[tassie jeeper]

i stumbled upon this for tho's of u running above stock size tyres with standard gearing it will show u how much your speedo is out by.

according to this converter chart by going from 215/65/16 to 245/70/16 my tyres are 9.26% bigger than standard and me speedo will be out by the same (ie if my speedo reads 100kms i will be traveling closer to 110kms)

thought there will be a few of u guys that may find this useful:
http://www.tyrestore.in/upsizing.htm

the below site will convert metric tyre sizes to inches and inches to metric:
http://www.extremeterrain.com/wrangler- ... lator.html

[Chop]

Three words, Gee pee ess

[alexxx]

gee pee what???

[303zuke]

tassie jeeper wrote:

according to ....... blah, blah, blah..........my tyres are 9.26% bigger than standard and my speedo will be out by the same

Not at all true, as there is almost zero possibilty that your speedo is 100% accurate with stock, factory tyres. According to ADR 18/03, when your vehicle is travelling at an actual 100 km/h your speedo is permitted to show anything between 100 to 114km/h. To avoid liability issues (ie driver's getting speeding tickets when an inaccurate speedo makes them believe they are under the limit), car manufacturers will invariably design their speedos to show the vehicle travelling at higher than actual speed.

Fitting larger tyres will sometimes bring the speedo closer to reading accurately, but accuracy should always be checked by other means than relying on just the speedo.

[tassie jeeper]

303zuke wrote:

Not at all true, as there is almost zero possibilty that your speedo is 100% accurate with stock, factory tyres. According to ADR 18/03, when your vehicle is travelling at an actual 100 km/h your speedo is permitted to show anything between 100 to 114km/h. To avoid liability issues (ie driver's getting speeding tickets when an inaccurate speedo makes them believe they are under the limit), car manufacturers will invariably design their speedos to show the vehicle travelling at higher than actual speed.

yes i know this, Speedometers are manufactured to be accurate to within 15% which is a pretty big margin and will most likely show u to be traveling faster than u actually are however the point of this post is it will show u have much your speedometer has changed from what it was with the stock size tyres.

[joel]

303zuke wrote:

tassie jeeper wrote:

according to ....... blah, blah, blah..........my tyres are 9.26% bigger than standard and my speedo will be out by the same

Not at all true, as there is almost zero possibilty that your speedo is 100% accurate with stock, factory tyres. According to ADR 18/03, when your vehicle is travelling at an actual 100 km/h your speedo is permitted to show anything between 100 to 114km/h. To avoid liability issues (ie driver's getting speeding tickets when an inaccurate speedo makes them believe they are under the limit), car manufacturers will invariably design their speedos to show the vehicle travelling at higher than actual speed.

Fitting larger tyres will sometimes bring the speedo closer to reading accurately, but accuracy should always be checked by other means than relying on just the speedo.

not sure where you plucked that much variation from, but i can assure you that is well above the prescribed acceptable limit, even by territory standards.

[atari4x4]

joel wrote:

303zuke wrote:

tassie jeeper wrote:

according to ....... blah, blah, blah..........my tyres are 9.26% bigger than standard and my speedo will be out by the same

Not at all true, as there is almost zero possibilty that your speedo is 100% accurate with stock, factory tyres. According to ADR 18/03, when your vehicle is travelling at an actual 100 km/h your speedo is permitted to show anything between 100 to 114km/h. To avoid liability issues (ie driver's getting speeding tickets when an inaccurate speedo makes them believe they are under the limit), car manufacturers will invariably design their speedos to show the vehicle travelling at higher than actual speed.

Fitting larger tyres will sometimes bring the speedo closer to reading accurately, but accuracy should always be checked by other means than relying on just the speedo.

not sure where you plucked that much variation from, but i can assure you that is well above the prescribed acceptable limit, even by territory standards.

Lot's of legal mumbojumbo in here about ADR 18/03 http://www.comlaw.gov.au/Details/F2006L01392

[JrZook]

What sources do you have joel?

