The issue with the pinch bolts is that the axle has to be pulled across to the right by the axle bolt so that the shoulder on the axle can clamp together the speedo unit, the left bearing, the spacer tube, the right hand bearing and the right hand spacer. If you tighten the pinch bolts first, the axle cannot pull all of the parts together - and you end up with a wheel that is able to slide on the axle.
But assuming all of your spacers are correctly installed, that is less likely on the rear wheel. Nevertheless, you don't tighten the pinch bolt until the axle is torqued fully.
Its a long time since I worked on an 1100, but I seem to remember a distance collar that fitted into the final drive hub from the left hand side when the wheel was out. It looks cylindrical, but mine would only ever fit correctly one way round, the other way, it didn't seat properly. I think one end was textured slightly. Someone will correct me if my memory is wrong or if this was a feature of only my bike.
I haven't got a clue what the cause of the problem is from the description but I know where I would start to look. So I will throw out some ideas to investigate as possible causes.
- Wheel bearings and final drive bearings. They wear and collapse over time. If they haven't been done that you know of, they might be a good starting point. Check the shop manual carefully to see which wheel bearing has to be driven in first. It matters, and it may be different for front and rear wheels.
- Wheel balance. You've just had tyres fitted, but if wheel bearings have collapsed the balance will probably be out.
- Pivot bolts and bushes top and bottom of the rear suspension unit
- Swing arm bearings. You need the correct tool to get these tightened properly. Too tight is even more frightening than too slack.
- Tyres unsuitable for the weight and suspension of the ST1100. Go back to Bridgestone - tried and tested with ST1100. Sidewall performance - it is important that manufacturers match this with the suspension for these heavy beasts. Bridgestone do. I dont know about others.
- Swinging arm integrity - these things can corrode from the inside.
- Shock absorber damping adjustment.
- Front fork alignment.
- Shaft drive casing - 4 bolt attachment to final drive housing
- Steering head bearings.
- Rear brake caliper bracket and stopper bolt in left swing arm. Just 'cos it would be stupid not to check that this is fitted correctly !
Afterthought - When /if you get to check the swing arm bearings - just make sure that there is nothing that is preventing the swinging arm from rising and falling through it's full range of movement. It's a wheel out and suspension detached job.