Re: rear align and tire rotation
i forgot to mention that i have staggard wheels. Would your advise still be the same as far as rotation goes? I have Kumho Ecsta ASX and i dont believe these are directional tires. Also what is that bolt/part called? part#?
I DO NOT recommend rotating any radial tire across the same axle, i.e. making it turn backwards, even if the tire is non-directional tread.
The bolt would be called a camber bolt or an eccentric bolt. Call your BMW dealer and describe the bolt to the parts desk.
The biggest benefit of rotating tires front to back is the back tire spend more time in a relatively flat contact patch. The front tires are riding on the inside shoulder in straight driving, and on the outside shoulder when cornering. Moving them to the back uses up the center of the tread and more importantly will square off any feathering. Feathering is when the front of a tread block wears faster than the back, giving a saw-tooth feel to the tire when you run your hand across it.
The reason you should never swap tires across the same axle is that radial tires develop something called radial set in as little as 500 miles. The radial bands of nylon, polyester, and Kevlar actually begin to shift in relation to each other and to the rest of the tire carcass. This movement is on the order of hundred thousandths of an inch. But turning the tire around and making it flex in the opposite direction moves the fibers the other direction. The result is a "slipped" radial belt.
The worst case scenario here would be the belt failing completely and the tire blowing out through the sidewall (one time in ten thousand). Another worst case would be de-lamination, where the tread, belts and carcass separate (think Firestone tires on Ford Explorers). The best case scenario would be a wrinkle in the sidewall that would cause uneven tread wear or a mild steering feedback during parking lot maneuvers (below 5 mph, at steering lock turns).
Staggered wheels sizes require a little more care from you the driver. Check the air pressure twice a week. Adjust the pressure based on driving and wear. If you drive alone, use the tire placard on the driver's door and use the unloaded tire pressures (30 front, 32 rear?). If you usually take 4-5 people and their clubs to the golf course, use something closer to the loaded pressures (35 front, 36 rear?). If you drive 80 percent highway above 50 mph and few turns, add 5 percent to all pressures (32 psi recommended becomes 33.5 actual). Do not exceed the tires' max pressure.
If the front tires begin to show outside shoulder wear, add 5 percent (unless the center is also wearing) or slow down the corners.
If the front tires show inside shoulder wear consider re-alignment with less negative camber. Or it may be time to put on some new springs (yes springs wear out)
Re: rear align and tire rotation
what difference would there be in rotating the tires front to back considering the rear(wider wheels) will now be n front and narrower wheels will be in the rear? i have a pressure gauge and do check tire press everytime i fill up currently @ 32psi i will let out some in front. I do take corners pretty hard but knowing it will wear my tires i will slow it down. also what would be signs of the spring/ shocks wearing out? i thought that they might be since i have S EDC (sports susspension) and the car seems to roll a little when cornering my friends thinks its due to the speeds i take corners at.
P.S. thanks for all the help n knowledge also what is your experience because you seem extremely knowlegable.
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.