ok,, i'll lookin to put 315's on the truck,, its leveled up now and i wanna know how bad its gonna hurt me as in mileage,, i am , in the near future, gettin a smarty, but wanna know, will the tst help with mileage as well??
i'm doing this because of my dad and grandpa sayin that i cant get better mileage than their trucks with the lifted truck and bigger tire,,, so i said that it was a challenge,, and i'm gonna do it come he#$ or high water.
HELP ME PROVE THEM WRONG!!!
the more info the better, thanks guys

 

It's all about how you drive. Also, if you're driving 90% freeway you might have a chance. Going up to 285's I think got better mileage but not to 315's. Smarty can improve your mileage but not the TST.

If you're doing for mileage.. don't do it. If you're doing 'cause it's cool.. than I say go for it!

 

They only reason Ive looked into going to 315's is to get better highway milage. I mainly only use my truck for traveling for long distances and dropping the rpms by a couple hundred should net me a mpg or two. If your tires are worn out anyway Id say go for it. Ive got 40k on my Michelens (265-75-16) and theyre hardly worn looking. I also dont tow much anymore either, so the 315's and the lift wouldn't affect me much as for the back end sagging.

Well, all in all, if it were a daily driver I wouldnt bother, but for me I may do it. Theres my .02

 

my truck had 315 BFG's on it when I got it. They're very smooth and quiet and really keep the revs down on the highway, but I didn't like how soft and squishy they felt. Coming to a complete stop the truck would rock back and forward like it was bouncing on baloons and the fronts always looked like they were low on air even at max pressure.

I've got 285 BFG AT E's on now, and I love them. not going back to 35's!

 

Okay - my 2 cents worth...

When I first got my truck it was rolling on 315's and had a TST PowerMax 3. Generally ran the TST on level 6. The tires were BF Goodrich M/T's. Truck would generally hit 18 MPG (hand calculated).

I use my truck for work and occasionally have customers that ride with me. Love the "cool factor" but it was not practical to keep the truck on 315's for my use. Frankly, I don't care for the 265's and I can't stand the 245's so I opted for the BF Goodrich 285/75/16 AT's. My driving style has not changed and I now pull about 19 MPG.

NOTE: I also had major problems with brakes and track bars wearing out due to the 315's. Too big a tire for the stock front end, which was a poor design anyway. If you want 315's or larger be prepared to upgrade front end components and DON'T buy "cheap" brakes. Almost forgot - big tires and more power will kill a clutch pretty quickly as well if you are not careful!

There is a misconception that lower RPM's always = better fuel economy. Think of the tires vs fuel economy as a bell curve. Larger tires / lower RPM's CAN improve your economy to a point. Pass that point and you will start to fall off quickly. Ask someone running 40+ inch tires how their fuel economy looks as an extreme. Each truck/mod will vary as to where that maximum point on the curve falls. Just remember that larger tires have more mass and greater rolling and wind resistance. All of this works against fuel economy. You will have to find the "sweet spot" for your truck.

As to the Smarty / TST - the Smarty can improve your fuel economy depending on the settings. TST makes no claim as to improved economy. Mine does help some, but it is negligable. Sure makes a LOT more power, just doesn't help much with the economy. Personnally I would have started with the Smarty and then stacked the TST later...

Don't know if any of this helps - just some food for thought.

 

What gear ratio? With 3.54s the 315s would probably hurt fuel economy. With 4.10s I think they help it.

 

Most 315s only have a Load Range D/8 ply rating. Even though they may be supposedly rated for 3200~ pounds per tire, I don't feel that they are enough for these trucks.

My truck had Load Range D/8 P.R. 315s on it when I purchased it and I would describe their performance as similar to what you have. However, I liked the size and didn't really want to step down any with the 4.10 gears. So I tried the Toyo Open Country M/Ts in 315/75R16 which are a true Load Range E/10 P.R. tire and have been extremely pleased with their performance. Had a Load Range E tire not been available in this size, however, I would have stepped down to 285 and just dealt with it. I believe that having properly rated tires is critical.

 

roger that, I considered an E rated 35, but they were all $275+ per tire. my BFG's were $173/tire at Discount

 

My Toyos were $225 each at Discount.

Still not exactly cheap, though.

 

I went from Michelin 285's (65 psi max) to Toyo A/T's in 315/75/16 (50 psi max). Lost 1 mpg!!

They now have the Toyo MT's in an E rating (mentioned above) with 65 psi max. This tire should not hurt mileage IMO. This will be my next set.
Smarty can help mileage...gained 1 mpg on economy setting for long trips. I have played with my TST box and find #2 and below are only settings that don't hurt mileage (fueling light stays out on hwy hills). but as for TST adding MPG... Not from my testing.

RJ

 

i drive long distance to work everyday, 80miles one way, and then i need to go offroad so i'm kinda in a bind here,, i NEED to get into some mud and such because of my job,, well don't need to but i'd rather walk 100 yds than 500,,and all of my tools will be there in the truck,,,
if i could better my mileage , even a lil bit, i will do it,,, every lil bit helps,
but i am still power nut,,, so i'm gonna go with the tst and smarty stack ,,
what would injectors do to this mix??,nuthing to big,, hurt me too bad??

 

If mileage is you main goal (along with power) I would add Mach 1.6's from F-1.
Tha Smarty & 1.6's will give you good mileage and nice power (about 350 hp), with the TST as backup for hard playing. But you will need more air before the TST is really usable.

RJ

 

You are probably going to loose mileage going to 315s. To a point, you can gain mileage with taller tires, but only if you are not increasing rolling resistance significantly, and moving to 315s almost certainly will increase rolling resistance.

Almost nobody wants to go this route, but 235/85 tires are fairly tall and pretty skinny, so they have very low rolling resistance. Michelin XPS Traction in this size will give you probably as good mileage as you are going to get with a M/S tire. Of course it doesn't have the floating ability of a fat tire, but as long as it can find the bottom of the mud/snow before you are axle-deep, they have good traction.

I'm currently running these tires and and rolling resistance is considerably lower than the 285 BFGs I ran for a while.

 

As far as tires go if you have the 3.5x gears 33" tall tires seem to work the best (at least in a 5 speed) the one truck we have runs those and gets about (or got befor ULSD) 23mpg but was down to almost 20 with the 315 h2 take offs. The 315's were just to much weight. The 33's were intermediate weight for that size at around 40pounds. now on my truck with the 410's I do very well with 315's befor ULSD I got 19mpg and with 140# 39" military tires I Got 17-18. I think the 37' BFG AT will increase my millage even more when i wear these out since there is only 1/2 pound increase in weight per tire going from 35" to 37" but will reduce my RPM's to the proper range. The best fuel millage verse RPM seems to be to keep your RPM where you make peak tourq

 

i run 315's. bumped up from 265's
never knew my milage, dont really care. the truck is fun to drive and pulls like a champ. if i want millage i drive teh beater honda. it looks good and runs great...

I do how ever agrreee with others.. the 315's just cant hold the psi mostly desired for our heavy trucks thus creating slight drag...

only time i calculated MPG was a trip to LA and back to pick up a 21 ft jet boat.

empty down, jet boat back.. 800 ish miles averaged 17mpg at roughly 65-70mph.....