Yes, 2009 manual. Thanks for the info.
I swapped my stock 14" steelies with factory sized tires for a set of 17" +35 offset rotas with 205/40/17 in front and 205/50/17 in rear (great set up btw). I haven't noticed any substantial changes in fuel economy, but my handling has gotten so much nicer from having a wider wheel. The 17's are of a much lighter alloy so the upsize vs material vs lower profile tires means the wheels weigh just a little less than stock. Something critical I realized was that my RPMs vs speedometer have not changed because the hardware has not changed, but the actual rate of travel has. I calculated that I cover approxamately 8% more ground than my car thinks I have. Which also means my speed is 8% higher ex- 70 mph is 75.6 mph. Correct me if I'm wrong but the speedometer cable can only measure the axle rotation, not the final wheel drive.
I think your rpm vs actual speed have to have changed. It looks like they have a speed sensor that measures the output shaft(or axle rpm) which spins at the same speed as the drive tires.
I put a set of 185/65R14's on, which are about a .5" bigger diameter wise. I used a gps app(unknown accuracy) and found that my speed was 4.3% faster than what my gauge said. Sadly, I didn't test my speed before the tire swap.
My first tank allotted me 321.9 miles with an average of 30.90 mpg. The second, 309.6 miles at 31.52 mpg and the third took me 300.42 at 31.06.
My mileage seemed to have gone down hill as I put more miles on after I purchased it and now seems to have picked back up.
I'm not sure if the tires made the change in my gauge inaccuracy or if it was off to begin with, or... if the gps app is not accurate. So, in conclusion my experiment was full of variables and probably means nothing, but I'm under the illusion that my mileage is back up!
P.S. Stumpy, I think I misread your post, I understand what you're saying now.
The question was will larger tires help to lower engine RPM? Yes.
A lot has been said about wheel size but it is the total circumference of the tire tread that determines how many revolutions a tire turns in a mile. The larger the circumference (regardless of the rim size) the fewer revolutions the engine turns.
Tire Size Calculator
I am a retired ASE mechanic and used to do a lot of suspension, tire, wheel-drive line, and brake work. When gas went from .25 cents a gallon to .65cents a gallon, people asked me to install a smaller displacement engine in their car. I advised them to change the differential ratio from something like a 3.36:1, to a 3.10:1 or 2.90:1 ratio instead. My Aveo has a 3.94:1 differential but I wish it had a 3.55:1 instead. Yes, 5th the gear over drive ratio helps.
I have a 2008 special Value 5 door with a 5 speed transmission, currently with 50K miles on the odometer. I drive very conservatively, shift up to a higher gear when the engine RPMs get to 2,000, start slow when the light turns green, coast up to red lights, drop some speed going up hills, only use about the first 25% of the throttle travel, inflate my tires to 35PSI, and generally don’t drive faster than 65 MPH. Most of my driving is in town but I do not encounter that many traffic lights that are not synchronized. On the interstate Hwy I get 39 MPG driving 65 MPH, and 35-36 MPG in town (35 MPH) driving about 10 miles each way to the major stores from home.
Thanks to all that contribute very useful information and pictures about the repairs they have done to their cars. I am about to replace my timing belt, idler, water pump on my Aveo. Despite what the car magazines and consumer advice people say, my Aveo is one of the best cars I have ever owned. I liked my 2008 so much I bought a 2009 just like it but it is a little more deluxe.
My car came with 185/60X14 tires and I replaced them with 185/70X14 tires.
For example a 185/60X14 tire has a circumference of 71.46 inches and rotates 889 time in a mile. A 185/70X14 has a circumference of 76.02 inches and rotates 835 times per mile. The link to the chart is representative of some tires. I have measured tires and found different brands to be over one size smaller but with the same marked tire size.
To address some of the fuel mileage complaints using larger circumference tires here is what I found. IF, and that is a big IF, the speedometer and odometer were accurate with the 185/60X14 tires, the 185/70X14 tires will result more distance traveled if the engine RPM were the same with each tire size. If the engine RPMs were counted per mile, there would be fewer engine revolutions per mile with the 185/70X14 tires.
