Alright, I'm replacing my tires and decided to go with the stock size. Gas is killing me and large tires are expensive anyways. According to my door placard, my truck takes a 235/75R15. I work in a tire shop and i looked my truck up on the computer and it shows another size for my truck (1990 f-150 302): 215/75R15. I was just wondering what everybody has on their truck and if the 215/75R15 saw better gas mileage.

Josh

 

Id say get the 235 as them 215s with look whimpy, and its not a big enough size difference to effect gas mileage. My stock F350 is 235/85/16 and i was gettin 13-15mpg. Then went to 36's got 8-10mpg, then got a spair set of wheels and tires, 265/70/16 and im back to 13-15. So from the 235-265 its the same, yea the 235's were taller and the 265's are shorter its all the same.

 

Stick with the 235s. They won't be turning quite as fast as the 215s, although the MPG difference is probably negligible.

I had a couple fairly decent 225/70s here from a GMC Safari that I'd intended to use on Big Red, but decided against it. Ended up just getting a pair of Uniroyal Liberators from Wally World for the back wheels and moved the Widetrack Baja H/Ts that were back there up front. Hope to replace those this summer or fall, they are getting some age on 'em.

 

Milage depends upon the engine, vehicle weight, gearing, and driving habits. What is your combination?

 

What rearend does your truck have?

I got better mileage in my '87 when I went from 235's to 31's. But then again I have a 4.10 rearend and a T18 so gearing is no issue. During the summer I put on a set of 35'' boggers on the back end, my mileage only went from 11-12 to 10.5-11.5. So its not necessarily the size of the tire that matters but its the gearing that means more.

 

Isn't a 31" smaller than a 235? So it would stand to reason that you got better mpg's with 31" wouldn't it? I understand that gear ratio affects fuel economy, but if you're not changing gearing...isn't smaller always better for mpg's?

 

31's are bigger then 235's I replced my 31's with the stock recomended 235/75Rx15.

I have my Original truck specs for my 1990 F-150 4x4 and it came stock with those 235/75Rx15 XL OWL Tires

 

Ok then...I had checked a tire conversion site and it said 235 = 31.7".

This is why it didn't make sense to me.

 

1996 ford F-250 ext cab black 460 v8 e40d trans 4X4 Doug Thorley headers with true duels no cats and 2 40 series flow masters add a leaf springs in the front euro taillights bbk twin 61 mm throttle body more stuff to come in the spring.....

Those are the mods


And when i had the 235/85/16 i got 12.5-13 mixed and 285/70/16 i got 10-11.7

even though the 285's look alot better on my truck once summer comes i'm getting a set of 235 because i can get around 40 more miles per tank...

 

I know what I did wrong....I put in my tire size 235/85/16 which gave me 31.7" instead of 235/75/15 which gave me 28.9"

 

yeah I was thinkin about that, Rim size would change the size, I had to put stock tires on to get a safety done, but my truck needs more work before I can justify droppin money on big tires.

 

My setup is a 1990 f-150 w/ the 302. The gears in the rearend are stock. I have no idea what they came with off the factory. Anybody?

Also, just so everybody knows (not being a know-it-all or nothing) but it seems like there's some confusion. The 235 is the tires' width in mm. The 75 is called the aspect ratio. It means the sidewall is 75% of the tire's width (164.5 mm). The 15 is the rim size. So, a 235 and a 265 tire's height would be determined by the aspect ratio and not the width. The reason I believe I'm getting poor mileage is that my truck has 265/70r15. Basically they're 30x10.5. The width is about 1.5" wider and almost an inch taller. Which means my truck is turning a little more rubber than it needs to be.

 

The axle code is on the certification decal, which should be on the driver's door latch pillar. Big Red has a code 19, which is a 3.55:1 non-locking axle. I wouldn't be surprised to see the same in your truck.

Here's something else to consider when you buy tires: What percentage of your driving is in town, and what's highway? How much do you haul? Do you go off-road? A lot of guys around here are running passenger tires on their trucks, all brands, with a lot of those wearing the cheapest rubber they can get. I'm talking Wal-Mart's Douglas Xtra-Tracs here. If you're looking for ultimate gas mileage, and you don't really care about off-road traction, you could go that route, but for God's sake, buy something that will last!

I wanted a good mix, and although they screwed up and put the LT-metric C load range Uniroyal Liberators on Red, I can't say they've hurt my mileage, and they definitely get the job done as far as traction and load capacity is concerned. They're a good, solid tire so far.

 

I'm running 32-11.50's on my 96 351w ext. cab. I added up my gas mileage yesterday and it came up to be 17MPG!!!! I was shocked.