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Run-flat tires and tire pressure sensitivity.

28K views 36 replies 18 participants last post by  Chrisdridley 
#1 · (Edited)
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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#2 ·
I've noticed this too...esp. over railroad tracks and dips/bumps :tsk: ULTRA sensitive!!
 
#5 ·
Oh yes, I've noticed that a lot actually..
 
#3 ·
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.
 
#6 ·
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:
 
#10 ·
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.
 
#15 ·
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.
 
#22 ·
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.
 
#28 · (Edited)
#32 ·
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.
 
#33 ·
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:
 
#35 ·
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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#36 ·
Nice pic :thumbup: and thanks for sharing your info about tire pressure!
 
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