In the past we have had some discussions about recommended tire pressure vs what works best for us as individuals. All the sudden I noticed something totally weird between my 79 SIII and my 87 SIII. There is a huge difference in recommended tire pressure between the two based on the stickers under the mirror in the glove box (photos below).

1979 XJ6 SIII:
Front/rear, 3 passengers up to 100mph: 27/26 psi.

1987 XJ6 SIII:
Front/rear, 3 passengers up to 100mph: 33/32 psi.

That's a 22% increase! Same wheel size, basically the same tire size, same car.

Anyone have any ideas why that was? The 79 was manufactured in June 1979 and, as such was one of the first ones made. In fact it has a series II dashboard (no trip computer) and one of the first three colors to come off the assembly line. Think that has anything to do with it?

 

Old stuff based on the tires of the day as well as the roads of the day. Plus they are compromise numbers.

Then consider the PSI recommended by the tire manufacturer!!


For me. 32 up to 35 do just fine, front and rear....

Carl