[tassie jeeper]

atari4x4 wrote:

Lot's of legal mumbojumbo in here about ADR 18/03 http://www.comlaw.gov.au/Details/F2006L01392

5.2.5. The vehicle is tested at the following speeds:

Maximum design speed (Vmax)
of the vehicle specified by the
vehicle manufacturer (km/h)
Test speed (V1)
(km/h)
Vmax £ 45
80 % of Vmax
45 < Vmax £ 100
40 km/h and 80 % Vmax
(if the resulting speed is ³ 55 km/h)
100 < Vmax £ 150
40 km/h, 80 km/h and 80 % Vmax
(if the resulting speed is ³ 100 km/h)
150 < Vmax
40 km/h, 80 km/h and 120 km/h

5.2.6. the test instrumentation used for measuring the true vehicle speed shall be accurate to ± 0.5 per cent;

5.2.6.1. the surface of a test track when used shall be flat and dry, and provide sufficient adhesion;

5.2.6.2. if a roller dynamometer is used for the test, the diameter of the roller should be at least 0.4 m;

5.3. The speed indicated shall not be less than the true speed of the vehicle. At the test speeds specified in paragraph 5.2.5. above, there shall be the following relationship between the speed displayed (V1 ) and the true speed (V2).

0 £ (V1 - V2) £ 0.1 V2 + 4 km/h

[tassie jeeper]

http://en.wikipedia.org/wiki/Speedometer#Australia

after 1 July 1995 (or 1 January 1995 for forward control passenger vehicles and off-road passenger vehicles) must conform to the previous Australian design rule. This specifies that they need only display the speed to an accuracy of +/- 10% at speeds above 40 km/h, and there is no specified accuracy at all for speeds below 40 km/h. All vehicles manufactured in Australia or imported for supply to the Australian market must comply with the Australian Design Rules.
[8] The state and territory governments may set policies for the tolerance of speed over the posted speed limits that may be lower than the 10% in the earlier versions of the Australian Design Rules permitted, such as in Victoria.[9] This has caused some controversy since it would be possible for a driver to be unaware that he is speeding should his vehicle be fitted with an under-reading speedometer. [10]

[303zuke]

joel wrote:

303zuke wrote:

tassie jeeper wrote:

according to ....... blah, blah, blah..........my tyres are 9.26% bigger than standard and my speedo will be out by the same

Not at all true, as there is almost zero possibilty that your speedo is 100% accurate with stock, factory tyres. According to ADR 18/03, when your vehicle is travelling at an actual 100 km/h your speedo is permitted to show anything between 100 to 114km/h. To avoid liability issues (ie driver's getting speeding tickets when an inaccurate speedo makes them believe they are under the limit), car manufacturers will invariably design their speedos to show the vehicle travelling at higher than actual speed.

Fitting larger tyres will sometimes bring the speedo closer to reading accurately, but accuracy should always be checked by other means than relying on just the speedo.

not sure where you plucked that much variation from, but i can assure you that is well above the prescribed acceptable limit, even by territory standards.

How can you assure any such thing? What do you think is the prescribed acceptable limit? Perhaps the NT runs it own separate system to Aust Design Rules that the vehicle manufacturers make different speedos to the rest of the country?
The speedo CANNOT read less than the actual speed, but the upper limit is 10%+4km/h, so at 100km/h the speedo is permitted to read 100+10+4=114km/h.

Here's the ADR:

http://rvcs-prodweb.dot.gov.au/files/ADR%201803.pdf

[303zuke]

tassie jeeper wrote:

http://en.wikipedia.org/wiki/Speedometer#Australia

after 1 July 1995 (or 1 January 1995 for forward control passenger vehicles and off-road passenger vehicles) must conform to the previous Australian design rule. This specifies that they need only display the speed to an accuracy of +/- 10% at speeds above 40 km/h, and there is no specified accuracy at all for speeds below 40 km/h. All vehicles manufactured in Australia or imported for supply to the Australian market must comply with the Australian Design Rules.
[8] The state and territory governments may set policies for the tolerance of speed over the posted speed limits that may be lower than the 10% in the earlier versions of the Australian Design Rules permitted, such as in Victoria.[9] This has caused some controversy since it would be possible for a driver to be unaware that he is speeding should his vehicle be fitted with an under-reading speedometer. [10]

The ADR has been updated from 2004, I wouldn't rely too much on Wikipedia. There is no +/- tolerance. The speedo can't read less than actual speed in any circumstance, but can read 10%+4 km/h over.

