Any alignment experts out there? - non-D question

[Dangermouse]

I need some advice on an alignment issue I am having.

I put new rear tires put on a RWD car 14,000 miles ago (3 years). Previous tires were worn down, smoothly across the width of the tire. And had an alignment done immediately. Left rear tire was replaced 8000 miles ago due to puncture, so the RR tire has a 6000 mile headstart.


Alignment was checked today after new front control arms were installed (by a third party).


http://dmctalk.org/attachment.php?attachmentid=49116&d=1487802819

As a side note, they told me that the RR tire was worn on the inside (down to 3/32” on the inside compared to 5/32” on the outside) Obviously replacement needed soon. LR is an even 7/32”, but it is newer tire.

However the alignment camber is out of range on the LH side, not the RH. There is no rear camber adjustment available without buying an extra kit. There is minimal camber adjustment on the front without an extra kit.

So,
Why is the RR tire worn, but that side isn’t out of alignment? The shop gave me an answer, but I am not sure I believe it.

Obviously I want to fix the underlying problem before throwing tires at it.


thanks in advance. I'll share the shops theory later, but want an open mind approach at the moment

[David T]

Hard to give you a good answer without knowing what kind of suspension the car has. Rear alignment can be affected by how much load you have in the car, if anything is bent or worn, and tire pressure. Typically if a non-adjustable alignment spec is exceeded, it is most often due to something bent or worn. Before doing an alignment any good shop will do a through visual inspection for worn or bent components. You cannot do a proper alignment if anything is bent or worn. Bad tire wear is a good indication of worn/bent parts and an alignment is not meant to "fix" that. It is done AFTER you find and fix any bent/worn parts to verify everything is "good to go". For example let's assume you have a solid rear (a housing from wheel to wheel with the diff and axles inside the case). If you have a camber issue the case is bent. On some cars it can be bent back into proper shape and others it cannot. Same with Toe. Castor is not adjustable or even measured. Independent rear suspension can be all over the place and should only affect the side with a problem although both sides can be bad but each with it's own problem. Maybe you need to find a shop where they know what they are doing. On some cars you really need to go to a dealer who is trained on their specific models.

[Will F.]

As a tech that has done many alignments. People always remove everything from the car, then get an alignment. Truck, and family car owners are notorious for this. The alignment is set to the weight and height the car sits static. If you get an alignment and then load the back of the car with a few hundred lbs your alignment is now off. Not sure thats what your doing, but people dont realize this. Also, load ratings are on the tires is very important. If underrated they will wear very quickly.

can you give more information? What year make and model car are we talking about? What is the car used for? Basic commute, hauling, towing, ect...


Will

[Dangermouse]

2005 M-B CLK used for light suburban use. No track, no towing. Toyo Proxes4 tires. Asymnetric F/R set up.

The only unloading was me getting out of it :)

I found the alignment sheet from 2013 and the "actual" values for the rear were very similar to the 2017 values so nothing seems to have changed there. And I also found the photos of the tires from 2013 (it was actually 4 years since the tires were put on) and there is noticeable wear on the inside on one tire. Unfortunately I didn't note which side it came off, but it would be safe to assume it was the RR also.

Would the camber being off on the LR affect the wear on the RR?

The shop guy claimed that the RR tire wear was due to excessive toe-in on the front tires which I don't follow. I would assume that excessive toe in on the front would cause wear on the front.

[David T]

Go back to an M-B dealer to get an alignment. Most independent shops can't do them correctly. If the front is not done right, under certain conditions, it can wear the rear and yes, the L/R alignment can affect the R/R tire. See it often when the back doesn't follow the front. The car drives down the road kind of sideways.