Winter tyre pressures 225/40/18 all round (non RF)

[Ooch]

Now that I have switched to nokian wr a3 (225/40/18 ) all corners(non run flat) I scratching my head about the pressures.
I have 32 psi all round at the moment....the sticker for run flats standard size is 39 psi rear.
Perhaps I should run a few more psi on rear...any ideas?

 

[bcworkz]

It seems the same pressures are recommended regardless of tyre size. I find it odd to need much more pressure in the rear in a car that is almost perfectly balanced front to rear. Still, I would go by the recommendations and run 39 in the rear. You may as well put a bit in the fronts too, you apparently have a coupe, judging by the 39 (roadsters are 38). Coupes call for 33 in front, at least according to my 2006 manual.

 

[123BillyB]

Got sort of a similar question.

I have just bought a set of 18" 8.5j AC Schnitzer Type IV Bi-Colour alloys and they apparently have a nearly new set of 225/40/18's (non RF's) all round (haven't seen them yet as not being delivered till Friday).

As the tyres are nearly new all round I'm not going to change the rears just yet to 255/35/18's so with the wheel size at 18" 8.5j, should the tyres pressures be the same as above or different?

Thanks,

Billy

 

[bcworkz]

That's the other strange thing, the recommended rear pressure is 38/39 for both 225 rears and 255 rears. The higher pressure for wider, lower tyres would make sense to me, but then they recommend the same for 225/40 on the rear. Despite my lack of understanding, I would do as recommended unless there was good reason to do otherwise.

 

[123BillyB]

That's the other strange thing, the recommended rear pressure is 38/39 for both 225 rears and 255 rears. The higher pressure for wider, lower tyres would make sense to me, but then they recommend the same for 225/40 on the rear. Despite my lack of understanding, I would do as recommended unless there was good reason to do otherwise.

Hmmm...

I'm no expert but sort of makes scene as with 255/35's the overall wheel diameter would be the same as 18"'s with 225/40's so I think the area of air volume inside the tyre would therefore be the same?

As I said I'm no expert but at least I got my trye pressure question answered.

Thanks bcworks and now roll on Friday so I get my alloys delivered

 

[Bing]

The pressures in the manual are for RFTs - when this has come up on here before people seem to run lower pressures on non-RFTs. As a result I run with 33 front and 36 rear on my tyres - both the summer 18s and the winter 17s, feel just fine. The stock pressures are a lot higher than any other car I have had, so I wonder if RFT pressures are supposed to be higher than non-RFT, and if they are then why ?

 

[lux]

I run 32 all round...is that wrong? :?

 

[Bing]

I run 32 all round...is that wrong? :?

The correct pressures are on a label just underneath the latch for the door lock on the drivers side inner sill. That'll tell you if you're wrong :wink:

 

[lux]

I run 32 all round...is that wrong? :?

The correct pressures are on a label just underneath the latch for the door lock on the drivers side inner sill. That'll tell you if you're wrong :wink:

It's in gobbledygook though Bingy....I need psi!!

 

[Bing]

Most air line machines can switch between PSI and Bar - confused me at first too though. The manual will tell you both though. Worth a read

 

[paulgs1000]

The pressures in the manual are for RFTs - when this has come up on here before people seem to run lower pressures on non-RFTs. As a result I run with 33 front and 36 rear on my tyres - both the summer 18s and the winter 17s, feel just fine. The stock pressures are a lot higher than any other car I have had, so I wonder if RFT pressures are supposed to be higher than non-RFT, and if they are then why ?

This is an issue which concerns me - seems likely that the higher pressures specified might be for the Run Flats - stiffer side walls would seem likely to need more pressure?

I'm tempted to go with the 32psi all round on my staggered set up (non runflats)

Any thoughts?

 

[Ooch]

Hmm looks like a can of worms..this is the question Should non run flats have a different pressure to run flats. My non run flat winter tyres are now 38 rear 33 front as per door card.
No idea if that is correct lol

 

[bcworkz]

stiffer side walls would seem likely to need more pressure?

I'm tempted to go with the 32psi all round on my staggered set up (non runflats)

I could see that logic, though I could see an argument for less as well :? BMW decided the rears need more pressure for some reason, I don't think that is negated by running non-RFTs. OTOH I don't really see the need for that much pressure in the rear myself.

Normally I would say monitor tyre wear, that will tell you if you're under or over inflated. But by running so much camber the tyres do not wear evenly anyway. The inner shoulder is a lost cause, but the rest of the surface seems fairly even running OEM pressures on non-RFTs. I'm going to stay with recommended pressures only because trying to rationalise anything else makes my head hurt.

@lux good, if all else fails, multiply bar by 14.5 to get psi. Write the conversion down somewhere for ready reference.

 

[Brasseye]

I found the pressure ratings for the 225 front and rear inside the drivers door shut on a sticker while fitting mine today.

But was in bar pressure units being German car.

 

[GordonM]

BAR PSI
1.80 26
1.85 27
1.90 28
1.95 28
2.00 29
2.05 30
2.10 30
2.15 31
2.20 32
2.25 33
2.30 33
2.35 34
2.40 35
2.45 36
2.50 36
2.55 37
2.60 38
2.65 38
2.70 39
2.75 40
2.80 41
2.85 41
2.90 42
2.95 43
3.00 44
2.05 44

HTH

1 st Post but will introduce myself soon in the newbies section.

 

[markeg]

These are my tyre pressure settings, for winters, 225/40xR18 .....it's what I'll be using (and yes, I've got a replacement sticker - another job on my to do list...)