Good Day, I keep my18" tires @ 38 lb.s, is that optimal ? actually I fill to 40 lb.s on the Front & let 'em settle to 36 lb.s before I re-fill 'em. The REAR I run 2 lb.s lighter. what is the general consensus on Mini Tire Pressure out there ? Thanks

Consensus has no place in what tire pressures should be.

Rather you should inflate the tires to the pressures on the tire pressure chart on I think the driver's door jam. The tires should be checked/adjusted when cold.

If you carry a car full of people/luggage pay attention to the loaded car tire inflation pressures. And my JCW offers inflation pressures for high speed (>100mph) driving.

Adding to what @RockC said:

(1) Observe the placard BUT

(2) Check the owners manual as well. If your MINI is like mine, there is a standard range — which is what is on the placard — and an “if you are going faster” range.

(3) ALWAYS observe the front / rear pressure differential unless you are observing scenario-specific guidance. The front and the rear of the vehicle literally have different loads (engine is in front — heavier).

(4) If you are running a non-stock wheel+tire size — especially if low-profile tires — seek additional guidance.

So here’s what I do.

I have stock 17” wheels. In my case (2017 Cooper S), the placard is 38 psi front 35 psi rear, while the ”if you are going faster” range is 41 psi front 38 psi rear. The stock tire size is 205/45 and the stock tire is run-flat. That’s a low-profile tire setup and the potholes where I live result in a ridiculous amount of tire replacement (sidewall bulge) and wheel damage (balance issues). I replaced multiple tires at above $300 each under this configuration.

At the advice of a tire shop I have trusted for over a decade — they do everyday driver all the way to racing, including specific wheel/tire/suspension tuning for MINIs on the track — I changed my tire size to 205/50. Small difference numerically but in terms of the problems I was having, all the difference in the tire pressure was spot on.

Beyond that, I decided to go to 41/38. Slightly stiffer ride and I like it.

Just to leaven and obfuscate ;-).

In my case, the tires, the season, and the temperature all play a part!

I've a fair spectrum - ranging from Massachusetts winter to the Tale of the Dragon during summer in Tennessee, and not ignoring Lincoln Nebraska.

I find in general that the tire pressure changes with temperature - my rule of thumb is one pound per 8 degrees. Temp change can come from ambient air, or from direct sun exposure, or from stress on the tire.

Winter:
Tires are Continental DWS 06+ at 215/45-17.
Temperature on morning cold start (ambient 20 degrees) - tire pressure 27 pounds front, 28 rear. When the car has warmed up but the day has not, the fronts will rise to 29, and the rear tires as well.
High stress performance is not an issue in this environment, but traction is.

Summer:
Tires are Falken RT660 in a 225/45-17 (The Yokohama A052 is quite similar).
Temperature on morning cold start (ambient 65 degrees) - tire pressure 32 pounds front, 30 rear. When the car has warmed up and the day has too, the fronts will rise to 35, and the rears to 32.
Sharper ride, sharper handling, good sidewall support. Still understeer at the limit.

Competition:
Tires are either of the aforementioned Yoks or Falkens.
Temperature at first runs on the course (70 degrees ambient) - tire pressure 35 front 36 rear. During competition fronts will rise to 37, and the rears also.
Balanced grip with just a touch of oversteer due to RSB weight transfer and relative contact patch dimensions front to rear.

Cheers,

Charlie

Pressure definitely changes seasonally with temp. Adjust accordingly even with no other fancy.

what started this thread is I'm into season/pressure change right now in Fl. & I always check my tires HOT. I'm staying with my front & lightening up my rear a .lb or 2,my tires are 215/40-18 & Z series (149+ mph) also I travel light, no weight, no pass. 95% of time. 38F - 35R are good #s for me. Thanks I buy 2 tires at a time. when the Front ones are worn out, I put new tires on those rims & put them on the rear & move the rear tires to the front.

its all personal preference. i like to have it around 32 - 34 psi. anything more and i feel its too jarring when i hit bumps on the PA road.

Checking the tires hot is just not the right way to check/set the tire pressure. The tires should not be run under inflated.

With the tires cold -- no use of the vehicle for several hours but I prefer to let the car sit overnight and it happens to be in an unheated/uninsulated garage -- then set/adjust the tire pressures to the what the car maker recommends and this should be on a chart on the door jam.

During times when overnight temperatures vary quite a bit -- recently from a low of 32F to high of 60F -- if I can't arrange to adjust the tire pressure on the coldest day I allow for that. Say the best I can manage is to set/adjust tire pressures with the tires having sat overnight with the low at 50F. I'll set the pressures higher by 2psi (I allow 1psi per 10F in temperature change) so the tires while they'll lose some pressure when the temperature drops to 32F they will still not be under inflated.

