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Gas Mileage Increase with Bigger Wheels

Will increasing the diameter of the driving wheels increase the mechanical advantage of any engine and give you more miles per gallon in any existing automobile?

In theory yes, however there are a few factors to consider, the engine will need to work harder to get the wheels turning so my guess is that the extra effort required to initally turn the wheels may negate the savings you experience once underway. also your speedo will be wrong.

increasing the diameter of the TIRES will result in less revolutions per mile , limited by the space within your wheel wells for suspension travel and turning radius. Whether or not you see significant mpg increase is subject to many variables; weight and mass of the bigger tire, if much heavier will take more torque to move.; low end ratio & take off rpm of engine could result in a need for more gas pedal to get it moving. You may be saving decimal points in mpg but at the expense of new tires.

Increasing wheel diameter will decrease the mechanical advantage of an engine. It’s the same as upshifting, or installing a (numerically) lower axle ratio.

Maybe maybe not. In any case you are likely to get a larger increase by switching to high mileage tyres (the ones with lower rolling resistance. You will need to measure the mileage carefully to see it however.

The question of the wheels depends on what the final effective gear ratio is now and how you drive and were you drive and how close the engine is to operating at maximum efficiency now and which way increased or decreased effective gear ratio would be to get to the magic number. BTW that magic number might reduce engine life (or even increase it).

In sort, don’t worry be happy.

I have a small truck with 16 inch tires and standard is 15. Anytime you can run the engine slower, you will get a little bit better mileage. It also makes it loose all pep. Mine jumps into overdrive about 50 mph on entrance ramps and has no power at all. If you drive it like you used to it will likely get worse mileage. Be careful what you wish for.

Anytime you can run the engine slower, you will get a little bit better mileage.

Put those monster smasher’s tyres on your truck (keeping the same gearing) and see what happens to the mileage.

In real life there is a best effective gear ratio and anything higher or lower will reduce mileage. Most cars are on the low side, because of derivability and other issues, but you can go overboard and loose mileage.

BTW it is possible that 16 in tyres may have a smaller circumference than a 15 in tyre.

All true. Another issue is getting the speedometer recalibrated at each change of overall tire diameter. Can’t calculate mpgs if he doesn’t have the right ‘m’.

I have played around with regearing my motorcycles, easy to do with chain drive, and found that going higher than stock gearing gets better mpg but there is a point of diminishing and even negative returns. Also, I find that gearing that is optimum for 55 mph is too high to be optimum at 75-80 mph. So, if you plan to cruise down the highway at 55 mph, increasing the gearing will most likely make a significant difference but if you like to go 80 mph down the highway, the stock gearing will be just as good if not better.

True - although where recalibration used to mean getting a different gear size, its not so easy (or even possible) with most electronic clusters.