Disappointing tire alignment

[bwilson4web]

Hi,

With new rear tires, 34,000 service miles on the old, I took the car in to get a 4-wheel alignment. I explicitly asked for zero camber and minimum toe:

• Initial camber (L/R): -1.40 / -1.53
• Final camber (L/R): -1.44 / -1.43
• Tire pressures: 34 psi front, 41 psi rear

However, the tech showed the camber and toe adjustment arms. I'll be able to fix it myself.

Initial driving impression, wallowing but the tires are not properly inflated. So my plan is to benchmark the car using my IR camera to record the temperature distribution after high speed runs late at night.

First I'll inflate the tires and re-run the test. Next, I'll raise the car and adjust the camber on both rear wheels towards -0.5 and re-run the test.

I want the thicker, outer tread to offload the inner tread. My goal is to even the temperature, slightly towards the outer, thicker tread. We have nearly 1 degree of camber so there is freedom to experiment. Handling will be a separate investigation.

I'll probably first look at a little more rear toe while monitoring the tire temperature distribution. I don't want to scrub the tires. As I explained to the technician, I have to steer the car anyway so rolling stability is not that important.

Thoughts?

Bob Wilson

 

[vreihen]

What are the factory specs for rear camber? I'm embarrassed to say that I own a car and don't know the factory alignment specs off the top of my head!

You mentioned that the tire sidewalls are different in thickness between inside and outside. Are they at least symmetric in height on both sides? Just wondering, because I have seen racing DOT radials intentionally constructed with shorter inner sidewalls to provide some static contact patch tilt for camber-challenged cars under some sanctioning body rules. Not that I think it would be done on legitimate street-driven DOT radials, since the contact patch would probably wear level rather quickly.

Ecopia 500's, 600's, or something else?????

 

[Anonymous]

You mentioned that the tire sidewalls are different in thickness between inside and outside.

I think Bob Wilson is referring to the tread pattern, not the sidewalls. On the Ecopia's, the outside bands of tread are more substantial than the inside bands of the tread. The sidewalls measure the same, inside and outside.

View attachment Tire.jpg

 

[vreihen]

OK, makes sense now!

Did the tires that came off have more wear on the inside shoulders than the outside shoulders? Just curious to draw a baseline on the factory camber specs and tire life.....

 

[bwilson4web]

You've got it right. IMHO, we should get 40,000 service miles out of each tire. But this requires attention to camber, toe, and tire pressure. IMHO, BMW USA has no technical expertise in this technical issue.

Bob Wilson

 

[vreihen]

I still have not located the official BMW alignment specs in Google. My gut tells me that -1.5 rear camber is a tad excessive, unless there is a really ugly camber swing from tire movement under hard acceleration. I don't think that there is a large enough amount of body roll to need that much static negative camber, especially on a non-sports car. Is this just a matter of "ultimate driving machine" mentality throwing M3 alignments on the i3?

Do you normally drive alone? If so, find an alignment shop that will let you sit in the driver's seat as they do the alignment. Being a few stones overweight, the alignments in my race car would shift notably as soon as this loose nut got behind the wheel. If there's a local race shop with an alignment rack, they will probably be your best bet for getting it done ballasted and to your specs.....

 

[alohart]

I still have not located the official BMW alignment specs in Google.

This manual includes front and rear alignment specs plus a lot more.

 

[vreihen]

This manual includes front and rear alignment specs plus a lot more.

That most definitely helps, with the caveat that it is targeted for the USA market and may not be same as the ROW specs.

With a disclaimer to check my math on the D-M-S to decimal degree conversions:

Front castor: 4.50 degrees, +/- 0.50
Front camber: -0.33 degrees, +/- 0.42 (L/R delta +/- 0.50 degrees)
Front toe-in: 0.12 degrees, +/- 0.03 (Total: 0.23 +/- 0.20)
Front kingpin offset: -1.99mm

Rear camber: -1.67 degrees, +/- 0.08 (L/R delta +/- 0.50 degrees)
Rear toe-in: 0.15 degrees, +/- 0.03 (Total: 0.30 +/- 0.20)
Rear driving axis: 0.00 degrees, +/- 0.20

Now, to confirm Bob's belief that BMW USA has no technical expertise in this area, can we find the UK or Europe market alignment specs? I'd like to know if there was some sort of engineering tradeoff for the USA market where they used a smidge more negative camber to eek out an extra mile of battery range to meet some obscure CARB requirement at the expense of tire life?????