Correct 20 inch front tire pressure for non run flats?

[shark715]

I have an '11 50i with the 20 inch staggered wheel option, and until now I've run the OEM summer Bridgestone run flats and Pirelli Scorpion run flats in the winter. I've experienced terrible wear on the outside 15-20% of both the left and right front tires (both summer and winter), even after taking the pressure up to 40 lbs. in an attempt to make the center of the tires wear at about the same rate as the outer edge. I assumed the answer was an alignment. Yesterday I had new Michelin Latitude Xi2 (non run flat) winter tires installed, and had an alignment done. The tech who did the alignment said that the truck's alignment was barely out of spec at all. So my question is what front pressure do I run the new tires at to insure they wear properly? The tire dealer filled the tires to about 35 lbs. The ride on a bumpy road is noticeably less jarring (I assume due to the non run flats, and I immediately noticed that the low speed steering is definitely lighter than before. I also sense there has been a slight loss of on center tracking at freeway speeds, and some loss in handling sharpness, (I assume both of these are due to the softer sidewalls versus the run flats) not really initial turn in, but a small bit of a sensation of swaying from the back of the truck that was not present with the 315/35 rear run flats. Note that I went with the same 275/40 on the rear as on the fronts because these tires are not made in 315/35 size, and I assumed the 275/40 size would be better in snow. Thanks in advance for your input.

[mitch808]

Its somewhere between what's on the inner door sticker and what the tire sidewall recommends. You just need to start there, I usually use the tire recommendations and adjust from there

IMO, everyone can benefit from the -0.5 camber arms BMW makes.

[shark715]

Originally Posted by mitch808

Its somewhere between what's on the inner door sticker and what the tire sidewall recommends. You just need to start there, I usually use the tire recommendations and adjust from there

IMO, everyone can benefit from the -0.5 camber arms BMW makes.

Thanks Mitch, appreciate you taking the time to respond.

I've started with 45 lbs to see if that keeps the tires from prematurely wearing the outer edges. With 45 lbs in the front tires, the ride and handling are much more like with the run flats. I will watch closely and report back with the results.

The camber arms that you refer to...where can I get them? Roughly what do they cost, and roughly what's the labor. Sounds as if the truck should have rolled out of the factory with them?

[joe_planet]

I run my conti dws at around 35 and I have even wear in 10 k miles. 45 is going to be way too high you'll wear out the center.

[Chio]

45 OMG way to high! i run my DWS at 35 also

[shark715]

Thanks for the additional responses. I've compromised and have taken the pressure down from 45 to 42. The door jamb sticker says 33, but again with the previous (runflat) tires I experienced really bad outside edge wear when I ran the tires at the suggested pressure or slightly above. So I'm somewhat concerned about ruining the new tires I just purchased. I'll keep a close eye on how the new tires wear and report back.

[mitch808]

Originally Posted by shark715

Thanks Mitch, appreciate you taking the time to respond.

I've started with 45 lbs to see if that keeps the tires from prematurely wearing the outer edges. With 45 lbs in the front tires, the ride and handling are much more like with the run flats. I will watch closely and report back with the results.

The camber arms that you refer to...where can I get them? Roughly what do they cost, and roughly what's the labor. Sounds as if the truck should have rolled out of the factory with them?

When I autox or do track days in my Subaru, I only add about 2-4lbs of air ever. That is more than enough to tune out sidewall flex, and adjust my pressures front to rear to add or remove oversteer.

As for front camber arms, they are a BMW OEM part. You buy them from the dealer. Probably looking at around $1k installed or there abouts.

[shark715]

Thanks again Mitch. Yuk, I don't want to spend $1000 for new camber arms if I don't have to. I'm going to first see if I can control the tire wear by adjusting the tire pressure. The ride comfort even with 45 lbs is no worse than the run flats, and I'm assuming in the end I will settle at less pressure than that. And the dry road handling does seem to be adversely affected. Noticeably better at 45 lbs versus the 35 the tire dealer put in. Of course I don't yet know if wet road handling will be negatively effected, and even more important if the 40+ pounds of pressure will hurt snow and ice traction.

