2004 BMW 325i Wheel Offset Question

I'm very pleased you're asking about this and that you know there can be consequences. Being on the rear, you shouldn't have anything to worry about as far as handling. It's a different story on the front. As for rotating the tires, you might consider a viewpoint I subscribe to for my vehicles. If you have an alignment issue that is causing accelerated tire wear, lets say on the front, rotating the tires periodically will cause all four to wear out at the same rate, then you buy four new, matched tires. If you never rotate the tires, the rear ones will last longer but the front ones will wear out sooner, so you replace only those two. You replace half as many tires but twice as often.

Another reason I don't rotate my tires is it isn't uncommon to get one that causes a tire pull. There's no actual defect; it's just a characteristic related to its rolling resistance. If I have no pulling problem, why risk causing one by putting the rear tires on the front where one of them COULD cause a pull? As an alignment specialist, I'm very aware of every little unexpected pull, noise, or vibration, even though my daily driver is 25 years old! I won't be happy with a pull on any of my vehicles, even if I know it's just a tire issue.

This doesn't apply to a few car models. In particular, the '80s Ford Escorts and Tempos came with extremely horrendous alignment problems that couldn't be corrected and tires lasted about 15,000 miles on the front. The rear could be fixed with aftermarket parts to reduce the terrible wear, but while that made the rear tires last longer, they no longer made up for the bad wear in the front. The front tires were tipped out on top a real lot and that made them shred the outer edge of the tread. If you rotated them every 5,000 miles, when on the rear, they were tipped in a lot so they only wore on the inner edge. The center of the tread looked like brand new, but by 15,000 to 18,000 miles both edges were scrubbed down to the cords.

There were also some large '80s front-wheel-drive Cadillacs that had alignment problems on the rear wheels, and there were no adjustments to correct that. Rotating those tires might extend the life of all four a little.

Your car doesn't have those issues. The wheels are set to normal alignment settings that give good handling and tire wear, and there are adjustments available when that becomes necessary during a normal maintenance alignment. The issue now related to the offset on the one wheel is not a factor on the rear. On the front, however, besides the brake interference you already are aware of, the offset also affects a non-adjustable alignment angle called "scrub radius".

I included my sad drawing of scrub radius I used to hand out to my students. I hope it shows up okay. Instead of the upper ball joint shown, your car has a strut, and the upper mount is the upper steering pivot. That, and the lower ball joint, is what line "B" is drawn through.

From this point, the following description is a copy of what I normally post for people wanting to lower their cars or lift their trucks. This is the toned-down version, and while most of it doesn't apply to you, it's faster than trying to type this wondrous information all over again.

If you look back from in front of the vehicle and draw an imaginary line through the upper mount and lower ball joint which are the steering pivots, that line was very carefully-designed to intersect the road surface in the middle of the tire tread. The half of the tire to the left of that point wants to scrub on the road and pull the steering system to the left. The other half of the tread wants to pull it to the right, and those two forces offset each other. When you do anything to alter scrub radius, especially when you alter ride height, that changes significantly. The tire will react to every little bump in the road instead of canceling them out. That makes for an extremely tiring vehicle to drive.

Scrub radius also has a big effect on handling in corners and braking. The brake hydraulic system is designed around a specific ride height, weight distribution, and weight transfer. When kids lower cars, they get the false illusion the car handles better and brakes in a shorter distance. In fact, less weight than normal transfers to the front under hard braking so the front brakes can lock up easier. A skidding tire has no traction or steering control so you can't press as hard as normal on the brake pedal. More weight stays on the rear wheels but those brakes don't get more stopping power.

You can be very sure lawyers and insurance investigators know all about scrub radius and will use it against you when they're trying to shift the blame from their client to you. That other guy may have run the red light but they will convince a jury that you were partly at fault for the crash because you were less able to avoid it, and they will be right.

Scrub radius has also been modified by the engineers for front-wheel-drive cars. Almost all of them use a "split-diagonal" brake hydraulic system, meaning the left front and right rear brakes are on the same system. On older and all rear-wheel-drive cars, the two front wheels were on one system and the two rear wheels were on the other. If you lost the front brakes due to a leak, you still had about 30 percent of your stopping power from the rear brakes. What most people didn't realize though, unless as a youngster with no money, you blocked off the fluid flow to one front wheel instead of fixing the problem, is with just one front brake working, when you applied it, that would tear the steering wheel out of your hand. You had to have both front wheels braking evenly to counteract each other by being connected through the steering linkage.

