Vehicle Regulations

[Aussie Frontier]

Stock tyres on a D40 were 255/70/R16 and the speedo would read approx 10km low at 100kmph.By installing 265/75/R16 the speedo is almost correct.The speedo is only reading revolutions per minute so if the rpm of the rear wheel is 100 at 100kmph ( hyperthetical numbers) then the larger the dia of the tyre then the higher the actual speed of the vehicle.
Below is the calculator from 1010Tires that shows actual speeds and rpm of the differing sizes.

 

[superiorcruiser]

Stock tyres on a D40 were 255/70/R16 and the speedo would read approx 10km low at 100kmph.By installing 265/75/R16 the speedo is almost correct.The speedo is only reading revolutions per minute so if the rpm of the rear wheel is 100 at 100kmph ( hyperthetical numbers) then the larger the dia of the tyre then the higher the actual speed of the vehicle.
Below is the calculator from 1010Tires that shows actual speeds and rpm of the differing sizes.

hey Maddogrc,have a look at the chart here...second last line,it says....speedo TOO SLOW....
Thank you..

 

[superiorcruiser]

Thanks for the chart Aussie Frontier,i know my speedo is out so i just sit on 95kms by the speedo and im on the speed limit..
no need for GPS,etc..
just couldnt get thru to Maddogrc about it reading too slow...

 

[maddogrc]

i know that running bigger tyres past the point of perfect tyre size makes the speedo read under...

i've always been saying that it i would expect it to be EQUAL 100 real and 100 speedo with only 2" difference vs 100 speedo and 105 real which is reading UNDER.

on the page back its this guy saying bigger tyres make it read higher:
quote:
Everyone i know who have upgraded tire size, all their speedo's read higher than actual speed, so dont know how it could read lower....
:end quote

like i said on the last page, i'll quote it...
for everyone else the speedo reads OVER what they're actually doing
yours is reading UNDER compared to everyone else

i also stated my observation...
quote:
i think its weird that going up 2 inches causes the speedo to be out by 10km/h instead of correcting itself to 100km/h real speed and 100km/h on the dash
: end quote

its 10km/h out because the stock tyres usually do 100kmh speedo and 95 real, i'm very surprised that only 2" difference would make it 100kmh speedo and 105 real, thus you're doing 10km/h more then you usually would.

stocko's read OVER
tyres past the point of perfect size to make equal speedo and equal real speed read UNDER

on my navara i had stock 195R14, not sure of that in normal configuration, and those ran so the speedo was OVER what it was really doing, i then put on 225/75R16 and the speedo ran perfectly. how do i know perfectly? cop said i did 110 and i was doing 110 on the speedo haha. its ATLEAST 2" bigger or more then the stock tyre so thats why i find it so hard to believe only 2" on the 4wd navaras make a huge difference where i did at least over 2" and got it on the sweet spot.

 

[Old.Tony]

Guys, can I point out the obvious here ... if you change tyre sizes, the important thing that also changes isn't the speedo - because that's inaccurate anyway and if you want accuracy, you should use a GPS - but it's the odometer that is out.

With stock tyres, my odometer reads near enough to perfect over those odometer check lengths. The speedo inaccuracy is all because of the needle itself. If it were a digital readout it would be really close to the mark.

With larger tyres, my axles will do less turns for the same distance, so the computer will think I haven't traveled as far - it will come up showing less km than I've actually traveled.

 

[MICK69]

mine is the same to do 100 i sit on 95 its the other way round with smaller tyres when i had 245 think they were 70s i was doing 95 when speedo read 100 that was with gps

 

[Brett 76]

Regulations in WA

Back to the topic at hand. Just a quick question while we are talking about WA regulations.

Did anyone manage to get info for WA about a body lift on a 4wd with a srs drivers side airbag? Or will i need that engineers cert?

Brett

 

[maddogrc]

body lift on an airbag vehicle is off the cards mate

 

[Brett 76]

body lift on an airbag vehicle is off the cards mate

Gah, no biggie i guess..

Cheers.

