MegaSack DRAW - This year's winner is user - rgwb
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My van takes 225/70/R15 tyres, my mud and snow tyre of choice (to match two already installed) is out of stock and has been for ages.
The tyres I use are pretty much the most off-road orientated tyre I can find that has the correct load and speed rating, the Toyo H09.
There is an alternative 4x4 tyre with a more aggressive (and suitable) tread but to get the load rating needed (112) I need to increase the width, giving me a tyre that is 255 wide, 30mm wider than standard. I would need to get a lower profile to keep the speedo in the right range.
Are there any 'unwritten rules' as to how wide you can go on a given rim width? I have seen sprinters with big off road tyres fitted, and they take the same size tyres as my van, but that doesn't mean its a good idea...
The tyre itself will have a range of recommended rim widths, check the spec from the tyre manufacturer.
Whether it then fits your van depends on how much clearance it has between tyre/suspension components. It might look like you can get away with just adjusting the steering stops, but make sure at bottom out you don't foul anything.
Speedos generally overread by about 10% so depending on the aspect ratio you go for, you may improve speedo accuracy.
Oh, and mind to tell your insurers!
Personally I'd not got more than 10mm wider. Not sure what is a safe level though.
Get all Carlos Fandango