According to the local radar check points set up in town, my speed is more accurate with the 185/70X14 tires I have on now than the 185/60X14 tires that came with the car. I go through the radar self-check points using my 185/70X14 tires and it shows I am traveling 35 MPH my speedometer indicates I am traveling 34~35 MPH. When I had the 185/60X14 tires, my speedometer indicated 35 MPH but the radar was showing33-34 MPH. I haven’t compared the 2 tire sizes I am talking about with hwy mile marker posts so I don’t know which tire size is more accurate, related to tire revolutions per mile.
I had one car I put on larger circumference tires and the speedometer registered 60 MPH and I was actually traveling between mile marker posts in something like 56 seconds. I don’t remember the exact time because it happened in 1981. I do remember on a 100 mile stretch of the interstate Hwy my odometer registered 91 miles.
My point is the miles registered on the speedometer after installing larger circumference tires, the car may have traveled more miles than register, thus making it look like the miles per gallon of gas has decreased.
This is not about gear ration but a continuation about ways to improve MPG but the experiences were carried out on a bike..
Now that I am retired (age 73), I ride my bicycle about 100 miles a month. I experiment with different bike tires. When dealing with bike riding, everything about human power is measured in watts. I ride a high end exercise bike in the gym. I can pedal and produce 350 watts of power but I can’t do it very long. I can ride the exercise bike for a long time and produce 125 watts of power.
One bike website I use measures the rolling resistance of bike tires. The low rolling resistance tires absorb 20 watts each, so that is 40 watts of power just to overcome the two tires rolling resistance. If I ride at 8 MPH there is only a little air resistance so I might have to only put out 60 watts of human power to go 8 MPH with the good 20+20 watt tires + 20 watt for forward motion = 60 watts total power required to go 8 MPH.
Some tires need 40 watts each to overcome rolling resistance so that is 40+40 watts for tires and another 20 watts for forward motion at 8 MPH. If I want to travel at 12 MPH, the air resistance increases 45 watts, plus the 80 watts for the tires and I am at my maximum energy output for sustained speed over a long time period.
I can go faster if I ride on a pair of the 20 watt tires but if I go faster the power required to overcome the air resistance goes up really fast. (side note people have lousy air resistance compared to Aveos.) With my two tires that absorb 20 watts each, maybe my speed would be 15 or 16 MPH considering that I only want to put out 125 watts of human power. In general bike tires with very flexible sidewalls us less power. Higher tire pressure requires less power. Smooth tread absorb less power. Some of these concept works with car tires, automobile shapes, and aerodynamic drag.
I know some big truck tires are purposely designed with higher fuel mileage as a main goal. I am certain this applies to car tires but isn’t talked about very much and where is tire rolling resistance even covered with a chart and/or list of numbers for each brand and model of tire has.
As a point of interest, the human powered speed record is (drum roll please) 89.95MPH.
Aerovelo tops human-powered speed record with 89.59 mph bullet bike
I am guessing the guy puts out well over 1,000 watts of power and the vehicle is designed to have a minimal amount of tire rolling resistance and almost no air resistance. The distance in a one hour long event is much lower but still impressive at 57 miles in one hour on a streamlined bike but only 33.9 on an upright bike. Think low weight, low rolling resistance, and low aerodynamic drag.
https://en.wikipedia.org/wiki/Cycling_records
Delayed response to many good points by OG-Lou...
Specialized low rolling resistance car tires definitely exist - they are fitted on many of the high-efficiency models (hybrids & electric vehicles). You can google LRR tire comparisons, but most focus on grip & wear above considerations of fuel savings.Originally Posted by OG-Lou
FYI, I once did a simple rolling resistance "coastdown" comparison of various tires on the same car, and the difference between them was pretty big:
Testing rolling resistance of the Various Tires of the Suzukiclone Fleet (RE92 wins) - Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com
For someone who maximizes coasting opportunities like you do (meaning, not racing up to stops & red lights, but instead letting off the gas as early as practical to coast in), LRR tires will pay dividends.
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