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  #1  
Old 01-24-2020, 08:05 AM
paramedic1079 paramedic1079 is offline
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Recommended Tire Pressure for 255/50/19

Hello all. I'm in the process of refinishing my BMW M-sport style 333 wheels and have been running a backup set of BMW 19 inch rims with 255/50/19 tires. I was originally following the recommended pressures in the door jam and running 33psi all around (275/40/20 front, 315/35/20) since my speeds were rarely 100mph+. What are you all running with 255/50/19 tires? I've tried finding recommended pressures for this size and I'm seeing a wide range. Thanks in advance.
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  #2  
Old 01-24-2020, 08:09 AM
paramedic1079 paramedic1079 is offline
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FYI...currently running 36psi. The car doesn't have 3rd row seating and it's really just me in it when driving.
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Old 01-24-2020, 08:17 AM
Autoputzer Autoputzer is online now
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Smaller tires required more pressure. My Schwinn Super Le Tour's tires took 85 PSI.

The owner's manual (and maybe the door jamb decal) should give the recommended pressures for all the tire sizes that came on the car//truck. It's been my experience that more even tire wear will be achieved with the pressures two to four PSI above the recommended pressures (measured cold in the early morning before sunlight hits the tires).
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Old 01-24-2020, 08:30 AM
paramedic1079 paramedic1079 is offline
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Quote:
Originally Posted by Autoputzer View Post
Smaller tires required more pressure. My Schwinn Super Le Tour's tires took 85 PSI.

The owner's manual (and maybe the door jamb decal) should give the recommended pressures for all the tire sizes that came on the car//truck. It's been my experience that more even tire wear will be achieved with the pressures two to four PSI above the recommended pressures (measured cold in the early morning before sunlight hits the tires).
I'm now seeing 32front/36 rear under 100mph and 35front/41rear 100+ in a manual online...obviously this is BMWs recommended pressure for a fully loaded vehicle. I'm definitely going to bump up the pressure in my 20s when I remount the tires. I noticed my 315s in the rear were a little choppy and obviously due to aggressive driving/lower pressure at 33psi.
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Old 01-24-2020, 09:02 AM
Autoputzer Autoputzer is online now
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I "dial in" pressures by taking precision tread depth measurements with a digital tread depth gauge (resolution to 0.001" or 0.01mm) when I rotate the tires, and by maintaining the same pressures over an entire rotation stint (to establish a correlation between pressures and measurable wear). From this, it's been my experience that BMW's spec's pressures that are really soft in the front and less soft in the back, when using tread wear as a basis.

Race teams dial in pressures by taking a temperature profile across the tires right as the cars come into the pits. My method is sort of an ultra-slow-motion version of that.

Frau Putzer's G01 X3 30i calls for 32 PSI in the front and 35 PSI in the back. I've settled in at 38 PSI in the front and 39 PSI in the back.
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Old 01-24-2020, 09:41 AM
ard ard is offline
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Mein Auto: '12 X5 35d/E39M5/996TTX50
36 F 33 rear.

Only one person. Never carrying much.

There is more weigh up front.

This is based on 150k miles of 'experience' looking at tire wear and handling. Mich latitude ZP HPs

Road trips w more people I will go to 36R
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Alignment here: The Definitive Alignment Thread

OE is Original Equipment aka 'BMW Original Parts' aka 'What you buy at the BMW dealer with a BMW label'

OEM is Original Equipment Manufacturer... EITHER the company that made the OE part or.... A part this is identical to the OE part, but is sold by the OEM under their own label


OEM is not what BMW sells


http://www.bimmerzone.com/category/T...ricks_OEM.html

https://www.turnermotorsport.com/t-OEvsOEM
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Old 01-24-2020, 10:08 AM
paramedic1079 paramedic1079 is offline
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Originally Posted by ard View Post
36 F 33 rear.

Only one person. Never carrying much.

There is more weigh up front.

This is based on 150k miles of 'experience' looking at tire wear and handling. Mich latitude ZP HPs

Road trips w more people I will go to 36R
How is your tire wear running 33 in the rear? Any chopping?

Thanks.
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Old 01-24-2020, 10:14 AM
ard ard is offline
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Even.

Of course alignment matters. I run 0.01 to 0.02 toe in, all corners.

Keep in mind that the 'placard' numbers are legal/regulatory requirements. Derived from safety considerations at full-laden conditions. If you have one 105lb woman driving and a few saddles in the back, you arent anywhere near 'loaded'.
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Alignment here: The Definitive Alignment Thread

OE is Original Equipment aka 'BMW Original Parts' aka 'What you buy at the BMW dealer with a BMW label'

OEM is Original Equipment Manufacturer... EITHER the company that made the OE part or.... A part this is identical to the OE part, but is sold by the OEM under their own label


OEM is not what BMW sells


http://www.bimmerzone.com/category/T...ricks_OEM.html

https://www.turnermotorsport.com/t-OEvsOEM
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Old 01-24-2020, 10:14 AM
pshovest pshovest is offline
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40 front 38 rear. I'll get 40K from these LS2's
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Old 01-24-2020, 10:24 AM
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Doug Huffman Doug Huffman is online now
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Quote:
Originally Posted by ard View Post
Even.