While I have a garage it does not have any electrical outlet so I can't have a small air compressor. While I have a 12V portable air compressor I only use it to inflate car tires in an "emergency". What I do is on the way home from the last use of the car for the day I swing by a handy air hose -- which happens to be outside the local Walmart Super Center automobile shop -- and inflate the tires some. I just give them a count of 2 or 3 to ensure they will all be overinflated by a bit. Then next day before I take the car out I'll use my trusty dial air pressure gauge to set the tire pressures cold. Because I added some air the day before this consists of careful bleeding of air to bring the pressure down to what I believe will be the right air pressure when the tires are at their coldest.

looked @ Driver's door sticker, it said 38/f/35r cold for 205-17. I have 215/40 ZR 18 but I'm going to COLD instead of HOT

Yeah, what @RockC said -- checking pressure while hot is not the move. I mean, you'll get a pressure reading, but every instruction you find out there including the placard (as Stu-Mon saw) and owner's manual on EVERY car is a cold inflation pressure directive -- NOT hot. So at minimum you end up having to adjust your cold guidance to hot guidance, and then the air you put in is cold in a hot tire so there's whatever that whole figure out is, and...

...for all that busywork, I'd just inflate to whatever the desired cold pressure is, and I'd do the inflate at the coldest or closest-to point in the day. Especially if dealing with evening/night temps that are well below midday.

Also, again what RockC said, underinflation will mess you up bad, and I'm not talking preferred feel. Google "Ford Explorer Firestone" for all you need to know about the very non-hypothetical of that one, 30 deaths, not pretty.

what a Pain In A** ! filling tires cold, drive around driveway, lower a few lb.s check tire pressure in VEHICLE STATUS, rinse & repeat 3 times to get 38.5 F / 35.2R. if you're on the road 40 F Hot / 37 R HOT are good #s. Tire Pencil Gauges are inaccurate.

Yeah, it's a pain. I ultimately figured out how to make all this easier on myself but it was a process.

FWIW:

- The max inflation pressure on the tire sidewall is also a cold inflation pressure.

- In the warmer half of the year, the difference between hot and cold temp on my tires is pretty much 3 PSI -- meaning that if I read 37 hot on the rear (following your reference), let the car sit overnight, and then check pressure in the AM, that cold pressure is pretty reliably down to 34. I prefer higher than the placard's 35 for basic stock rear tire size so I adjust up anyway, but you get the point.

- In the colder half of the year (call it late October through at least Feb), I have to watch for underinflation big time, because the cold temps will drive the tires down to 30 PSI or lower if I don't top them up. Doesn't matter that they'll warm up during driving. They warm up 3 PSI or less in that season and driving underinflated at all is a bad idea (even if only in terms of tire care), barring specific circumstances.

- The accuracy of the tire pressures in Vehicle Status, which comes from TPMS, will vary. Say "accuracy" and "TPMS" to a tire shop pro and watch them either snarl or cackle. Doesn't mean it's useless. Just know that it's relative -- meaning your use of it to observe pressure differentials is on point -- but your only *true* friend remains a pressure gauge at the valve stem. I used to have 1 tire that was always weird in the readings -- turned out it was because that was the one original tire+TPMS sensor left from original (used) purchase of the car. It was just different from the other 3 - calibration, manufacture, who knows.

- As much as I try to get things right down to the decimal point "Because Reasons" before there were digital gauges that wasn't possible and nobody flew off the road because they were 0.5 PSI off of what the placard said. 0.5 off of a dead underinflated or seriously overinflated tire, maybe. But otherwise, nah.

Hope this is useful. Party on.

i use a basic hand-powered bicycle pump. its 'high volume' setting puts 1 psi per every three pumps or so. i just bought a cheap backlit digital gauge (calibrated to a basic ansi standard) because the pump's gauge and my pencil gauge are inaccurate. it's been really nice to not have to drive around the block to get a good reading, and to be able to easily set pressures in the dark.
i set pressures cold when i can but if i need to fill hot tires i'll under-inflate a little. i've been doing 34psi square for my 1.5l 3 door with 16" pirelli run flats which has made the ride very comfortable and grippy. the door says 35, but if i go this high for the cold, the car tramlines more than i'd like in the heat and crashes too loudly over our rough pavement. i've found this is a good compromise for the big desert temperature fluctuations out here. i might even go 33 cold in the summer because the temperatures will span a much larger range!