New Ram owner here. I got my 96 1500 4x4 quad cab 2 weeks ago. I have put 20 gallons of fuel in it so far. So far the best mileage I have been able to get is 10.7 mpg. I know this number is inaccurate because it has 275/75/16 tires on it and the door says the stock tire is 225/75/16. How far off do you think that number actually is? I need a truck and was prepared to get 13-15 mpg but 10-11 is horrible. I like the bigger tires but I am concidering going back down to the 225's. Do you think it will save me a decent amount of gas? All of my mileage numbers are city driving with about 10-20% highway.[/align]

 

tires do affect MPG by at least 2

Just a month ago a new US Federal Law was passed and signed by the President that will require the sidewalls of tires to have a new mark showing how easily the tire rolls in tests. Look for this next year.

Until then,
here's the best info I know about on tires & MPG for trucks and SUV's:
=====
TIRE CHOICES for BETTER MPG

Increasing the air pressure in your tires, and picking a narrow 'rib tread'
commercial delivery truck type tire that has low rolling resistance
definitely will help MPG.

Raising the air pressure by 15 psi to the max 70 psi in Goodyear Wrangler
HT 235/85R16E tires increased my mpg by +1 in a 311 mile
test run - but the ride was bone jarring. A narrow, highway rib tire like the
HT gives the lowest rolling resistance. Wide, aggressive tread tires can be
three times harder to roll. It might pay to have a 4 tire set for the weekday
commute, and a weekend mudder wide tire set.

Several Cummins Diesel Ram owners have reported that buying special
wheels and converting to 19.5 Commercial truck tire designs have
improved both MPG and tire tread life - but these tires are generally
heavier. RicksonTruck is one such special wheel seller:

http://www.ricksontruck.com/

Consumers Reports is the only organization I know of that tests for rolling
resistance of tires but even they do not report the Crr number.
Quote from CR:
" Fuel mileage at a price. Some tires roll with less drag than others. The
lower a tire's rolling resistance, the more fuel you can save. Those savings
can be significant. {Pickup and SUV} Tires with the lowest rolling resistance
delivered nearly 2 mpg more at a steady 65 mph in our highway tests {2003
four-wheel-drive Ford Explorer XLT 4x4} than those with the highest rolling
resistance. The catch: While some high-scoring tires had low rolling
resistance, most tires with the lowest rolling resistance also had lower
overall scores."

In their 11/2004 Pickup & SUV tire test CR the
lowest rolling resistance tires rated 'excellent' were the:

Bridgestone Dueler H/T (D684)
Michelin Cross Terrain
Continental ContiTrac
BF Goodrich Radial Long Trail T/A

The Pickup & SUV tires with the worst rolling resistance were the:

Pirelli Scorpion STA
Kelly Safari Signature
Yokohama Geolander H/T-SG051

A tire with a 'very good' rolling resistance and high scores in other handling
and braking tests was the Hankook DynaPro AS RH03

Hankook recently announced that they had spent $10 million developing a
tire called the fx-Optimo that has even lower rolling resistance and can
give up to a 3% MPG improvement:

http://www.moderntiredealer.com/t_in...p;storyID=5961

Michelin has also recently introduced an ultra-low rolling resistance tire for
use on diesels in Europe that is available in 15 and 16 inch sizes:
http://www.autoblog.com/2007/09/07/m...nserving-tire/

In another test of "All Season" tires in November 2005,
CR rated these tires as 'excellent' for low rolling resistance:

Michelin X Radial DT
Michelin Agility Touring
Michelin Harmony
Hankook Mileage Plus GT H707
Kumho Touring 795 A/S
Toyo 800 Ultra
Sumitomo HTR T4

In the same November 2005 issue
'All Terrain' tires were also tested
but only the
Continental ContiTrac TR
got an excellent rating for low rolling resistance in this group.

