Tyres may not be the most exciting components in the world of wheeled AFV, but they are amongst the most important. A few thoughts on the mobility considerations of UK's new Boxer, from a tyres PoV (tires for our US friends). 
Boxer has some pretty hefty wheels on it, requiring some specialist tyres. Whilst a range of suppliers exist, most Boxer customers and indeed most European wheeled users tend to gravitate towards Michelin's offerings.
The Michelin Military Tyres portfolio is based on four families of 'X-Force' tyres. In their various configurations, these seek to give some ability to tailor to the usage profile somewhat, albeit always at a sacrifice to a contrasting terrain.
Any tyre that gives you additional performance in one terrain tends to sacrifice performance in another. Broadly you get on- or off-road oriented grip - the more aggressive the cleats, the better it will grip in mud/snow/sand but the less it can grip a road or hard surface.
Within soft terrain there are further design elements at play, but broadly you can see the more gaps and grooves, the more surface area for soft terrain off-road, but less hard/smooth surface contact on-road. Mud & snow chains can mitigate where a tyre is not aggressive enough
Take a road tyre off-road and it will just spin and not bite into the mud. Take an off-road tyre on-road and you have minimal contact area and consequent loss of grip.
The XZL is the closest to a general-purpose tyre (albeit still at least an A/T profile). Relatively aggressive giving reasonable mud performance, but not so much as to have no road handling.
Newer XZL 2 is much more oriented to roads, tracks and hard surfaces. You can see much reduced tread depth and far more contact area for road usage. Upside is higher road speeds and long-distance optimisation, but at cost of mud performance.
XS is a sand tyre so not particularly relevant to this specific discussion, but of relevance when we think about MENA users and a globally deployable force that may have to deploy at short notice to such regions.
XML is the last one and is the mud tyre. Essentially a military oriented tractor tyre, it has huge cleats for digging into the mud and gaining big tractive force. Conversely, it suffers on road.
Selecting a tyre is a balancing act of what you need and when. Relatively simple for civilian vehs, but a challenge for military. STRIKE is the epitome of this - 3,000km of road march followed by indefinite period of battlefield operation in Eastern European mud (and snow).
The UK has selected XZL, the 'general purpose' tyre with reasonable road, mud and rock performance. Whilst you can argue many things, this is doubtless the right choice.
But there are always trade-offs. That 3,000km road march to Estonia could be faster, safer and easier with XZL 2, but you'd almost certainly need to swap tyres for the battlefield itself (see later for the logistical consideration of this).
Equally, operating dispersed and largely unsupported in typical Eastern European terrain really warrants XML performance, but then you'll likely not get there without burning out tyres on roads and potentially increased RTAs en-route with lower road handling.
Each tyre has a much bigger impact than just how much it grips. Each of these has a load index - the max weight each wheel can carry. For the XZL that UK has selected this is 5,600 kg, meaning Boxer cannot exceed 44.8t total weight. XZL 2 is 5,000kg (40t) and XML is 4,500kg (36t)
Those total weights assume perfectly balanced axle loading. Any heavier loading on one or more axles from location dependent components such as turrets, then the max may not even be reached as the individual axle limit has been hit.
This makes more tactically mobile tyres like XML an issue - if UK wanted to acquire that higher mud performance you would reduce your GVW limits. UK Boxer in planned configurations is GVW of 38.5t – more than the XML 36t effective limit.
More broadly, Boxer is no different to any contemporary 8x8 in that the wheeled configuration compromises off-road mobility. Often people say the gap is near peer with medium tracked armour, but this simply is not true.
In broad summary, an 8-wheel AFV will never get higher than ~80% of the comparative performance of a tracked vehicle in the same conditions, best case scenario. Worst case its less than 25% of the performance of a tracked platform.
At its core it is simply physics – your contact area can be played with a little via pressures, but you simply do not have the surface area of a tracked vehicle.
Relevance is that with inherently reduced mobility you need to wring every advantage you can, including from tyre selection. Its a balancing act, and a very challenging one.
A final note is a very shallow comment on support. Never mentioned is how Boxer would be supported at distance in these STRIKE scenarios. These tyres are large – 1,300mm across, 500mm wide and weigh over 110kg each. A single Boxer’s worth of tyres is a significant load.
Now extrapolate these issues over the whole STRIKE Brigade. Who carries them, in what vehicle, how are they distributed and how are they fitted? V. unlikely MoD would buy a large volume of spare rims so tyres need to be fitted to existing rims locally.
Alongside broader support of the whole force, this is a big slice that struggles to gel with vision of dispersed and highly mobile force operating for extended periods at reach. Experienced planners/logisticians in the Army will doubtless be able to debunk me here, I hope!
Some brief thoughts on some of the interesting issues around tyres and Boxer. A LOT more depth and breadth to explore on wheeled mobility, but hopefully shows some interesting ideas with a UK Boxer slant /end
