# Run-flat tires and tire pressure sensitivity.



## buckybadger (Dec 21, 2008)

After reading posts on run flat tires on this forum, I wanted to experiment a bit with different road textures and tire pressure. To my amazement, I found that it may not be a problem with run flat tires but sensitivity to tire pressure. I've noticed that even a decrease in 1-2 PSI below normal recommended tire pressure causes our cars to ride rough, tramline more and increase road feel (BMW normal tire pressure recommended: 32F and 35R).

After keeping my tire pressure at the recommended PSI on both F/R tires, I noticed the ride was pretty good, tramlining was almost negligible and road feel was decent - not too much and not too less. This was true even on rough textures. The car felt really good, handling/feel was great and it drove smoothly on rough texture and I didn't had to hold tight the steering wheel. However, I noticed that after I hit a pothole (purposely) at about 30-35 MPH, my tire pressure on three of the tires reduced by 1-2 PSI below recommended. Then I drove the car and all the bad things that we've talked about here started to come into picture - tramlining, more road feel etc... So I went back after couple of days and hit the same pot hole with the same speed. Wasn't surprised to see a drop of 1 PSI. 

Now I've got back to the recommended tire pressure and the car drives really well. I'm pretty happy with the ride quality. I'm starting to believe that as long as I maintain the correct tire pressures, the car will drive the way it is supposed to. I'm also starting to believe that our RFTs are way sensitive to bumps, pot holes as far as tire pressure goes. 

So even if you hit a small pothole, there's a very high chance that your tire pressure has reduced by 1-2 PSIs. 

Again, this is just from my experience. I'll have to play around a bit more with tire pressure to comfirm for sure and in the meanwhile I wanted to share my thoughts.

Note: All tire pressures were measured when it was cold, first thing early morning.


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## BMW_GAL (Apr 7, 2009)

I've noticed this too...esp. over railroad tracks and dips/bumps :tsk: ULTRA sensitive!!


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## johnc_22 (Sep 14, 2004)

When I still had the staggered 18" RFTs I found that 1-2psi over the recommended pressures was actually better riding (more air, less stiff sidewall). Underinflating didn't seem to help.


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## Neutrino45 (Feb 5, 2008)

thanks for sharing. i have similar experience


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## buckybadger (Dec 21, 2008)

BMW_GAL said:


> I've noticed this too...esp. over railroad tracks and dips/bumps :tsk: ULTRA sensitive!!


Oh yes, I've noticed that a lot actually..


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## buckybadger (Dec 21, 2008)

johnc_22 said:


> When I still had the staggered 18" RFTs I found that 1-2psi over the recommended pressures was actually better riding (more air, less stiff sidewall). Underinflating didn't seem to help.


Yeah, I think a buffer of 1-2 PSIs will help but too much air might make the ride floaty. I don't know if this is the solution to all our complaints about Run flat tires but I'm starting to believe slowly.. I still need to convince myself further though. Sometimes the simplest solutions can solve the most complicated problems! :smokin:


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## Spagolli94 (Jan 27, 2009)

I have non-RFT so we're not talking apples to apples. That said, my ride is noticeably less harsh at 30/33 than the recommended 32/36. Sure the car is a little less crisp maybe, but not much. However, ride quality is much better with the lower pressure..


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## bl335i08 (Sep 15, 2008)

I'm running 36/38 just in case I wanna push triple digits.


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## BerfsBimmer (Aug 25, 2007)

I’ve found +2 psi gives me the best ride and handling.


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## butterfly52 (Jun 29, 2009)

I've had the same experience. I had a horrible ride for the first month of ownership. Then I bought a really good pressure gauge and found the dealer had way over-inflated my tires. I reduced the pressure to bang on the recommendations and it vastly improved the ride. I check every couple of weeks now and am pretty happy with my run flats. But I will go for the 3rd generation of Bridgstones when they are available and my tires need replacing - probably next year.


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## bigwong (Jan 6, 2007)

deznium said:


> note: All tire pressures were measured when it was cold, first thing early morning after 12-14 hours of driving.


