I thought people were bluffing about how much difference PSI makes in these rocks called run flats. Just had my tired rotated and I had the guys up the PSI to 40PSI as per a few different threads here and other sites I found on Google. What an amazing difference in ride!

 

What wheel/tire sizes do you have?

 

17" 5 Star Spoke with Pirelli P7 All-Seasons

 

What PSI were you running before?

 

36 all around. Came from dealer that way.

 

It seems to me just based on the higher PSI it would be a "harder" ride with less traction...but then again it is a run flat tire. I haven't researched higher PSI for the run flats at all.

My experience with my FJ...I keep the PSI at 40 for the road and "air down" to get better grip when off the road. With the lower PSI I get a much softer ride with ultimate traction.

What changes are you experiencing with the higher PSI?

 

I'm up to 38 PSI on my 17 A/S - it certainly feels different.

 

I always run the pressure that the mfg recommends in the door jamb. Works great for me and I get 35K to 40K out of our tires. (We rotate every 5K as well.) If I want a softer ride I go to non run flats.

My wife and I actually run non run flats in the summer and run flats in the winter since I just don't want to mess with a flat in the winter.

 

Better ride?

"it certainly feels different." gives me some hope...so N up?

 

I'm confused. The sidewall says 51 psi. I checked and mine are at 35. I've got just over 7K on them and wondering when I'll hear a TPMS warning. (or will I?).

Also when I go hot into a right turn or stop hard I'm hearing a beeping. Thought it was the TPMS warning. What am I hearing?

Thanks

 

The tire wall is number is the max pressure. You should follow the label on the door.

 

Also you should reset your TPMS sensor once you have the tire pressure set to the proper pressure. This should also be done with cold tires. IE no movement in the last 2 hours. I typically set my TP in the am after the car has been sitting all night.

 

I have never exceeded the pressures on the door jamb sticker by more than a couple of pounds...unless an autocross is the venue!

When you over-inflate the tires, you reduce the size of the contact patch between the tread of the tire and the road. This can actually be a dangerous situation, especially in wet conditions. I strongly suggest keeping your pressures on the stock tires very near the ones printed on the door jamb label.

A reduced contact patch is the reason why over-inflation seems to make the ride of the RFTs seem a bit less punishing. You actually have less tire on the pavement!

An exception to the "no over-inflation" rule would apply if you are modifying the suspension and/or changing the suspension geometry. In that case, you will want to use a needle-probe pyrometer and a test track/circuit. Your goal would be to make suspension/pressure adjustments until the tire temperatures taken across the tread (from inside shoulder to outside shoulder) are close to identical.

If fact, even if you aren't modifying the suspension, a probe-type pyrometer is a great tool to use. I have one and use it on every set of new tires on my cars to tweak the inflation. Again, I am looking for a pressure that results in (close to) identical tire temperatures taken across the tread: inside shoulder temp, center tread temp, and outside shoulder temp. After I adjust the pressure, I drive the exact same circuit at identical speeds and repeat the process until each tire's pressure is adjusted correctly. Doing this will maximize the tire's contact patch. Log the pressures for each tire; I write them in a small log book 'cause I'm older than dirt.

If your tires are over-inflated, the center tread temperature will be much higher than the shoulder temperatures. If under-inflated, the shoulder temperatures will be much higher than the center tread.

Remember that having adjusted the pressures using pyrometer, you will need to repeat this process if you make any subsequent changes: new tires, shocks, springs, sway bars, strut bars, etc.

FWIW,

 

on my countryman s all4, using a tire pyrometer and chalking the tires, i have settled in on 42psi front and 36 psi rear.

i have Pirelli Cinturato P7 225/45R18 91V runflats, the OEM tire

with almost 4500 miles on the tires, i have even wear, edge to edge both front and rear

raising the pressure also all but eliminated the extreme harshness these tires had at the factory 32psi and made the turn-in much crisper

i have no idea if these pressures will work with any other size/brand of tire, but if you have the oem 18" pirellis, give it a try

i now do not hate my run flats, if fact the handling is excellent, both wet and dry, but i doubt i will replace them due to the cost

my next set of tires will more than likely be Michelin Pilot Super Sport in size 225/50R18, current price $172 ea at tirerack as opposed to $299 ea for the Pirellis

scott

 

38 PSI is the sweetspot for my 17" Pirelli RFs

 

Well said. We are having very even tire wear and great wet traction. I had the tires rotated at 5K miles. We will keep monitoring it of course.

 

 

38 is better over some bumps, but it slows me down from 45 to 40 going around a favorite freeway ramp, so I need to take it down a little, say - to 36...

 

My 17" with Pirelli a/s came from the dealer with 45#s!
I dropped front and rear to 38#s, and things seem much smoother!

 

Door Jamb Pressures:
17" Pirelli P7 All Seasons

32/32 PSI (F/R)
38/38 PSI (F/R - when 100+MPH)

I've found that 35-38 all around smoothes out the bumps/bump steer considerable vs. 32PSI all around.

My hypothesis is that the additional pressure gets you up off the sidewall a bit (hard sidewall of run flat) and that the air cushions a bit better even at a higher pressure than the RFT sidewall on the bumps/expansion joints etc.

 

my dad's all4 came with the 17" pirelli p7 all season runflats and standard suspension.

he is running 35psi rear 38 psi front

i must say that these tires are quite good, very quiet, nice turn in, good dry grip, excellent wet grip

dad is 91 years old and on his car, probably will replace the runflats with runflats

dad's all4 is opposite of mine, black top, white body, black wheels ... took a couple of weeks for the neighbors to figure out there were 2 different all4 that could be on the front driveway

he has a sunroof and auto climate control, neither of which i have

i dislike the sunroof, but the auto climate control works quite well, even in this exteme heat

dad also has the automatic transmission and it works very well

in sport mode, either auto or manual, is very fun to drive ... dad uses sport mode most of the time

so if you are in the chicago area and get blitzed by a black over white all4, wave at my 91 year old dad

scott