Yet another tire pressure question.

[Web Architect]

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?

 

[jmm176]

What is hour 60 mph rpm

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[Web Architect]

Not sure at 60. 2500 at 70

 

[Berzerker]

I run 28 psi in my 35x12.50r17's

 

[cozdude]

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.


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[OverlanderJK]

I run 28-30 PSI in my 35's.

I think you are supposed to run 91 octane also.

 

[wayoflife]

I run 28-30 PSI in my 35's.

I think you are supposed to run 91 octane also.

Yup and yup. About 30 psi for 35's and you're ride will be a lot nicer and 91 for a RIPP is standard.

 

[RockyJk]

Yup and yup. About 30 psi for 35's and you're ride will be a lot nicer and 91 for a RIPP is standard.

Isn't 91 standard for any forced induction

 

[OverlanderJK]

Isn't 91 standard for any forced induction

Yes.

........

 

[jnabird333]

Isn't 91 standard for any forced induction

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