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Old 07-24-2009, 01:25 PM   #1
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14 vs 15 inch tires

My 2009 Yaris Hatch came with the 15 inch wheel option. Im wondering if this is helping the mileage any? (I assume the gears in the tranmission/final drive etc are the same...or am I wrong about that?) I know compared to my ECHO the Yaris just wants to go in a straight line. It takes a far higher effort to make it turn, possibly due the the electric PS (which only seems to work at low speed) and possibly due to the larger wheels. Its much steadier on the highway compared to the ECHO but the ECHO is much nimbler.
So hopefully Im gaining some in the mpg department?
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Old 07-24-2009, 02:46 PM   #2
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in specific to engine rpm's, yes the taller tire will result in lower rpm's at highway speed.
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Old 07-24-2009, 03:00 PM   #3
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I think it really depends on the type of driving you do... If you normally drive in the 30-40range where rpm's are generally pretty low the smaller wheel for its weight reductions would probably be best. However, if you do a lot of highway driving (55-75) and the rpm's are higher the taller wheel will help lower rpms.

Go too big tho, and you'll prolly run into torque & weight issues which would negate any benefit.
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Old 07-24-2009, 04:17 PM   #4
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electric PS in Yaris totally blows. I believe it is one of the culprits in why Yaris handles so weird at highway speed.

as for the original comment/question, I really don't think you're gonna see much gas saving based on 14 vs. 15 tire comparison.

I think there's more gas to be saved by just getting an ecometer and drive steadily.
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Old 07-24-2009, 04:34 PM   #5
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Quote:
Originally Posted by Cosworth View Post
electric PS in Yaris totally blows. I believe it is one of the culprits in why Yaris handles so weird at highway speed.
the only "weird thing i've noticed about its highway handling is how it can be blown around a bit in the wind... but really... any car its size & weight is that way. I've got over 30k on my yaris so far.... of that, 20-25k is highway.

I think people make a lot of statements about how it performs simply because they are used to completely different vehicles. You want to drive a vehicle that is scary at highway speeds... try driving a mid 80's jeep cherokee... small wheel base made the thing turn on a dime... high center of gravity meant it could tip easily... ruts would suck it in and make it feel like you were out of control.

Also... I think a lot of these "weird" issues are reserved to drivers of automatics.... not sure if that says something about the people who buy automatics... or the transmission.
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Old 07-24-2009, 05:18 PM   #6
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Quote:
Originally Posted by talnlnky View Post
the only "weird thing i've noticed about its highway handling is how it can be blown around a bit in the wind... but really... any car its size & weight is that way. I've got over 30k on my yaris so far.... of that, 20-25k is highway.
My direct comparison is between an EG hatchback which weighs ~2,300lbs. The hatch drive straight as an arrow on the freeway regardless of cross wind. Yeah, it's not as tall as a Yaris, but weighs nearly the same with essentially same wheel base (if not shorter). My opinion still stands. Yaris electronic PS =
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Old 07-24-2009, 06:46 PM   #7
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Quote:
Originally Posted by talnlnky View Post
the only "weird thing i've noticed about its highway handling is how it can be blown around a bit in the wind... but really... any car its size & weight is that way. I've got over 30k on my yaris so far.... of that, 20-25k is highway.

I think people make a lot of statements about how it performs simply because they are used to completely different vehicles. You want to drive a vehicle that is scary at highway speeds... try driving a mid 80's jeep cherokee... small wheel base made the thing turn on a dime... high center of gravity meant it could tip easily... ruts would suck it in and make it feel like you were out of control.

