by NowForThe5th on Tue Jan 07, 2014 3:51 pm
OK. First thing to understand is what is offset and how does this change with different wheel widths.
Offset is the measurement from the centre of the rim to the face that sits against your hub. So a 0 offset wheel will have equal amounts of its' width to the outside and inside. Positive offset means that the face is moved towards the outside of the wheel which, in turn effectively moves the wheel rim inwards.
Consider the ridiculous case of an 8" (200mm) wide wheel with 100mm positive offset. The face that mounts against the hub would be level with the outside edge of the wheel because it has been moved 100mm (half the width of the wheel) from its' position at 0 offset which would have been right in the middle.
So, if you increase the width of the wheel (say by 1" or 25mm)and maintain the same offset you would be adding half of the increase to the inside and half to the outside. So the outer edge of the wheel would now be 12.5mm further out than a 7" (175mm) wheel. Of course the inner edge would be 12.5mm further in than the 7" wheel, too.
You need to take this into consideration when making comparisons of wheels with different widths.
The standard offset on a Triton wheel is +38mm. This places the Triton tyre well inside the outer edge of the wheel arch mould which leads to the popularity of putting on wheels with a lower positive offset (thereby moving the wheel out) which fills the arch better without running foul of the various regulations.
When fitted with a 265mm wide tyre and on a 7" rim an offset of +20 will place the tyre just inside the edge of the wheel arch mould and the mudflap will cover enough that it won't draw the attention of Constable Plod sitting behind you. A zero offset is too far out.
As a bit of an aside here, I believe that the Triton was originally designed with the intention of 265mm wide tyres. This is apparent from the somewhat inwards placement of the 245s, that the MK had 265s and the Challenger has 265s with exactly the same front running gear.
If you widen your wheels then part of this extra width has already been taken up width the wider wheel. So a +20 on a 7" wheel is the same as +32.5 on an 8" wheel. (38-20=18, 18-12.5=5.5, 38-5.5=32.5)
Since most aftermarket wheels come in offsets to the nearest 10mm,then +30 in your 8" wheel would put the outside of the tyre in pretty much the same position as your +20 7" wheel.
What changes, apart from position? Well, first of all a wider wheel allows the sidewall to stand up a bit straighter. This means less sidewall squirm when cornering, so a slightly sharper response may be expected. I do note though, that you intend to fit muddies and these normally have a fair bit of tread squirm as well, so the difference won't be marked.
Standing the sidewall up a bit more will give you more height, too. Although the difference won't be very much. Still, a mm or two can mean the difference between scraping diffs, or not.
The wider wheel allows the tread to sit flatter on the road (pushing down more on the edges) so a small improvement in handling can be expected from this too.
Increasing track width will give you a bit more stability offroad. Noticeable if you have a lift as well.
The wider wheels, if they're steel, will weigh more than your alloys. This can result in a detrimental effect on handling, shock absorption and particularly braking. My muddies add maybe 30% to braking distance on standard size alloy rims. I don't think I'd like to add the effect of the extra load on the brakes trying to stop a much heavier wheel from turning and I have 4 pot calipers at the front and discs at the back. Other members have reported effects such as ABS not working with steelies, reduced braking performance and changed ride characteristics.
Chris
If work is so terrific, why do they have to pay us to do it?
... Can I interest you in a sarcastic comment??? 
cops are generally a bit friendly in country towns with that sort of thing though
