5% larger tires (effect on odometer/MPG calculations?)

[thomason2wheels]

Originally Posted by mcrews

Imagine that!!!!
Lowering the final rpm at cruise REALLY does work!

Lol, my old vette, a 98 c5, only turned like 1350 rpm at 55. It would get an honest 30 mpg, something my wrx struggles to do with an engine less than half the size. All wheel drive costs plenty at the pump...

[royanddoreen]

Originally Posted by mcrews

Imagine that!!!!
Lowering the final rpm at cruise REALLY does work!

I know I could use even higher tires because my best mileage is at 45 mph.

[mcrews]

1. would you have had enough clearance?
2. How much city driving vs final cruise speed driving do you do?

I know there has to be some point on item #2 where toooo much city driving (getting those larger tires rolling) eats into the mpg.

[royanddoreen]

I was thinking more about changing my final drive ratio.It's 3.54 right now and if I had a rear end from an auto 350z it would be 3.3. I would prefer around 3 to 1 but that would be from a nissan pickup amd would have to swap ring and pinion could be to costly. My driving is rural/highway where low gearing is benefical to me.

[mcrews]

that would be the way to go.

[litesong]

Originally Posted by mcrews

.... would you have had enough clearance?

Here's an old thread about replacing standard diameter tires with larger diameter tires, & questioning the clearance. Going to much larger diameter tires, you may determine you have "clearance". However, going to much larger tires, almost guarantees the need for winter, smaller diameter wheels/tires, that will take snow chains..... with clearance.

[Vman455]

Are chains really that common outside of a few areas? Even though I lived in Tacoma area until I was 22 and drove across Snoqualmie in the winter plenty of times, and Rochester NY after that, I have never in my life used chains and don't even own any now.

[hat_man]

Is it tire circumference of revolutions per mile? I would think they would be the same (as a percentage) but when I put my stock size and new size into a calculator I got slightly differing percentages.

https://www.tacomaworld.com/tirecalc

I usually go with a flat 5%. I add 5 miles for every 100 I drive or 1 mile for every 20. I'm not sure .3% makes a huge difference, but if you want absolute accuracy which one would you use?

[California98Civic]

The only way to "know" is with GPS and/or a good legnth google maps route. I have used 80-110 mile routes to derive a multiplier.

[ratgreen]

Its a trade off, so depends on your normal driving.

Larger tyres requires more torque to get moving = uses more fuel to get up to speed.

Once you are up to speed then they will lower your rpm (usually better for mpg, also probably the most torque-y part of your engines powerband). They will also traverse bumps in the road better.

So they make sense if you do lots of highway driving but not if you are a city driver.