225/40R18 tyre pressure

arcamalpha · 13 Aug 2006 at 21:17

I've got an 2006 model A3 which says the tyre pressure should be 38/35 psi for 225/40R18s.

This seems rather high for even 18" wheels. What do others run with similar size tyres? ps claimed car weight is 1370kg.

Scania · 13 Aug 2006 at 21:26

My 225/50/18 front & 255/45/18 rears are currently @ 33psi.

e38 BMW 728i Kerb weight 1925kg.

Clarkey · 13 Aug 2006 at 21:39

Does seem pretty high but I guess they know what they are talking about.

Slackworth · 13 Aug 2006 at 22:14

My A4 Quattro is 38 PSI all round at standard. Extra load requires more.

Greg · 13 Aug 2006 at 22:31

adwhitworth said:
My A4 Quattro is 38 PSI all round at standard. Extra load requires more.

no offence, but thats not really any help if the tyres are a different size to the ones asked for above.

Mine are at

40PSI - Front
35PSI - Rear

Ford Mondeo ST TDCi Size= 225/18/40R

Greg

[TW]Fox · 13 Aug 2006 at 22:40

Greg said:
Ford Mondeo ST TDCi Size= 225/18/40R

You kept THAT quiet! No thread? No pics? :eek:

MehulLakhani · 13 Aug 2006 at 23:03

On my Boxster, they are 225/40/18 at the fronts, and the recommended Psi is 29.

R

Mehul

Gaygle · 13 Aug 2006 at 23:26

Hell yeah, he kept that quiet. Greg post some pics!

MagicBoy · 14 Aug 2006 at 00:13

That does seem a bit high.

I suspect weight and lower profile tyres will increase the pressure required. Does your A3 have an V8 hemi in there?

My 1300kg Fabia vRS runs 2.3/2.1 bar which is 34/31psi on 205/45/16s. W rated tho for some unknown reason!

Conanius · 14 Aug 2006 at 06:43

Greg said:
no offence, but thats not really any help if the tyres are a different size to the ones asked for above.

Mine are at

40PSI - Front
35PSI - Rear

Ford Mondeo ST TDCi Size= 225/18/40R

Greg

EXCUSE ME.

where was the MSN telling me that then you cheeky oik !

Goliath · 14 Aug 2006 at 08:21

The RS is on 225/40 R18 extra load, and they are at 33psi front and 31psi at the back.

arcamalpha · 14 Aug 2006 at 08:45

33-35 does seems to be the norm, but Audi seem to be consistently higher. I originally thought it was something to do with max speed as higher speeds generate more heat in the side walls. But then there are far faster cars around with lower pressures!

MehulLakhani - what are your rear pressures and what does your Boxster weigh?

What are the main variables relating to tyre pressure anyway?

Weight

Tyre size (I assume lower profile tyres need more pressure to ensure even load across the width)

Maximum speed

what else?

edited to make the stupid bullet points work!

Dr Who · 14 Aug 2006 at 09:05

The pressure is based on what gives the tyre the correct profile and contact patch...

Go by what the book says, they have done extensive testing...

NickXX · 14 Aug 2006 at 10:23

The fronts on my 330d are that size and running at 2.4bar.

arcamalpha · 14 Aug 2006 at 11:05

A 330D must be a bit heavier than my A3 over the front wheels, so I guess my high pressure is to acheive better fuel economy.

Cheers for the input guys.

Dandle · 14 Aug 2006 at 14:40

Our A3 says the same. Any lower and you run the risk of hitting the rim of the wheel if you hit a pothole as there isnt much sidewall. The book weight of ours is 1460kg but the actual weight of our car on the vin is 1573kg(options must add a fair amount of weight), they are heavy cars.

ZXSpectrum · 14 Aug 2006 at 16:30

30psi all round on my S14a 200sx

blueboy2001 · 15 Aug 2006 at 00:21

My ST TDCi has the same sized wheels and tyres, although they are XL with a 92 load rating. The manual states 38PSI front 35PSI rear so yours sound about right.

Lopéz · 15 Aug 2006 at 00:27

Greg said:
no offence, but thats not really any help if the tyres are a different size to the ones asked for above.

Mine are at

40PSI - Front
35PSI - Rear

Ford Mondeo ST TDCi Size= 225/18/40R

Greg

No offence but that isn't a help if it's a different car.

Go by whatever the manufacturer recommends for the vehicle.

On the Pug 28 all round works well.

arcamalpha · 15 Aug 2006 at 07:37

No offence but that isn't a help if it's a different car.

It is helpful because it gives a ballpark figure to compare. It's easy to add a percentage based on car weight...

Go by what the book says, they have done extensive testing...

I have no intention of running at any other value, but remember the manufactureres test the cars at maximum speed with maximum load etc when the tyres are under the most stress. I generally don't go above 80ish with 2 people when the car can do 150 with 4 people with all their junk in the boot...