Actual Speed

[greenday-rulz21 6]

Yea, that is correct, some magazines test for speedometer error and publish it in their stats list.

I generally fall victim to the cruise control set at 110 trap, drives me nuts. I find backroads are the only way to travel in NZ if you want to maintain speed..

I agree, GPS says you're going the speed limit and you're still running up behind everyone and passing them on the motorway. I do still slow down though if I see a cop/speed camera etc just for extra safety.

[shaneg 0]

I usually travel between 120-110 on long straights, and maybe up to 160 when passing so im not on the other side of the road too long, but if im doing say 120 and see a cop i just keep going at the same speed, i think unless they see you suddenly brake, their eyes arent glued to the radar speed of your car and they are concentrating on driving themselves so they dont pay much attention..

Well thats my theory and i havent been pulled up for speeding yet and have gone past plenty of cops at 120, think i went past a cop at 140 the other day, i just kept going like nothing was wrong.. and they kept going too..

[Apex 693]

Would be quite obvious you were travelling at 120 in the North Island as only a very small amount of motorists travel at those speeds anymore, the majority don’t even crack 100. No sh*t. True story. I kid you not.

Ten years ago 120 was what I travelled at if I didn’t want to get pulled over. Seems we are slowing down. Maybe the advertisements are working.

[cliffdunedin 8]

Well thats my theory and i havent been pulled up for speeding yet and have gone past plenty of cops at 120, think i went past a cop at 140 the other day, i just kept going like nothing was wrong.. and they kept going too..

Dude 140 past cops...you obviously don't value your license as much as i do

My friend checked my cars speeds at 50, and my Bimmer was out by approx 6, my Subby by 3 and Paj by 11

[pureboiracer 0]

i find whenever i convoy somewhere.. for some reason 120-130 seems ok to the cops that go past when there is 3 or 4 of you in a row..

[shaneg 0]

Course i value my licence.. but im already doing that speed and theyve seen me, slowing down isnt going to make a difference.. its not like im doing 120 round a 65 or anything, just 130ish on straights, it seems to sit at about 10km/L on 2500rpm, easy work for the big 6

Its open road driving by the way, i regularly drive between qtown and dunedin and not the auckland motorways.. thats just a bit silly as youd stick out like a sore thumb as i agree people do drive a lot slower on them. i do, lots of cameras on them.

Also agree with the convoy thing, sometimes i tend to find another car that is going at a good pace and just stick behind him which is a bit of fun on a 3 hour drive..

[bravo 35]

does GPS take into account elevation? like if you were going up an incline of 20 degrees.... does that factor into the GPS unit and adjust your speed shown on the GPS unit?

Im sure all of you know what i mean....

Depends on the unit. GPS is a 3D system, but some cheaper units only determine 2D solutions, so can't account for inclines. If your unit also tells you your elevation, then it is probably determining a 3D solution. You need a minimum of 3 satellites for a 2D solution, and 4 for a 3D. For it to be accurate, more satellites is better, but it's the geometry of the satellites that makes the most difference. Ie you won't get a very good position if you're driving hard up against a steep cliff as you only have satellites on one half of the sky, and you have reflected signals bouncing off the cliff-face.

Elevation determination is not as accurate as position, so if you want to calibrate your speedo, find a fairly flat piece of road. Most highways are less than 10% grade anyway. I know they look steeper, but trust me, they aren't.

[OLLIE 26]

All cars are 7-10kph out on the speedometers, it’s a safety feature. I thought this was common knowledge.

If you can access yours cars dealer menu you will see the real vehicle speed displayed against the speedometers.

Wrong ...

All cars are accurate within 7kph between 0 and 7 kph. All cars are dead accurate at 0 kph

but ... most cars are out by up to 10% and as stated above they are normally conservative and read higher than they should.

[CamB 48]

Speaking of the dealer menu, on my car if you set the OBCs speed limit function (it makes a noise when you get to that speed), the speedos indicated speed is about 5% higher.

[bravo 35]

I've adjusted my e30 speedo to be as close to correct as possible. It now nearly exactly matches the OBC speed (test by hitting reset on average speed as you are travelling along), and similarly nearly exactly matches the GPS. Also interesting is that it's within 1-2km of the electronic speed signs at Whangarei, and just north of Puhoi.

There is a slight scale error (ie it's out by more kms at 100 than at 50) but I've more or less eliminated the constant error.

[my_e36 43]

Can you not use different profile tyres to "adjust" this difference in "real" and "displayed" speed?

[greenday-rulz21 6]

Yep. Thats probably the reason a lot of older cars are out because during their lives someone has put on the wrong sized tyres.

[Young Thrash Driver 1020]

There is a slight scale error (ie it's out by more kms at 100 than at 50) but I've more or less eliminated the constant error.

Ive heard of bikes being out by 25, 30kmh when at top speed, ie indicated 310 but radar only returns about 280