Master
SupporterMy current project is a SIII LWB "toy", which will be used around the farm and for off-road playing, as well as occasional trips to town etc. I was planning on fitting it with 235/85R16 tyres, as for a long time that was the largest tyre I could legally fit under the NSW +15mm diameter rule.
However..... Looking at the RMS website, I have found VSI No. 6 which describes the requirements for engineering certification of modifications to a light vehicle. It makes interesting reading generally, but of particular note is the tyre section which states a requirement for certification of:
"Replacement of tyres that change tyre overall diameter by more than 7% of the overall original diameter"
It also gives an example of a tyre with an increase of 26mm (4%) not requiring certification. This is different from other RMS documentation that states the +15mm diameter rule, or did only a couple of months ago when I last looked.
It means that a 255/85R16 tyre is now a legal fitment on a vehicle that originally had 7.50R16's (by about 1mm!!).
255/85R16 gives a 6% increase in high range gearing, quite useful because I can't fit an overdrive (PTO winch). The increase whilst in low range is not a problem, a change of cogs means my transfer box already runs lower than standard, +6% from tyres and I'm still lower than normal.
My concern is whether the increase in width will have a significant impact on the steering effort or handling. Going from 7.5" (190mm) to 235mm doesn't seem to be too much of a struggle (though that's comparing different vehicle from memory), so will another 20mm create problems? Because this is a toy, I'd be looking at muddies so there's less rubber on the ground than with AT's which should reduce the effort.....?
Does anyone run 255/85's? Do they work? I've read about people happily running 265's, which would suggest that 255's should be OK.
Thoughts?
ForumSage
SupporterMy thought is that heavy steering is only a problem in car parks.
My LWB Series III had the usual 750x16 tyres and I never noticed the steering being particularly heavy once the speed got above walking pace.
However, it usually seemed to require a significant amount of driver input when I was parking.
1973 Series III LWB 1983 - 2006
1998 300 Tdi Defender Trayback 2006 - often fitted with a Trayon slide-on camper.
Wizard
31 x 10.5 x 15 is the size that came standard on the Games so the same width as a 255. They have a +15 offset wheel though rather than the +33 or so that seems to be standard. This could be why they have flares as well. Definitely hard to steer when parking but fine any other time.
I have some 0 offset 16" wheels with 235/85/16 and they fit nicely on the Game with the flares and are just, maybe, 100% legal on the S3 109 Trayback ute I have. Basically unless you move the offset out you will reduce the turning circle with the wider tyres and you may need flares once you do that. I found these rims and tyres give a much better turning circle and therefore a better driving experience than the 31x 10.5. Much better on tight trails to have some turning circle.
Cheers,
TimJ.
Snowy - 2010 Range Rover Vogue
Clancy - 1978 Series III SWB Game.
Henry - 1976 S3 Trayback Ute with 186 Holden
Gumnut - 1953 Series I 80"
Poverty - 1958 Series I 88"
Barney - 1979 S3 GS ex ADF with 300tdi
Arnie - 1975 710M Pinzgauer
Master
SupporterI agree that a smaller turning circle is good, but tyre size and offset don't affect turning circle directly (other than by the change in distance between the outside edge of the tyres!), so I guess you're talking about the need to change steering stop?
I haven't made any measurements to see what will physically fit on the vehicle, but it's a military chassis so I have a bit more height at least than the standard LWB.
Reducing the positive offset will increase steering effort in addition to any increase from the wider rubber, so I suppose it comes down to how much of a reduction is needed to fit the tyres under the guards! I have a set of Wolfs (+20.6mm) that might be a reasonable compromise......
The attraction of the 255/85 is the taller gearing, rather than the width!
RoverLord
Well, if you don't adjust the steering stop you'll get a nice polished patch on each spring, lose the knobs on the inside of your tyre, and still have a lousy turning circle. Probably acceptable on an 88, but a serious problem in a lot of circumstances with a 109. The military chassis does not affect this.Originally Posted by Warb
John
John
JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol
ChatterBox
I was using 32x11.5R15 AT's with +0 offset on my 109, didn't adjust steering stops, although there was a shiny spot on the rear part of the guard just above the chassis.... I also had an LSD in the front with no freewheeling hubs, was heavy to steer at low speed but doable...
When I went back to 31x10.5R15's I was disappointed with the lowering in gear ratios. It did steer easier but I felt that it drove better on the bigger wheels.
The RWC guy made me put on flares:
Master
SupporterAgreed, the military chassis just gives me a touch more space above the wheel, but I'd guess that's not a limiting factor. The turning circle issue comes down to how much "lock" I would need to adjust out for any given combination of tyre diameter and wheel offset. I'll have to get out the tape and do some measuring!
Master
SupporterThey certainly look good with wider tyres, and personally I don't mind the flares!
It's interesting that the RWC tester made you fit flares but didn't check for chassis contact. I'm used to chassis and brake pipe contact being the first thing they check for.
Without adjusting the steering stops did it rub badly or just touch - assuming you applied full lock rather than stopping when it made contact!?
ChatterBox
Hey that's a good point! He didn't check for contact. I didn't know they touched until I saw the shinny spot, i'm pretty sure that it just brushes the guard. It is possible that I have my steering stops would that little bit out from factory or max turn possible - I normally air on the side of caution.
Master
SupporterA bit of calculation, using theoretical figures, suggests that a 255/85R16 tyre is 53.6mm larger diameter and 65mm wider than a 7.5R16. A 235/85R16 is 19.6mm larger diameter and 45mm wider.
The 272309 has a width of 5.5" and an offset of 1-13/16 (46mm), whilst the Wolf is 6.5" wide and 20.6mm offset. So the centreline of the tyre moves out 25.4mm.
This means the inside edge of the tyres, compared to the 7.5R16, moves:
235/85R16 - out 2.9mm and fore/aft 9.8mm
255/85R16 - in 7.1mm and fore/aft 26.8mm
Where "out" is away from the engine and "fore/aft" is the increase in radius.
A quick measure indicates that with my steering lock stops in their current position, the 235/85R16 tyre will easily clear chassis and springs, and the 255/85R16 tyre will just touch it's trailing side on the leaf spring clamp.
Obviously this doesn't take in to account tyres that are not quite the theoretical size. But it looks like 235/85R16 is safe, and I could possibly (!) gain some lock adjustment, and 255/85R16 will just rub unless I lose some lock. Or gain a set of 0 offset wheels!
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