Of course alignment matters. I run 0.01 to 0.02 toe in, all corners.

Keep in mind that the 'placard' numbers are legal/regulatory requirements. Derived from safety considerations at full-laden conditions. If you have one 105lb woman driving and a few saddles in the back, you arent anywhere near 'loaded'.
Do you have a citation for the “legal / regulatory requirements?” I have turned the web on ear and given it a good shake looking for a calculation of tire pressures.
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Old 01-24-2020, 01:20 PM
B4_685 B4_685 is offline
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Old 01-24-2020, 09:35 PM
ard ard is offline
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Quote:
Originally Posted by Doug Huffman View Post
Do you have a citation for the “legal / regulatory requirements?” I have turned the web on ear and given it a good shake looking for a calculation of tire pressures.
No, but could probably find something in 'labeling requiremets'.

The 'legal/regulatory' aspect is "the mfg SHALL affix a label that informs customers of[list of things]". I doubt that there is some kind of regulation around how they must calculate tire pressure. Just that the mfg must state the pressures and tire sizes and ratings. Its up to the mfg to set the pressures- their call. But for legal/risk reasons, they pick a 'safe' number that works on a car with max weight. IMO that pressure is then used for all of the compliance and certification testing on the car. CAFE/mileage testing, etc.
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Alignment here: The Definitive Alignment Thread

OE is Original Equipment aka 'BMW Original Parts' aka 'What you buy at the BMW dealer with a BMW label'

OEM is Original Equipment Manufacturer... EITHER the company that made the OE part or.... A part this is identical to the OE part, but is sold by the OEM under their own label


OEM is not what BMW sells


http://www.bimmerzone.com/category/T...ricks_OEM.html

https://www.turnermotorsport.com/t-OEvsOEM
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  #13  
Old 01-25-2020, 07:02 AM
Autoputzer Autoputzer is online now
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Ride quality is a factor when the car manufacturer selects pressures. That's what was probably the main underlying cause of the Firestone-Ford Explorer fiasco in the 1990's. Ford lowered the recommended tire pressures to make the truck based, live-rear-axle SUV ride better.

Another factor in selecting pressure is to allow the car to maintain adhesion when encountering discontinuities in the pavement. If the pressures are too high, a discontinuity such as an expansion joint or slight change in pavement surface elevation will cause a loss of adhesion. "Static" friction (when the tire isn't sliding on the pavement) is greater than "dynamic" friction (when the tire is sliding). Once the tire starts sliding, the higher level of friction (to turn, or slow down the car) isn't regained until the tire stops sliding on the pavement.

Here's the tread wear data from Frau Putzer's G01 X3 from ~10k miles to ~17k miles. During the rotation stint, I had the pressures at 36 PSI front and 39 PSI rear, four PSI over what the decal recommends. I measure or adjust the pressures to be at the average morning low temperatures. (If the forecasted average morning low temperature for the next ten days is 60F, but it's 70F in the garage when I measure and adjust the pressures, I subtract one PSI from the pressure I adjust the pressures to.)

Misalignment causes excessive wear on one side of the tire. But, it also causes less wear on the opposite side of the tire. Over-pressure causes more wear in the middle of the tire. Under-pressure causes more wear on both sides of the tire. I assess the alignment by comparing the inside wear to the outside wear. I assess the pressure by comparing the average of the side wear (inside and outside) to the average of the middle wear.

The data shows that the average front side wear was 0.18/32" greater than the average front middle wear. That indicates an under-pressure condition in the front.

The data shows that the average rear middle wear was 0.14/32" greater than the average rear side wear. That indicates an over-pressure condition in the rear.

The tires came "round shouldered" when new, with 9/32" of depth in the inside and outside circumferential channels, and 10/32" of depth in the two middle circumferential channels. To extend the tires' life, my goal is to introduce slightly more wear in the two middle channels. So, for the next rotation stint I've raised the pressures in the front tires from 36 PSI to 38 PSI. I've maintained the rear tires at 39 PSI, to keep that 0.14/32" greater average wear in the middle channels.

The data also shows that the outside channels on all four tires are wearing slightly faster than the corresponding inside channels, an average of ~0.27/32" in 7k miles. This all happened between 10k and 17k miles. At the 10k mile measurement, the inside and outside channel depths were almost identical. So, I'm having the alignment checked. If the alignment values are in the middle of the tolerance window, I'll have them reduce the toe-in on all four wheels (from the middle of the window to the lower end of the window).

You can't see 0.27/32" with your eyeball or even with a mechanical, analog tread depth gauge. That's where the high-resolution, digital tread depth gauge becomes valuable.

These are low-performance SUV tires, and they're symmetric. If the excessive wear on the outside channels continues after the alignment, I can extend the tire life by having all four tire inverted on the rims (~$125) at around their mid-life point (~30k miles). I did this trick on a Chevy Silverado 1500 pick-up truck years ago, and ended up getting 74k miles out of the original tires.
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Last edited by Autoputzer; 01-25-2020 at 07:06 AM.
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