Everything runs up the same tracks.Front wheel assist tractors are usually converted to 3m centres as that is easier than bringing a combine back into 2.5_2m centers. Obviously then with 40ft widths u can then run 80ft rigs up every second run, then alternate the next time to avoid wheel track issues with dust and stress. Had a feeling that midwest had a 45ft centre mount, definatley had a 45ft front at farmfest this year sitting on a 9650 from memory. The theory is that with "tramlining" all traffic run on the same, usually 3m track and no vehicle is allowed to leave them, even the grain carts. According to the boffins, up to 80% of a field has some kind of wheel track roll over it during the period of a season_year_cycle. But when tramlining is introduced this can be cut down to below 30%. Huge improvements in soil quality, infiltration rates of water, Far more efficent in chemical, seed and harvesting as the front is always full. Much less hp required as soil structure is so much better and you not trying to bust up old wheel tracks as you go. Also has problems too but what system doesn't. Combines usually have those extention spouts added to them, I have seen photo's of 2388's with support cabling fitted to a stay mounted above the pivot point, out to the end of the auger for extra support. White industries also make a chaser bin with a special hopper on the side of the bin which brings the grain to the centre of the bin and spreads it evenly.