:dunno:


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## Joeb427 (Jun 23, 2009)

Spagolli94 said:


> I have non-RFT so we're not talking apples to apples. That said, my ride is noticeably less harsh at 30/33 than the recommended 32/36. Sure the car is a little less crisp maybe, but not much. However, ride quality is much better with the lower pressure..


Same here!
I run with 31/34.
I'll have to try 30/33.


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## Spagolli94 (Jan 27, 2009)

Joeb427 said:


> Same here!
> I run with 31/34.
> I'll have to try 30/33.


The softer you go, the quieter and smoother the ride. But you'll reach a point of diminishing returns and if you go too low, you'll just wind up with a mushy, sloppy ride. I've tried 31/34 before (based on your recommendation, I think). I liked it. Not much of a difference between that and 30/33. You gotta figure your pressure is going to fluctuate about 2 PSI just based on ambient temp that day anyway.


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## Joeb427 (Jun 23, 2009)

Spagolli94 said:


> The softer you go, the quieter and smoother the ride. But you'll reach a point of diminishing returns and if you go too low, you'll just wind up with a mushy, sloppy ride. I've tried 31/34 before (based on your recommendation, I think). I liked it. Not much of a difference between that and 30/33. You gotta figure your pressure is going to fluctuate about 2 PSI just based on ambient temp that day anyway.


I'm going to go to 30/33.I'm not going to worry about wear because I don't do too many miles per.
Speaking of presure..
Gotta buddy who details cars and sells nitrogen so I'm going over to nitrogen too.
I have an 11 gal airtank he can fill for top offs.
Ever think of going with nitrogen?
IMO,it doesn't do much but hold air pressure longer than regular air.


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## Alpine300ZHP (Jan 31, 2007)

I run 34-35 psi all around in the E90 335 and run 35-36 all around in the 135 coupe. This has worked out to give me the best overall balance, tire wear and responsiveness. I am getting perfectly even wear on both cars and the handling seems to be the most neutral as opposed to other settings I have tried.


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## Alpine300ZHP (Jan 31, 2007)

Joeb427 said:


> *I'm going to go to 30/33*.I'm not going to worry about wear because I don't do too many miles per.
> Speaking of presure..
> Gotta buddy who details cars and sells nitrogen so I'm going over to nitrogen too.
> I have an 11 gal airtank he can fill for top offs.
> ...


Too low man. I tried 30 psi front and saw signs of feathering within 500 miles and I got constant steering wheel vibration. Try it, but I doubt you will like it. Our cars are identical so I recommend you go no lower that 33-34 in the front.


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## Joeb427 (Jun 23, 2009)

Alpine300ZHP said:


> Too low man. I tried 30 psi front and saw signs of feathering within 500 miles and I got constant steering wheel vibration. Try it, but I doubt you will like it. Our cars are identical so I recommend you go no lower that 33-34 in the front.


On RFT?
RF seem to have the feathering along with cupping problem.
I have regular tires.


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## Spagolli94 (Jan 27, 2009)

Alpine300ZHP said:


> Too low man. I tried 30 psi front and saw signs of feathering within 500 miles and I got constant steering wheel vibration. Try it, but I doubt you will like it. Our cars are identical so I recommend you go no lower that 33-34 in the front.


I have non-RFT tires and have been running these pressures for quite a while. Nice and smooth. No signs of abnormal wear. And they do a much better job of flexing to absorb all the cracked, rippled and patched pavement around here.


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## Spagolli94 (Jan 27, 2009)

Alpine300ZHP said:


> Too low man. I tried 30 psi front and saw signs of feathering within 500 miles and I got constant steering wheel vibration. Try it, but I doubt you will like it. Our cars are identical so I recommend you go no lower that 33-34 in the front.


If I lived in Palm Beach, I'm sure I'd be running 34/38 and enjoying the responsive handling. Last time I checked, most roads in FL don't look like this... I wish I could say this pic was an isolated area, but it's not. It's very common around here and getting worse with the recession. The never really fixed the potholes from last winter and all the repaving jobs seem to focus on the highways. I doubt you'd be enjoying those high pressures if you had to drive on this crap. I need to ditch this car and get an SUV.


