Tyres - How big can I go?

Submitted: Tuesday, Jan 24, 2012 at 12:25

ThreadID: 91426 Views:6062 Replies:2 FollowUps:1

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Tyre Size Calculator

Use this page to work out the radius, circumference and diameter of any size tyre. You can also run comparisons between different tyres and work out the differences in size and odometer corrections.

Patrol GU VI

I am looking at getting a spare set of tyres for my '08 GU Patrol for offroad use. I currently have a spare set of the factory 17in Wheels that I can use, but am also happy to sell them on eBay and buy some 16in rims. I also have a 2in Old Man Emu lift.

Some questions I have are:

- What size tyre can I go up to? Are 35's too big with only a 2in lift?

- Is it better to stay with the 17in rims or replace them with 16's?

- I also have read about rims with offsets. What exactly does this mean, and what impact does it have on things like tyre wear, balancing and handling?

- How do you convert the metric tyre measurements (e.g. 285/70R17) to the imperial measurements (e.g 33x10.5-16)

A number of questions I know, but assistance is appreciated.

p.s. I have also posted this question on the Patrol4x4 forum as well.

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Reply By: MrBitchi (QLD) - Tuesday, Jan 24, 2012 at 13:24

Tuesday, Jan 24, 2012 at 13:24

Here's a Converter..

http://www.redrock4x4.com/tireconversioncalculator.html

Legally you can only be 15mm larger than standard for on road use.

AnswerID: 475881

Reply By: Robin Miller - Tuesday, Jan 24, 2012 at 13:33

Tuesday, Jan 24, 2012 at 13:33

How big can you go with 2 inch lift - 33 comfortably.
You can go bigger but rim offsets can be needed.

Legally depends where you are , I refer to Vic.
Most only allow 15mm bigger than standard , but the definition
of standard varies. Most think its the compliance sticker ,
however it actually means bigger than biggest fitted to that
model car.
In GU handbook one version uses much larger 245/85/16 tyres and
15mm bigger that technically allows you to go 33's.

Also you have to consider how wide , not just big.

I have several sets for my GU and like narrow tyres , so I use
whats called 34inch or 255/85/16 which are available in BFG KM2.

These just scrap on the dumb front mudflaps when turning , however
the mudflaps can be re-worked easily to push rearward the mount blot.

If I had wider ( 285/75/16) they touch on the inner guard.
To prevent this I use 6mm offset spacer plates with that set.

Go 16inch steel rims if you can as it makes it easier to lengthen the footprint
and belt them back into shape.

OFFSET - relates to where the wheels touch the discs.
Negative offset means the outside of the wheels sticks out further, wider track.

Rims come in different offsets - I use 7in Trak 11 steel rims which have
a 10mm negative offset , standard Alum wheels tend to have zero offest.
(These rims weigh 4kg each less than 8in steels, and 1kg more than standard.

Issues
1/ when you fit larger diameter wheels you raise the cars centre of gravity
and even Patrols eventually fall over so to compenstate having the wheels further apart (negative offset) helps.

2/ The diesels have trouble turning bigger wheels, so engine mods/tranfer case re-gearing are best, espically if an auto.
4800's no issues with power.

3/ Big offsets , big tyres, heavy rims are hard on wheel bearings and hard on fuel use.

Conversion example
255/85/16 means tyre diameter is 255X85= 217mm
217mm X 2 = 434 mm
434mm + rim of 16 inches(407mm) = total of 841mm

841mm = just over 33 inches