315's --- Better Mileage?

[prmizeski]

With My Auto Trans And 410 Gears, Would Increasing The Tire Size To 315/70/17 Lower The Final Drive Ratio Enough To See Any Improvement In Highway Fuel Mileage? I Know Rolling Resistance Is A Factor.

 

[GECCO]

My initial instinct is no. I feel what you gain in gearing you loose as much (if not more) in rolling resistance and the fact that you now have a heavier tire. Each time you accelerate you must not only move the extra weight but you must spin it as well. Any rotating weight, whether it is in the engine, transmission, axles, whatever, is a big factor. The larger the radius the weight spins on, the more important it is to lower it (and the tires are the largest rotating part of the entire driveline). This is the logic behind drag cars having pizza cutter wheels and tires on the front. Add into the equation the additional cost of the bigger tire and I think you'd be better off with the stock size.



Of course, this is just my opinion and it's worth exactly what you paid for it! #ad

 

[FFL8N]

Quick answer is No!!!! I lost about 2 miles to the gallon with the bigger tires and lift.

 

[testraub]

Bigger tire less mileage Doesn't matter gearing or anything else.

 

[Bob4x4]

I lost about 1 mpg going to 315's on the 05,but gained some on the 94



Bob

 

[Diesel Nut]

Funny, when I pulled the stock 235 80R17's off my 03 dually and switched to the 265 70R19. 5 tires (34. 6") I icked up about 2 mpg on the freeway, with 3. 73 gears. As far as in town, I don't even worry about mileage as there are just too many variables its just not worth it. In town I would see them hurting you, but on the freeway if they are properly inflated, with you having 4. 10's, I'd see them helping. Just don't forget to recalibrate your speedo so your mileage calculations are right on.

 

[betterthanstock]

If you keep them on stock wheels, that will not require a lift, so the truck will only rise about 1. 75 inch. (Aftermarket wheels usually stick out more and hit the cab when you turn, which require a lift). Your aerodynamics won't be as bad as going with a lift kit, and your mileage, if you keep them inflated hard will be about the same, maybe barely better.

But if you drive at 70 or above, empty a lot, the engine will rev just like the 3. 73 axle, and that may make you happier with the noise. Acceleration from a stop will be a little slower.

 

[CJPerry]

City mileage decreased but highway mileage increased when I went form 265s to 37s. I was very surprised since I have lost mileage with every other truck I have upped the tire size on. The gearing with the larger tires has put the rpms in my truck's "sweet spot" at about 65-70 mph. I do not have a lift and the tires are on stock wheels so I didn't pick up a lot of additional wind resistance. My truck is a 2003 HO with a 48re and 3. 73s.

 

[Nate]

I got about 16-17mpg average with 3. 55s and 315s.



Not sure now with the 4. 10s I put in. I'm still haven't gone through a tank of diesel.

 

[Nate]

I got about 16mpg average with 3. 55s and 315s.



Not sure now with the 4. 10s I put in. I'm still haven't gone through a tank of diesel.



I turn about 2000rpm at 65-70 mph

 

[TexBamBam]

Go with 37's and install BIG injectors... . big improvement if you can keep your foot out of it!!!

 

[SKing]

315s rub on turns why would you want that. I had 315s on stock wheels and they rubed and did not last because you need at least a 10 inch wheel. If you dont have a lift then they rub. Dont let anyone tell you they dont rub. All 03s and up will rub on the lower arms just find a truck with 315s on it and look for the rusty rub mark or the fresh black paint they touched it up with. .

 

[GWBourne]

315s rub on turns why would you want that. I had 315s on stock wheels and they rubed and did not last because you need at least a 10 inch wheel. If you dont have a lift then they rub. Dont let anyone tell you they dont rub. All 03s and up will rub on the lower arms just find a truck with 315s on it and look for the rusty rub mark or the fresh black paint they touched it up with. .

the ONLY time mine rubbed was at FULL lock in a left turn. right was no rubbing. on hard bumps at 25mph or more and half turned wheels they would SCUFF the wheel liner. this is on a 2wd... . 4x4 sits a bit higher on the front as we all know. its not a large deal. i agree the center does wear fast on the fronts due to being a D rate. there are E rate 315's out there. i find the ride is much better with D rates and i swap out tires when i tow to my E-rates. H2 tires are cheap so i use them when empty. i just had to leave them in AZ when i dropped off my trialer as i punched a hole through the sidewall of one. i would prefer to ahve 19. 5's to keep the width down and the height up... .



as for mileage, i dont know. my overhead read the same, but factor in that my spedo was never recalibrated. i could not do hand calc and the math the computer was using is wrong, so the overhead is off. i do know with 315's i had a needle width more fuel in the tank when i got back to So Cal from Pima AZ. i can do the trip in one tank if i stay at 70 MPH the entire way. a needle width is better, but it could have been conditions or traffic... too hard to say.



i think its the same, just from having it. as for the slower off the line deal... i doubt you will notice it unless you break out the stop watch.

Grant

 

[Coolslice]

You WILL lose mileage. I gained mileage w/ 33's and lost mileage with 35's.

 

[Nate]

On my truck I rub the wheel liner a little bit.



My roomate has 315/75/17s on his 2500 (Hemi though) and it hasn't rubbed anything, and he's brought it out on the trails with us in the Jeeps :-laf

 

[betterthanstock]

You WILL lose mileage. I gained mileage w/ 33's and lost mileage with 35's.

He has 4. 10 not 3. 73 final. With the 48re and 3. 73, 35's are too big for around town (converter slips too much), but not with 4. 10 gears.

 

[Bob4x4]

315s rub on turns why would you want that. I had 315s on stock wheels and they rubed and did not last because you need at least a 10 inch wheel. If you dont have a lift then they rub. Dont let anyone tell you they dont rub. All 03s and up will rub on the lower arms just find a truck with 315s on it and look for the rusty rub mark or the fresh black paint they touched it up with. .

I can't agree with any of that... ... ... A tire rubbing at or very near full lock on the control arm does not matter!A 10" wheel is not needed. :-laf



Bob

 

[sarj]

mine didn't ever rub before the lift, & I don't care what anyone says... that's a fact. city milage dropped maybe 1 mpg tops, highway gained 1. 5, but with 12K miles, I'm not broke in yet. The best I've seen is 21. 2, but it's usually at 18. 5.



The ride smoothens nicely, and you definitely lose some braking. I don't notice that part now. My next tires will be on 18" rims, no problems or regrets with the 315's though.

 

[j.m.mcfly]

I just installed 35 in xterrains have superlift level kit which is new springs in front with 17x8 eagle alloys wheels and the tires do not rub at all not even on the mud flap and my milage is the same as with the 285 70 bfgs,may be due to the bfgs were on the heavy stock steel wheels and the eagel wheels are very light power is allmost the same also

 

[Udaloy]

I had 315's on my '02 Ram with an auto and 3. 55 gears. I lost mileage all around. The problem was that I couldn't keep my foot out of it. With 4. 10's I think you'll be fine. You just have to be easy on it until it gets rolling to save some fuel.