40 psi in the tires makes a huge difference. i went from 33 to 40

 

I just did a tank this past week and kept the speed as close to 65mph on the interstate as I could and got 38.8mpg, my best tank yet. Not sure it's worth the effort for say a mile or 2 per gallon difference from my normal 68-72mph driving.

 

also, you guys should read up on using acetone in the gas. if you put 2 oz in 10 gallons of gas, your gas mileage will increase. every car is different but the increase is always 10-30% depending on the car. even 10% is 3mpg but it has to be 100% pure acetone. not the fingernail polish remover with benzine in it

 

What are the down-sides to over-inflation like this?

 

they are not over inflated until you go over 44 psi. (as indicated on the sidewall) however, the ride at 40 psi is bumpier if you're on really bad roads.

 

Actually, they could be over inflated - defined by premature wear of the center of the tire.

An example will explain this: I have a Ford F350 Duallie as a second vehicle. This was my first duallie and I didn't realize the impacts of over pressurizing the tires. Well the first time I needed rear tires, Les Schwab (big tire chain in the Pac NW) put on the rear tires and inflated to the maximum pressure rating of the tire which was 80 psi. Well about 20,000 miles later, the center of the tires were baked off. In essence there wasn't enough load on the tires and only the center of the tires were making contact with the road (I had this 1 inch band around the circumference of the tire that was worn off in the center of the tire). After this little lesson in life, I found out how the truckers inflate and deflate their tires to maximize tread life with the weight they are carrying. This formula works great and it's nothing special.

maximum PSI rating of tire / maximum weight rating of tire * actual weight experienced by this tire ONLY. Nothing special just keeping the same ratio of design max psi to max weight rating of tire.

Now to answer the question at hand - Is the Scion tire over inflated at 44 psi? No not from the point of view from exceeding maximum PSI rating for the tire (if that is the rated maximum psi rating - I didn't check). Will the center of the tires bake out - betcha they will. Also you won't have as much footprint on the road, driving in the rain may get a little crazy. Roll in the added cost of replacing your tires ahead because of premature wear in the center, may not be cost beneficial when compared to the gas savings.

 

actually, in rain you want less footprint on the road. you are less likely to hydroplane and you have more wight pre sq inch touching the ground.

as for over inflating, I agree with a big truck those tires are rated at higher pressures and so without a load they will stratch out. but on factory skinnies that the XA comes with, 44 psi is the max pressure without over-rounding them. low profile tires are more succeptible to wearing out in the center due to the wideness and lack of support down the center of the tread.

I'm gonna keep an eye on my tread to make sure the centers don't wear down but from what I've learned they shouldn't wear out abnormally unless you go over 44 psi.

but as always, i could be wrong! and nowadays tires are cheaper than gas.

 

Good point on the footprint in the rain - you're right.

Keep an eye on the tread wear in the center of the tire (assuming your running stock tires). I would like to see how these smaller tires perform over inflated (from a weight perspective).

 

I'm gonna run a few tanks with my 18's on to compare with the stock pizza cutters. wind drag alone should lower my MPG lol

 

My second tank wasn't a hell of a lot better @ 23.5 MPG, and I was driving like a granny as much as I could stand.

After that tank I took off w/ my wife for a 750 mile round-trip roadtrip and got 30.5, 27, and 30.5 on the three fill-ups. This was up I5 with an average cruising speed of 83MPH.

An imporvement, but Im still hoping for better...

 

Dude: Getting 30 MPG and doing 83 mph is great!

I just filled up again. My overall MPG with 2450 miles on the car is 39 MPG.
Driving max 60 mph, shrt shifting at 2K (I have a 5 speed), in 50% city driving.
I have got as high as 43.2 MPG.

 

While running my 17's I upped the pressures from 30psi to 35psi and the mpgs. went from 29 to 33. It didn't ride that much harder either. I'll have to keep an eye on those pressures in the future.

 

cuppajack, have no fear, I was concerned about the same thing...and as I broke my engine in, my mileage went up. My first few tanks were sub-30's, but now I am averaging 35 mpg everyday driving, a/c or not...don't worry, it will change. I also swapped out the stock 15's for 17's, which cost me a few mpg's, but worth it for the look.

 

I checked my tire pressure over the weekend and found it to be between 29-30 on all four corners. Next fill-up I'm going to inflate these to 40PSI and see how that effects things...

Why does the info-panel in the door-frame specify 30PSI? That seems ridiculously low to me. After all, the stock tires are spec'd to 44PSI.

 

Check my response above regarding how truckers inflate and deflate tires to accomodate changing loads on the tires.

Your tires can take a maximum of say 44 psi, however for the designed load distribution on the tires for the vehicle,, for maximum tread life the door indicates the suggested psi.

 

Check my response above regarding how truckers inflate and deflate tires to accomodate changing loads on the tires.

Your tires can take a maximum of say 44 psi, however for the designed load distribution on the tires for the vehicle,, for maximum tread life the door indicates the suggested psi.

 

First, don't assume that every car has the same supplied tires.

Second, 44 is most likely listed as the max pressure. Set it at recommended, and increase it only to accomodate increases in the load you're carrying. With a Thule carrier and a car full of camping gear, I increased pressure to 40. With the car unloaded, 40 is too much.

While small changes of a few psi aren't going to cause too much troubles, the air pressure in your tires is only one part of many in the suspension equation. Gross vehicle weight, spring rate and height, wheel mass, tire pressure, and tire rigidity all affect ride and handling. Tire life and mpg are secondary to maintaining adherance to the road.

 

you guys are off topic. we're talking about gas mileage not tire wear. i always run max pressure and get 35-40K out of a set of tires so the wear isn't a problem on light little cars. we're not driving big rigs.

 

For max MPGs run front pressure at 35psi and rear at 33psi and be done with it. Just check them every month cause you'll lose a couple pounds.

 

I increased the PSI to 36, and my last two tanks have been 23.5MPG.

I can barely go 250 miles on a tank of gas...

Could there be something mechanicaly wrong that isn't throwing a CEL? What should I be looking for?

Do I have any recourse with the dealer's service department?