If you look on
your current tyres you will see the tyre size on the side.
It will look something like "215/70/15 98H". The first three
numbers break down the size of the tyre, the "98" relates to
weight capacity, and the "H" relates to speed capacity.
The 215/70/15 figure defines the width, and inside and outside
radius of the tyre so that it fits the required wheel, and has a
road-side circumference suitable for the speedo calibration. The
actual mathematics of these figures for typical x-trail tyres
If tyre size is represented as x/y/z
Inside diameter (wheelsize) = z * 25.4
Width of Tyre = x
Sidewall height = (y / 100) * width
Outer radius = wheelsize / 2 + sidewall
The weight capacity and speed figure (eg 98H) is a little less
complicated, with the basic rule of thumb that any new tyre
needs to be able to handle at least as much weight as the
existing one. i.e.. 98 or higher.
www.miata.net/garage/tirecalc.html have a very handy online
calculator for measuring the differences in tyre specs.
Each state will have its own regulations
on how much you can change the tyre size on the x-trail, which
your local tyre dealer will be able to assist you with.
Many tyres will also advertise their suitability to off-road on
The standard Toyo OE's that come with the X-trail are rated
90/10 - 90% on road, 10% off road use. Dunlop also make the
RV501 which is cheaper and has the same 90/10 ratio.
The next stage is all-terrain or light-truck tyres. All terrain
typically are suited to 70/30 ratios or 50/50. Bear in mind that
50% off road driving is a lot of off-road driving!. These types
of tyres will give improved grip off road and have stronger
sidewalls so that can handle the low pressures required for sand
driving better, but will make more noise on-road and are more
expensive. Typical tyres in this category are: Cooper A/T's,
Toyo Open Country All Terrain, Bridgestone Dueller 693 and
Dunlop Grandtrek AT2
Check the forum for a more in-depth discussion on x-trail tyres
and peoples first hand experiences.