What speed am I doing with larger tyres

Gidday Zapper , your speedo could quite easily be out 10%, think the LC 105 came out fitted standard with 265 x 70 r 16, 285s are about 10% larger rolling diameter.
I am pretty sure you can have it corrected, I'm sure someone on this forum will know, or just ahve a search.

See ya
Guy

G'Day Zapper'

I have the same size tyres on a 100 series and at 100 km/h you will be doing 105 km/h. We checked this by driving through one of those roadside speed indicators. The other way to check is by using a GPS .
regards Col

Zapper,

Sorry to be the bearer of bad news but my son has those tyres on his 100 series and we have checked them against his gps and my normally shod LC and guess what, 7% error was the figure we came up with.

Haven't adjusted the speedo, but have slowed a tad.

Every car is diffferent.. Mass produced speedo's cant all be accurate.

Buy a GPS, you know it will come in handy for other things!

Going from the standard 265/75-16's to 285/75-16's gave me a 3.7% difference on my 80 Series according to the Tire Size Calculator but I guess it all boils down to what the original tire size was, what the accuracy was originally like on the speedo and probably even the brand of tire you have - I've heard of two different brands of tire labelled as the same size actually being different in size.

Question: If you can only be found guilty of an offence to the degree that you are aware you are commiting the offence (ignorance of the law aside) and you buy a vehicle with a Safety Cert or RWC with larger than standard tires and aren't aware of this fact, is this grounds to appeal? They may make you get the speedo recalibrated instead which could be more exxy than the ticket but so might not be worth it! ;-)

Cheers
Scoey

Zapper,

As some others have suggested, use a GPS to ascertain your true speed then either commit it to memory (I would'nt trust myself or someone else driving the vehicle) or get your speedo corrected or check out Jaycar or similar. I'm sure they have a device (adjustable) to fix/replace your speedo.

If you find out the revolutions per kilometre of the original tyres and the new ones you could then do a simple calculation to work out the new speed. The tyre stores have this info and it's on the tyres pamphlets as well.

Hi Zapper,
Are you aware that the ADR's for vehicles allow for a 10% variation in speedo accuracy when on new original tyres.
That is deemed acceptable by the various state authorities but the so called "Justice Depts" wont accept that as a valid reason if the "non-revenue raising speed cameras" take your picture.
Having said all that there are two ways of checking your speed.
1. A fairly long set of mathmatical calculations.
2. Buy or borrow a GPS and check the speedo against that.

Good Luck

Disco

The exact differences can be calculated at www.1010tires.com , click on tire size calculator. If the originals are 265x70x16 and the tires/wheels on the car now are 285x75x16 then the rolling diamter is now 6.8% larger which in turn would show the speedo reading 93.2KMh instead of 100. It puts the speedo out 7.2%.

Such an increase in rolling diameter is not recommended for various reasons.

i have gone from std to 305/70/16 on my 100series and found it is out by 5kms(speedo says 100 and actually doing 105 by GPS and freeway speedo chk on western fwy!)i am shortly going to make a speedo correction box to correct this as better half constantly forgets that its not correct.cheers Paul

Are you confused yet Zapper? If not, we haven't done our job properly ;)
If the GPS option isn't an option, then the tyre calculator already mentioned is a good guide. But..... there are all the other factors like massed produced speedos(also known as dick-stickers LOL), different diameters for different brands and also the diameter changes with wear (which hasn't been mentioned yet). If you use larger diameter tyres(which alot of us do) and are worried about speeding fines just drive 10kms less than the speed limit according to your speedo; that's the simple answer.

You can get your speedo re-calibrated various ways. When I bought my new 2005 Hilux they did the recalibration at the dealer via the box under the glove box. You can also drive past various speed check overheads, the one on the Hume for example I drive pass all the time. I have found my speedo to over-read my speed by around 4-5KMh at 100KMh which is a good thing.

Speaking of Speed Camera's, the thriving metropolis of Kununurra has one lurking in the bushes now. A town like ours has a lot more serious problems which should be dealt with before our terrible accident record due to speeding.....like people sleeping on roads etc

Cheers Andrew