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Old 05-05-2021, 05:31 PM   #1
Bluebaby
 
Drives: 2007 3 door
Join Date: Feb 2021
Location: Halifax Canada
Posts: 3
BETTER fuel economy at recommended tire pressures

I got an '07 3-door manual a few months ago, my first car of my own. The clearcoat's fucked but I don't love her any less because of it.

Since then I've been running between 36-38 psi because that'll get me better fuel economy right? At between 6.5-6.9L/100km between fillups (I normally fill about 400km into a tank), I was pretty happy.

Wrong. 2 fillups ago I lowered my 2 month old 175/65/14 Hankook Kinergy ST's to the doorjam-recommended 32psi, curious about how much more fuel I'd use. To my shock, over the first 400km I got 6.0L/100km on the dot. I was skeptical, thinking the pump I'd used for that fillup cut off earlier than other ones. But today I went back to the same pump after 350km of driving and recorded 6.1L/100km. No changes in driving style, weight of the car, other maintenance, nothing. Only the tire pressure changed.

Might go lower them to 28 and see if I get 5.5
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Old 05-06-2021, 07:01 AM   #2
rayfloyd170
 
Drives: YARIS
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Quote:
Originally Posted by Bluebaby View Post
I got an '07 3-door manual a few months ago, my first car of my own. The clearcoat's fucked but I don't love her any less because of it.

Since then I've been running between 36-38 psi because that'll get me better fuel economy right? At between 6.5-6.9L/100km between fillups (I normally fill about 400km into a tank), I was pretty happy.

Wrong. 2 fillups ago I lowered my 2 month old 175/65/14 Hankook Kinergy ST's to the doorjam-recommended 32psi, curious about how much more fuel I'd use. To my shock, over the first 400km I got 6.0L/100km on the dot. I was skeptical, thinking the pump I'd used for that fillup cut off earlier than other ones. But today I went back to the same pump after 350km of driving and recorded 6.1L/100km. No changes in driving style, weight of the car, other maintenance, nothing. Only the tire pressure changed.

Might go lower them to 28 and see if I get 5.5
Whats the ambient temp there in your place? It has been noted in several discussions that during winter you will normally get poor mileage.
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Old 05-06-2021, 04:43 PM   #3
KALISPEL II
 
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I averaged 41-42 MPG over the 4 year ownership of my 2015 Yaris SE 5-MT hatch, & always had my tires at 34-35 PSI. Here in AZ, USA it doesn't get cold enough for it to affect MPG really, so it remains consistent year round.
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Old 05-06-2021, 06:10 PM   #4
NYC-SE
 
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Too many variables in play. Summer gas perhaps? There is a direct relationship between MPGs and tire pressure. You are describing an inverse relationship. I don't see how this is possible. I don't doubt your numbers but there must be another explanation.
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Old 05-07-2021, 08:02 AM   #5
Bluebaby
 
Drives: 2007 3 door
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Location: Halifax Canada
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Quote:
Originally Posted by rayfloyd170 View Post
Whats the ambient temp there in your place? It has been noted in several discussions that during winter you will normally get poor mileage.
Can't say I kept track, of the weather, though temperature here in Nova Scotia fluctuates wildly on a day-to-day basis. I got about 7-7.5L/100km in winter conditions with winter tires for the first 3 or 4 weeks of ownership, then it was all season time. Since then, it's been anywhere between 0-15 degrees C on any given day.
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Old 05-14-2021, 11:39 AM   #6
Neinris
 
Drives: 08 Yaris 3 Door Hatchback
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I have a manual transmission and are on 185/60R15 tire/wheel combo, every two weeks that I fill up I check and maintain 33psi in my tires. I do a lot of city driving, and I have a leaded foot, so I'm lucky to see 32mpg (7.35/100km). I only saw 40+mpg (5.88-/100km) when I drove from Maryland to California, thanks to the cruise control that I installed. I only got pulled over once when I was in Texas for going 80 on a 75?!! Oh and I was on the far left lane when I was the only one on the road.

Instead of messing around with the tire pressure, why not just buy bigger tires next times when it's time to replace them? 185/65R14 or get new wheel and tire combo 185/60R15.
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