For those running 18" wheels / tires:

1. What tire pressure do you run? And what is the basis for running this pressure (e.g. tire shop, your own expertise, your favorite mechanic, your wise uncle, heard it on Jeopardy, etc.)?

2. What are you using for a spare tire which is the same or almost the same diameter? If it's a donut / space saver spare (from a modern car), from what make & model car did it come?

 

1, 35PSI
2, no spare

 

Outside diameter of the wheel+tire package is what's important, and if you can help it, matching section width is good.

I would prefer to keep a matched set on the differential if at all possible. IE, if you're running the same wheels and tires all around, and blow a rear tire, put the spare on a front wheel and move the front wheel to the back. This of course assumes that the front wheels have worn similarly to the rears, otherwise move both front wheels to the back.

 

255/45/17 ZR tires-It really does not matter much about the rim/tire size in how much pressure I run-Its the tire's maximum pressure rating that I use as a guide, the harshness/softness of the car's suspension, and personal experience over the last 20 years. It all started back in the early 90's when I took a high performance sedan driving course with Michelin Sponsored tires. One of the days, Michelin had a 1 hour lecture about tires and the summary was:

1. Do not run the tire pressure on the door sill of the car-That is set by the manufacturer for the best comfort and quietness of the tires. Almost universally that listed pressure is too low for moderate performance driving, better tire wear, and better gas mileage.
2. Upping the pressure significantly based on the side wall rating will increase the performance of the tire without much increased harshness, within reason.
3.Higher tire pressures MANDATE tire rotation, if possible, since uneven wear is more of a concern.
4. Higher tire pressures make the tire stronger and run cooler-road hazard and highway blowout protection is better.

For the C3, between 35-36 PSI-tire max rating 44 PSI. Most of my other cars with Z rated tires on 16/17/18/19 rims-40 PSI. I generally get 40-50,000 miles out of Z rated tires which is way outside the norm for this speed rated tire...

Hope that helps

 

For a spare Tire I carry a Tire Puncture repair kit and a 12v Compressor.

 

35 PSI air pressure and a later C3 space saver. I believe you can also use a C4 space saver but you would need to verify that as I have no personal experience.

 

I am running 18" wheels do to the 14" Wllwood brakes needing the room. I run at 30 psi. Does anyone know if the space saver spare will fit with the larger brakes?
I don't have a spare now.