Front-wheel-drive cars have a lot more drive train weight on the front, so a loss of the front brakes would leave you with less than 20 percent stopping power from just the rear brakes. The rear wheels would lock up, the tires would skid, and they'd find you in the next county before the car would stop! The split-diagonal system addressed this. A failure of one of the two hydraulic systems always will leave you with one functioning front brake and 50 percent of normal stopping power. Now the issue is to offset tearing the steering wheel out of your hand when you brake, and that is done by modifying scrub radius. Line "B" has been moved out so section "Y" of the tire tread is much smaller, and "X" is larger. Since this is looking back at the left tire, section "X", being bigger, wants to scrub, or tug hard to the right, and section "Y" is way too small to counteract it. However, the same thing is happening on the right front tire. The result is both front tires are still offsetting each other, and the car goes straight.

What this addressed though is when there's a leak in one of the brake hydraulic systems. Suppose the right front / left rear circuit stopped working and you only had the left front brake as the major contributor to stopping power. The tire itself is going to try to stop, and acting as a lever, that is going to tug on the steering linkage as before on rear-wheel-drive cars, and tug the steering linkage and steering wheel hard to the left. BUT, ... Section "X" of the tread is going to tug hard to the right. Chrysler has had this so well-perfected that other than the red "Brake" warning light, you won't even know something happened. On most other cars, all you might see is a tiny wiggle in the steering wheel, and even that won't be near enough to cause loss of control or a significant change in steering direction. You only have half your braking power, but you can stop in a safe and controlled manner with no unexpected reaction in the steering system.

All that wondrous design effort goes out the window when you change scrub radius. Now you can see that anything that moves line "B" is going to change how the car responds when steering and when braking, and this is why lawyers and insurance investigators love to find any of these kinds of modifications, ... On the other guy's car. You can see that installing a wider wheel / tire, a tire with a larger outer circumference, or a wheel with a different offset will change scrub radius. This is what you have to consider every time you see a silly-looking car or truck with giant wheels and almost no tire sidewall. But remember that raising or lowering ride height changes the relationship between the upper and lower steering pivots and that also changes line "B".

I know that covers a lot more than you asked, but I'd rather you be informed before you start altering things. As a former suspension and alignment specialist, I make sure all of my cars, including a few '70s muscle cars, are exactly at the specified height, and nothing has been altered that could have me answering questions in front of a jury.

Okay EnvyYou, I'm live again! I understand that 7mm isn't that significant, but to be safe AND to address the brake issue, you might look for a wheel spacer that you can install behind the wheel to correct the offset problem. I can relate this to an alignment issue on larger pickup trucks. Many of them from the '90s had really tough suspension systems but there was no way to adjust "camber", one of the main alignment angles. To correct a pull, there was a set of three wheel spacers available. First you tried a 3.0mm spacer. If the pull was solved, you were done. If it pulled the other way, you exchanged it for a 1.5mm spacer. If the pull was better but not gone, you installed the 5.0mm spacer. For a really bad pull, you could order a 7.0mm spacer but you also had to install longer wheel studs. I never had to resort to that, but that gives you an idea of how moving a wheel out only 1.5mm could greatly affect a pull. This offset is what you want to avoid on the front. What I would do is just leave that wheel on the rear where it wont affect anything, until and if you want to find the right wheel.

The wheel isn't going to cause a problem on the rear. Sanding the brakes is to remove any glazing. That can cause a brake squeal but not a pull.

If you have a copy of the printout from the alignment, post the "after" values for front "camber", "caster" and "toe" and I'll interpret them. In particular, camber affects which way the car pulls but "total toe" can make a car pull alternately in both directions.

