Tires VS MPG

[The_Duckslayer]

As a result of my last post I ended up replacing the fuel pressure regulator valve in an effort to get my gas mileage back up. That did not fix the problem. One of the questions airjer asked was are the tires inflated properly? Actually they are all about 4 PSI low and I have not corrected that. I do not think that would cause a 4MPG drop in mileage though. Then I started thinking about it and thought that we recently took the worn out Goodyear tires off of it and replaced them with Cooper Discoverer CTS tires. I wonder if that could be the culprit? I would like to think that the Cooper CTS's which are a higher end tire than the low end Goodyear's we had on should be every bit as good of a tire if not better. Would changing the tires make that much difference? WHat do you guys think? Thanks in advance././Jimbo

[Jeremy airjer W]

A 22% change in fuel economy is huge. We also had some of the coldest weather of the year last week. Really low tire pressure can account for 8%-12%. New tires, I couldn't tell you. I do know that if the temp is below 22 to 23 degrees my fuel economy goes way down! I can go from just under 18 to about 15 on the freeway with a couple of degrees in temp. I have no idea what I get on a warm day, we'll find out this spring. I know 14 is a drastic drop but it might be worth waiting for the warmer temps to see if it rebounds? Unless anybody else has some insight??

[lawdog]

On a related note, we always hear proper inflation for tires and I believe that, but like in Duckslayer's case, he's changed tires, do you still inflate to what it says on the door sticker or do you go the max PSI on the tire? I never figured out how that sticker could be bible if you've changed tires since it was new... I have a hard time buying 22% change in fuel economy due to change in tire brand, but would the inflation change matter???

[Jeremy airjer W]

You always inflate to what the vehicle placard on the door/glove box/owners manual/ etc. says. This is especially true with TPMS (tire pressure monitoring systems). If you change tire sizes there may be an exception and if you have a vehicle with TPMS you may be able to reprogram it to the new tire size pressure requirements as long as the tire was offered in the O.E. lineup for that vehicle.

In short the tire pressure should always be set to the vehicles recommendation not the tire manufactures max load x,xxx at xx psi!

[Scott K]

Since you changed tires, one thing comes to mind, are the new tires a different size? Even if they list the same size on the tire, I have seen differnences in circumfrence as much as an inch or more, which can change your speedo a couple miles per hour. In which in a tank full of gas can change your calculations a quite a bit! Just a thought.

[The_Duckslayer]

Tires are the same size.

I had always heard that you should inflate tires to what the pressue that is listed on the side of the tire. I was told that number is the optimum pressure for that tire to run at to get the longest possible tread life. I was told that the pressure listed on the door jam was a compromise of the tire manufactures spec in order to get the lower pressue needed to maintain a nice comfy ride. Take care and N Joy the Hunt././Jimbo

[Jeremy airjer W]

For some reason I'm stuck on owners manuals today. They really do have a lot of good info. This is page 5-57 of yours duckslayer.

Inflation -- Tire Pressure

The Certificationflire label, which is on the driver’s door edge, above the door latch, shows the correct inflation pressures for your tires when they’re cold. “Cold” means your vehicle has been sitting for at least three hours or driven no more than 1 mile (1.6 km).

Notice: Don’t let anyone tell you that underinflation or overinflation is all right. It’s not. If your tires don’t have enough air (underinflation), you can get the following:

*Too much flexing

*Too much heat

*Tire overloading

*Bad wear

*Bad handling

*Bad fuel economy

If your tires have too much air (overinflation), you can get the following:

*Unusual wear

*Bad handling

*Rough ride

*Needless damage from road hazards.

This is from the Good Year tire site,

"Check Your Air Pressure

Keep your tires properly inflated and you could improve gas mileage by more than $1.50 every time you fill your tank. The recommended tire pressure for your vehicle is located on a sticker inside your driver-side door or noted in your owner's manual."

This is from the cooper tire site,

"It’s important to have the proper air pressure in your tires, as underinflation can lead to tire failure. The “right amount” of air for your tires is specified by the vehicle manufacturer and is shown on the vehicle door edge, door post, glove box door or fuel door. It is also listed in the owner’s manual."

[The_Duckslayer]

Ayup... After I posted that I went looking as well. All the sites that I checked, ask, firestone, cooper and good year say inflate to the door plate. I guess I will be making some trips from the basement tonight hauling up some air. I never realized how strong I was until I started hauling air up from the basement! I can carry 100 pounds of it with very little effort! Thanks for all the help Airjer and others. Take care and N Joy the Hunt././Jimbo

[Jeremy airjer W]

I guess I will be making some trips from the basement tonight hauling up some air. I never realized how strong I was until I started hauling air up from the basement! I can carry 100 pounds of it with very little effort!

WHAT????

[The_Duckslayer]

The only 220 outlet in the house at the moment is in the basement. My air compressor is sitting in the basement and I haul a small 1 gallon tank from the basement to the garage. That way I can carry 100 pounds of air (pressure) in the tank to the garage. Thanks for all your help. Take care and N Joy the Hunt././Jimbo

[jwhjr]

I thought maybe you were referring to that heavy winter air that airjer reminds us about...

[Jeremy airjer W]

[Dave S]

Tread patterns will have an affect on mpg also. I put a set of Revo's on my 4-Runner and lost 3 mpg over the stock tires. Granted, the Revo's were heavier than stock which also affects mileage but a tighter tread pattern will have less rolling resistance than the more open block patterns.

[deadeye]

It sounds to me like a combination of a few factors that everyone has listed. The cold weather really kills my mileage. I loose about 4 mpg when its cold with my Blazer. I get 23mpg highway in the summer and about 19 in the winter. City driving, forget about it, I dont even want to tell you what that is.

If you changed the tires, that will make a difference as well as having them inflated properly. Its just a bunch of little things that add up.

[The_Duckslayer]

It sounds to me like a combination of a few factors that everyone has listed. The cold weather really kills my mileage. I loose about 4 mpg when its cold with my Blazer. I get 23mpg highway in the summer and about 19 in the winter. City driving, forget about it, I dont even want to tell you what that is.

WOW... On a real good day, going down hill, with a tail wind I get barely 20 with my Jimmy. Overall I get about 18-19 with it. City driving? What is that? I drive from the house to the highway and that is thee only city driving my truck ever gets. Well cept to run to the liquor store! Speaking of the liquor store… I stopped there last night on the way home and the fire dept had it surrounded and the snorkel up over the top of it. Dunno what was going on but suspect they smelled something and called the fire dept. Needless to say there was no Morgan and Coke for me last night! Take care and N Joy the Hunt././Jimbo

[jltimm]

There's a guy on another site that claims to get 19-21 mpg with a Dodge Durango with a hemi?

[deadeye]

I have done a couple things to help with the mpg. I got imco muffler and magnaflow cat. I also have a cold air intake too. Some will say that those things dont help but I didnt get over 20mpg before I did that stuff. I also replaced the injection unit with a new one which is a improved design. A lot of money, yes, but it was stuff that had to be replaced due to wear anyway. I found that it was cheaper to get performance replacement parts for certain things anyway. More power and cheaper, what could be better.

The main thing for me is just being easy on the gas. If i stand on the throttle the mpg goes out the window. Its hard to do, but its the best way to save gas. Thats why in the city my mpg is more like 13-14, I am off and on the gas and I dont like being the slowpoke merging on the highway doing 45mph. Who knows, I guess it goes to show that when I make a trip up north im saving gas compared to fishing in the city!

[fishorgolf]

I switched from the stock road tires to a much more aggressive tire on the 3/4 ton sub. and lost aprox. 20% in milage. So yes tires can make this much difference.