Tire Pressure Question

[jinda]

So 2 days ago, Tuesday, I went out and noticed a notification about my tire pressure on the IC.

All four tires are below the threshold due to sudden drop of temp here in NY.
Both front have 28 psi and both rear have 30.

The sticker on the door frame shows tire pressure as:
Front - 225/45R18, 35 psi
Rear - 225/45R18, 41 psi

Sticker is showing same tire size all around even though I have staggered setup as stock, 225/45R18 front and 255/40R18 rear.

I still put the tire pressure as 35 and 41 psi though as stated.

So questions are:

1. Should I worry about my rear tire pressure since the indicated 41 psi is said to be for the 225/45R18 when I have a 255?
2. That day it was low 40s and today it's 70s again so I assume due to gas expansion, my tire pressure is more than what I put 2 days ago. Should I reduce it?

Thanks guys.

[jinda]

No one?

Anyway, I think I found the answer to my question #2. I saw this somewhere online:

it's important to know that the recommended tire pressure for your vehicle (as specified in the owner's manual and the tire placard for the vehicle) are both based on cold inflation pressure.

And that a change in temp of ±10ºF will result to about ±1 psi.
I guess the change in Temp within the same day is almost negligible to the tire pressure.

Anyone got any answer on my Q#1?

[Njerts]

Not sure if this will help, but I always assumed that cold inflation pressure means no friction heat from driving not weather wise.
I also found 41 on my rear wheels way too hard, I only inflatable them to 38 psi for a more comfortable ride on runflats.

[0w40X1]

I've got the 225/45r18 and 255/40r18 staggered stock on s28i.

Sticker says 35f 38r, and that is what I run which is set at temps of 60-80 deg.

Even if temps are 40deg the day or tires won't get as hot so still use 35 38.

Fronts have 23k miles and are haLF WORN P7's summer tires.

Rears are 2/3rd's worn, and I tried running less, since they seem to wear more in center.

It's probably THE WAY TIREWAS MADE BECAUSE anything lower than 35 38 cold feels mushy.

[jinda]

Originally Posted by Njerts

Not sure if this will help, but I always assumed that cold inflation pressure means no friction heat from driving not weather wise.
I also found 41 on my rear wheels way too hard, I only inflatable them to 38 psi for a more comfortable ride on runflats.

So far I haven't notice a rougher ride but in case I do, I might reduce it to 38 as well. Thanks.

Originally Posted by 0w40X1

I've got the 225/45r18 and 255/40r18 staggered stock on s28i.

Sticker says 35f 38r, and that is what I run which is set at temps of 60-80 deg.

Even if temps are 40deg the day or tires won't get as hot so still use 35 38.

Fronts have 23k miles and are haLF WORN P7's summer tires.

Rears are 2/3rd's worn, and I tried running less, since they seem to wear more in center.

It's probably THE WAY TIREWAS MADE BECAUSE anything lower than 35 38 cold feels mushy.

So does the sticker specify a staggered setup showing the rear is 255/40R18?

[Lucky13]

I’ve got the same size tires on my 2013 X1 s28 MSport with run flat Goodyear Summer tires, 35 front and 38 rear. I generally put 1-2 lbs more in because they lose about 1 lb a month or more. On my M235 which is 32/38 they recommend a couple lbs higher pressure if you plan on driving 100+ miles an hour.

[0w40X1]

Originally Posted by jinda

So far I haven't notice a rougher ride but in case I do, I might reduce it to 38 as well. Thanks.



So does the sticker specify a staggered setup showing the rear is 255/40R18?

Yeah, it lists my size tires 225/45r18 and 255/40r18.

I've run HPDE and tried the tire temp way, and came up with 38 38 cold, but that's too high for front.

If fronts get to 42#+ hot it'll slide.

40hot front is max, and 42 or 43 hot rear MAX.....

