Notices

New Tires and lost 2MPG?

Old 11-23-2008, 07:17 AM
  #1  
Admirals ClubCaptains Club Member Admiral's Club Member
THT sponsor
Thread Starter
 
John_Madison CT's Avatar
 
Join Date: Aug 2001
Location: Old Saybrook, CT
Posts: 14,480
Received 744 Likes on 404 Posts
Default New Tires and lost 2MPG?

I put new OEM tires on my Suburban. (Goodyear Wrangler AT/S 265 70/17's) The old tires (same exact brand/model etc) gave me over 60K miles of good service. If it wasn't for winter approaching, I may have kept them another 3-4 months.

Anyway, I noticed today that my fuel economy has gone down by about 2mpg. I suppose there's a possibility that something is up with the engine but it seems very coincedental. The new tires, although the same, have a lot more tread.

Does this make sense to anyone?
Old 11-23-2008, 07:21 AM
  #2  
Senior Member
 
Join Date: Mar 2008
Location: Copiague, N.Y.
Posts: 203
Likes: 0
Received 0 Likes on 0 Posts
Default RE: New Tires and lost 2MPG?

Check the pressure?
Old 11-23-2008, 07:38 AM
  #3  
Senior MemberCaptains Club Member
 
Join Date: Nov 2004
Location: Amelia Island, FL
Posts: 4,782
Likes: 0
Received 111 Likes on 49 Posts
Default Re: New Tires and lost 2MPG?

A guess, if not air pressure, would be that the overall circumference of the new tires is larger. Longer distance to complete a revolution, therefore it shows traveling less distance to the odometer, ie lower mpg? ;?


Hypothesis?
Old 11-23-2008, 08:10 AM
  #4  
Senior MemberCaptains Club MemberPLEDGERPLEDGER
 
Join Date: Apr 2006
Location: Struggleville
Posts: 7,547
Likes: 0
Received 92 Likes on 61 Posts
Default Re: New Tires and lost 2MPG?

Reel Boobs - 11/23/2008 10:38 AM

A guess, if not air pressure, would be that the overall circumference of the new tires is larger. Longer distance to complete a revolution, therefore it shows traveling less distance to the odometer, ie lower mpg? ;?


Hypothesis?
Bingo.
Old 11-23-2008, 09:01 AM
  #5  
Senior MemberCaptains Club MemberPLEDGER
 
Join Date: Jan 2005
Location: Suburb of Sugar Tit SC
Posts: 14,997
Received 9,524 Likes on 5,169 Posts
Default Re: New Tires and lost 2MPG?

One more possibility, do you consistantly fill up with gas at the same place. If so, did they recently change to 10% ethanol gas? My truck (2008 Dodge 1500 w/ Hemi) as well as my fathers 2007 Suburban consistantly drop by about that much when gas containing ethanol is run through them.
Old 11-23-2008, 01:47 PM
  #6  
Admirals ClubCaptains Club Member Admiral's Club Member
THT sponsor
Thread Starter
 
John_Madison CT's Avatar
 
Join Date: Aug 2001
Location: Old Saybrook, CT
Posts: 14,480
Received 744 Likes on 404 Posts
Default Re: New Tires and lost 2MPG?

Nope, we've had Ethanol fuel here for awhile. It seems that the rolling resistance has gone up or something. Very odd. I was in the car today and kept resetting the MPG computer. It's worse at highway speeds. I used to easily get 18mpg when I drove reasonably. Now, it's closer to 15mpg.

Old 11-23-2008, 03:17 PM
  #7  
Senior MemberCaptains Club Member
 
Join Date: Jul 2006
Posts: 2,349
Likes: 0
Received 10 Likes on 10 Posts
Default Re: New Tires and lost 2MPG?

as stated different tire circumfrence les turns per mile if you are checking rpm versus speed you would see it. new tire is also heavier more energy needed to spin.
Old 11-23-2008, 03:19 PM
  #8  
Senior Member
 
Join Date: Jan 2006
Location: Sunny florida
Posts: 25,530
Received 5,508 Likes on 3,521 Posts
Default Re: New Tires and lost 2MPG?