Also... I think a lot of these "weird" issues are reserved to drivers of automatics.... not sure if that says something about the people who buy automatics... or the transmission.
Good point. I had a '83 Prelude, 1st yr of 2nd gen, 5-speed, handling was great. Got a '86 Prelude to replace it, extra weight of auto seemed to really throw the handling off some. Did not enjoy it near as much.
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Old 07-24-2009, 10:42 PM   #8
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Considering this the the Fuel Economy Section... Electric Power Steering is great!
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Old 07-24-2009, 11:19 PM   #9
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most mpg difference between the echo and yaris will be due to engine tuning, gearing, rolling tire diameter, and the aerodynamics of the yaris vs the echo (i think the yaris has a lower coefficient of drag)
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Old 07-25-2009, 09:04 AM   #10
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Originally Posted by rningonfumes View Post
Considering this the the Fuel Economy Section... Electric Power Steering is great!

EPS is a delusion just like the Prius is a delusion. If its so good how come the Yaris is rated 29 mpg and the ECHO is rated 34 mpg?
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Old 07-25-2009, 09:05 AM   #11
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Quote:
Originally Posted by thebarber View Post
most mpg difference between the echo and yaris will be due to engine tuning, gearing, rolling tire diameter, and the aerodynamics of the yaris vs the echo (i think the yaris has a lower coefficient of drag)

Dont forget the Yaris is ~300 pounds heavier than an ECHO too. We need LIGHTER not HEAVIER. That Yaris is one sick pup...
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Old 07-25-2009, 10:46 AM   #12
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I love my mass delusion with my cereal... gets me great mileage.
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Old 07-25-2009, 11:02 AM   #13
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Quote:
Originally Posted by thebarber View Post
most mpg difference between the echo and yaris will be due to engine tuning, gearing, rolling tire diameter, and the aerodynamics of the yaris vs the echo (i think the yaris has a lower coefficient of drag)
The important aerodynamic measure is the CD X cross sectional area. I don't know all of the numbers for the two, but the Yaris is clearly a bigger car than the Echo, as well as being heavier. I could get 3-4 MPG more out of my daughter's Echo than I can from my Yaris. (And I had more headroom.)

But as for EPA ratings, the Echo was rated by an older test method, and the Yaris under the new standards which give lower numbers across the board.
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Old 03-02-2010, 01:12 AM   #14
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Note that the two options are 175/65R/14 and 185/60R/15

So it's not just the wheel. The 14 inch wheel gets a tire which is 0.4 inched narrower, but due to the 65 profile the sidewall is actually *taller*. The end result is that the 15 inch wheel option is only about 3.4% greater diameter than the 14.
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Old 03-02-2010, 10:15 AM   #15
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Quote:
Originally Posted by sbergman27 View Post
Note that the two options are 175/65R/14 and 185/60R/15

So it's not just the wheel. The 14 inch wheel gets a tire which is 0.4 inched narrower, but due to the 65 profile the sidewall is actually *taller*. The end result is that the 15 inch wheel option is only about 3.4% greater diameter than the 14.
actually the sidewall on the 14" tire is 175mm*0.65 = 111mm and the sidewall on the 15" tire is 185mm*.6 = 111mm

sidewalls are the same, just the wheel is 1" smaller....so the overall height of the wheel/tire setup is 1/2" shorter....thats the 3.4% difference in diameter
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Old 03-02-2010, 05:29 PM   #16
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actually the sidewall on the 14" tire is 175mm*0.65 = 111mm and the sidewall on the 15" tire is 185mm*.6 = 111mm
175mm * 0.65 = 113.75mm, unless I'm missing something.
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Old 03-02-2010, 06:02 PM   #17
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Originally Posted by sbergman27 View Post
175mm * 0.65 = 113.75mm, unless I'm missing something.
nope, you're right....must have typed it wrong this morning

still, the bulk of the difference is not in the sidewall of the tire
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Old 03-03-2010, 09:21 AM   #18
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Originally Posted by thebarber View Post
still, the bulk of the difference is not in the sidewall of the tire
The taller sidewall offsets the smaller wheel size by 20%. But my point is really that, overall, there is not much difference between the two configurations. The 15 is 3.4% higher diameter. The 14 is 4.9% narrower.
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