Hello everyone,
I have a problem and hoping someone can help me out. Last week, I went from the stock 16" tires to an 18" tire. The next day I had a 550 mile drive while on the road I used my normal pulse/glide driving method and on average my mpg needle hovered in the 30-40 mpg mark. The only bad ting I noticed was that my steering would vibrate on and off when I hit about 70-80 miles per hour. I called a friend of mine who worked at the tire place i went to and he told me that my tires probably needed to be rebalanced. I went to a different tire place to get them rebalanced, the guy there said that all 4 tires were in need of a rebalance which he did and it was fine, he also told me that whoever did my tires put too much air in them, he said they were at about 50psi and that they should be between 30-35psi.

Now my problem is that my steering wheel doesnt shake anymore at high speeds but my mpg need is all over the place, now when I acceperate it goes all the way to 10 and usually stays there and when I take my foot off the gas it goes all the way down to 60. There is really no in between. I just put gas in the tank so my mpg of course went down and checking it to see how it does. But Im kind of concerened

Should I bring the tire pressure up?
Did the tire guy do something wrong???

Thanks
Shawn

For mileage, raise the pressure to the maximum it says on the sidewalls.

I would not go over that number, whatever it says.

an 18 inch rim is going to weigh a whole lot more than the OEM rim that was designed for FE. so you are going to take a hit in FE because of that.

Also, you probably went with a wider tire too. This will hurt FE as well.

I figured I would take somewhat of a hit, but it seems like when the tire was at 50 psi everything was going well.

Every tire has maximum PSI printed on the sidewall and I think it is rated as cold tire pressure, but still I would pump it bellow the number to allow for warmer temperatures and tire heating up while driving. As long as the pressure is bellow maximum, you should be fine, but it will make the ride stiffer and it could affect traction a little, especially in the rain, but otherwise you should be fine. The vibration was caused by tire not being balanced and that should not affect anything, especially that you didn't drive for too long with vibration being present. If you want to sacrifice a little comfort with better MPG, just increase tire pressure, it is probably one of the biggest and easiest ways to increase MPG in any car. Your tire guy is old school, where 28-32 PSI was the norm. Keep in mind, the famous Firestone tire blow ups in some SUV's few years ago were caused by low tire pressure, not high. FYI, the spare tire in your trunk is rated for 60 PSI, but it is designed as such.

old school or not, the fact is that I have noticed no difference from OEM recommended tire pressure and MAX psi (on sidewall). The only difference I noticed is a better handling car and better traction in the rain... especially hard braking. So that's why I inflate my tires to +10 psi over oem (but under max).

If you drive on smooth highways, there should be no difference, but on the bumpy road or dirt road I can tell right away the tire pressure is high, ride is harsher. The theory is that lower tire pressure would make larger contact with road surface, providing better grip, with high tire pressure smaller footprint is achieved with most of the car's weight in the center of tire, but that's only theory, if you get better grip , higher MPG and the same comfort with overinflated tires, more power to you. Just keep in mind, every time you take car to the dealer and if they do check tire pressure, most likely they will lower it, so you'll need to pump it up. Also you loose something like 1 PSI for every 10 degrees of temperature drop and my tires slowly leak out the air, something around 1-2 PSI every 3 months or so, I heard aluminium is porous and it will let air go very slowly.