[jbE84]

I have a 2012 x28 stock 18 staggered 225 front,0255 rear. tire pressure on door state front 35psi and rear 38psi.

now running a winter square 18 setup 225 all around I am running the same tire pressure as above, ride feels about the same

jb

[GTony]

Hi jinda,
ORIGINAL - 225/50/17 RFT SQUARE 40PSI> Even wear till they had to be replaced. PSI seemed a bit high on rough roads.
NEW STAGGERED - MPSS NON RFT.
225/45/18 38PSI.
255/40/18 40PSI.
Fully loaded Car, high speed Freeways and roads leading into the City, couldn't fault ride and handeling.
I guess it depends on your circumstances, what they feel like on your road conditions and how your Tread Wear looks like after X amount of Miles that would determine your Tire Pressures.

[0w40X1]

Originally Posted by GTony

Hi jinda,
ORIGINAL - 225/50/17 RFT SQUARE 40PSI> Even wear till they had to be replaced. PSI seemed a bit high on rough roads.
NEW STAGGERED - MPSS NON RFT.
225/45/18 38PSI.
255/40/18 40PSI.
Fully loaded Car, high speed Freeways and roads leading into the City, couldn't fault ride and handeling.
I guess it depends on your circumstances, what they feel like on your road conditions and how your Tread Wear looks like after X amount of Miles that would determine your Tire Pressures.

These 38 40 that you run on MPSS is after they have warmed up or around 100 deg, right?

[jinda]

Originally Posted by GTony

Hi jinda,
ORIGINAL - 225/50/17 RFT SQUARE 40PSI> Even wear till they had to be replaced. PSI seemed a bit high on rough roads.
NEW STAGGERED - MPSS NON RFT.
225/45/18 38PSI.
255/40/18 40PSI.
Fully loaded Car, high speed Freeways and roads leading into the City, couldn't fault ride and handeling.
I guess it depends on your circumstances, what they feel like on your road conditions and how your Tread Wear looks like after X amount of Miles that would determine your Tire Pressures.

I'm in the northeast with all these crappy roads. I will check tonight and make sure its 41 at this weather (60s). So it will be about 38 during the winter at 30s.

Thanks for the responses guys!

[GTony]

Originally Posted by 0w40X1

These 38 40 that you run on MPSS is after they have warmed up or around 100 deg, right?

No, I run 38 40 all the time, cold or hot.
Although I haven't checked the pressures after they have warmed up.
I will check next time. Hopefully soon so i can advise.
Thanks.

[12 Handicap]

40 front and rear all year long, it stops the swing/ drifting at HWY speed.

[0w40X1]

Originally Posted by 12 Handicap

40 front and rear all year long, it stops the swing/ drifting at HWY speed.

That swing is crazy!

I was chasing guys on the Auto bahn after 1500 miles on it, and and it seemed a gust of wind could make it change lanes at 120 mph.

Several of us debated about it being aero or suspension.

I picked that it was the 2 inch narrower track in front with my staggerd 8 x18 and 9 x18 wheels, so I put 12mm BMS spacers on front ONLY, and could find the 147 mph real top end in control for once.

It firmed up the too quick electric steering also without noticable fron tire wear.

I tried the higher pressures for same reason, but settled back down to 35F 38 R cold.

[HBWT]

I run 35 and 35 on my MSport staggered set up. If I run any higher in the rear I’ll wear out the centers. Found that out running the recommended pressure. Checked cold and adjusted monthly.

[0w40X1]

Originally Posted by HBWT

I run 35 and 35 on my MSport staggered set up. If I run any higher in the rear I’ll wear out the centers. Found that out running the recommended pressure. Checked cold and adjusted monthly.

I noticed the same that the rear tread seems concave as in wearing out the center.

I tried to run less like the 35, but to me it loosens the rear as in side to side sway, so I went back to 38.

I'm almost to wear bar in rear centers, and car was planted really good during last rain.

I think some tire configurations just wear funny especially since these Run flats have such strong sidewalls.

[Njerts]

My car was very unstable with the runflats lately, it would follow every uneven part of the road, pulling on the steering like crazy. Then last weekend I switched to my winter setup (XIce) and I was surprised how great and stable they are.
I will have the runflats checked out before switching back.

[0w40X1]

Yeah, some of twitchyness is from any of the Runflats.

I'll be on Michelin pss soon enough or the new sport4.