Camber is simply how much the tops of the tires lean to the right or left. On most cars, camber is supposed to be set at around 0.25 to 0.50 degrees positive, meaning tipped out on top. 0.00 degrees is standing perfectly straight up and down. 90.0 degrees would have the wheel and tire laying perfectly flat on the road. 0.50 degrees is a common setting that gets the weight of the car placed right over the larger wheel bearing. There's more to the story as the wheel goes through tipping motions as the vehicle goes up and down on bumpy roads. For reference, 0.75 to 1.00 degree is getting pretty high and will lead to scrubbing off the outer edge of the tire tread. Those Ford Escorts and Tempos I mentioned came with just a fuzz under 2.50 degrees and there was no way to correct it!

In addition, you should find your left camber is just a little higher than the right side. That creates just enough of a pull to the left to offset "road crown". Road crown is roads slanting to the right so rain runs off. That would cause cars to drift to the right if both front cambers were equal.

Caster on your car is the tilt of the strut as viewed from the side of the car. The top is more to the rear than the bottom. 3.00 degrees is typical for most cars. That causes the left wheel to want to turn right REALLY hard when the weight is on that wheel. The right wheel wants to turn hard left, and the two counteract each other when the steering linkage is connecting them together. Caster provides the steering wheel return after you go around a corner. It has only a very little affect on tire wear. Higher caster makes for much more directional stability at high speeds but it causes a much higher turning effort. In the '60s when we started driving faster, caster was increased for the stability, then we added power steering to overcome the higher effort. Before that, you could turn the steering wheel on a large truck without power steering because it had lower or even negative caster, meaning the upper ball joint was more forward of the lower ball joint. If you think of the two caster values like the two sides of a teeter totter, they have to be equal to make the car go straight, but a little higher caster on the right can also be used to offset road crown. Caster isn't adjustable on the majority of front-wheel-drive cars, and when unequal, it doesn't cause a pull, simply because of the interaction of all the other alignment geometry they use. Caster DOES cause a pull on rear-wheel-drive cars so it will always be adjustable on them. In case you care, caster has half the affect on pulling as does camber. That means if you need 1/4" degree more camber on the left to offset road crown, you could do the same thing with 1/2" more caster on the right wheel.

Total toe is probably the most important alignment angle to look at when the car might pull either way. "Toe" is the direction each wheel is steering. Almost all cars call for a little positive total toe, meaning the fronts of the wheels are about 1/16" closer than the rears. Road force and braking stress pull the wheels back while driving so they're perfectly parallel. Too much total toe makes the tires skid going down the road, sort of like a V-type snow plow. That will set up a very distinctive wear pattern on both tires even if just one is misadjusted. If the two wheels aren't set exactly the same, the steering wheel will be off-center.

The more noticeable problem is when you have total toe-out as opposed to the normal "toe-in". Toe out means both wheels are steering away from the center of the car. The car can't follow both tires. It follows the tire with the most weight on it which is usually the right one. When the left tire hits a bump or when the road slants to the left momentarily, like at an intersection, the car will follow that one and veer to the left.

Before the car was aligned, the mechanic should have inspected the steering and suspension components, but control arm bushings often get overlooked because they're hard to make them move when there's forces acting on them from the weight of the car. Twenty years ago it was pretty much unheard of to have a worn control arm bushing, but lately this seems to be a common problem on all car brands. A worn bushing will allow the control arm to wander around, and none of the alignment angles will stay were they were set. The numbers on the alignment computer screen can appear to be perfect, then change just from slamming the door or wiggling the steering wheel.

The last issue is wide tires. If you'd drive a Pontiac Trans Am from the '80s, you would feel every little twig and pebble on the road, both in the seat and in the steering wheel, as the tires responded to those irregularities. Some people call that "road feel", but it can make for a tiring car to drive long distances. It gets worse when the car wasn't designed with wide tires in mind. I have tires on my minivan right now that are 1/2" wider than normal, and I can feel the difference. It's an odd feeling though; not the normal pull to one side, then the other. It feels like you have to tug on the steering wheel to keep going straight, but if you let go of the wheel, the van still keeps going straight. Steering effort hasn't changed but that is the illusion I get. Fortunately these tires will be worn out soon, then I'll be searching for the original size for replacements.

I'm not accustomed to reading the angles in degrees and minutes, but luckily the specifications are listed here too. I'm not even going to comment on the "Previous values" because those are the result after parts were replaced. The alignment could have been perfect before that. I AM pleased with the "Final value" for total toe. Both wheels are adjusted while the steering wheel is locked in the straight-ahead position, so since both wheels are equal at 0.9mm, the steering wheel will be straight. Dandy.

