Defender is uncontrollable when driving through puddles / standing water

I have 265/75 R16 BFG AT's on a V8 station wagon. In general I've not had a a problem with them in 15 odd years, but...I do know what you mean about being careful on water. I like the tyres, but water is their weak point. Most comments noted above about width already, but if you then have to steer to recover the 2" lift will not be helping you much either. I run my tyres 28 at the front and 32 at the rear.

Also are you actually sure you are hitting the water at ‘30mph’ or is this a guess? I drive through a lot of standing water yesterday at genuinely around 30mph (I looked at the speedo) and it wasn’t an issue at all.

Or are you hitting it faster than you realise?

As others have said, these are classic symptoms of aquaplaning. As the front wheels hit the puddle a wedge of water is forced underneath the front tyres and lift them off the road enough for the steering to go light. Worst case the rears lift as well you lose control completely.

Nothing to do with the steering geometry and everything to do with the incompressible nature of water. Any tyre will aquaplane if you are travelling fast enough (airliners can aquaplane on landing and they have relatively thin tyres for the weight), but wide tyres will plane at lower speeds as the weight loading per square cm on the contact patch is less, making it easier for the water wedge to form and because water cannot squirt out of the way so easily. Narrower tyres cut through the plane of water to the road surface more easily and require a higher speed to start to aquaplane. Light vehicle weight makes it worse, speed obviously makes it worse, tyres with a poor water dispersal design (including some off road tyres) make it worse, worn tyres make it much worse, a flat non-porous road surface makes it worse. The depth of water required to start aquaplaning depends on the tread pattern of the tyre (slicks will aquaplane on a few mm, a mud tyre might need 2 or 3 cm). Deep water obviously tends to slow the vehicle quickly enough that a stable aquaplane rarely forms.

Defenders run fine with 285s, but now you know your vehicle is more prone to aquaplaning just be cautious. Risk of widespread flooding today - stay safe.

I'd agree with what most are saying ref aquaplaning. I've not tried BFG ATs but my 90 (with Goodyear Wrangler MTR 235/85R16) is a lot more stable than you are reporting. Yes it 'pulls' when going through standing water but is quite controllable with neligable effect @ 30mph. I also have a 'return to center' steering damper fitted which possibly helps. My 'other' Defender has Yokohama 265/75R16 Geolander ATs and that is also more stable through water than yours but does slide about more on wet fields.
Your tracking could be out and/or it could be a combination of things but it doesn't sound safe at all.

miktdish said:

Yes it 'pulls' when going through standing water but is quite controllable with neligable effect @ 30mph.

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Pulling to one side when one wheel goes through a puddle is hydrodynamic drag not aquaplaning and it happens to all tyres - though again tyres with a bigger contact patch will suffer more drag. When a wheel aquaplanes there is almost no drag at all as the wheel is not fully in contact with the road, hence no traction, no braking and no steering. If the OP's issue is a loss of directional control when one wheel goes into water and the other doesn't, then I would increase the tyre pressure to at least 35 PSI (I run 40 PSI on my BFG KO2s on the road), I would also consider replacing the steering damper as it is not doing its job properly. You also need to anticipate the effect and hold the wheel firmly to prevent it turning towards the wheel that hits the water.