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Tire size - Fuel Mileage

Old 06-09-2003, 01:15 PM
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Tire size - Fuel Mileage

I have been told by several die hard diesel guys that going from the stock tire to a 35" tall tire should show gains in the mpg department.

Right now I am running 285/75/16 tires, if I move to 34x10.5 Super Swamper LTB's would that pose a gain in mileage since the tire is staying the same width, just gaining in height?

Or would I be better going back to stock tire height to gain better mileage?

I have a 93 W350 single cab that is my towing truck which pulls a 27' car hauler with an 84 Ramcharger built for offroading. I do alot of traveling to offroad meets and I want the max mpg out of my cummins. Is there anything else I can do (remember I am looking for fuel efficiency not power)? I currently have have an AFE magnum intake setup and a Banks stinger setup. Thanks for any suggestions.
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Old 06-11-2003, 11:37 PM
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Re:Tire size - Fuel Mileage

No experiences with larger then stock tires?
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Old 06-12-2003, 12:14 AM
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Re:Tire size - Fuel Mileage

Changin tar sizes is like changin gear ratios. Putting on a taller tire may adversely affect your towing ability. If you have 4:10 diff. gears installing 35's may improve your mileage running unladen. Tread design affects mileage as does width of the tire - something to do with rollin resistence.<br>Swampers are not known for their mileage and wear characteristics. Beeg lugs slappin pavement don't help mileage!<br>Check out the threads in the towing/RV forum for mileage figgurs.<br>M .o2 worth, Chris
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Old 06-12-2003, 01:13 AM
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Re:Tire size - Fuel Mileage

I tend to agree... you'd best plan on losing some MPG rather than gaining...<br>Those tires take a fair bit more effort to turn and keep turning.<br>This is based on an '82' Toyota shortbox.... don't laugh....<br>That truck was a full balance/magnafluxed/ported &amp; polished/twin Webber/supercharged 5spd conversion with middle of the road gearing.<br>The mileage took a serious dump when we put the big 'dogs' on for our hunting trip each year.<br>BTW, that little rocket would turn 6000 RPM and hum all day without so much as a burp.<br><br>On the up side we got thru water that broke over the hood and hit the windshield... nasty..<br><br>bob.<br>
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Old 06-12-2003, 08:07 AM
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Re:Tire size - Fuel Mileage

This is my exp. Not much but it also confers with the above. When I went from the stock tires to B/F Goodrich I went to 33 inch tires. This is the max I could put on my stock suspention. In face the left tire will hit the fender on a right hand turn with a little bump. I would say without measuring it is about one to one and a half inches from the lower front of the fender.<br><br>When I went to the taller tires I didn't notice much difference in milage but I noticed a big difference in acceleration. I have 354's in er and it really gave er longer legs. If I were goin to do it again I would consider a lower rear with the taller tires. I do like the looks of them better than the stockers though. When pullin it doesn't take much for me to have to drop down to 4th to keep the 12k fifth wheel rollin. At 60mph I am only turnin about 1600 rpm. Unless I am on the highway most of my drivein is in 4th with the fifth.
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Old 06-12-2003, 02:51 PM
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Re:Tire size - Fuel Mileage

I don't think a toyota qualifies as an example, main reason the torque behind the diesel.<br><br>The main argument of the guys telling me mileage will improve with taller but same width tires was that the torque output of a cummins is so high. That is why I say the toyota isn't a good example. In one of my Ramchargers, I dropped in a 440 and with 40x17 offroad tires and 4.56 gears and I was getting 12 to 14 mpg, where most stock guys were getting less then that with a Ramcharger (10 to 12). That is why I do see their point with the torque and tall tires.<br><br>I have 3.54 gears in the cummins right now, they had said if it was 4.10's to diffenetely get 35&quot; tall tires, but with only being 3.54 should I go back to stock tire height? I am running 285/75/16 mud tires now.<br><br>Thanks for the replies!
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Old 06-12-2003, 06:49 PM
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Re:Tire size - Fuel Mileage

When I went from the stockers to 33x12.5s I saw about a 1/2mpg decrease BUT it corrected my speedo ;D <br><br>As soon as I can get a lift kit I'll be going to 35s and possible 4:10s<br><br>Jay
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Old 06-12-2003, 07:12 PM
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Re:Tire size - Fuel Mileage

What is your fuel mileage at? Right now my 285/75/16 are roughly 33x11's and I get 18 mpg with trips running in the 75 mph range. I see why you lost mileage, mainly due to using a wider tire, more surface area equaling more friction and drag. Anyone using any 33&quot; or larger tire in the 10.5&quot; wide range?
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Old 06-12-2003, 10:47 PM
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Re:Tire size - Fuel Mileage

I consider my 285/75/16s as 33X10.50s and found that my mileage stayed about the same. The speedo is correct with 3.54s. My fuel mileage is only 15mpg with an automatique, but I'm pulling lotsa long grades at 70mph from 2,400ft to over 7,000ft.
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Old 06-12-2003, 10:50 PM
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Re:Tire size - Fuel Mileage

what size are stock tires?
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Old 06-12-2003, 10:55 PM
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Re:Tire size - Fuel Mileage

235/85/16 ? I think!
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Old 06-12-2003, 11:02 PM
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Re:Tire size - Fuel Mileage

the guys running the 33x12.5 tires are claiming loss in mpg, but since the true height isn't 33&quot; it shows that they are losing mpg because of tire width.<br><br>You having the same size tire as I which is 33&quot; tall but more narrow and you said you stayed the same.<br><br>The LTB's I am talking about are only 1&quot; different in height then the 285/75/16. I guess they really wouldn't hurt then?<br><br>I guess nobody has recorded better mileage by increasing tire height and keeping same width. Stock tires if 234/85/16 are about like 32x9.5's, so going up an inch and wider an inch netted nothing. Maybe because the height gained but the width took away?
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Old 06-12-2003, 11:20 PM
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Re:Tire size - Fuel Mileage

The Firestones that were on my truck were shorter and narrower than that, they were leettle. They also had a very mild highway type tread design. I suspect that tread design plays a big role in mileage, that's why I would avoid swampers. The tires I have now are a typical 4 row AT tread, a little more resistence than the other tires - I needed that type of tire for driving on snow and ice.<br>Chris
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Old 06-13-2003, 01:16 AM
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Re:Tire size - Fuel Mileage

although it is true that a wider tire puts more contact patch to the ground thus increasing friction, there are many things that come into affect. when you combine all these things together even if the tire is the same width or larger you increase rolling resistance.. the increased mass or what is refered to as unspung weight also increases. all these things unsually lead to a decrease in fuel mileage. not to mention by raising the truck you increase the drag. drag increases exponentialy above 55 mph that is why the federal government use that speed limit. your best gas mileage is usually gotten at the lowest rpm peak torque is generated at. so determine what size tire will put the engine at peak torque at a given speed and that should give u the best mileage at that speed.
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Old 06-13-2003, 02:34 PM
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Re:Tire size - Fuel Mileage

to me unsprung weight and even rolling resistance from going 1&quot; taller and wider shouldn't matter to a diesel. The diesel is a different animal then gassers. I think people base alot of assumptions on gas engine experiences, but to me those are irrelevent since the diesel is making almost twice the torque outpower (power).<br><br>I am not sure if this is true, but to me a cummins is much like a gas engine truck that has really really low gears, by going with taller gears or tires, mileage can be improved. At least that is what I have been told, my main reason for asking everyone for experiences with cummins and larger tires is to see if that is true.<br><br>Thanks all for the replies, and to thuse who will post more.
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