First mileage test
02-11-2013, 08:12 PM
#11
Senior Member
Join Date: 09-08-2012
Location: Vancouver. B.C.
Posts: 143
There are 2 different factory wheel/tire sizes and each have their own recommended pressure on the door jamb. The 17 inch is 35 all around. I think its 32 for the 16's. This is what you are supposed to run, regardless of what it says on the sidewall of the tire.
If you increase your pressure, you have a chance of wearing out the middle of the contact patch....which basically wrecks your tires, or at the very least shortens their lifespan.
There would also be a performance difference in cornering and braking....especially if you really amp up the pressure.....might as well have motorcycle tires on your car....lol
Anyway.....just my 2 cents fyi.
If you increase your pressure, you have a chance of wearing out the middle of the contact patch....which basically wrecks your tires, or at the very least shortens their lifespan.
There would also be a performance difference in cornering and braking....especially if you really amp up the pressure.....might as well have motorcycle tires on your car....lol
Anyway.....just my 2 cents fyi.
02-11-2013, 10:04 PM
#12
Senior Member
Join Date: 10-21-2008
Location: hemet, calif.
Posts: 1,831
I installed the Autometer 2 years ago, a year and a half driveing to the SoCal BarBQ in Irvine at a steady 72 MPH was getting 34.7 MPG for the 70 mile one way and the same on the way home, I think because of the Cold air air filter. 
02-15-2013, 07:53 PM
#13
Senior Member
Thread Starter
Join Date: 01-24-2013
Location: FRESNO CA
Posts: 188
You have a point. When I refueled today my DIC told me 28.9 ave but when I ran the numbers off the ODO it was 27.9.
beware..when calculating from the odo..that alot of these cars are running 'up to' 3 mph slower then indicated...bump it against your GPS and you'll see..so your odo calc will be off, to the good, that is indicating a higher mpg then actual....so your DIC may be more accurate then you think.
02-15-2013, 11:39 PM
#14
Senior Member
Join Date: 08-26-2008
Location: Sequim Washington
Posts: 1,488
Sleeper, my tag on the doorjam GM put on it says 30 front and rear. However, mine came with almost new rubber and they say on the sidewall 35psi. Not psi cold. I will have to look into it but I may try 33 for a tank and see what happens. I keep track of all my fillups from the first to the last so over time we will see. I log the following: tire pressure, season outside air temps and conditions, miles driven, gallons used, price per gal, price per fillup. I took one of the jet engine trim sheets and reworked it for tracking fuel mileage. I like this thread you guys made here. I thought I was the only one that kept track of things like this.
Stock LS and 1LT come with 215/55R/16 Standard Load tires
Door tag shows 30psi cold front and rear.
Stock 2LT comes with 215/50R17 Standard Load tires.
Door Tag shows 35lbs. cold front and rear.
That is the recommened tires pressure based on the Gross Vehicle Weight including driver, passengers, and any other cargo etc.
If you carry less then the recommended max weight in the rear you could reduce the psi from the stock setting to reflect the actual amount of weight you carry.
The rear weight can vary but the front stays approx. the same unless you occasionally have no front seat passenger or make alterations to the stock car.
The Max air pressure shown on the tire is just what it says, and reflects the Maximum air pressure allowed at the Maximum weight allowed on the tire.
Remember that both tire sizes are used on more then just the HHR and they can weigh in differently then the HHR.
The tire used on each different vehicle must be able to carry that load safely and that is figured into each new car when the tires are chosen.
SF
Last edited by Silverfox; 02-16-2013 at 12:14 AM.
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