Tire Wear

[djbock]

Have Toyo Proxes S/T 2's that I run in the summer on a 20" staggered set-up (275/40R20 Front-315/35R20 Rear). Anyway when I recently installed them again when the weather warmed up noticed that both front tires are cupped on both inner and outer edges.

Am I looking a suspension/alignment problem or is it the tires? The winter tires (Pirelli Scorpion Ice and Snow in OE 19" Size) are worn even and square on all 4 tires.

[ard]

So never changed the alignment at all?

Ran proxies all last summer; took them off; ran Pirellis for a season, even wear, no issues, but now proxies had this uneven wear when reinstalled?

I always, always, always ask 'what is the alignment'. Ive learn that you simply cannot think that 'even wear says alignment is good'. Tires can look OK for the first 10k, then turn to crap quickly.

Spend $100 on an alignment. Ask if you need recommendations, but DO NOT just think 'in spec' is OK

[djbock]

Originally Posted by ard

So never changed the alignment at all?

Ran proxies all last summer; took them off; ran Pirellis for a season, even wear, no issues, but now proxies had this uneven wear when reinstalled?

Spend $100 on an alignment. Ask if you need recommendations, but DO NOT just think 'in spec' is OK

Correct, 2 summers with the Toyo's and 2nd winter with Pirellis. No alignment done in between. Knew they were cupped when I pulled them off last fall, but forgot they were this bad.

It's the cupping on the inner and outer edges of both front tires that have me stumped.

[ard]

Originally Posted by djbock

It's the cupping on the inner and outer edges of both front tires that have me stumped.

So if it were just one edge, what would you do???

I suspect same as two edges....

[djbock]

If it was just one edge I would be more apt to assume that it was a suspension component that is failing. Whereas the fact that it is wearing on both edges has me thinking that it is the tires, hence the reason for the post.

Am just trying to confirm my suspicions be asking other members that may have some insight.

[ard]

Tire wear >>>> Alignment

If a tire is toed and 'scrubbing' you can get oscillations that lead to 'cupping' on opposite sides of the tire. Dynamically the whole tire just wiggling back and forth, causing uneven wear on both sides. People tend to think very one dimensionally and in terms of what their eyes see- "oh, the inner edge is camber"... or 'the tire wear seems uniform, just only got 8k miles on the set so the alignment must be good"

[Doug Huffman]

How reliable is the X5 alignment, please? Tire wear seems an expensive and imprecise indicator.

The previous car required re-alignment once, after being dragged sideways out from under a tornado collapsed building - 27 April 2011, Ringgold, Georgia. We drove home crabbin' sideways, with the mirrors hanging from their wires and flapping against the bodywork.

[ard]

"reliable"? Very.

"set perfectly from the factory"?

Rarely.

[Doug Huffman]

Should we have alignment set to factory specs (despite the problems of angular measurement set-up precision - limited trigonometry baseline length) or tire reaction forces?

In my engineering career, we jumped through lots of hoops to avoid cosine error. Again, I am a new BMW owner.

[ard]

Originally Posted by Doug Huffman

Should we have alignment set to factory specs (despite the problems of angular measurement set-up precision - limited trigonometry baseline length) or tire reaction forces?

In my engineering career, we jumped through lots of hoops to avoid cosine error. Again, I am a new BMW owner.

??

Well, as you allude to there are two ways to spec alignment: angle of the wheel (which is independent of the tire./wheel size) and "inches at the tread" (which will depend on the diameter of the tire.

Little tidbit: All stock OE tire sizes, 18" rim, 19" rim, 20",m 21" have the same TIRE DIAMETER. This lets them slap any tire on and car rolling off the line and not have to calibrate anything.

So you can use angle or inch.

I like inches at the tire OD. Old school. String, chalk, spin wheels, measure.

The trick is NOT to get caught up with "what the BMW engineers speced". You'd like to think they speced this on the basis of "best handling, best driving, best wear". Not at all. Criteria was 'fastest and easiest to hit, minimize our cost and field labor'

-.01 to 0.02 per wheel, all 4, mid spec on camber. Caster whatver. Ideally balanced side to side.

The "BMW factory spec is HUGE- you can get 45,000 miles on one alignment and 8,000 miles on anohter- both will be "in spec". Hard for people to wrap their head around this, no?