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here you go Leeds - had a dig around on difflock, as it was discussed recently and a nice diagram was made to explain it, see attached;
it shows the center point of the wheel and the nave in relation to the center point. The thick black line is the outer face - so you can see which stick out further in relation to each type of wheel.
Another bloody dent...
Now if I understand wheel off set correctly to get the tyre to sit out as far as possible then you need the smallest offset possible OR even a negative offset.
This means that you will have a slighty great wheel track which should give you a better turning circle.
So is my thinking correct?
Now all I need to do is measure some rims!
The wheel industry don't use "offset" as a measure. They use something far more useful called "backspace".
Backspace is the measurement from the inside of the rim to the mounting plate. So a 7inch rim with a 3 inch backspace will have a 4 inch offset (ish). The important bit is that backspace stays the same regardless of the rim width and, for turning circle purposes, the smaller the backspace the better.
Offset is a measurement from the outside of the rim to the mounting plate and, although it gives some indication, it doesn't really tell you how much clearance you have.
Most off road rims use a 3-4 inch backspace so if you buy 8 inch rims you'll get a bigger offset measurement for the same backspace. An 8 inch rim with 4 inch offset will restrict the turning circle more than a 7 inch rim with a 4 inch offset.
Offset measurements are pretty useless unless you also know the rim width.
Backspace is sometimes referred to as inset and as Dave stated this is the measurement that affects how far you can get the wheels to turn before fouling on something, also a thing to note is the larger the diameter of the tyre the sooner it will foul on a same size wheel hence a 205/80/16 will give you the chance of a better turning circle than a 255/85/16 on the same wheel (by quite a large amount).
nope - he meant diameter. although width does come into play as well on extremely wide tyres. But as most peeps use 235, 255 or 265 width the difference is only an inch (ish). Having larger shoulder lugs on aggressive muds can make up more than an inch anyway... so unless you go for daft widths there aint much in it.
anyway - tyre diameter....
just look at the agri-rover with them massive 52" tractor tyres... you'll only get half a turn on the wheel before the inside edge of the tyre hits something!
same goes for choosing between a 31" and 33" and 35" tyre. The distance between the hub and radius arm on a coiler is fixed, so the bigger the diameter of the tyre - the quicker this distance will be covered when rotating such a large 'disk' on the same axis.
"more sticky out wheels" will get round this to an extent by increasing the effective distance from the hub to the radius arm........
there is also the issue that using very sticky out wheels causes bump steer.
Also the tyre is no longer turning on the center point of the hub - but outside of the center point - it moves in an arc rather than about its axis. So on full lock, the wheel is no longer still on the axle center line, but one is in front and the other behind the center line. not good for steering geometry
Another bloody dent...
Excessively sticky out wheels also put more strain on swivel housings, top and bottom swivel bearings and luuuuv to kill wheel bearings just for the hell of it , it all boils down to the best compromise for the use of the vehicle, how often does Dave trial on his Simex's ? how come a RR on 205's can just about out turn a 90 on 255 or 265's, if you were a real anorak you'd drive to the event on road tyres and bring your set of trials tyres with you , different tread/sizes dependent on weather, time of year and site we were using . You might even be called Lewis or Sebastian but you'd still have to leave the 500k transporter/support truck at home though.
Thanks Nick and Matt for explaining things to me.
Not going to go to extreme diameter, width or tread pattern. Am happy with 255/85/R16 MT for general use, travelling etc. So will go for modulars. Must admit I did not realise that mods are made to different specifications so will have to be care ful and make sure that the backspace etc is the same as the set I already have. Don't want problems later by mixing the two sets later if they do have different dimensions.
When I finish my RRC (when, that is! ) then I will be left with a perfectly good set of alloys with road tyres on them and was thinking of driving to the further events with my MTs in the back and swapping them when I get there... Then I decided that this probably would not be within the spirit of the club's "compete with what you drove here" policy (which I really like).
What would be the view on this please?
Just renewing this old thread.
Been looking at off-set/back space for the new wheels for project auto or grouches money pit as my dear wife calls it
I think the best offset modular in the usual 16 x 7 size is those supplied by silverline 4x4 which are ET0, in other words the wheel centre is exactly in the centre of the rim, ie 3 1/2" back space.
When compared to some other modular rims it can clearly be seen, they also appear to have a lot more welding of the centre to the rim and not just spot weld like some.
GOSH! Dumb old me just assumed that a modular was a modular was a modular...
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