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I would run the 31x10.5 tyres. They are they same diameter as the other tyre and they both air down to provide a footprint length which is the same, but wides provide more floatation as the skinny tyre due to lower ground pressure. Wides also provide more stability as hey don't move around as much. You will notice all sand specific tyres are wide. That said, both will be fine for Frasers sand, but do air down and drive sensibly.
Thanks again guys. GuyG - that doesn't sound very good, does it. Maybe I should reconsider (but the family is all excited about it now :( )
Slunnie - I'll be taking it extremely carefully wherever I go, as my wife has severe osteoporosis so I was considering being the last car in our little convoy so the others could warn me of obstacles, washouts, etc. Also, my 7.50R16's are definitely a good inch larger in diameter than the 31x10.5R15's. I've measured them both off the car. I know it's stuff all and I guess it won't make much difference which one I use in the end as it'll mainly be the pressure that determines the ease of driving. :)
Sorry didn't mean to put you off, its not all rocks, just at the couple of bypasses. Theres a couple of photos in the GCLRO general thread from when I went up there. The beaches change so quickly up there, the rocks could easily be covered when you arrive:). The white coffee rock was just north of Dundaburra, exposed when I went up but was covered when I came home, admittedly there were a few weeks between, but also means that close to 2 foot of sand had moved to cover them. Its all part of the experience, you don't really want it to be the same every time you go.
In my experience most 31's are closer to 30.5 and standard defender are towards 32".
Your wife's osteo brings a whole new dimension into it and probably overriding factor for tyre choice. 7.50s are generally quite stiff tyres.
Thanks gents, after you commented GuyG I had a look on Dr Google and found this map of Fraser with apparent problem spots. Everyone still seems keen (even the Minister of War) so it looks like a goer. Thanks for the advice Slunnie re the 7.50s; both sets of tyres are looking like this'll be their last trip so maybe I'll try the 31x10.5s, eh? (Sounds like I'm confused doesnt' it?)
cheers Gerald
Didge,
As per the earlier posts, I'm afraid I have to differ with Slunnie. It's a complete myth that the wider tyres gives you more floatation and it really shouldn't be your reason for your final choice.
The only thing the "stiffer" sidewalls will add is more security at lower pressures as the sidewall will bulge less. You will however have a significant longer footprint which will both be more comfortable and significantly better in the sand.
Enjoy the holiday and take plenty pictures.
Cheers,
Lou
Thanks Loubrey, so with stiffer sidewalls I'm going to get a longer footprint and given enough deflation a reasonably soft ride. That right?
Hi Didge,
Short answer - yes. The weight of a loaded Defender makes any sidewall pliable enough to have a comfortable ride at lower pressures. The larger diameter will in turn give you the longer footprint you need with the resultant good sand performance.
Cheers,
Lou
Lou, you did say in your first post the best Defender tyre would be a 255 75 16 but my 31x10.5R15's are 215 wide so only very marginally wider whereas the 7.5R16's are only 165 wide (5.5 inches - cheese cutters).
Just accurately measured the tread faces and that's what they are as noted above. I did think the 10.5's would be 265 so was quite surprised the total difference in width is only 50mm. I guess it the width combined with the extra height that makes the 7.5R16's look so skinny.
Just had a look at some tyre dimension pics that show the "Loaded action width: being the deformed width of the tyre where it touches the ground and the section width ie 10.5 in my case at the total width of the tyre from sidewall to sidewall. So, given the extra height and minimal width difference it looks like the 7.50s are the go.
cheers Gerald
Gerald,
Just a personal thing, but I'm not fond of any wheel size other than 16" on a Defender. The 255/85/16 has such a large rolling diameter that the resultant soft footprint is immense compared to most other profiles and dimensions.
Like I wrote before, the width plays a very very small part in sand performance (other than actually hinder you if too wide) and the only real consideration is the physical diameter measurement (tread to tread across the hub) to determine low pressure footprint and performance.
Even if there were more difference in the width, I would still have taken the 7.5's.
Cheers,
Lou