Speedo Adjustment

supernova2, Jan 2, 11:59am
Perhaps you can but what is the true correct calibration? New tyres, half worn or bald? Which brand of tyre? What tyre pressure, how much weight in the vehicle?
No matter what you do the speedo will never be 100% perfect.
To me it makes sense that it be set to read slightly high. Remember the speed limit is not a target but a maximum.
clark20, Jan 5, 6:58pm
Also for flat tyres, speed changes of one tyre
lookoutas, Jan 6, 11:30am
When the maximum is ridicules, it is a target!
The problem is differentiating between what vehicles can travel at what speed. Imagine driving down the motorway in your late model car at 100 kph, surrounded by about 50 stock standard 1920's cars with crap handling and stuff-all brakes!
Would you feel safe?
They're allowed to do it! But they shouldn't.
soundie1, Dec 29, 8:31pm
I have a Prius.I think the speedo is about 7km and hour out .How do I know this mainly using my GPS on my phone and comparing it to the speed indicated on the dash.
Can I get it adjusted. or do I just know about it and adjust my driving speed accordingly.
I'm in the Hutt
Thanks for your advice
pettal, Dec 29, 8:35pm
faster or slower . ?
gph1961, Dec 29, 8:38pm
not again?
intrade, Dec 29, 8:42pm
if you put new tyres on it be only 3kph out from the bald tyres you currently drive on.
i went as far as fitting tyres from a amarok to my van lifting it so i can see over most f. wits roof in there suv trasheaps and i see over most vans also. Plus my odometer reads now 2kph slow saving me 2km per 100 in roaduser charges . that i paid way to much for way to long when it read 4kph less .
So yes you have to adjust driving speed accordingly.
sw20, Dec 29, 9:55pm
Fit bigger tyres. I have 195/60R14 on my Wantanbes rather than the stock 185/60R14 and now the speedo is bang on.
s_nz, Dec 29, 10:41pm
Speedo's and odometers typically don't align. Speedo is designed to over-read and ODO is designed to be fairly accurate. When I had a scantool, the speed off it was quite a bit lower than what the dash reported.

Still you will be saving money on RUC's with your larger diameter tires.
lookoutas, Dec 30, 10:15am
Some cars have different speedo drives at the gearbox.They can be changed in order to give a different result at the readout.
Might not be in the modern cars which could run off a pulse. Referring to the 60's & 70's, haven't fiddled there for years.
loud_37, Dec 30, 11:21am
All cars speedos read higher than the actual speed your going, that's why I drive at 110 on the speedo and most people think I'm speeding as they are driving at 95 on their speedo, where in fact I'm doing 100 and they are doing 87.
bigfatmat1, Dec 30, 12:51pm
prius uses a average of 4 abs sensors. The inaccuracies are a design feature built into speedo not odo.
mechnificent, Dec 30, 1:02pm
Are you saying that they use the abs sensors for the speedo nowdays Mat ? Genuine question. not stirring.
201, Dec 30, 7:38pm
A friend who has been selling new & used cars for close on 40 yrs has always told me that New cars are calibrated to show 100kph when in fact they are doing 96kph. So basically you have a 4kph "buffer zone" which makes sense when cops get tough & book anyone over 104kph.
tweake, Dec 30, 7:42pm
except the difference is anything from 2kmh to 10kmh, and not always a percentage either, some will read bang on at 50kmh and be off by 10kmh at 100kmh.
gph1961, Dec 30, 8:31pm
some have done for yonks
tweake, Dec 30, 9:24pm
+1
a few still have gearbox sensor as backup, other have no gearbox sensor at all its purely run off the abs sensors.

typically you can get the display corrected to show the correct speed.
androth2, Dec 30, 9:42pm
Roads have curves but GPS is a straight line speed .So it can only be checked on a very straight long road
dublo, Dec 30, 9:52pm
Had to have the speedo on my Triumph 2000 overhauled decades ago. Sitting at indicated 62 miles per hour (100Km/h) on the AKL motorway I got abused for holding up traffic while I was overtaking slower vehicles. Didn't realise until I fitted a tachometer that I was really doing only about 56 mph. Technician said he always calibrated them at least 10% high. I later had it corrected.
The speedo on our Triumph 2500 (fitted with a 2500S panel with tachometer but original speedo) was spot on when checked on measured kilometres at constant speed - looks great when tacho and speedo needles sit parallel at any speed in 4th gear!
Overhauled speedo on my 1964 BMC 1100 was spot on when checked against a "Your speed" sign at 70 km/h, and our 1999 Accord's reads only about 2-3 km/h high at 100 km/h. A recent rental Nissan Tiida gave more than 10% high readings on both speed and km!
mechnificent, Dec 30, 10:29pm
Oh yeah ok. Thanks. I'm out of touch.
oldboyjohn, Dec 27, 12:47am
I had a BMW 750. It developed a sensor fault and a light came up on the dash.
Then the speedo stopped working. New sensor speedo starts working again. Definitely connected