[tassie jeeper]

303zuke wrote:

The speedo CANNOT read less than the actual speed, but the upper limit is 10%+4km/h, so at 100km/h the speedo is permitted to read 100+10+4=114km/h.

tassie jeeper wrote:

Speedometers are manufactured to be accurate to within 15% which is a pretty big margin and will most likely show u to be traveling faster than u actually are

[303zuke]

tassie jeeper wrote:

Speedometers are manufactured to be accurate to within 15% which is a pretty big margin and will most likely show u to be traveling faster than u actually are

So before Joel jumps in, where do you find the 15% figure? The ADR clearly says up to 10%+4km/h.

Most likely? Absolutely definately will show you to be travelling faster than you actually are.

[tassie jeeper]

303zuke wrote:

There is no +/- tolerance. The speedo can't read less than actual speed in any circumstance, but can read 10%+4 km/h over.

this is nice to know however it is irrelevant to my initial point which was to show users that by entering their tyre dimensions into the above calculator they could determine how much their speedo reading would have changed from its stock accuracy. (i mean no disrespect by this comment) just trying to show my initial intention

303zuke wrote:

tassie jeeper wrote:

Speedometers are manufactured to be accurate to within 15% which is a pretty big margin and will most likely show u to be traveling faster than u actually are

So before Joel jumps in, where do you find the 15% figure? The ADR clearly says up to 10%+4km/h.

10%+4km @100km = 14% by stating 15% i was simply rounding off

[Samwich]

tassie jeeper wrote:

303zuke wrote:

tassie jeeper wrote:

Speedometers are manufactured to be accurate to within 15% which is a pretty big margin and will most likely show u to be traveling faster than u actually are

So before Joel jumps in, where do you find the 15% figure? The ADR clearly says up to 10%+4km/h.

10%+4km @100km = 14% by stating 15% i was simply rounding off

Its not even 14%.... From what i can read as per 303zuke said... its 10%+ 4km/ph at any speed. Not just 100km/ph (which was the example)

So.... 14% and 10% + 4kms/ph are completly differnet at other speeds other then 100km/ph?

So you're still wrong?

[tassie jeeper]

Samwich wrote:

Its not even 14%.... From what i can read as per 303zuke said... its 10%+ 4km/ph at any speed. Not just 100km/ph (which was the example)

So.... 14% and 10% + 4kms/ph are completly differnet at other speeds other then 100km/ph?

So you're still wrong?

ur right its not even 14% but then at 120kms it would be out by 16kms (MORE THAN 15%)
like i said i was being rough the whole point of the thread is to give a rough indication of show how much the speedo read out will change from stock size tyres no need to nit pick at every single detail FML

[atari4x4]

welcome to the interwebs

[tassie jeeper]

atari4x4 wrote:

welcome to the interwebs

tell me about it everyone has an agenda

[got_bar_work]

Non of this matters because if u have larger then stock tires u should have it recalibrated
mines like 2% out at 110 with 31 treps acording to my cert

[Teracis]

If you have an electronic speedo this should be able to sort out the issues. http://www.jaycar.com.au/productView.asp?ID=KC5435 I'm about to order one (if I ring the store and they don't have any) so that I can run the stock tyres or larger ones when heading out and still have a reliable speedo reading. It should be pretty easy to note down the numbers required for each tyre size and change the switches in the box to suit.

[ozhummer]

At the end of the day try telling the police who have just pulled you over for doing 110 in a 100 zone that your speedo read 100 and is ADR compliant cause it's within the 14%.. I think he/she will say, thats nice - here's your ticket and prob give you a defect too and you will need to pay to have the car tested to proove it meets not only ADR but state laws too. Remember, there are VSB's (Vehicle Standards Bulletins), and state rules that override ADR's - I am pretty sure there is a VBS that states the accuracy of a speedo for a motorvehicle must read no higer than 10% actual but must not read less than actual - ie at 100 kph true speed your speed can ready from about 90 to 100, no less and no more ....

[tassie jeeper]

ozhummer wrote:

At the end of the day try telling the police who have just pulled you over for doing 110 in a 100 zone that your speedo read 100 and is ADR compliant cause it's within the 14%..

point is my speedo is out from factory setting by about 10% so at 100kms its out by about 10k so on the highway i sit on 90 and around town i sit on 55 then u dont have to have a chat with the boys in blue, if u do have a chat with them dont bother arguing with them, for 1 your speedo is not accurate and 2 90% of police officers have a superiority complex which was taught to them in academy and i wouldn't piss on them if they were on fire. the only laws they inforce are the ones they gain revenue from