*5 years I think from memory is the limit of what tyre companies say is the life of a tyre, Grabbers are in that list of not the most road friendly tyre. So to confirm tyre age, look for "DOT" on the tyre, the last i think 4 digits are the week and the year the tyre was made, and the digits are sort of set in the tyre, some tyres dont have "DOT" but still have the digits set in, so 0513 would mean made in the 5th week of 2013.
*To pin point, try altering tyre pressures, from very hard, say 50 - 55psi, it should be pretty bad, then down to 40psi, if it improves, I'd suggest its tyres.
*Surely there is some very keen AULRO member with a Defender close to you that would do a swap in the driveway for a few beers, a chat, and a laugh.
*A front steering, suspension, tyre shudder is very different to a drive line shudder, if unsure, a decent repairer should pick this up.
*Driveline back lash on a Defender TDCi is a different unrelated issue.
*Road surface (in general) has no effect on a Defender, in fact one characteristic of pretty well any Land Rover regardless of model, if in reasonable condition they all sit on the road a lot better than pretty well any other vehicle in the same class / year model.
Regards
Daz

