After doing all mods to your HHR ,what is your increase in mileage from baseline, i own a new 2008 LT 2.4 auto 4000 miles.
i am interested in all mileage increase mods than horsepower gain, first i added a ss bola muffler only, K&N aircharger, I gain 4mpg on freeway doing 75-85mph getting 29.8 mph compare to 25.7 stock , 31.4 mpg at 2500 rpm is the best gas mileage range, i noticed a big performance increase with only the muffler and aircharger, next is to add 20" wheels larger dia. tires to lower rpm at 75-85 range to increase mileage, i drive 826 miles every other week all freeway never drive under 70 mileage is my goal, first trip was the muffler, second was aircharger, next will be tires, then to lower 1.5" with goldline springs, then high tech car waxing day of the trip, soon a oil change what oil??
i get better gas mileage on hot days compare to cold days, night driving was the worse for mileage, i quess its the air density, i am looking for more suggestions and mod. done that worked.

 

I get 32HWY completely stock.

 

At 75-85MPH?

 

Tony, the 20" wheels are NOT going to help fuel mileage. They are big flywheels and heavier then the stock wheels/tires. It takes extra power to get them rolling and slow/stop the car. The other issue would be additional rolling resistance from the tires themselves.

The taller tire/wheel may act as a taller gear ratio, but the speedo/computer will not read out the difference. You are going slower then the speedo will read out. Unless GM has put a way in the computer to adjust the speedo, then you will not be able to read the difference on the DIC system.

 

Here is another one to try, I got it don to mine and increased the mpg by 2.4. It is having nitrogen in the tires instead of air. it was about $45.00 to do and it was worth the change in hwy driving. I have had the Candid-1 for about 3.5 months and have 13000 miles on it.

 

I do all my driving between 75-85 +mph for 5 hrs, Interstate 5 all wide open freeway few CHP that's the flow of traffic , only time i see 70 then i stop to eat.
I set my cruise control on 80 as cars begin to pass me i up it 85+ for about an hour or so.
I did 60-65 and got 30mpg, once i hit the 75-85+ speed mileage drop to 25 and less the faster i cruise so i did mods to increase mileage at the 75+ speed, looking for more mileage i will be putting 25k plus per year

 

Subject:Info - Use of Nitrogen Gas in Tires #05-03-10-020 - (12/22/2005)


Models:All 2006 and Prior GM Passenger Cars and Light/Medium Duty Trucks (including Saturn)
2003-2006 HUMMER H2
2006 HUMMER H3
2005-2006 Saab 9-7X

GM's Position on the Use of Nitrogen Gas in Tires

General Motors does not oppose the use of purified nitrogen as an inflation gas for tires. We expect the theoretical benefits to be reduced in practical use due to the lack of an existing infrastructure to continuously facilitate inflating tires with nearly pure nitrogen. Even occasional inflation with compressed atmospheric air will negate many of the theoretical benefits. Given those theoretical benefits, practical limitations, and the robust design of GM original equipment TPC tires, the realized benefits to our customer of inflating their tires with purified nitrogen are expected to be minimal.



The Promise of Nitrogen: Under Controlled Conditions

Recently, nitrogen gas (for use in inflating tires) has become available to the general consumer through some retailers. The use of nitrogen gas to inflate tires is a technology used in automobile racing. The following benefits under controlled conditions are attributed to nitrogen gas and its unique properties:

• A reduction in the expected loss of Tire Pressure over time.
• A reduction in the variance of Tire Pressures with temperature changes due to reduction of water vapor concentration.
• A reduction of long term rubber degradation due to a decrease in oxygen concentrations.


Important: These are obtainable performance improvements when relatively pure nitrogen gas is used to inflate tires under controlled conditions.


The Promise of Nitrogen: Real World Use

Nitrogen inflation can provide some benefit by reducing gas migration (pressure loss) at the molecular level through the tire structure. NHTSA (National Highway Traffic Safety Administration) has stated that the inflation pressure loss of tires can be up to 5% a month. Nitrogen molecules are larger than oxygen molecules and, therefore, are less prone to "seeping" through the tire casing. The actual obtainable benefits of nitrogen varies, based on the physical construction and the materials used in the manufacturing of the tire being inflated.
Another potential benefit of nitrogen is the reduced oxidation of tire components. Research has demonstrated that oxygen consumed in the oxidation process of the tire primarily comes from the inflation media. Therefore, it is reasonable to assume that oxidation of tire components can be reduced if the tire is inflated with pure nitrogen. However, only very small amounts of oxygen are required to begin the normal oxidation process. Even slight contamination of the tire inflation gas with compressed atmospheric air during normal inflation pressure maintenance, may negate the benefits of using nitrogen.


GM Tire Quality, Technology and Focus of Importance Since 1972, General Motors has designed tires under the TPC (Tire Performance Criteria) specification system, which includes specific requirements that ensure robust tire performance under normal usage. General Motors works with tire suppliers to design and manufacture original equipment tires for GM vehicles. The GM TPC addresses required performance with respect to both inflation pressure retention, and endurance properties for original equipment tires. The inflation pressure retention requirements address availability of oxygen and oxidation concerns, while endurance requirements ensure the mechanical structure of the tire has sufficient strength. This combination has provided our customers with tires that maintain their structural integrity throughout their useful treadlife under normal operating conditions.
Regardless of the inflation media for tires (atmospheric air or nitrogen), inflation pressure maintenance of tires is critical for overall tire, and ultimately, vehicle performance. Maintaining the correct inflation pressure allows the tire to perform as intended by the vehicle manufacturer in many areas, including comfort, fuel economy, stopping distance, cornering, traction, treadwear, and noise. Since the load carrying capability of a tire is related to inflation pressure, proper inflation pressure maintenance is necessary for the tire to support the load imposed by the vehicle without excessive structural degradation.
Important: Regardless of the inflation media for tires (atmospheric air or nitrogen) inflation pressure maintenance of tires is critical for overall tire, and ultimately, vehicle performance.

 

would that be 35psi with nitrogen?
can you carry small canister nitrogen refill kit as a spare?

 

I had it done at my local chevy dealer. They check the pressure whenever they do the standard check-ups. It is true if you keep good pressure it really doesn't matter what is inside of the tire. I decided to try it and I like it.

 

where do u get it from?
Tommy