Would larger tires hurt mpg's
 

I have a 1992 Honda Civic VX and I recently was given some P185/65R14 tires and rims. It appears the tires overall diameter is very close to six percent larger.
So my speedometer reads slow and the odometer reads slow and the engine also turns over slower. With the VX geared so high already, would the fuel economy be affected?

The only way to know for sure is to try it and see. Generally, though, your highway mileage will improve with larger tires, even with tall gearing. It seems that even efficiently-geared 4-cylinders could still go a little taller. I say this, of course, with no experience driving a Civic VX. What kind of revs are we talking about, and at what speed?

You tell us!

The O2 sensor was bad
 

I may not know until I swap the smaller tires back on.
The O2 sensor was bad before I put the larger tires on.
Only after the tires were installed did I put a new O2 sensor on.
I was only getting 30 miles to the gallon before I installed the new sensor.
With the new sensor and tire I average between 40 and 45 miles to the gallon.

I went from 235/75R15 to 31x10.50R15 and had no change in fuel economy.
May have even improved slightly.
I was expecting to lose fuel milage.

Maybe. Here is the best test on the issue of tire sizes and weights done on this site: http://ecomodder.com/forum/showthrea...tml#post246084. And here is a forumla: http://ecomodder.com/forum/showthrea...tml#post308276

My post will be no help at all.

I jumped up 2.7% in tire size, and I noted a difference in efficiency. But my engine was also just in the breaking process, so that is not conclusive, and there was no formal testing.

It appeared to be an increase.

Nice to know my work is still the "gold standard," lol.

Just installed tires 5% larger and also much lighter so not sure which is helping my better mpg.Have to do some testing but for me seems to be a win win situation. I'm using a v6 so could be diff from a 4.

I recently had changed the tires on my 2000 Mustang. I went from stock 205 width to 245, so about 4cm wider on each tire. I noticed a large change in MPG (2-3 mpg overall) I used them for about a month and decided I couldn't live with the change. They looked amazing, but with the amount I drive, I couldn't stand the loss.

My overall changes went from around 24-25 on normal driving to 22-24. Highway went from 28-29 down to 26-27. I changed them back about a month ago and it has corrected to normal. My tank from yesterday was actually a new record of mine, 34 on a 220 mile highway trip.