The California Air Resources board is pressing the tire companies to make
rolling resistance measurements on tires freely available to the public by
2008, one of the few reasonable things CARB has ever done in my opinion

The lower profile 17 and 20 inch tire designs used on the 2003-2005
5.7Hemi Rams have a 'sticker' tire tread and higher rolling resistance than
earlier year Rams. It is probable that if a manufacturer makes available a
235 85 R17 tire in Load Range E it would be lower rolling resistance
than the stock tires and might improve MPG by 1-2 at 70 mph.

The 2006 Ram press release says the new model will have 'low rolling
resistance tires.'

In April 2006 the "independent and non-partisan" US National Academy
of Sciences completed a report on the rolling resistance of tires and how
MPG for the entire country might be easily improved if tire makers
increased their research into how to make tires roll even easier.
The 'meat' of this report starts about page 50 at this weblink:

http://www.trb.org/publications/sr/sr286.pdf

 

Your new tires are 10% taller than stock. Therefore, when you compute your gas mileage you need to add 10% to the odometer reading before you divide by the gallons used. Like this:

If you used 20 gallons and computed 10.7 mpg, then your odometer reading was 214 miles
(10.7 x 20). Your stock tires were 225mm wide. A 16" wheel is 406.4mm. With an aspect ratio of 75, your tire hieght would be 743.9mm (225 x 75% x 2 + 406.4mm). The new tires are 818.9mm. 818.9/743.9= 1.1. So you actually traveled 235.6 miles (214 x 1.1) on 20 gallons, which is 11.8mpg.

 

And by the way, the wider tires do offer more rolling resistance. With stock tires you would probably get close to 13-14 mpg city.

 

That's good information to know. Last month I went from a 285/70/17 ATto 305/70/17 MTand have dropped from about 11 to 9.5 mpg. I probably need to add at least 5% to my odometer reading to get a accurate reading.

 

This was told to me by a old man in the tire business 30 years. He said the tires that come from the factory are not really '225'as printed on the side. To prove it he rolled out a 225 tire and stood it next to my 'factory tire'. Even with the tread gone, there was an obvious difference. The 'right' tires were at least 2 sizes smaller.

My sister found this out when she took her car in and had the 'right' tire put on. It looked like they put on donuts or something.

If you were to put a set of 225's on a Dodge it would looke like it had it's pant's down in the back and girly up front. If it is a 4x4 multiply this by a factor of 1000.

Please do not take my word for it. Go to any dealer and get a real 225. I will bet you do not have them put on your truck no matter what kind of gas mileage you get. I run 265's which are about 31" in diameter. They are heavy, but they look great. ROWL for me.

KevinFoshee: With this in mind, I think those calculations may be off, since the 225's were not actually 225's from the factory. UNLESS they did the calibration with one tireand put on a different tire for the sale.

 

This makes me really think about downgrading tire size. I think I might go with a 245/75/16. A little skinnier, a little shorter but not too much. But I am not getting an all weather. I'm gonna stick with an a/t tire.

 

You are caught it a catch 22 with your 4 x 4. You need the lugs for doing 4x4 things, but these reduce your gas mileage. Take a look at Dunlop Stampede's. Nice lug, I get 16 hwy with my 2wd. They are 265's. Got them at CTB.

 

I don't know how much of a difference you'll find since it seems to varry person to person. I went from 265/75/16 to 285/75/16s and I lost about 1mpg WITHOUT taking the speedometer difference into the equation.

When I do calculate my mileage taking the speedometer into consideration I still get 13.5 around town, and 15 on the highway, and my tires are pretty luggy.

I think your culprit may lie somewhere else, did you check the plenum for leaks yet? Maybe change out your front oxygen sensor. These seem to be the things that seriously rob people of gas mileage. They're also things that if the previous owner was too stupid to realize,might bethereason he sold the truck in the first place thinking"it's just old".

 

I know this is Ram forum but when I switched from 235s to 31s on my dakota I lost about 1.5 mpg. The 31s are about 10% bigger. My old 235s were a/ts and performed very well even in snow and ice. Plus the heavier weight of bigger tires might affect mileage? I would get a good a/t tire close to stock size. just my 2 cent