Tyre Pressures

For the first few years of Zed ownership, I used 33psi/33psi as advised by my local Nissan Dealer. This was on J-spec wheels which are 7.5" front and rear and take a 225/50 ZR16. I changed to UK-spec wheels which are 7.5" front (225/50 ZR16) and 8.5" rear taking a 245/45 ZR16. The Dealer then told me I should use 33F/33R for these and should have been using 33F/36R for the J-spec sizes. Hmmm.

When I changed from J-spec rears to UK-spec rears, the tyre mileage dropped by half: from around 18,000 miles per rear set to less than 9,000 miles. Still don't know if this was because of pressures or the wobbly rear end (part HICAS, part rear shocks) over the years.

So having changed back to J-spec rears and (Jan 07) fixed wobbliness by new rear shocks from MJP, I got anorakly obsessed by tyre pressures as you can see on these two threads from the 300zx forum and the ZClub forum.

I used the excuse of a new set of Falken 452s to ask Falken by email what the pressures should be. The reply came back from Micheldever Tyres and said "use the ones in the handbook". I emailed back:

The Owner's Manual for the Nissan 300ZX Z32 does not include any tyre pressures. I checked every one of the 150+ pages. The official Nissan Service Manual doesn't either - and I have read every one of the 25 pages in General Information, the 33 pages in Maintenance, AND the 25 + 35 pages in Front and Rear Axle & Suspension sections.

They got in touch with the Tyre Doctor from Dunlop who referred me to their guide which was clearly wrong as it says the 300ZX has 7.5" front (correct) and 8" rear (nope). I have been corresponding with them since but there is still no definitive answer (Feb 07).

The Nissan Manual does refer to a tyre pressure sticker. A few nice people (Michael from Denmark, Andy P and Jeff TT - thank you, all) looked at and sent photos of various stickers and here they are. (BTW M+S = mud and snow.) From this small sample it seems that UK/Euro cars had a sticker under the arm-rest lid and JDM cars had a sticker on the driver's door pillar.

arm-rest lid from Michael Oestergaard - his LHD Euro Z
arm-rest lid from Jeff TT at Zedworld - RHD UK breaker

Because both these lid stickers have the same appearance (even the part number 37P02) and are from Euro cars (assumed from both the source and the languages used), I reckon UK/Euro cars have a tyre pressure sticker under the arm-rest lid (where these two were) whereas the JDM cars had their tyre pressure stickers on the door pillar like the two below (photo'd at Zedworld Feb 07). If you have different evidence, let me know and I'll edit this.

In kg/cm2, I guess. Guesses in (brackets)

(front)
(rear)
(225/50)
2.3
2.5
(space saver)
4.2
4.2

In kg/cm2 . Guesses in (brackets)

(front)
(rear)
(225/50)
2.3
2.5
(no idea)
2.0
2.0

So putting everything together, we get the following table which seems to confirm that JDM and UK/Euro use the same pressures of 33 Front and 36 Rear as long as you are using standard rims.

Front Front Front Rear Rear Rear
psi kg/cm2 bar psi kg/cm2 bar
normal JDM 225/50 ZR16 225/50 ZR16
normal JDM 33 2.3 2.26 36 2.5 2.45
normal UK/Euro 225/50 ZR16 245/45 ZR16
normal UK/Euro 33 2.3 2.26 36 2.5 2.45
over 112mph UK/Euro 37 2.6 2.55 40 2.8 2.75
snow UK/Euro 225/50 R16 92H M+S 225/50 R16 92H M+S
snow UK/Euro 33 2.3 2.26 36 2.5 2.45
JDM/UK/Euro Spare Spare Spare Spare Spare Spare
psi kg/cm2 bar psi kg/cm2 bar
125/90 - don’t use over 50mph 125/90 - don’t use over 50mph
60 4.2 4.12 60 4.2 4.12
Conversion factors taken from the National Physical Laboratory www.npl.co.uk/pressure/faqs/unitvalidity.html and www.npl.co.uk/pressure/punits.html#notes
        100,000 pascals = 1 bar
       98,066.5 pascals = 1 kgf/cm2
       6,894.76 pascals = 1 psi (lbf/in2)
2.3 kgf/cm2 2.26 bar 32.7 psi
2.5 kgf/cm2 2.45 bar 35.6 psi
2.6 kgf/cm2 2.55 bar 37.0 psi
2.8 kgf/cm2 2.75 bar 39.8 psi
4.2 kgf/cm2 4.12 bar 59.7 psi