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BMW 3-Series (E90 E92) Forum > E90 / E92 / E93 3-series Technical Forums > Wheels and Tires Forum Sponsored by The Tire Rack > Tire Pressure with New Non-Run-flats PSS



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      04-18-2013, 02:20 PM   #1
Rmnelson12
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Question Tire Pressure with New Non-Run-flats PSS

Just mounted and balanced some new Non Run Flat Michelin PSS to replace the stock Run Flats. The ride is great, I love em. But the tire pressure in the fronts are 45 and rears 48~.

NRFT or not, should the tire pressures still match does on the door frame and manual spec? OR do these tires require a different, higher tire pressure (PSI)?

Thanks
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      04-19-2013, 09:01 PM   #2
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Discount tire advised me to keep it at the same pressure, runflats or not. Hope this helps.
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      04-19-2013, 09:10 PM   #3
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Been reading about this too and most people say to start at somewhere Fronts and Rear at 35. Anyone knows? Also, does the PSI change if we're running 19" vs 18"? I will be acquiring 245/35/18 and 265/35/18 and frankly i have no idea what PSI to run at =(
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      04-19-2013, 09:29 PM   #4
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Quote:
Originally Posted by Rmnelson12 View Post
Just mounted and balanced some new Non Run Flat Michelin PSS to replace the stock Run Flats. The ride is great, I love em. But the tire pressure in the fronts are 45 and rears 48~.

NRFT or not, should the tire pressures still match does on the door frame and manual spec? OR do these tires require a different, higher tire pressure (PSI)?

Thanks
Whoa! Check the label on your driver side door.

Tire pressure should still be the same, RFT or non-RFT, doesn't matter.

With that said, I have Hankook Ventus 12 at 235/40/18F, 265/35/18R and I increased the pressure slightly, running 35psi front and 41psi rear for the occasional run up beyond 100mph. Yellow label on my door indicates 39psi front and 45psi rear for speeds up to and beyond 100mph for our rides, regardless of tire type.
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      04-20-2013, 01:05 AM   #5
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The tire pressure needs to remain the same as posted on your driver side door entry labels... The weight of your front and back axle load did not change, you have the same engine and components summing up to the same weight as with RFTs or Non RFTs...(not counting wheels and tire difference) Remember if you up your rim size or change your tire specs your PSI will be different from your mark label

Tire PSI Equation
(Axle weight / 2) / Tire Capacity weight ) x Tire Max Pressure = Inflation Pressure.
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      04-20-2013, 01:07 AM   #6
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I just got these tires recently and my pressures are 38 psi front and 45 psi rear.
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      04-20-2013, 01:12 AM   #7
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Quote:
Originally Posted by The Wildcard
I just got these tires recently and my pressures are 38 psi front and 45 psi rear.
This is right when running 18s with stock tire specs...
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      04-20-2013, 08:23 AM   #8
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Tire pressures should differ for 19inch rims I believe right? I've got a pair of PSS and SF-71s sitting at home right now waiting to be mounted. Just waiting for my new suspension components to come in.
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      04-20-2013, 01:06 PM   #9
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Quote:
Originally Posted by melloww22 View Post
This is right when running 18s with stock tire specs...
weird - my door says 35 front, 42 rear - e93 N54 w/sport package
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      04-20-2013, 03:57 PM   #10
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I just put in 38 all around on my PSSs.... is this incorrect? Should I run 45 in the rears?
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      04-21-2013, 01:56 PM   #11
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Normal operating PSI for 18's are 32f, 35r .
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      04-21-2013, 02:15 PM   #12
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i run 42f 38r which works great for me
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      04-21-2013, 04:29 PM   #13
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38psi all around on 19" Michelin PSS. Seems to be about right using the arrow indicators on the sidewalls.
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      04-21-2013, 06:22 PM   #14
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I have no idea why people in the tire industry think the tire placard shows correct pressure for Non-RFT performance tires. My only guess it they don't want to be legally liable for their advice. The stock pressures are described according to the manufacturers preferred trade-off about ride comfort vs other considerations (!). Generally its not related to any mathematical calculation about weight loading, tirewear, handling or anything else.
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      04-23-2013, 09:23 AM   #15
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In actuality, the vehicle manufacturer's recommended tire inflation pressures have a lot to do with load capacity, handling, and a variety of other factors the OEM must consider before putting their product into the hands of the general public.