I always set my alignment computers up to read camber to hundredths of a degree. They can be set to read to only the tenth of a degree too. Some mechanics do that because aligning a car to less precision is faster. I found a lot of cars that needed 0.06 degrees more on the left to offset road crown, and that's too small to see unless the computer is set to read to the hundredth of a degree. If I remember correctly, there's 60 minutes in a degree, so you have camber of roughly 1 Â degrees negative on the left. That means that wheel is tipped in on top quite a bit. You can see that ideal is negative 20 minutes which is about 0.33 degrees. That's a long way from 1 Â degrees. More importantly, the left wheel is tipped to the right a real lot more than the right wheel is tipped to the left. The car should be pulling rather hard to the right.

My guess is camber is not adjustable on your car or it's at the end of its range, otherwise the mechanic would have corrected this. I looked up the procedures and some models list camber as "not adjustable" and a few models say a special tool is needed. Caster also is not adjustable. The mechanic didn't measure your caster. That is one of the few readings that isn't taken automatically by the computer. The mechanic has to turn the wheels left, then right, then the computer calculates caster. It can't be measured directly.

I already mentioned that 3.00 degrees caster is common and typical, and we don't get too excited to find it over 4.00 degrees, but yours calls for over 5 Â degrees. That's a bunch but not unreasonable. Some Mercedes and some Jeep models call for over 11.00 degrees. Caster that high will cause you to have to make very few tiny steering corrections at highway speed. Higher caster reduces a car's tendency to wander. The downside is the higher caster goes, the greater the tendency is for a returning steering wheel to overshoot and go beyond center, then come back again. That can set up a very scary oscillation affectionately known as the "death wobble".

King pin angle is a really old-fashioned term for "steering axis inclination", (SAI). I wont bore you with the details, but all that's important is it has to be the same on both sides. Yours is perfect. Typically within 0.20 degrees is close enough. GM has a big problem with this on their front-wheel-drive cars. The cross member has to be removed for a number of repair procedures, and it's critical that it be reinstalled in exactly the same place it was. If the mechanic didn't mark it with spray paint, it can be installed off-center from where it was. That changes SAI AND camber, but unless the mechanic knows he has to check SAI, we normally don't take the time. Resetting it correctly isn't that difficult, but if you don't, the resulting incorrect camber can usually be adjusted to APPEAR to be correct, but this leaves you with an unbelievably miserable car to drive. It will dart from side to side in response to the slightest little bumps in the road. This is like driving a car that's rigged to show what driving drunk feels like.

Rear toe is off too. In particular, the right rear wheel is turned in 4.1mm. I can't say how much that will affect tire wear, but overall, the rear of the car is steering to the left. That alone isn't cause for concern. All cars are off a little. That's why we always sell four-wheel alignments. Even if we don't actually adjust anything on the rear, the computer uses the rear wheels as a reference to calculate where we have to adjust the front wheels. That is how we insure the steering wheel will be straight. In effect, even if the wheels aren't parallel to the frame or body, they're parallel to each other. I would estimate the rear of your car is running to the side by perhaps as much as  ". That's not uncommon and is perfectly acceptable. The amount or steering error on the rear is called "thrust angle", and that's what they show at the bottom of the printout. I'm not sure how they relate that to millimeters, but the 12 minutes they show is not significant.

The first thing is to have the brake rotors machined to get rid of the shaking, then see if the pull is still there. If it is, ask the mechanic if left camber can be made adjustable to get that right-hand pull out of there. Some cars are not adjustable from the factory, but strut mounting holes can be elongated to provide the needed adjustment. Often replacement struts come with one of the holes elongated already. Your strut design isn't adjustable like they are on Chryslers and GM products, so you'd have to look if there's something that can be done with the lower control arm to reposition it a little.

If you have a reason to suspect tires of causing a pull, switch the two front ones side-to-side. If the pull goes the other way now, it's one of those tires. You can figure out which one, usually, by switching the two left tires, and / or the two right ones. If the pull is gone, leave them where they are. They can last a long time like that. If the pull doesn't change after switching the front tires, it's an alignment issue.