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## Bcube (Apr 12, 2007)

Screw the SUV, I was thinking of a H1 Humvee. I could ride six inches off the rear bumper of a Prius till it crapped itself. Might solve some of my commuting issues.


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## Spagolli94 (Jan 27, 2009)

I've attached a pic of my other ride. Believe it or not, it's a lot SMOOTHER than the 3. Sure, the suspension is very firm, but never transitions to harsh. Handles just fine too.


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## jlsbimmer (Aug 1, 2008)

Be aware that tire pressure gauges are notoriously inaccurate ... I have 3 decent ones and they all show different readings ... +-3 lbs ... I actually don't know which one to trust ... so I play it safe and go a little higher than I'd like.

Can anyone recommend a gauge they like and trust ??

jls.


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## Jim E. (Apr 23, 2002)

Joeb427 said:


> Same here!
> I run with 31/34.
> I'll have to try 30/33.


I dumped the runflats even before I got my car so I've actually never driven on them.

I have 19's with 235's and 265's front + rear respectivelly.

with Michelin PS2's I run 44 front and 49 rear. No harshness that I would complain about. rides kind of nice actually.

But damn, I'm way more than you guys. :dunno:

I have a 335d lci btw.


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## Joeb427 (Jun 23, 2009)

Jim E. said:


> I dumped the runflats even before I got my car so I've actually never driven on them.
> 
> I have 19's with 235's and 265's front + rear respectivelly.
> 
> ...


Damn!:eeps:
What's the max air pressure allowed in those tires?You must get a jolt when driving over a paper cup.


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## Jim E. (Apr 23, 2002)

Joeb427 said:


> Damn!:eeps:
> What's the max air pressure allowed in those tires?You must get a jolt when driving over a paper cup.


Actually it's not bad at all. The max I believe is around 50.

For speeds over 100 the minimum is 39/42 without extra weight.


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## Joeb427 (Jun 23, 2009)

Jim E. said:


> Actually it's not bad at all. The max I believe is around 50.
> 
> For speeds over 100 the minimum is 39/42 without extra weight.


50...you better make sure.
I know you have to raise the pressure for high speeds but 49 around town?
Oh my...Jim.


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## Thunder Dump (Jul 16, 2009)

Jim E. said:


> with Michelin PS2's I run 44 front and 49 rear. No harshness that I would complain about. rides kind of nice actually.


For street driving that's some crazy high pressure. I can't believe it doesn't feel like you're riding on the rims at that pressure, and you're damn close to the max cold pressure on those tires. Be careful if you set them to that pressure when the ambient temp is cold out and then it warms up a lot (say winter vs summer) or you could find yourself in trouble.

Aren't you wearing out the centers with that kind of pressure?


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## buckybadger (Dec 21, 2008)

jlsbimmer said:


> Can anyone recommend a gauge they like and trust ??
> 
> jls.


1. http://www.amazon.com/BMW-Genuine-E..._1?ie=UTF8&s=automotive&qid=1251485958&sr=1-1

2. http://www.amazon.com/Moroso-89560-..._1?ie=UTF8&s=automotive&qid=1251492512&sr=1-1

3. http://www.amazon.com/Accutire-MS-4..._1?ie=UTF8&s=automotive&qid=1251492520&sr=1-1

I have all three and I found the BMW gauge to be the best. It looks and feels more solid and causes minimal air leakage while measuring.


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## Joeb427 (Jun 23, 2009)

deznium said:


> 1. http://www.amazon.com/BMW-Genuine-E..._1?ie=UTF8&s=automotive&qid=1251485958&sr=1-1
> 
> 2. http://www.amazon.com/Moroso-89560-..._1?ie=UTF8&s=automotive&qid=1251492512&sr=1-1
> 
> ...