Usually, vehicle manufacturers default to the worst case scenario of fully loaded and higher speed use, which puts a pretty high psi recommendation on the placard. Fortunately BMW takes hings further since they take the time and effort to tune and then recommend multiple inflation pressures based on how the vehicle is being loaded and driven. Depending what year your car was produced, the doorjamb placard may show only one inflation pressure recommendation, (intended to keep things simple) but BMW will show you alternate pressures for higher load, high speed driving in the vehicles owners manual and on some years on the tire placard itself.

To answer the OP's original question : The engineering rules that govern tire design and load capacity don't distinguish between runflat and conventional (non-runflat) tires. In a given tire size, a specific psi = ### load. Add to this what I've described above and as a starting point using the placard psi in your non-runflat replacement tires is the best place to start. You're free to adjust from there, but we strongly discourage considering going lower than what is recommended by the BMW.
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      04-23-2013, 11:56 AM   #16
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I have 18" staggered PSS on my 08 328i (w/ sport suspension), and go with the recommended pressures on the door sticker: 32 psi front, 41 psi rear. The ride is great, and the tires stay firmly glued to the road even when cornering hard. No complaints here.

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      04-23-2013, 12:36 PM   #17
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Quote:
Originally Posted by flip4335 View Post
Whoa! Check the label on your driver side door.

Tire pressure should still be the same, RFT or non-RFT, doesn't matter.
+1

45/48 seems very high for the tire pressure, OP. Adjust accordingly.
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      04-24-2013, 02:17 AM   #18
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Quote:
Originally Posted by Gary@TireRack View Post
In actuality, the vehicle manufacturer's recommended tire inflation pressures have a lot to do with load capacity, handling, and a variety of other factors the OEM must consider before putting their product into the hands of the general public.
I'd agree there are a lot of factors. Not one pressure for everyone and every type of usage. However I don't know anyone who adjusts their tire pressure when going on highway trips or if they get 2 additional passengers.

A lot of people seem to choose the PSI figure for 2 people in their car, and then wonder why their tires don't wear evenly, why they get mushy handling from their high performance tires, and why they occasionally damage rims. Part of the problem is probably due to short trips in city traffic where they normally don't get the tires up to operating temperature. BMW's approach is different from most manufacturers and they give more detail, but I personally don't think its useful. Generally I think it leads to people underinflating their tires.

Last edited by John_01; 04-24-2013 at 02:30 AM.
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      04-24-2013, 08:23 PM   #19
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Quote:
Originally Posted by melloww22 View Post
The tire pressure needs to remain the same as posted on your driver side door entry labels... The weight of your front and back axle load did not change, you have the same engine and components summing up to the same weight as with RFTs or Non RFTs...(not counting wheels and tire difference) Remember if you up your rim size or change your tire specs your PSI will be different from your mark label

Tire PSI Equation
(Axle weight / 2) / Tire Capacity weight ) x Tire Max Pressure = Inflation Pressure.
This equation is interesting, but obviously not right since BMW is known for 50/50 axle weight distribution and yet recommends a higher psi for rear axle. It's apparent that loading is missing as a variable in the equation.

I recommend experimenting. As long as you are around the recommended air pressure, probably at or up to 4 psi more, you'll prob have no problems. I like the firmer ride of adding +2 psi over recommended with conti dws nonRFT.
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      04-24-2013, 08:37 PM   #20
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Quote:
Originally Posted by stupordave View Post
38psi all around on 19" Michelin PSS. Seems to be about right using the arrow indicators on the sidewalls.
I heard about the arrow indicators and not sure I believe it.
These arrows are designed to point out where the thread wear bars are.

Perhaps the only true test is to have the car under normal load run over some water or wetting fluid and run over paper such that it imprints the paper with the fluid. Getting the right "footprint" would indicate the "right" air pressure. Sounds like a pain to do, but if you really want to know, maybe it's worth the cost/time.
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      04-24-2013, 09:32 PM   #21
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I run 34-38 on 17in PSS.

I've been running 29-36 (sticker advised) and it was bad (mushy turn in, mostly). I've also tried 33-33 all around, it was ok but it didn't felt tight and I could see traces or riding the sidewall after some hooliganism. I found that anything over 35 front was understeer prone, didn't like at all.

The arrow thing (michelinmans in PSS case) does work. At 34-38 the wear limit reaches exactly the top of michelinman's head.
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      04-25-2013, 10:13 AM   #22
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Quote:
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These arrows are designed to point out where the thread wear bars are.
+1
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