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      10-20-2012, 08:16 PM   #1
rayusaFL
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What is your tire pressure?

Hello everyone!
I have a 2013 335i Sportline with 18" wheels.
The tire pressure is 32 psi for the front and rear tires. (That's how it came from the dealer)
The info on the driver's side door says 32 psi for the front tires and 38 psi for the rear.
Should I be putting 38 psi on my rear tires?
Your input in highly appreciate.
Thank you in advance.
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      10-20-2012, 08:43 PM   #2
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Yes, do what the door says.
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      10-20-2012, 09:07 PM   #3
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Quote:
Originally Posted by rayusaFL View Post
Hello everyone!
I have a 2013 335i Sportline with 18" wheels.
The tire pressure is 32 psi for the front and rear tires. (That's how it came from the dealer)
The info on the driver's side door says 32 psi for the front tires and 38 psi for the rear.
Should I be putting 38 psi on my rear tires?
Your input in highly appreciate.
Thank you in advance.
Yes, you should.
And, if you drive a lot of consistent high speed miles, and/or want a bit better wear, you can increase 3psi on each end.

Weather has gotten a good bit colder around here. I have to recheck and adjust my tire pressures. Thanks for the reminder.
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      10-20-2012, 09:14 PM   #4
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Thanks for all the replies.
I just wonder why the dealer left 32 psi all around.

Am i going to notice any difference in handling when increasing the rear tires to 38 psi?
Thx.
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      10-20-2012, 10:14 PM   #5
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If you are sensitive to what a car is doing, you will notice. Frankly, most will not.
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      10-21-2012, 07:12 AM   #6
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Hope it's not a stupid question... But why more psi on the rear tires??
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      10-21-2012, 08:14 AM   #7
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Quote:
Originally Posted by rayusaFL
Hope it's not a stupid question... But why more psi on the rear tires??
Something to do with how the car sits down under acceleration maybe?
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      10-21-2012, 08:49 AM   #8
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I put 35PSI front 38PSI rear, no problems at all. The loaner (luxury 328i ) was set too 30PSI all round, thats way to low IMO.
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      10-21-2012, 10:13 AM   #9
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Quote:
Originally Posted by johnbmw6
I put 35PSI front 38PSI rear, no problems at all. The loaner (luxury 328i ) was set too 30PSI all round, thats way to low IMO.
I damaged my runflats setting them at 30 psi because any imperfection on the pavement would impact directly on the wall support of the tire. 30 is definitely too low for a runflat, but i run my pilot sport plus at 29 front and 31 rear COLD! Remember that at highway speeds the heat inflates the tires up to 2 or 3 psi. Great handling, great steering feel and 7 series ride quality!
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      10-21-2012, 10:36 AM   #10
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Quote:
Originally Posted by rayusaFL View Post
Hope it's not a stupid question... But why more psi on the rear tires??
Not in the least bit stupid.

BMW is balancing the feel and handling of the car partially trough the choice of tire pressures. Every tire has a pressure at which it provides maximum grip. As the pressure is lowered or raised from this point,the grip decreases. Intererstingly, grip falls off more quickly with lowered pressure than with raised pressure.

The F30 is a street car which has a good amunt of understeer designed into it. This is much safer and most comfortable for street drivers. BMW has determined that the handling balance it wants is best accomplished through a significantly higher rear tire pressure. The rear tires exhibit more grip than the front with this setup, contributing to the understeer BMW wants.

Raising the front tire pressures will increase grip and will balance the handling more toward neutral by decreasing understeer. It will not eliminate understeer as a lot of understeer is built into the suspension geometry, alignment, etc.

Try the stock tire pressures and compare the handling to what you have been experiencing. My guess is that 32-35 PSI all around provides the best overall grip and handling for the car.
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      10-21-2012, 11:00 AM   #11
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According to the door, 2.2bar in the front, 2.4bar in the back. I have the staggered set up on my car, so 255's out back.
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      10-21-2012, 11:57 AM   #12
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As a BMW driver for many years, I start with door plate/placard pressures for normal loading, reference the wheel/tire size. Then tweak the pressures for best driving/road feel and wear/balance for the tires. Typically find BMW are not far off for my driving use.

I've found RFTs usually require a slightly higher pressure to prevent odd wear patterns. Some of this is the slower warm up rate and tires fail to reach full working pressure on short trips, or in cooler ambient temperatures.

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      10-21-2012, 05:10 PM   #13
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Quote:
Originally Posted by Elk
Quote:
Originally Posted by rayusaFL View Post
Hope it's not a stupid question... But why more psi on the rear tires??
Not in the least bit stupid.

BMW is balancing the feel and handling of the car partially trough the choice of tire pressures. Every tire has a pressure at which it provides maximum grip. As the pressure is lowered or raised from this point,the grip decreases. Intererstingly, grip falls off more quickly with lowered pressure than with raised pressure.

The F30 is a street car which has a good amunt of understeer designed into it. This is much safer and most comfortable for street drivers. BMW has determined that the handling balance it wants is best accomplished through a significantly higher rear tire pressure. The rear tires exhibit more grip than the front with this setup, contributing to the understeer BMW wants.

