Thread: Changed your wheels or going to? Read this first.

now there's an idea, I think i'll hang on to my old tyres incase it needs to get measured

[quote=DEFENDERZOOK]

Originally Posted by p38arover

Rolling diameter is slightly less than the diameter of the tyre when infaltged to normal operating pressure. The weight of the car will balloon the bottom of the tyre thus causing this reduction.

Ron

<span style="color:blue">irrespective of what a tyre is infaltged to.....they measure everything without the weight of the car pressing down on it.....or measure from the top.....



it will also be affected by the tread wear......
most 4wd tyres have upwards of 10mm useable tread....most are around 17mm of tread.....</span>


Infaltged

Isn't that the measurement of pressure difference between cold tyres and hot tyres?



Cheers
Simon

Hi,
Humm sorry to put a dampner on things but all this is going to change in the near future. the National code of pratice is about to change.

in short if appoved we will be able to breath a bit better

ps all the measurements are done on paper, not the tyres themselfs regardless what pressure is in it

Originally posted by abaddonxi
Infaltged

Isn't that the measurement of pressure difference between cold tyres and hot tyres?

Nope! That's what happens when you pour red wine into an airhead! ops:

Ron

Originally posted by downundersteve
I thought this was useful to know, OK you might know it already but I didn't.

From Licensing office:
Rim width must not exceed the maximum rim width specified by the manufacturer by more than 25mm (1")

The wheel is contained completely within the body work of the vehicle which includes acceptable flares.

Rim diameters must be the same as specified by the manufacturer.

The track must not be increased by more than 25mm (1") over the maximum specified by the manufacturer.

Reducing the wheel track less than the original manufacturers specification is not permitted.

my rangie fits all the above criteria

I'm afraid that most people with 4wd's are probably running illegal tyres.
The national regulations (except Tassie apparently), specify no more than 15mm diameter over what is on the placard. This is the rim INCLUDING the tyre. It has absolutely nothing to do with rolling diameter.
Take for instance Discovery Series 2 :
Tyre Placard states standard tyre is 235-70-16.
This means
Step 1 - convert 16 inches to mm = 16X25mm = 400mm
Step 2 - convert Width as a percentage of sidewall height = 235X70% = 164.5mm (which is theoretical edge of tyre to rim). As there are two sides of the rim, you need to multiply this figure by 2)
Step 3 - Arithmetic! Sidewall height(X2) + rim = 164.5X2 +400 = 729mm

If you factor in the above maths for common tyre upgrades for Disco's, this is where the problems begin.

Assuming 245-70-16's , 171.5mm X2 + 400 = 743mm. This is 14mm over standard which is theoretically legal.

Many people are using:
245-75-16's = 183.75mm X 2 + 400 = 767.5mm. This is technically illegal as it is 38.5mm over standard.

These are the tyres I would like to get, but come an accident, insurance will tell you to pi$$ off if you have oversize tyres. That being said, I really hope these new regs come into effect soon.

The figures quoted above are mathematical only, and don't (and cannot) take into consideration tread depth, wear etc. If an insurance company wanted to be picky, they would do it mathematically, rather than prove that BFG 235-70-16's are bigger than Toyo 235-70-16's.

Cheers everyone.

NSW RTA says 15mm diameterincrease is maximum. Now my muddies have 20mm of tread, when they wear down by half to 10mm, that is a 20mm change in diameter, and when they are totally worn, say to 5mm left, thats 30mm change in diameter. So with my bigger than standard tyres, if any one complains, I'll say I'm just wearing them in

Originally posted by Grimace+--><div class='quotetop'>QUOTE(Grimace)</div><div class='quotemain'><!--QuoteBegin-downundersteve
I thought this was useful to know, OK you might know it already but I didn't.

From Licensing office:
Rim width must not exceed the maximum rim width specified by the manufacturer by more than 25mm (1")

The wheel is contained completely within the body work of the vehicle which includes acceptable flares.

Rim diameters must be the same as specified by the manufacturer.

The track must not be increased by more than 25mm (1") over the maximum specified by the manufacturer.

Reducing the wheel track less than the original manufacturers specification is not permitted.

my rangie fits all the above criteria[/b][/quote]

I'm not fussed either way, mine was done with the assistance of an engineer. OK I didnt get it approved but that neither here nor there!

Its safe, reliable and enjoyable!

And the local copper(s) like the vehicle, often spoken to them at great length and they like it! And never has one even said a thing about the questionable front plate mounting 8)

Cheers
Mike