Tire decision

I have an '89 metro hatchback. I recently, like everyone else with 12" tires, needed to get new tires. I could'nt find any locally. I really wanted to change to 13" wheels so that it would'nt be such a challenge to get tires. Anyway I went to the parts yard and happened across a '89 or '90 metro convertable with almost new 13" wheels and tires for $100. What a find. They drove great, but when I checked my gas mileage , as I always do, it went from 46 mpg to 41 mpg. And yes, I do calculate for tire size. I have to accept the fact that unless I switch back to 12" tires I'm not going to see that mileage again. One plus for the size change is safety though. Although I drive careful in the rain because the car is so light, I feel much safer as far as breaking and steering traction and its worth the 5 mpg loss. I'm curious if anyone else had similar experience.

How can you be sure that the mpg change is due to the tires?

So many things affect the mpg!

Temp drop in Fall & Winter.

Gasoline brand.

Slight Variations & Errors in fill-up gallons.

Driving conditions - city vs country, Rain, Wind...

I would bet that over the long haul - several months in Summer - that the 13 inch
tires make no difference in mpg over the 12 inch ones.

Why would they?

I wish I had known about the 13 inch wheels fitting a Metro before I bought two
sets of 12 inch wheels - one for Summer the other for Winter tires....

I've got too much invested to spend more $$ on more wheels.

DoctorBill

I attribute the mpg loss to the tires because whenever I get gas I fill up and check my mileage, and its consistant every time. I did nothing else but the tires and it dropped, and its consistant now also. It was a little baffling that I pulled the speedo gear out of the convertable with bigger tires and it was the same as the one in my car. I had suspected the mpg would drop due to tire drag, but not that much. I don't think the diameter is the problem, I think its the width. Although its not much, but the car isn't a peppy as it was. When I had the 12" tires on it I ran 35 psi in the tires to squeeze a mile or two more mpgs. I do the same with these but you can tell their not as hard on the road. It definetly is a better riding and handeling car now. If you hit a pot hole it doesn't feel like the whole front end is going to break off as it did before. It looks better too. By the way, the bolt pattern on the wheels was right but to use them on my car I had to use a modified washer because the lugs were bigger on the convertable.