 

[maddogrc]

airbag = big safety deal with impact sensors, rah rah.

body lift moves the sensors from the standard location/set height from the factory and so if you had a crash they may or may not trigger (most likely would though), but yeah, the government doesnt approve.

you can do up to 150mm high body lifts, but thats only on non-airbag and still need an engineering cert.

rule of thumb to keep safe and not obvious from the police:
2" tyres
2" suspension
2" body lift (but i only recommend on non-airbag cars)

body lift is really only for clearing bigger tyres, and 2" bigger then stock shouldnt cause you any troubles cept an 'out' speedo.

 

[greesie]

Hey, had a pretty good read through hear, I have 1 inch bigger tyres and going to get a 2 inch lift, makes it 3 over standard, so that more than 2. Does this mean if I Get an engineers cert for my suspension lift and the larger tyree that my car will be fine insurance wise? And do I need to grt over pits or do lane change test since it's suspension lift not body?
Were in Perth does eng certs?
Do you rekon it'd be likely insurance would give me greif for only 1 inch over the alloud modification limit?

Cheers and sorry for so many questions haha

Mike

 

[Lasoya]

Anything over 2" from standard requires engineering, and yes lane change is required when engineering lifts over standard limit. Once engineered needs to go back to pits as far as im aware and they need to sign off on it....

 

[greesie]

Ah I see, cheers for your help mate, alot of dollars to be spent for a small amount of lift....bloody strict rules in aus,

 

[Old.Tony]

I'd be checking with the motor registry technical department for your state, first.

Increasing the wheel diameter is not technically defined as "lift". "Lift" is increasing the distance from your axle centreline to the underside of your vehicle.

Your wheel sizes are governed by a different section of the legislation. That being the case, you could increase tyre size and do a body/suspension lift and it wouldn't need to be tested - but please check first, because all of the states seem to want to do it differently.

 

[greesie]

yeah, thats true, also wheel diameter is from top to bottom...so them being 1 inch larger means only lifting axle half of increase in tyre size...so really only about 1/2 inch higher. Will definatly be chasing that up, cheers Old.Tony!

 

[nav]

so intofacto, if i want the 2 inch bodylift, ontop of my already 2 inch suspension....i have to get an engineers cert. which will then require me to organise a lane change test and all of that. so im lookin at like 600 for the cert, then like another 400 to organise the lane change test overall ???
just wanna know the coin before i go ass over tit with it
if anyone can verify this...greatly appreciated

 

[greesie]

Hey mate this is the exact email o got from an engineer in Perth when I was looking into it-
Hi Michael,
You email crosses over a few things.

DOT WA may require certification from the vehicle manufacturer
that the air bag and suspension ADR are not reduced. Not Navara
I don’t think.

4x4s , if they pass a lane change test can have 50 mm increase diameter
over original tyre size as written on the tyre placard. The diameter is in
the Tyre & Rim Association book. Multiply the width from that book
by 1.5 to get the width. The tracks are recorded also and add 50 mm to
those for maximum.

Any lift over 50 mm has a lane change test.

Looks OK from what you have said.

Put $1000 aside for to allow for things.

Regards

Rod Style

 

[nav]

cheers greesie
so with the 265/75 mtzs i got on im pretty sweet with them, so im pretty much maxin it out with the 50mm of my suspension.
i gotta get written certification from nissan to say it wont affect the operation of airbags and sensors.
n then give it to engineers for pits n lane change.
and in the lane change i have to organise all of that shit myself ey ??
alot of shittin around aha

 

[greesie]

No worries mate, found this email is abit better.
Hello Michael,
Put in the application to DOT WA for the lift and see if they include the Nissan requirement
about airbags. If they don’t forget it.

Then install the stuff.

I get a copy of the application and the DOT reply letter, then do an inspection with the
necessary checklists. If it is OK then the lane change test.

No vehicles have gone over a $1000.


We can design and calculate and simulate the suspensions, but the lane change is used on
every new vehicle built in the world for the mass market because that is the only safety
test proof.

If your vehicle fails, that is the driver won’t go at 110, then you are not safe in the vehicle
with that suspension lift/tyre combination.

Your vehicle will pass with some lift kit/tyre combination, this test will find which will
have you safe on the road.

Regards

Rod Style


Hope that helps ya bud, if ya interested can also give ya his email

 

[greesie]

Yeah alot of shittin round, but they look pretty trick with 4 inchs of lift and big tyres haha