Raising the front tire pressures will increase grip and will balance the handling more toward neutral by decreasing understeer. It will not eliminate understeer as a lot of understeer is built into the suspension geometry, alignment, etc.

Try the stock tire pressures and compare the handling to what you have been experiencing. My guess is that 32-35 PSI all around provides the best overall grip and handling for the car.
Great info!!
Thank you for your input.
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      10-21-2012, 08:59 PM   #14
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Quote:
Originally Posted by rayusaFL View Post
Thanks for all the replies.
I just wonder why the dealer left 32 psi all around.

Am i going to notice any difference in handling when increasing the rear tires to 38 psi?
Thx.
Looking at the manual, tire pressures are different between 328i and 335i, due to the weight and weight distribution between the cars.

Tire PSI for up to 100mph:
328i with non staggered 18's:
32frt and 35rr.

328i with staggered 18's:
32frt and 32rr

335i with non staggered 18's:
32frt and 38rr

335i with staggered 18's:
32frt and 35rr

If you typically drive over 100mph often, for example you drive on the Autobahn daily, you should raise your cold tire pressures.

For a 335i with non staggered 18's, over 100mph pressures should be, and can go up to:
38frt and 46rr

335i with staggered 18's:
38frt and 41rr

I am currently using 37frt and 40rr.
I use these pressures, between the nominal and high speed, for better tire wear, and potentially better highway MPG.

I got these numbers from the manual, but it's usually best to use the sticker on the door jamb as some factor may have altered the psi to use on the particular tires your F30 came with.

Regarding what ride or handling characteristics you may feel, the easier to notcie aspect is that you may notice harder/harsher bump quality on sharper/larger hits when using higher pressures, as the added pressure will stiffen the sidewall, thus having less sidewall flex to help absorb some to the bump energy. OTOH, the stiffer sidewall can give some positive handling aspects resulting in sharper turn in and quicker transitional handling, as the sidewall flexes less it can result in quicker response.

RFT's in general are harsher with big bumps and hits than non RFT's.
By increasing the psi you may notice a bit harsher hit on those larger hits, but it's not crazy bad.
Handling difference can be harder to detect as it depends on your sensitivity and how fast you tend to drive in corners.

Even harder to detect is how psi changes between front and rear can alter under-steer or over-steer.
If you change the psi difference between front and rear, you may notice under/over steer changes, but again it depends on what you can notice to begin with.
For example, your nominal under 100mph pressures are 32frt and 38rr, a 6psi difference. If you have some noticeable under steer, you can play around with the pressures on just one end of the car, and then drive it to see if there is a positive change to handling.
I wouldn't recommend going below the nominal psi though
You can use the nominal and high speed psi range to play around witih.
It may not be night and day differences though, as it can be more subtle and it can be positive or negative based on what pressures you use.
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      10-21-2012, 09:07 PM   #15
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Quote:
Originally Posted by rayusaFL View Post
Thanks for all the replies.
I just wonder why the dealer left 32 psi all around.

Am i going to notice any difference in handling when increasing the rear tires to 38 psi?
Thx.
32psi all around are the pressures for the 17" wheels/tires in both non staggered and staggered sizing.
And, 32psi is the pressure for a 328i with staggered 18's.

The car prep guy probably didn't know what he was doing.
One would think that a certified tech would do the final dealer prep, but I see the porters doing some of the more mundane tasks like proper tire inflation.

Last edited by RPM90; 10-21-2012 at 09:42 PM.
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      10-21-2012, 09:42 PM   #16
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Quote:
Originally Posted by Koer View Post
I damaged my runflats setting them at 30 psi because any imperfection on the pavement would impact directly on the wall support of the tire. 30 is definitely too low for a runflat, but i run my pilot sport plus at 29 front and 31 rear COLD! Remember that at highway speeds the heat inflates the tires up to 2 or 3 psi. Great handling, great steering feel and 7 series ride quality!
If you're running 29 front and 31 rear COLD pressures, then you are running with UNDER-inflated tires, and your going to get greater wear, and more importantly you have less grip.

Remember, COLD tire pressures already take into account that the tire will heat up and psi will rise. How much psi will rise depends on certain factors, like ambient temps, how fast you're moving, and your cold tire pressure.
That's why tire pressure is set to the recommended psi when COLD not hot.
Again, the hot psi depends on various factors and thus it's not used as the base starting point.

If you run with under inflated cold temps, you may very well end up with HIGHER hot/running temps, because an under inflated tire doesn't have the proper psi to maintain the needed sidewall stiffness. So, as you're driving the tires heat up. The low pressure puts more tread in contact with the road surface increasing friction and heat, more than with proper PSI. Also, the lower psi soft sidewall will flex MORE and that will generate even more heat and higher psi. This added flexing is what leads to premature sidewall wear and greater potential for sidewall failure/blow out, along with the greater tread wear from the added friction and hotter running temps.

