50mm 4wd tyre diameter increase

try here.
http://cgi.ebay.com.au/Betty-Boop-BlueThick-Shoe-Laces_W0QQitemZ6223745296QQcategoryZ13660QQrdZ1QQcmdZViewItem.
cheers

Last seen in the mouth of a rather large marsupial :)))))

I think you'll find your shoelaces in the same place as your t-shirts.

In the bit bucket :)

Have a look at the wheels and tyres section of the draft code of practice for light vehicles which is open for public comment at the moment. You will find it at www.dotars.gov.au. One thing you need to keep in mind is the bigger tyre/wheel diameter you run the less brake efficiency you will get for a given size disc or drum brake assy.

Not so sure about the braking thing. Aren't the same size brakes still slowing down the same size vehicle???

Phil

Bigger wheels - worse the braking. Thats why a Braking test is done to get bigger tires engineered.

Yeah, I've seen it somewhere that you should stay within 3% of the original diameter??? or you risk the possibility of brake failure.

The reason the brake efficiency reduces is because the lever effect increases.The distance from where the tyres contact the road to the centre of the axle increases so it makes it harder for the brakes to stop the vehicle.

I don't think that most people who want to put bigger wheels on their 4WDs would be happy with one profile size. 4% will create a very small height difference. When you look at the number of 4WDs running 33's and 35's with a slight body lift, they would be most miffed with one tyre profile size increase.

From my point of view, as long as I can purchase a set of serious off road tyres in the legal size, I am happy with that. The problem has been and still is to an extent that the newer sizes come as car type tyres and there is nothing in the way of a tough tyre that could safely go on an outback trip. To get a decent tyre, you usually have to go up a couple of sizes and they are more than 15mm larger in diameter.

4% would allow most LandCruiser and Patrol owners to run 285/75/16 and Prado/Mitsubishi owners etc to run 265/75 or 235/85R16. These 3 sizes are the best for outback travel.

If people wanted to go bigger than 4% then I reckon its up to them to get it engineered. People with bigger tyres than that are either show ponies or weekend warriers - its not a necessity.

Phil
1) not everyone is into outback travel.
2) that are either show ponies or weekend warriers: so what would they call you?

Having done these calcs for a 2005 GU, I can suggest that 265/75 16's are the max legal size offering a 14mm height diff. 285/75 16's make a 44mm diff, comparing to the stock 275/65 17's. Even looking at the 44mm diff, I assume this only equates to a clearance gain of 22mm, as the other 22mm is on the other side of the tyre. Not a lot really, the real gain is in the durability of the tyre assuming you are buying good quality off-road tyres.
A good site for comparing wheel sizes to calc OD increases and speedo errors is http://www.1010tires.com/TireSizeCalculator.asp?

Neetas.

The question is though : Is it ACTUAL measured size of the tire - OR the marked side of the tire?

There are threads on several forums asking this.

EG: some 285/75's are 10mm different in MEASURED size to others. As are other sized tires. Some 33's measure 32actual

Surely there must be a variance for tyre brand of +/- x%. It could be as high as 3%.

What about depth of tread in your calcs.
Most new tyres I have seen have 9 to 13mm of tread, some MTs more.
Coopers being one that offers extra tread depth.
They may have to look at offering less tread depth to stay legal :-)

I think this is getting all too hard.

Pump your tyres up hard and you most probably gain 5mm over standard road pressure.
Let them down to 20 psi and you must loose about 15mm.
Will the authorities confirm at what tyre pressure these measurements are done at if it is the true dimension?

I think it has to be worked on tyre placard size, rather than actual size.
Could be a few stretched tape measures otherwise :-)

"Really officer, my 285/75 16 tyre are under 32" OD, look what my tape measure shows!" And measure on the spot.

One profile difference is fine for the many drivers who are stuck with a tyre size that doesn't have any light truck construction or mud tread options! e.g Pajero - 265/70R16 - try finding a legal mud tyre, and the only AT option in LT in that size is the BF Goodrich AT. Tyre manufacturers just don't want to cater to this size unless it's passenger construction - even Cooper STs are passenger construction in this size.

Truckster said
" 1) not everyone is into outback travel. "

Couldn't agree more - my reference was purely in response to Sky Pilot's who stated that bigger tyres were needed for safe outback travel - which I don't think is the case.

And what would they call me?? I'm sure you can come up with something :-))

Cheers
phil