tire air pressure

[natsoundup]

Just trying to do a survey on tire air pressure for Q45's

The recent 94Q that I bought seems to be optimum in the 30-31psi range..

The 90Q that I have seems to be a bit better in the 28 range....

What do you guys do?

94Q 83.4k90Q 159.5k

[PalmerWMD]

40 psi in the front 37 psi in the rear.

Fred...

[pmcd1966]

I have the stock tire size and run 29 PSI all around. I use 29 because that's was listed on the door sticker.Fred, why do you run your so high? Any benefits?Patrick

[PalmerWMD]

Improved control and steering feel.

Fred..

[Q45tech]

The tire placard is the absolute minimum safe cold pressure for the oem tire that came on the car brand new.

Each tire in each brand/model different from the oem tire will need a differing pressure to be sure........some may be the same but you don't know.

The general rule of thumb is to add 3 psi COLD just to be sure.......32 psi........hopeing that the heat generated by driving friction will raise the pressure to 35 psi on the road.

35 psi is the standard temperature in which all parameters are measured in the lab for load index.Notice the placard warns to use 35 psi [cold inflation] if you plan on exceeding 130 mph for an instant.........this can be translated to the need for 35 psi if you hold 80 mph for hours on end in Summer heat as the tire carcass will exceed the 70F ambient lab test temperature by 50-60F [120-130F] as the road temp will be way over 100F and the tire will be hotter!!!!!!!!!!!!!!!!!!!

Always err on higher inflation as tires won't explode at even 55 psi or 65 psi. But they sure overheat at 25 psi.

29 psi is too close to low inflation to be sure unless you check the pressure every morning, 32-35 psi gives you some margin so you can check once per week/bi monthly.

[AZhitman]

I run the same pressures as Fred... 40/37.

[sultan]

i run 45/35 (different brands/sizes front and rear)

[pmcd1966]

Great explanation. Time for me to add some air I think.

[maxnix]

For my 1995 G50:

On 225/60-15 Yokohama AVS dB 38F and 35R.On 215/65-15 Michelin XGTV 40F and 38R.

For my wife's 2000 FY33:

On 245/50-16 Firestone SZ50 EP 35F and 33R (still experimenting).

With the change in seasonal temperature, be sure to check your pressures again with an accurate dial gauge that compensates for changes in barometric pressure.

I found my wife's electronic gauge to be somewhat variable. In part, this was due to a lack of a trigger as to when it read the tire pressure. The gauge must be be perfectly engaged and seated against the valve with NO leakage for an accurate reading.

[Jeff Williams]

Rear 255/45/17 42 PSIFront 225/50/17 40 PSI

I agree with Fred. Better feel, as well as lane changing. If you look at the load rating on the tire, it specifies a minimum air pressure for the specific load.

The Q is harder on the inner edge, than the center. More air pressure will take some of that load off the edges of the tires.

If you are having trouble with wheelspin, let some air pressure out. If you intend to do some slalom racing, pump it to 50 PSI in the front, and about 45 PSI in the rears.

[szh]

On my 1995 Q45 with Firestone Firehawk SZ50EP 225/60-15's, I used 36psi front and back (cold pressure check!) after experimenting at 34psi for a while.

On the Falken Ziex 512 245/45-17, I was using 34psi, but I had only driven about 700 miles when I sold the car, so cannot tell what the best value was.

Make sure that your tire gauge is accurate!

Z

[Highway Q45]

On my 91t with 245-16's I run 40R/37F. For some reason the HICAS seems more functional with a higher rear PSI, anything lower than 36R makes the car feel like it's searching for a line on fast on/off ramp curves and open road sweepers.

[greg_atlanta]

I like 30-32 psi best but I go up to 34-36 psi in winter (with Yokohamas) since that seems to reduce flat spotting in cold weather. I do a lot of 10-15 mile trips and the tires never get warm enough to work out the lumps. Gotta be careful in rain, though.

Lower psi is better for braking & handling, though at the extreme it can feel a little gummy.....

[Jesda]

What is flat spotting?

[VimyJ]

Flat spotting occurs when a tire sits motionless with a load applied as when parked overnight. The tires are out of round and cause a vibration until they are warmed up again. Can be quite severe in very cold weather.

[greg_atlanta]

Flat spotting is worse on high performance tires with soft rubber, esp. summer tires. Also more likely on lower quality tires.

[louiegz]

I use 32psi on my Michelin Pilot XGT H4 215 65 R15. 1995 Q45. They seem to be wearing nice.

[SmithSR]

Flat spotting is worse on high performance tires with soft rubber, esp. summer tires. Also more likely on lower quality tires.

The real problem lies within the casing construction and material used in the casing, not so much the tread. Rayon, if I recall, is one material used in some UHP tires that is known to cause, in a sense, "flat spotting" from sitting idle.

Just like some of the bias-ply mud tires that must be run at speed to become "round" again... the same theory holds true with many car tires.

If you remember, in a recent post from Q45tech, the page he posted from Infiniti about balance procedure specified running the car at 70mph for 30mins(i think) then immediately checking balance. This would help eliminate such flat spotting. -Master of the obvious.

[Jesda]

37 PSI all around.

I recently busted one of my new Douglas Performance tires (bought clearance item in a tiny town 80 miles out, no warranty), and replaced it with a Firestone Insignia. Decided to just make both the back Firestone Insignias and get a small discount. Fronts are still Douglas. Wonder how this will affect handling.

-Jesda

[szh]

37 PSI all around.

I recently busted one of my new Douglas Performance tires (bought clearance item in a tiny town 80 miles out, no warranty), and replaced it with a Firestone Insignia. Decided to just make both the back Firestone Insignias and get a small discount. Fronts are still Douglas. Wonder how this will affect handling.

You like living dangerously, don't you? Please make it a point of never going over 85 mph on a dry road ! I think you are introducing unknown variables that might make your handling charatceristics to become quite suspect - your spin-out issue that you described in another thread sounds like it might recur again.

Z