Did they do an alignment and screw it up?
Old 11-23-2008, 04:01 PM
  #9  
Senior MemberCaptains Club Member
 
Join Date: Feb 2005
Location:
Posts: 928
Likes: 0
Received 111 Likes on 60 Posts
Default Re: New Tires and lost 2MPG?

they put the tires on backwards.
Old 11-23-2008, 04:52 PM
  #10  
Senior MemberCaptains Club Member
 
Join Date: Feb 2004
Location: Raleigh & Surf City, NC
Posts: 13,019
Likes: 0
Received 1,007 Likes on 513 Posts
Default Re: New Tires and lost 2MPG?

circumference = " x d (where's the freakin pi symbol)

so: worn out c = 87.96" (28" x pi)

new c = 91.1" (29" x pi)

63,360" per mile

worn out tire rotates 720.32 times per mile

new tire rotates 695.5 times per mile


what does this tell us? I think a similar question was on my Mensa exam
Old 11-24-2008, 05:56 AM
  #11  
Senior MemberCaptains Club Member
 
Join Date: Mar 2004
Location: NC
Posts: 3,268
Received 8 Likes on 4 Posts
Default Re: New Tires and lost 2MPG?

Normal. MPG will return after a thousand miles or so o the new tires.
Old 11-24-2008, 07:48 AM
  #12  
Senior MemberCaptains Club Member
 
Join Date: Mar 2003
Location: ocean county,nj
Posts: 2,135
Likes: 0
Received 10 Likes on 6 Posts
Default Re: New Tires and lost 2MPG?

folly basser - 11/23/2008 7:01 PM

they put the tires on backwards.



Not sure about the Wrangler model but the Goodyear Futera model can only be put on one way. They have direction of rotation arrows on the sidewalls. Have had mine for a year, great tire in rain and snow.



Ron
Old 11-24-2008, 08:13 AM
  #13  
Senior MemberCaptains Club Member
 
Garett's Avatar
 
Join Date: Feb 2003
Posts: 24,905
Likes: 0
Received 1,165 Likes on 661 Posts
Default Re: New Tires and lost 2MPG?

Less gas mileage doesn't surprise me.

Tires are made with different grades of rubber at different thread depths.
The outer most layer of a new tire is designed to impress the heck out of the buyer. Yes the new tire should have more resistance to it because the outer layer is designed to give the buyer a sense of increased handling, stopping abilities and overall smooth ride ability. The outer layer of a new tire is soft rubber. But this outer layer doesn't last to long because it is so thin. Then the tire gets down into it's second, third and forth layers as the mile add up which give the tire different characteristics. The hardest rubbers used in the building of the threads is down at the bottom of the thread to give the tire it's longevity. And we all know that a hard rubber will give less resistance then a soft rubber will. Tires are designed so that the user never notices the tire degrading in performance.
Now I can't say the above without saying, not all tires are made equal. Therefore the building of any particular tire will be different then another, but the above is the program behind the building of tires. Haven't you ever wondered why one tire is rated for X amount of miles and another tire is rated for double that amount? Well that's why.
Old 11-24-2008, 08:17 AM
  #14  
Senior MemberCaptains Club MemberPLEDGER
 
Join Date: Feb 2003
Location: Thornton's Ferry,NH,USA
Posts: 10,755
Likes: 0
Received 81 Likes on 47 Posts
Default Re: New Tires and lost 2MPG?

lol. Larger diameter tires give you better mileage over distance not less. They may need more energy to accelerate though but unless you're always screeching to a stop and then burning rubber to get going I'd be surprised to have a noticable difference from such a small variation in diameter.

I'm with the "pressure" point of view. Good luck!
Old 11-24-2008, 02:45 PM
  #15  
Admirals ClubCaptains Club Member Admiral's Club Member
THT sponsor
Thread Starter
 
John_Madison CT's Avatar
 
Join Date: Aug 2001
Location: Old Saybrook, CT
Posts: 14,480
Received 744 Likes on 404 Posts
Default Re: New Tires and lost 2MPG?

