gas mileage vs wheel size.

[toonces]

I got my Festiva with 14" wheels so I have no way of knowing what effect it had on the car when they got installed.

When I put bigger wheels and tires on my truck, I lost about 2.5 mpg.
I thought that the larger diameter would have given me better mileage but that is not the case. They were much heavier and had more rolling resistance which caused the mileage loss. They did look rather nice though. I'm wondering could this be the case with the Festiva also.
The diameter of the wheels and tires I have now are 22.75". I'm also wondering how much that has thrown off my speedo/odometer readings.
Anyone got some useful feed back for me on this issue?

[DontFearTheReaper]

You have 14 inch tires where originally there was 12 inch tires, WOW.

Your speedometer will be wrong. Load on your engine will be greater. WOW 14 inches eh!

I just got my sporty out on the road yesterday from a rebuild. I went to wal-mart and purchased a $79.00 (cheap) hand held GPS unit. I used it to check how accurate my spedo is.

Will the car make a tight turn without your tires rubbing?

[69shelby]

It all depends on the overall diameter, if they are 30 series, should be close)

[mattswabb]

I have 14's and they are a smaller diameter than the stock 12's. It all depends on the tire profile. Use this calculator to check the difference in tire sizes:

http://www.1010tires.com/TireSizeCalculator.asp?action=submit

[toonces]

I know the load on motor is greater. I also know that my speedo is off. I just don't know by how much. No. I don't have any interference problems. Turns fine. No rubbing.

That is a neat site for comparing tire sizes. I guess I need to know the stock tire size to use it though.

If I can find someone here locally with a stock wheel, I would like to weigh it and compare it to my 14" wheel.

[25Horseplay]

Try this calculator it gives speedometer accuracy with tire size comparison.

http://www.net-comber.com/tirecalc.html

[Safety Guy]

The overall diameter is only one factor affecting your mileage, etc.

Other factors are:

-tire and wheel weight (especially important as this is unsprung, rotational weight!)
-frontal area added to your car which will affect drag (wider tires)
-increased or decreased height, which can affect drag
-tire composition, which can affect rolling resistance
-tire width, which will also affect rolling resistance
-offset, which can stick the tires out and affect drag

There may be other factors I 'm missing.

Karl

[toonces]

safety Guy,
Those are some interesting points. Things I hadn't thought about.
One alone may not do much but the sum of all or some could make a significant difference. Thanks for your input.

What are the stock tire size recommendations for the Festiva?
I'll try that calculator.

The wheel and tire combo I have now sure look nice but I'm after the best gas mileage. They may have to go. I'll have to make that decision soon as my current set of tire need replacing.

Toonces

[DontFearTheReaper]

165/70/sr 12. was the info given to me off this site.

[todd00]

i dont know i have the 155 r12's on mine.

[Safety Guy]

Stock tire diameter sizes will be met very closely by the following:

-145/80-12
-165/70-12
-175/60-13

The first two are "from the factory stock" sizes.

The 155/80-12 size is most often substituted for the harder to find 145/80-12. However, it raises the ride height about 8mm and will thus indicate a slower speed.

Karl