[smyles]

Slightly off, but fellow DWS users, how's your mileage? I switched from Toyos STII to DWS and my average went down from 24.5 to 22.6 (this is for 3.5d) - same route & driving style, correct pressure, etc. etc. I didn't expect that, frankly speaking...

[mitch808]

If you go by BMW's inner door sticker, I think it's 30PSi fr/rr (4 adults)or 30psi front/40psi rear (Based on a fully loaded car, 5 adults and luggage), this based on 20" tire fitment. The lower reading is way too soft IMO. I like around 35-40 all around, you can play around with this value up or down all around, or tweak the front or rear being +/- 2-3psi to tweak handling characteristics.

[PAX5]

Originally Posted by shark715

... I've experienced terrible wear on the outside 15-20% of both the left and right front tires ... I assumed the answer was an alignment.

... Yesterday I had new Michelin Latitude Xi2 (non run flat) winter tires installed, and had an alignment done. The tech who did the alignment said that the truck's alignment was barely out of spec at all...

Publish the actual alignment BEFORE and AFTER measurement values and we'll tell you if the tech was right.

I suspect that the alignment was done to within the BMW specifications, but not to the optimal value for the toe-in.

Do you remember if they loaded the car down with weights during the alignment?

[shark715]

Originally Posted by PAX5

Publish the actual alignment BEFORE and AFTER measurement values and we'll tell you if the tech was right.

I suspect that the alignment was done to within the BMW specifications, but not to the optimal value for the toe-in.

Do you remember if they loaded the car down with weights during the alignment?

I used a Tire Rack installer, which may have been a mistake. While they did have a Hoffman laser alignment rack, this was not the highest tech shop in the world. They did know to send me down the street to fill the fuel tank before the alignment, but I was not aware at the time that BMW specifies the weights that they do. They did not give me any sort of printout upon completion as I have seen done at other shops.

[PAX5]

Originally Posted by shark715

I used a Tire Rack installer, which may have been a mistake. While they did have a Hoffman laser alignment rack, this was not the highest tech shop in the world. They did know to send me down the street to fill the fuel tank before the alignment, but I was not aware at the time that BMW specifies the weights that they do. They did not give me any sort of printout upon completion as I have seen done at other shops.

Your alignment measurements are stored in the machine. Go back and ask for the printout ... or complain and re-do the alignment. Ask for a print out this time. Show us the results.

Or ... ask to re-do the alignment and set the toe-in "close to zero, but not quite zero". Aim for a value of 0.02. This will take patience on the tech's side, sometimes as much as half an hour if the laser beam drifts ... make sure the equipment is recently calibrated.

Attached are my most recent results: we tried to hit 0.02 for the left and right toe-in (took about 20 minutes total), but each time we hit it and tightened the eccentrics, it would drift back to 0.00. So we left it. The machine displays the reading in RED, because it is technically outside the spec.

BTW, this was done at my favorite local Honda/Acura dealership - $89.00!

[shark715]

I appreciate the insight, but I really don't want to go back there. I left the shop a negative review on Tire Rack's website. Not only did I have to sit there and wait 5 hours for them to replace 4 tires and perform an alignment (I had an appointment, although admittedly I did not ask them up front how long it would take, but who ever heard of it taking 5 hours for new tires and an alignment?), on top of that they advertise on Tire Rack's website 30% off the price of an alignment if you have it done with the installation of 4 tires from Tirerack. Turns out the 30% off price ($89.95) is bogus as it's the same price anyone who walks in the door pays (New Jersey state law requires auto repair shops to post a price list and that's the posted price in their shop for an alignment). But the worst part was that I thought I heard them using a air gun to tighten the lug nuts, and while I was driving home I felt a significant vibration from the rear axle. Sure enough, when I checked the lug nut torque I found two that were barely finger tight as well as several that were so tight that I could barely loosen them with a 25 inch breaker bar (and I'm a pretty strong guy) before properly retorquing them with a torque wrench. Who knows, perhaps I did get a terrific alignment job and that's why it took so long, but needless to say I'm not confident.