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kaflyboy 04-14-2011 05:58 PM

Tire Pressure?
 
When i picked up my jeep the dealer said they checked the tire pressue (they didn't). all 4 tires were at 41psi which must have been set at the factory.

i drove around for a day or so and was gettign 21.7 on the interstate for mpg.

i lowered the tire pressure to 36psi as recommended on the door and my gas mileage has dropped to around 19 on the interstate.

i'm a big fan of getting all the gas mileage you can get out of a car, so, should i increase the tire pressure a few pounds to try and get better mileage? i know the tires will not wear as designed with higher pressure.

netcoolery 04-14-2011 06:15 PM

Re: Tire Pressure?
 
Quote:

Originally Posted by kaflyboy (Post 396058)
When i picked up my jeep the dealer said they checked the tire pressue (they didn't). all 4 tires were at 41psi which must have been set at the factory.

i drove around for a day or so and was gettign 21.7 on the interstate for mpg.

i lowered the tire pressure to 36psi as recommended on the door and my gas mileage has dropped to around 19 on the interstate.

i'm a big fan of getting all the gas mileage you can get out of a car, so, should i increase the tire pressure a few pounds to try and get better mileage? i know the tires will not wear as designed with higher pressure.

Well the reason your gas mileage is better is that you have a smaller contact patch, thus less rolling resistance. To be honest though, I'm surprised it was so dramatically better, esp at freeway speeds where most of the resistance is air resistance, not rolling resistance.

Bear in mind that the smaller contact patch does cost you a little bit of handling and braking, although realistically nothing that would be noticeable on the street.

The other thing to consider is the max psi rating of the tire - you don't want to be too near that at cold fill because the pressure will go up as you drive and heat the tire.

I dunno - I think the first thing you should do is repeat the experiments and really confirm that there's a 2.7 MPG difference between the two tire pressures.

Dan JGC 04-14-2011 08:29 PM

Re: Tire Pressure?
 
You shouldn't be getting that much of a mileage difference.....you can't go by the the real time gauge per se. Plus maybe one way was up hill and the other down hill??? Anyway, I just don't think 2.7 mpg is accurate.

Breitling65 04-14-2011 08:44 PM

Re: Tire Pressure?
 
Quote:

Originally Posted by Dan JGC (Post 396129)
You shouldn't be getting that much of a mileage difference.....you can't go by the the real time gauge per se. Plus maybe one way was up hill and the other down hill??? Anyway, I just don't think 2.7 mpg is accurate.

Agree, he might be looking on jeeps mpg display which is calculating numbers funny way. I just drove 3k miles to Florida and back to NJ and saw how this indicator increased my mpg up to 26 mpg for a while since I dropped car speed from 80m/h to 70m/h. After about 100 miles it returned to 23 mpg as it suppose to be on highway.


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