Quick question, but ill preface with a bit of info first. Car is a 2003 bmw 525i e39, its my younger brothers with 160k miles. The year old rear tires wore the inside slap out and i notice all the rear suspension components are toast so i replaced them and told him to get an alignment but he never did. Dad just replaced the rear tires yesterday and i asked if he got it aligned, no says he so we take it to a local tire chain shop. I ask just for the rear to be aligned and the guy argued with me saying you cant do just the rear, im super surprised by this as i cant figure out why but ive never aligned a car, thats the only thing i farm out. He says you have to do the front to be able to do the rear he says its a "system" thats has to be done together but then why can they do just the front? It still makes no sense to me but dad says whatever just do it although the front was aligned a few months back. They just called saying the front control arms need replacing and they cant or wont align it.
So before i go up there to argue more i ask the hive. Can just the rear be aligned? This car from the factory has negative rear camber but i think it was toed in to wear out the inside. I just need to know its straight before my brother burns off another set of new rear tires.
On those BMW's there's no camber adjustment on the front from the factory, just toe adjustment.
Also the control arms need to be replaced every 50-60K due to the non-serviceable balljoints. Tie-rods and drag links also wear out and cause issues. All of those parts are available via RockAuto and other vendors (I saw one complete front end kit for about $500 for my 740iL, which is the same as the 5-series).
As to the 4-wheel alignment, they are watching out for their liability and its good policy to check all 4 since one end can impact the other.
Fix the car (not a bad idea)
Find another shop (try to find one that does race cars, since they are more flexible)
Learn to do it yourself. Takes a bit longer, but you can get as good or better results using a set of 4 jackstands, some string, rulers and an angle gauge (hint: look at the Camber app for iPhone/Android)
https://www.youtube.com/embed/wjZUu_d08t8
The process of only aligning the front goes back to the ear of solid rear axle cars which now are only found on trucks. The "stick" rear was not adjustable and only became an issue is something was worn out or broken back there.
With modern IRS cars at both ends you at least need to do the front as it's the end that steers the car, does most of the braking, and in many cases, (FWD) pulls the car down the road.
I would bet however that one could align the rear IRS only if one wanted to but the chain shops are there to generate revenue so their procedure is to do both or the front only. There are many reasons for this besides perhaps the OEM calling for it. I can't fault them since if they give you a guarantee for the work they want to do it the way the OEM calls for.
Ill fix the front end in due time. The issue is between my brother in question, my parents who pay for his car, and myself we live in 3 different cities all at least 100 miles from the other. Him and i both in school messes with some of the timing aspect. So im only concerned with the rear, since thats the end i recently replaced parts on and its proven to us to munch through tires every year and these guys dont want to just do a toe and go on the rear. And the fact there are no race shops that do alignments here (race shop here means 1/8 mile drag or dirt track). I guess my only option is the string method which i left all my tools (was only planning on timing a sbc while i was here) at home and ill only be down here until sunday morning. Hmmm quite the pickle im in.
It's because if the rear thrust angle is changed, that makes the front toe off-center afterwards. You'll possibly have an off center steering wheel but that's it.
Example:
On the rack you have 0.05 toe on both fronts, and rear toe is 0.10 and 0.00.
This means there is an 0.05 thrust angle(rear tracks slightly off center to the right), but steering wheel is straight before alignment.
So you correct rear toe to 0.05 on both sides.
Now with the steering wheel locked in place(which should be the whole time), go back to the front, now it shows about 0.07 and 0.03 up front.
Still the same total toe so won't affect wear, just wheel cocked off center. When you drive down the road, toe evens out left to right, the wheel goes off center.
So many people think toe off causes pulls. It doesn't(unless talking loads of total negative toe... Will be darty but not pull in one direction unless camber/caster are also at play. It amplifies a pull). Or if it has EPS and steering angle sensor being off causes unwanted assist because the wheel is off center.
Front toe is based off thrust angle on alignment machines.
Thanks that makes sense. But if i asked "set rear toe to 0" would it still have messed with the front?
In reply to chiodos:
If the rear toe is off to one side or the other... Then yes. Front toe will need reset to center the steering wheel.
If you can live with the wheel off center a bit, its not causing problems though.