Garett: Your post is very informative. I'll keep an eye out as they get broken in. I probably have no more than 300 miles on them since install.

BTW, all the tires are at the proper pressure spec. (30PSI)
Old 11-24-2008, 03:08 PM
  #16  
Senior Member
 
Join Date: Jan 2006
Location: Sunny florida
Posts: 25,530
Received 5,508 Likes on 3,521 Posts
Default Re: New Tires and lost 2MPG?

Typical tread is ..what..13/32 0r 15/32 inch deep. So, diameter will increase by two tread depths, or less than 1". 1" against 30" diameter is about 3%, which would be the difference in rolling distance between new and old tires.
Old 11-25-2008, 06:04 AM
  #17  
Admirals ClubCaptains Club Member Admiral's Club Member
THT sponsor
Thread Starter
 
John_Madison CT's Avatar
 
Join Date: Aug 2001
Location: Old Saybrook, CT
Posts: 14,480
Received 744 Likes on 404 Posts
Default Re: New Tires and lost 2MPG?

Oh yeah, I also looked for arrows on the tires regarding direction. There weren't any so I don't think they're mounted wrong.

The tires I bought from TireRack.com and used one of their recommended installers in CT.
Old 11-26-2008, 07:37 PM
  #18  
Senior Member
 
Join Date: Mar 2007
Location: So. Calif
Posts: 494
Likes: 0
Received 0 Likes on 0 Posts
Default Re: New Tires and lost 2MPG?

The guys that are talking about tire diameter may be right if you put on tires that are larger. No one told the computer the tire diameter changed, it can only see rpm's. With bigger tires you are now going farther with each tire revolution.

Mike
Old 11-26-2008, 07:48 PM
  #19  
TSA
Senior MemberCaptains Club Member
 
Join Date: Nov 2007
Location: St Pete/Islamorada
Posts: 6,123
Likes: 0
Received 3 Likes on 3 Posts
Default RE: New Tires and lost 2MPG?

John:

the rolling resistance will improve as the tires "break in." as mentioned above, about 1k miles or so...........that's it. plus cooler temps right now don't help either.
Old 11-27-2008, 05:01 AM
  #20  
Senior MemberCaptains Club Member
 
Garett's Avatar
 
Join Date: Feb 2003
Posts: 24,905
Likes: 0
Received 1,165 Likes on 661 Posts
Default Re: New Tires and lost 2MPG?

mike343 - 11/26/2008 10:37 AM

The guys that are talking about tire diameter may be right if you put on tires that are larger. No one told the computer the tire diameter changed, it can only see rpm's. With bigger tires you are now going farther with each tire revolution.

Mike
My old Nissan 3/4 ton 4x4 had 31" x 10.5" x 15's on it from the factory. One of my tire changes I put 32" x 10.5" x 15's on it.....just one size up.

Well if I didn't see it twice I wouldn't buy into this story. The first day the truck had the larger tires on it, man did the truck start running like crap.......coughing, sputtering, smoking, hard starting, no acceleration. .like it was sick. It was running so poorly I made a service appointment at the dealership. Now go figure this, 24 hours after installing the new tires, the truck running like total crap and making an appointment with the dealership the truck started running perfectly again....like I was accustom to. It’s like someone had flicked a switch. I canceled my service appointment. Now for reasons not worth mentioning here one thing lead to another and the tires were removed/ replaced back to factory size in several hundred mile. I’ll tell you, when the tires were changed back to factory size the truck starting acting up just like when I up-scaled the tires. Again like the first time, 24 hours later and the problem fixed itself.

Now what know: with that truck it didn’t matter how lean or rich I’d set the fuel system to or how far off I’d set the timing mark to that truck’s computer would ALWAYS change my settings back to factory settings. Therefore, with the tire change, all I could ever figure was the computer running the truck had a hard time in figuring out how to adjust itself to the different size tires on it.....hence why the truck ran like it was sick, both times.

In that particular truck’s case I never experienced a gas mileage change one way or the other because of the different size tires on it.

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information -

Copyright © 2021 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.