Taller tires for better MPG ?

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Unless they are also at maximum load, they are overinflated. We are not talking about passenger car tires here.
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"Phil Rhodes" < snipped-for-privacy@NOSPAMcomcast.net> wrote in message
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ply because we tow the trailer... they said "max pressure 65 psi" so I ran them at that..
When we took it back in for rotation, he freaked and lowered it to 35 front and 40 rear... said to go to 45/55 when towing..
Mac
https://home.comcast.net/~mac.davis https://home.comcast.net/~mac.davis/wood_stuff.htm
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snipped-for-privacy@yahoo.com wrote:

In every single case I have ever put larger tires on the result was lower mpg. While the effective ratio should improve it, the engine has to work harder to turn the larger tires. I've yet to see a case where it improved mpg.
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wrote:

Miles makes an excellent case here. Some years ago we had a great e-mail list, it was called the RTML, or Ram truck mailing list. Some current newsgroup members were on it. One of the members ran an experiment with his overdrive. He ran back to back tanks of gas, one using overdrive as normal, one with it locked out. He got one MPG less with it locked out. Overdrive on a Dodge is .69, about a 30% reduction in RPM for given road speed and MUCH more than you'll get with a larger tire.
One of the other caveats is rolling resistance, one of the major considerations of the factory selection is rolling resistance, and most aftermarket tires don't give this much thought. I've seen people lose two MPG with aggressive off road tread tires. If you use a larger diameter and usually wider tire, you may gain some rolling resistance.
Lastly I've seen discussions of axle ratios and fuel economy, too low a ratio and fuel economy suffers, too high a ratio and it suffers again. The discussion I'm referencing took place before automatic overdrives were offered. The synopsis at that time was about a 2.9 final drive was about optimal for fuel economy. This obviously was also well before fuel injection was commonly available. But consider this, most half ton trucks today come with 3.42 to 3.55 ratios standard and automatic overdrives offer a 30% reduction of RPM's and now we're down into the 2.5 range. IMHO, this is mostly for emission control to reduce amounts of pollutants per mile, NOT to increase fuel economy. Maybe with the better atomization of fuel with injection this is the new optimal ratio, it's hard to say, I could be wrong. But if we're already this high in axle ratios, how much could a little taller tire help?
Now if you want taller tires because they look better, I'm with you there. Just don't want you to do something expecting one thing and not getting it.
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wrote:

I went from 215/75-15s to 235/75-15s on my Dakota and lost a couple of mpg.
Ken
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I would guess at about 7 or 8% error with that tire change... Mac
https://home.comcast.net/~mac.davis https://home.comcast.net/~mac.davis/wood_stuff.htm
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wrote:

Tire retailer said recalibration wasn't necessary. I'm going back to 215s or maybe to 225s real soon.
Ken
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should have been maybe double that error with 2 sizes... Mac
https://home.comcast.net/~mac.davis https://home.comcast.net/~mac.davis/wood_stuff.htm
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miles wrote:

What about going to a "slightly" taller tire that is lighter and more narrow like 235/85-16s (I checked 225/85-16s but no one makes them). My current 245/75-16s weigh 53 pounds (Michelin), the 235/85-16s weight 45 pounds (Continental).
If not, would at least this help us; go "skinnier" - what about going with 215/85-16s. It's just about the same height, less friction with the road and the tires weight about 18 pounds less than the stock tires. That should help with MPG, right?
thanks
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Not always enough to see and you will notice a reduction in traction.
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