Hi from sunny South Africa!
Herewith a post I did on a local 4x4 forum, regarding the T3 tire size.
"Though I'd also give some more detail on tires, as this was quite the mission to decide. The purpose was for me to get as good a all terrain set of rubber on the Treg as possible. This also meant that I needed to get as much sidewall height as possible, to make use of deflated tires in sand and other conditions, while loosing as little ground clearance as possible. The smallest rim size that will fit the V8 TDi, is 18", due to massive front brake callipers. There are no aftermarket wheels available for Treg here in ZA, that has the correct PCD (5/130), right offset to clear callipers and also load rating that will take the vehicle weight and punishment of off-roading.
Looked at VW options, but one 18" wheel would cost in the region of 8000 to 9000 ZAR! In no scrap yard, could I find anything either. Next stop was Porsche, due to Cayenne sharing same platform as Touareg. Here there is a second hand market for wheels, but shop around! It took a lot of searching and phoning, to get a set that was well priced - ended up forking 6000 ZAR for set of 4, with minor scratches - had them refurbed nicely for around 1500 ZAR. I then quickly realised I needed a 5th wheel, if I wanted a full size spare. Long story short, I had to get another set of 4, as nobody wanted to break up a set! Now I sit with 3 extra, hahaa.
That sorted the wheels. Tires was another time consuming research exercise. I looked at all the major (and minor) brands locally, did comparisons on speed rating, load rating, sizes for width, overall height, rolling circumference and naturally reviews - got a very detailed and long excel sheet that documented all possibilities. Settling on 2 size options in mind to maximise the wheel arch space without rubbing, it came down to two Cooper tire "models", that passed all the tests for speed, load, size and review ratings. Autoquip in Alberton was very helpfull in helping me source the first set of rims, but then also ordered all the tires I wanted to test fit! The end of it was, that the Cooper Zeon LTZ was my choice, in a 285x60xR18 size. You will see in the attached images, how well these display! I was really impressed wit these tires on tar (wet and dry), but more importantly off the tar. Road noise is also not a problem - slightly louder than normal tires, but probably also due to good noise insulation of Treg. Road holding on dirt roads was very good, even up to 150 km/h (good Namibian dirt roads), traction in mud, sand, rocks, also very good. Though I must admit, I dont have a reference of any other AT tire on the Treg, but surely had no issues in any conditions.
With the increase in rolling circumference, watch out for speed. The Treg is generally very close to true speed (according to Garmin). True speed is around 1 - 2% lower than speedo with normal tires, at 100 km/h. With the Coopers, true speed is about 6% over clock reading. This bothered me a bit in the beginning, as I was not sure how it would affect gear ratios and essentially power at the wheels, consequently affecting its hill climb capability. This was very quickly put to rest during the trip, as I did not have any problems with steep climbs, thick sand etc.
There was very minimal rubbing to wheel arches during sharp turns in sand, where tire flexed inwards while turning in thick sand and while deflated to about 0.8 bar. There was admittedly one small "modification" I had to make. The nut protruding from the upper whishbone, did slightly catch the tire on the edge of the inner sidewall (front only). I cut the 5 mm that was protruding from the locknut, and all was sorted. As the wishbone moves up and down with tire, there were no more issue and it was a very easy fix. If you dont like this option, I can suggest the Cooper Discoverer A/T3, 265x60xR18. I tried this one as well, plenty clearance, but sacrificing bit of width and sidewall height."
Attached some photos of the wheels fitted and in action in Namib desert