Re: rear align and tire rotation
Staggered wheels should NOT be rotated. Just cared for and monitored.
YOU ARE ABSOLUTELY RIGHT WHEN YOU SAID the wider rims/tires need to stay on the back. And probably won't clear the wheel wells on the front in tight cornering.
Shocks and struts usually last 50k or 3-5 years under normal use. That drops to 25-30k with spirited driving, heavy loading or rough roads (anything other than a serene highway). Extreme seasonal temperatures can also shorten their life. And if you have the suspension taken apart enough to replace shocks consider the economics of replacing ball joints and bushings. ALWAYS replace the shock boots (dust covers) as even a small amount of dirt can destroy new shocks in months.
The upper rear shock mounts are impossible to get to..... remove the rear seat. remove the rear seat backs. Remove the rear corner courtesy lights. Remove the rear "C" pillar covers. Remove the rear dash cover. Remove the rear deck sound proofing. Cuss the damn Germans that designed this stupid system...... and try not to touch anything with your dirty fingers because the fabric won't clean and the headliner won't match when you have the pillars reupholstered. And then cuss the damn Germans that came up with the system.....
Springs will begin to exhibit some weakening around 100-200k again depending on use. Heavy loading is the hardest thing as the extra weight will change the static point in the spring. When I say heavy loading I'm not talking about 4-5 people. I mean hauling home landscape rock from Home Despot (not Depot, Despot). Geez get a pickup! Metal fatigue will eventually cause the spring to sag and respond less actively. Extreme overloading will demonstrate Hooke's law of elastic limits.
Rapidly flexing a piece of metal will eventually cause breakage. Auto springs are massive enough and thermally conditioned (annealed) to resist the fatigue, but the principle remains.
The body roll is probably just that you are driving a 5000 pound car. My 1997 740 has independent rear suspension and no anti-sway bar on the rear. I think it's a design flaw, but the 7 is a luxo sedan, not a sport touring sedan. Yours probably doesn't either as I don't see a mounting point for the linkages or underbody clearance for the bar. But the Sport/EDC might include a rear sway bar. (Anyone wanna set me straight on this?)
A spring kit is something to think about. I'm not big on the aggressive drop kits (more than 1.5 inches). Part of the problem with dropping the ride is you now have moved the shocks and struts out of their designed neutral zone. And I haven't seen any E38 kits with purpose built shocks.
I know you spent close to $200 each on those tires. But if they last only 30K then your $800 is actually only 3 cents per mile! If you are as heavy on the pedal as I am, you are getting about 14.5-16 mpg. That means GAS costs about 17-20 cents per mile. By comparison tires are very cheap.
PS. I got my strut compressor at Harbor Freight Tools. I have a scissor type ($35) and a twin clamp type ($12). The twin clamp was easier to use on progressive diameter coil springs (like the 7 has) but the cheap construction only lasted through 2 cars (my 7 and the old lady's Focus). But for $12 worth of Chinese junk, I think eight struts was a noble lifespan.