The BMW gauge is probably made by Accutire.
I have a couple of Accutire gauges.If a gauge is off,it's usually about .5 lbs.A newer gauge that is.


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## buckybadger (Dec 21, 2008)

Joeb427 said:


> The BMW gauge is probably made by Accutire.
> I have a couple of Accutire gauges.If a gauge is off,it's usually about .5 lbs.A newer gauge that is.


Probably, but I highly doubt it.. Accutire one causes most air leakage while measuring and the grip is annoying.. BMW one is definitely a better design IMO.. Morso is not bad either.. :smokin:


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## Joeb427 (Jun 23, 2009)

deznium said:


> Probably.. Accutire one causes most air leakage while measuring and the grip is annoying.. BMW one is definitely a better design IMO.. Morso is not bad either.. :smokin:


Yeah,I guess it depends on the Accutire model.I have a couple that work fine.


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## Orient330iNYC (Jul 30, 2002)

the BMW gauge is an accutire... an old one that accutire does not sell anymore, you used to be able, back in 2001 at least, buy an accutire gauge that was half the price of the bmw one, but was only different by the logo.

they've been selling the same gauge for years, i almost bought one when i got my 330i way back when.


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## buckybadger (Dec 21, 2008)

Orient330iNYC said:


> the BMW gauge is an accutire... an old one that accutire does not sell anymore, you used to be able, back in 2001 at least, buy an accutire gauge that was half the price of the bmw one, but was only different by the logo.
> 
> they've been selling the same gauge for years, i almost bought one when i got my 330i way back when.


ohhhh thanks for the info dude :thumbup: I find the BMW gauge to be more easy to use. It causes minimal or no air leakage Vs. Accutire. I always leak too much air while trying to get a good grip/contact between Accutire and the pressure valves :dunno:


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## Orient330iNYC (Jul 30, 2002)

deznium said:


> ohhhh thanks for the info dude :thumbup: I find the BMW gauge to be more easy to use. It causes minimal or no air leakage Vs. Accutire. I always leak too much air while trying to get a good grip/contact between Accutire and the pressure valves :dunno:


simpler is better... the new ones can probably double as stun guns or MP3 players...


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## docedkin (Apr 21, 2009)

Just did a two day track program at Watkins Glen. I do not have track tires and am running the Bridgestone RFTs that came on my E92, 335i w/sport package. I talked with instructors and other drivers and decided to set the tires at 32/36 for the first session to see what the heat would do and determine how the tires responded to the track surface and speeds (max for me was 120). Everyone thought that psi in the 38/44 range was just too high given the expected increase induced by speed heat. My instructor, who has experience with RFTs on his wife's sedan, thought the feel and response at 32/36 was good so those settings remained in place for all six sessions including two on wet surfaces. Overall, stick was good, and they screamed only three or four times while at my limits for cornering speeds. Of course this was for two medium weight adults and everything else that would move taken out of the car. (The attached pic was taken while on tour after my ED this past spring.)

Wayne
Blossvale, NY


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## buckybadger (Dec 21, 2008)

docedkin said:


> Just did a two day track program at Watkins Glen. I do not have track tires and am running the Bridgestone RFTs that came on my E92, 335i w/sport package. I talked with instructors and other drivers and decided to set the tires at 32/36 for the first session to see what the heat would do and determine how the tires responded to the track surface and speeds (max for me was 120). Everyone thought that psi in the 38/44 range was just too high given the expected increase induced by speed heat. My instructor, who has experience with RFTs on his wife's sedan, thought the feel and response at 32/36 was good so those settings remained in place for all six sessions including two on wet surfaces. Overall, stick was good, and they screamed only three or four times while at my limits for cornering speeds. Of course this was for two medium weight adults and everything else that would move taken out of the car. (The attached pic was taken while on tour after my ED this past spring.)
> 
> Wayne
> Blossvale, NY


Nice pic :thumbup: and thanks for sharing your info about tire pressure!


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## Chrisdridley (Jun 29, 2009)

I use a Psiclops extreme tire pressure gauge from Tire Rack
For me, nothing else even comes close


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