Yet another tire pressure question.

W

Web Architect

New member
Seems most 35" tires are on 16 or 17 inch rims. Mine are 18 inch rims.

At 35 psi, it's bouncy. Dropped to 33 and its way better, but gas mileage apparently dropped too. Dropped 2 mpg or worse. Seems a bit excessive.

2007 JKU. It's RIPP supercharged, which is great, so I called. Tech said I ought to be running 91 octane. That's a new one to me.

Road trip about to happen, and 13 mpg is just plain ugly.

Thoughts?
 
cozdude

cozdude

Guy with a Red 2-Door
I'm running 30 psi in my 35's. I get about 14 city and 17-18 highway. I haven't regeared yet either so I tend to downshift often on the highway.


Sent from my iPhone
 
jnabird333

jnabird333

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rockyjk07 said:
Isn't 91 standard for any forced induction
Click to expand...

Depends on compression ratio and ignition timing.... I have ran lots of forced induction cars (low PSI) with no early detonation or "ping". On the flip side, My Stock F250 w/ a V10 rattled like mad unless I ran 89 or higher.

On the PSI... I always use the formula below to get me close and then finalize with a chalk test and butt feel.

Old tire width divided by new tire width, then multiply with old tire pressure. Assuming you previously had stock tires it would look like this.
(10.0/12.5)*36=28.8
 
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