A 335i with non staggered 18's should be running 32psi front and 38psi rear.
You're 3psi too low at the front and 7psi too low at the rear!
Also, I don't know where you live, but ambient temps can swing a good bit from early morning to afternoon during the fall and spring seasons.
If you set your tires to 29frt and 31rr in the afternoon and it was let's say 70F, then in the morning if the temp is 50F, now your cold tire pressures will be 27frt and 29rr, even lower than where they should be.
Static, non moving, tire pressure can change by an average of 1F for every 10F degrees.

Yes, the ride may be comfy, because the sidewalls are soft, but your tires won't last as long, and your MPG is suffering, and worse you're compromising traction/grip resulting in worse handling and braking.
I don't know how your car can have "great" steering feel and handling with such low psi mussy sidewalls.
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      10-21-2012, 10:00 PM   #17
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Quote:
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I just wonder why the dealer left 32 psi all around.
Simple. The tech wasn't paying attention to his job. Its epidemic!
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      10-22-2012, 10:02 PM   #18
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I usually run 3-4psi more then what the door says.
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      10-23-2012, 03:09 AM   #19
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I usually run 3-4psi more then what the door says.
Me too.
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      10-23-2012, 10:16 PM   #20
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Quote:
Originally Posted by RPM90 View Post
If you're running 29 front and 31 rear COLD pressures, then you are running with UNDER-inflated tires, and your going to get greater wear, and more importantly you have less grip.

Remember, COLD tire pressures already take into account that the tire will heat up and psi will rise. How much psi will rise depends on certain factors, like ambient temps, how fast you're moving, and your cold tire pressure.
That's why tire pressure is set to the recommended psi when COLD not hot.
Again, the hot psi depends on various factors and thus it's not used as the base starting point.

If you run with under inflated cold temps, you may very well end up with HIGHER hot/running temps, because an under inflated tire doesn't have the proper psi to maintain the needed sidewall stiffness. So, as you're driving the tires heat up. The low pressure puts more tread in contact with the road surface increasing friction and heat, more than with proper PSI. Also, the lower psi soft sidewall will flex MORE and that will generate even more heat and higher psi. This added flexing is what leads to premature sidewall wear and greater potential for sidewall failure/blow out, along with the greater tread wear from the added friction and hotter running temps.

A 335i with non staggered 18's should be running 32psi front and 38psi rear.
You're 3psi too low at the front and 7psi too low at the rear!
Also, I don't know where you live, but ambient temps can swing a good bit from early morning to afternoon during the fall and spring seasons.
If you set your tires to 29frt and 31rr in the afternoon and it was let's say 70F, then in the morning if the temp is 50F, now your cold tire pressures will be 27frt and 29rr, even lower than where they should be.
Static, non moving, tire pressure can change by an average of 1F for every 10F degrees.

Yes, the ride may be comfy, because the sidewalls are soft, but your tires won't last as long, and your MPG is suffering, and worse you're compromising traction/grip resulting in worse handling and braking.
I don't know how your car can have "great" steering feel and handling with such low psi mussy sidewalls.
Interesting! i was always used to leave my tires at a low pressure and set them at a higher pressure on the weekends when i went out for a drive in the twisty mountains.

Now unfortunately the place where i live (Mexico City) has the worst street conditions you could imagine, so its a gamble; put your tires to the correct pressure and you will end up screwing up your steering and suspension due to the vibration and impacts of the low quality pavement. Lower your tire's Psi and you protect your suspension and steering, but certainly my tires are not going to last as long.

It all depends on the place you live. Some people are blessed with butter smooth streets and no potholes. Some are not that lucky.
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      12-19-2012, 04:52 AM   #21
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I am regularly filling 32 psi all round, running on 18"ers style 397 wheels square setup on my F30 328i. I am getting decent performance with the current tyre pressures.

The reason to keep low tyre pressure is that in Mumbai, India the road quality is pathetic, sometimes the pot holes are almost the size of a crater. So keeping the tyre pressure lower than specified will help a bit in cushioning the ride quality & also not hampering the suspension as the tyre will absorb the bumps.

Can some one please elaborate on the pros & cons of keeping 32 psi all round / lower than company specified

Note : Running on 225/45 R18 Goodyear Excellence RFT setup
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Last edited by 7 4 7; 12-19-2012 at 04:58 AM.
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      12-19-2012, 08:10 PM   #22
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Quote:
Originally Posted by Koer View Post
Interesting! i was always used to leave my tires at a low pressure and set them at a higher pressure on the weekends when i went out for a drive in the twisty mountains.

Now unfortunately the place where i live (Mexico City) has the worst street conditions you could imagine, so its a gamble; put your tires to the correct pressure and you will end up screwing up your steering and suspension due to the vibration and impacts of the low quality pavement. Lower your tire's Psi and you protect your suspension and steering, but certainly my tires are not going to last as long.

It all depends on the place you live. Some people are blessed with butter smooth streets and no potholes. Some are not that lucky.

asi es paisano la cuidad de los baches y topes. yo las traigo en 36 adelante y 38 atras, probare con tus psi a ver como se siente. saludos
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