I know the settings for your tire pressures are supposed to be measured cold, or in the morning. I measured my tire pressure last week in the morning at 32/29 (front/back), but then this morning, a little cold front blew by and they're only 30/28 (front/back). I'd probably say 10degree drop in temperature. Should I pump them back up to specs...meaning, is 32/29 supposed to be the least it ever gets to, since you measure them cold?

 

Depends on how **** you want to be. You could drive yourself nuts by checking it everyday, but I'd stick with the once a month method to keep a good average.

 

The rule of thumb is for every 10° Fahrenheit change in air temperature, your tire's inflation pressure will change by about 1 psi (up with higher temperatures and down with lower). The difference between cold nighttime temperatures and hot daytime temperatures in most parts of the country is about 20° Fahrenheit. This means that after setting tire pressures first thing in the morning, the vehicle’s tire pressures will be almost 2 psi higher when measured in the afternoon (if the vehicle was parked in the shade). While that is expected, the problem is when you set your vehicle’s tire pressures in the heat of the day, their cold pressures will probably be 2 psi low the following morning. Finally, if the vehicle is parked in the sun, the sun’s radiant heat will artificially and temporarily increase tire pressures. And by the way, if you live in the North and park in an attached or heated garage you will "lose" pressure when you leave its warmth and venture into the real world outside during winter.
I would set your tires to what your average outside ambient temperature is in the morning. Check them once a week because you could drive yourself crazy changing the air pressure every morning.

 

That explains it. Another question...
If factory specs are 32/29psi, what pressures would you recommend for a 1000mile non-stop roadtrip?

 

Well, realize that 32/29 is a compromise setting between ride comfort, tire wear, and performance. It's not some "magic" number which is the sweet spot for the tire; a tire is asked to do many things, and can't do all of them well at any single pressure.

A variation of 2 psi one way or the other from the recommended pressures is not going to change the tires' characteristics very much. 30/28 probably feels and behaves very similar to 32/29.

Note that mild overinflation, like setting cold pressures of 34/31, will probably make your tires last a wee bit longer and perform a wee bit better while taking a slight decrease in ride comfort.

 

I would still recommend starting off with the factory specs checked cold before you leave at a minimum. If it were myself, I would prob increase it by 2 psi front and rear before you were to leave for a bit beter handling and milege. So maybe 34/31 checked in the morning.

 

if you were to have the car at factory specs in the morning then during that day or as soon as they warm up... wouldn't that it wouldn't average out to be about 2 psi above the specs ? Wouldn't that be bad? *scratches head* or is that acceptable?

 

if you check the manual, the spec's themselves will answer this for you- the specification is for a COLD measurement- meaning operating temp is *meant* to climb a few degrees, and pressure as well. it also states that an extra 4(?)psi front and rear is good for extended high speed driving. the important part is to maintain the 3psi difference front to rear.

i've found about 2 psi difference betwwen hot and cold measurements, consistently.
i keep my tires at 36/33 f/r, measured cold, as specified. i get the same 2psi increase at this inflation level, so that gives me 38/35psi normal operating pressure for my freeway driving habits.

this is exactly within spec.

 

I second that. Well put

 

thanks a lot. I don't drive an EVO so I don't have a manual. Thanks for the information though. Well put.

 

That seems very high, but if the manual says it, I can't go wrong, right?

 

right.

to ease your mind, check the manual itself, it's right there. also, check the side of your tires, you'll find the max pressure to be somewhere north of 44-46 psi.

any setting you use in the range we're talking about is based on your ride comfort and handling prefs. it's personal taste.

 

I recently upgraded to bigger 18x8.5 rims with a bigger tire but I havent been able to find the sweet spot for PSI.

I was running the stock spec 32f/29rear but the car was pulling all over the place and didnt handle well in wet conditions (which I still think is the Dunlops im running). I recently upped the pressure to 36f and 34r and I noticed a much better response/handling.

Im curious what PSI people are running on their 18" setup? And also, Im wondering if people change their setup for the winter tires (even on the stock 17" tire)?

 

265/35 on 18x9, Goodyear Eagle F1 GS-D3 ... 38 psi all around for street use.

Has worked well for me with both stock suspension and now lowered on Swift Spec-R springs. At first I ran the stock tire pressure, and they felt very soft (almost squishy) and had fairly sluggish response. The higher tire pressure took care of that. Be advised, though, that the exact pressure is as much dependent on the tire itself as it is on the tire size.

I've since noticed that larger, lower profile tires generally seem to be run at higher psi. Point-in-case, both my R32 and A8 recommend about 32-34 psi on 17" wheels, and 36-39 psi on 18" wheels. On the R32 I run 32 psi on the 17" winter tires and 38 psi on the all-season factory tire, which irritates the hell out of my wife, since the TPMS warning light is on all winter (too lazy to tweak the setting).

l8r)

 

ok, dumb question of the day... does anyone know the reason for keeping the 3 psi difference between front and rear other than "that's what the manual says?"