Does rim or tire size change mileage?

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To the person who said MPG goes down with larger tires. That may be, but it has nothing to do with your answer, which said larger tires are heavier, and more to do with how the car is driven and engine power curves. A larger tire size is going to add at best a few ounces to the weight of the tire. In fact, the lead balancing weights might make more of a difference in tire weight. A few ounces on a 3,000 car makes no difference. The power to start a vehicle from a dead start would be affected by tire size, but not due to tire weight. This whole concept is demonstrated by the fact that vehicles need a transmission. (If the car just had one gear, 4th, the engine would not have enough power to start the car from a dead stop. That's why there is a transmission.) A larger tire would make a vehicle a bit harder to get moving. But, the trade off means the vehicle would take less energy to keep it moving with larger tires. Therefore, if a car is used primarily for highway driving, overall MPG may improve with larger tires. For city driving, with lots of starts from dead stops, MPG may get worse with a larger tire. This has a lot to do with transmission design, where vehicle manufacturers gear the cars for a good blend of city/highway fuel economy, also based upon the power sweet spot of the engine (and tire size!). However, for cars used for a lot of highway driving, significantly better MPG may be achieved by gearing the transmission to use lower engine rpm's at highway speeds. (Especially with diesels). But regearing, if even possible, costs a lot of money. Increasing tire size is a cheap way of doing the same thing. A bigger tire will go farther distance during one revolution, meaning you need less engine rpm's to turn it.

As for the original question, tire size is DIRECTLY related to speed and mileage readings on your speedometer/odometer. Your speedometer expects the car to go a certain distance for each revolution of the tire. Imagine: If the tire is HUGE, the car will go very far with one revolution. (Your speedometer readings will change with new tires vs old!) Almost every vehicle in the country is purposely made to READ about 5 mph HIGHER THAN actual speed. I say the manufacturers do this to make the vehicle odometer rack up the miles more quickly, which is "Gotcha Capitalism" at work. But, the manufacturers avoid massive class-action lawsuits by claiming they must do this to make absolutely sure that the car isn't going FASTER than speedometer speed so they don't get sued by people who get a ticket.

JT- BSEET

Hey. Just after I typed this, I saw a video which confirmed everything I just said. View it here: http://www.ehow.com/video_4997503_bigger-size-increase-gas-mileage.html

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From a purely geometric perspective, changing the tire diameter could effect the "Perceived Mileage" - assuming the odometer (and speedometer) tabulates the revolutions (RPMs for the speedometer), the traveled distance would be greater than the measured distance if the tire size was increased. (Just as someone would run slightly further if they ran around a track in lane two versus lane one.) Calculating the MPG would provide an error unless the odometer/speedometer was recalibrated for the different size of tire.

A friend of mine was once pulled over for exceeding the speed limit shortly after putting larger tires on his vehicle. His speedometer measured his speed right at the speed limit, but his actual speed was higher.

This error does not "change your mileage", rather just gives an erroneous value if you are using your odometer. If you are using known distances in your calculation instead of your odometer, you would avoid this problem.

However, newer/luxury cars may be using GPS or other high-tech detection methods to determine distance and speed, rather than tracking the revolutions of the axle - thus eliminating the error and the need to recalibrate.

From a mechanical perspective, an increase of tire/rim diameter might effect the efficiency of the transfer of energy or torque upon the axle. However, I would speculate that the change would be negligible.

In summary, I would suspect that the change in tire size would have minimal effect on your "actual mileage", but the "measured mileage" could easily vary as a result of calibration issues.

Call again - looks like you know the number...

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On the ground, GPS reception is too unreliable for use in automotive speed measurement. What kind of luxury car would show no indicated speed when in a tunnel?

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yes rim size does affect the mileage and speed of your vehicle. as you increase the speed your traveling at the difference in the reading on your speedometer and actually traveling at. you can get some devices to recalibrating your speed weither you have a mechanical or electrical sending unit .

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larger diameter heavier tires take more energy to spin and will lower your MPG Imagine a tire on spindle and you have to turn it by hand, now imagine a tire twice as heavy, you would have to put alot more effort into keeping it spinning at the same speed. It can have a significant effect on milage both by increased weight and the fact that on a larger diameter tire the weight is farther from the center

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Is there any official resources out there regarding tire size to mileage? I happened upon this site because i was trying to find out if there is any recorded legal issues in regard to car dealerships selling smaller tires on a vehicle to increase the odometer mileage from the actual mileage. I never even thought it would make that big of a difference but on a long drive i maintained a speedometer reading of 90MPH but was traveling about the common rate of traffic. when i passed a CHP mounted radar it said i was traveleing 74MPH when my spedo showed 84 MPH. My thought behind this is that the dealership is selling smaller tires to make their in house 3,00 mile warranty expire sooner.

Anyone with any input to this please letme know. specs: the tire that is on my vehicle is a 225/60/r16 the manufacture spec should be 215/65/r16

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First off you have 225 the spec is 215 so you have bigger tires than the spec. but the width is shorter by about 5mm, and the rims is the correct size. The width will effect the power transfer and grip of the car but the size is affecting your speed.

Another thing that might be affecting your speed is wind resistance. If you bring your speed down to about 60MPH or 65MPH next time you cross one of the CHP mounted radar your speed should be corrcet. Also check to makesure there are no other cars around you that the radar could be reading. And also depending on where you are driveing 90MPH is normal, L.A. for example.

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Here is how you really read the numbers on your tires.

example:

225/75/15R

225 is in mm, this is the width of the tire from side wall to side wall

75 is a percentage, take 75 percent of 225(width) and this is the hight of the tire wall.

15R is the rim size.

hope this helps to clear some things up.

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i have recentl put a semi agressive mud tire on my s-10 blazer and mpg dropped 6 mpg instantly so my answer is yes it does make a difference

First answer by ID1072112494. Last edit by John tsouris. Contributor trust: 0 [recommend contributor]. Question popularity: 138 [recommend question]