Nate2085

What should my tire pressure be on 225/40/18 for my tC?

LoungeLizard

It really is best to keet the pressure the same as they were on the stock tires.

Nate2085

i have i think 32 in front and 29 in the back for 17's...so 18's are the same? i for some reason figured there may be a slight difference.

FModFTD

Contact the manufacturer of the tire, or the place you bought the tire. (Try TireRack.com, even if you didn't get them there.) They should be able to recommend the right pressure.

SciFly

there is a wide range of possible, safe pressures.

Load and comfort requrements are often at odds in deciding your best standard air pressure.

In general: if the tire is wider than stock then it need not have more air pressure than stock.

Consider the contrasting example of the temporary spare tire. It is narrow and so, to maintain it shape under load it is spec'd for 60PSI.

All tires can be inflated safely up to the pressure listed on the sidewall. Rarely, though, is this a good idea.

We want the tire face to wear evenly. Inflation in fitting proportion to the load will allow the tread face to wear evenly. And will assure minimal heating of the flexing sidewalls if you run at highway speeds. (heat destroys tires. underinflated tires run hotter)

A tip I read at a responsible site advocates this means of setting tire pressure: air enough to create an even temperature rise across the face of the tread.

A non-contact IR thermometer could be handy for precision setting of your tire pressures. Scan across the face after a drive. Adjust pressure upwards if the sides are hotter than the middle, and etc.

hope this helps,
reid