time for new tires - should I go with 315/75/16 ?
 

Time for new rubber. Bigger rubber. Old tires were 285/75/16 and they looked small in the wheel well. I'm using stock rims. Truck has a 2.5" leveling kit...I've read that 315/75/16 will fit. I think that a 35" tire (approximate size) would look about right on the truck. Is there anyone out there with that size tire that likes it, dislikes the size or has any opinion or driveability, looks, or anything else.......?

Remember for every 4 pound of rubber you add to the truck you going to require 1 more HP to keep it rolling which in turn means you MPG's will drop. If you doing is for show it going to cost you in fuel every day to just show off.

I normally alway suggest smaller lighter tire for MPG purposes. Even for offroad use I run 235's or 265's for offroad stability keeping my center of gravity down.

I truly work in offroad conditions getting firewood, working with the local fire dept chasing wild fires, etc....

265's
http://i42.tinypic.com/qrnjg9.jpg

My 235's...
http://i55.tinypic.com/2icbf2u.jpg

I went with 305/70/16's. These fill the wells better than on my brothers who has 315's... The only issue I've found with this tire size is availability.

I have 285's on mine right now but I am thinking about dropping down to 265's. However, like lobsterman said the bigger tires do look better but fuel aint getting no cheaper

So so true... :w2:

$4.109 to $4.259 here in Idaho. Every where I go is at least 100 mile trip. MPG mean much more to me than looks. :humm:

$3.99 in central TX...And Tire size should be factored WITH ring n pinion ratio. I'm glad I have 305's w/4.10's. If I had 3.54's I'd go with 285 or 265...just depends on price for Coopers.

25% difference between 265 and 315 in rolling distance. That's a lot higher gearing especially with an automatic transmission. Each tire size jump is about 5% change in circumstance. At speedometer reading of 60 you'd be actually going 80. If you tow, that's a big difference. You'd be best to change gear ration in both axles if you go that route.

Other minuses not discussed...

You tires are going to weigh roughly 100-120 pound with rim and tire. Nearly double the rotational mass of what 235's so your going to require more torque which now put more strain on your Auto Trans then since the tires are bigger you brakes don't work as good because the tire leverage again is greater so brake parts wear more. Then since we are talking tire leverage again the ball joints, tie rods ends, and track bar all wear more and fail sooner. The the pure stress on the steering box typical fails sooner also requires the steering box brace. It goes on and on.

Seriously consider everything before just slapping on tires because they look cool...

Statement makes no sense considering 265 and315 are widths :humm:

Do a search for tire size comparison and see for yourself. Tires do get taller as they get wider. Tiremann should know that. Lol.

Really easy...

Take a tire size like 265/75 R16

So its 265mm across the face. So you take 265mm (10.4 inches) x 0.75 = 198.75mm (7.82 inches) in sidewall height.

So now do a 315/75 R16... 315mm in tread face 315mm (12.4 inches) x 0.75 = 236.25mm (9.30 Inches) in sidewall height.

Just for fun... 235/85 R16 - 235mm (9.25 inches) x 0.85 = 199.75mm (7.86 inches)

Now you see.

So if you want to finalize the math. so on the 315's...

9.30" (tire) + 16.00" (rim) + 9.3" (tire) = 34.6 Inch total height (315/75 R16)

7.82" (tire) + 16.00" (rim) + 7.82" (tire) = 31.6 Inch total height (265/75 R16)

7.86" (tire) + 16.00" (rim) + 7.86" (tire) = 31.7 Inch total height (235/85 R16)

Now it should make total sense being I shown all the math of it... :w2:

Moparman (Michael), you're awesome! Glad that you're here! :pca1:

It all makes sense now!!! I always wondered how that worked. Thanks for the info. I enjoy reading your posts, you have a lot of knowledge!:pca1:

Now there is more... Now comparing tires.

Since I've got 2 sets to do for this example.

I'm running 235/85 R16 Load Range G's for summer and 265/75 R16 for the winter.

265's left and 235' right.
http://i54.tinypic.com/snox6o.jpg

Weighing the 235's
http://i51.tinypic.com/2nbrddv.jpg

... and the 265's are 85# a tire.

So now.

235's - 4 x 62# = 248# of rotational mass. (Hence why I gain 2-3 MPG with these)

265's - 4 x 85# = 340# of rotational mass. (Hence why I lose 2-3 MPG with these)

340 - 248 = 92# Difference.

Rule of thumb: For every 4 pounds of rotational mass you ditch you require 1 less HP to keep rolling.

92# / 4 = 23 HP difference between 235 and 265's...

So to compare 315's to 235's.

I dug on the Internet to find rough weight of 315's plug the rims typical are 110-120 pounds. So to be nice I'll use 115# for this...

115# x4 = 460# pounds Rotational mass.

Compare to my 235's...

460 - 248 = 212# pound difference...

212# / 4 = 53 HP more will be used to keep you rolling. (Reduction in MPG)

This why its impossible to get high MPG's with large tires.

Now if you flip the other direction. Racing slicks typically weigh in about 20-25 pounds per just tire for rear tires... This allows for the least amount of rotational mass, least amount of rolling resistance (smooth face), and allows for max HP/TQ to be place to the ground.

Proof...

I was at a dyno event back in 2007 when I ran mine. I was proud of my 381/831 run. My buddy got up on the roller with a 97 Dodge 1 ton. Ran 372/805. I raze and teased him hard core about is truck. He demanded to get off the rollers. He went out in the parking lot and pulled the outer duals off and got back up and whipped me by 5 extra HP. Rotational mass hurts HP/TQ output of the engine. Bigger the tires the less power to the ground regardless of gearing.

So I hope this has been a learning experience...

But if you could find some tall skinny tires that weighed less, you'd have a taller geared rig without adding weight. Bicycle tire if you will.

i am switching to 255-85-16 tire when i get new ones. its a 33inch tall tire but its narrower than a 285 so you dont get as much hp robbing. i took my 33x12.5x17 tires off and put stock wheels and tires on for winter. wow what a difference in power!!! and mpg went up a little bit too of course