it back closer to what the actual speed is. 

the thing is the car value is given by how many kilometres you have done in it. servicing is at a designated mileage readings

not to mention the km / tank of fuel. switch to the proper size, rpm goes down, fuel use goes down, more km / tank, lowers running costs and the value of the car doesnt go down as fast

[campbeam]

If you want to tweak tyre sizes, following is a handy calculator.

https://tiresize.com/calculator/

 

 

[PengNZ]

For my 2014 XAV50, when the speedometer says 100kph, the actually was 96kph on my 215/60/16 wheels and tyres and its 95 on my current 225/45/18 wheels and tyres. I was thinking that probably that was because the previous owner used a bigger or smaller wheels set and then tampered the meter and when he sold that he never bothered to tamper that back.

[Hiro]

22 hours ago, PengNZ said:

For my 2014 XAV50, when the speedometer says 100kph, the actually was 96kph on my 215/60/16 wheels and tyres and its 95 on my current 225/45/18 wheels and tyres. I was thinking that probably that was because the previous owner used a bigger or smaller wheels set and then tampered the meter and when he sold that he never bothered to tamper that back.

Why would you think that the speedo had been adjusted/tampered?  Over-reading is perfectly normal (and in a lot of cases, required by the law) and 4% is well within the expected toleranec range - current ADRs state that speedos cannot under-read (ie the speedo says 95 but you're actually doing 100) but can over-read by up to 10% +4km/h (so you can be doing 100 but the speedo can read up to 114)

[Pittsy]

Yep normal for most cars.....

 

I had a family member connect one of those computer monitoring programs into his 4 yo Holden Calais. Funnily enough it shows his speed exactly the same as the GPS but the speedo shows less. So the car knows exactly how fast it’s going but the techs have programmed the speedo to deliberately over read.

 

His GPS showed 100 km/h while the speedo showed 95 km/h.

My Presara does exactly the same.

Probably the same on all cars by design to make sure we don’t speed however we all know anyway!!

Edited September 20, 2019 by Pittsy