Towing with F-350 Tire size question

[classy_gene]

Hi guys, I have a 94 F-350 psd with a 4.11 rear end that I tow my 5er with that weighs in @ 15k#'s. I am in need of replacing my tires soon. My question is what size tire should I go with? My truck came with the 215 pizza cutter tires originally. I just don't like running 2500 rpm @ 70 mph. I figured that if I stepped up to a 235 it might cut my rpms down some, I just don't want to lose very much of my towing ability either. I've always heard that the psd's can pull about anything, I'm not sure about that since I have run mine pedal to the metal fully loaded and couldn't keep up with my cummins friend. But oh well. So what size does anyone recomend? Thanks

[96STROKE]

215 vs 235 is width in MM. This does nothing to your gearing. What matters is the aspect ratio to width. If both the 215 and the 235 have the same aspect ratio, then the 235 is a slightly taller tire.

I assume that you are talking 235/80-16, if so here is how to come up with the height of that tire.

235 mm = 9.25 inch, 80 is aspect ratio which is the percentage of width to make up side wall height (80% of 9.25 is 7.4, times by 2 = 14.8"), 16 is wheel size. Add sidewall height to wheel size that gives you a tire of 30.8".

We need more info on tires you are compairing to understand which is a taller tire and what it will do to your overall gearing.

15k of trailer is a lot, you may need to stick with shorter tires to pull that much.
I like towing at 2000-2200 rpm, but thats me with my set up.

[classy_gene]

Well I guess I didn't give all of the spec's did I. That is what I get for posting @0300. The tires that I have are a 215/85/16, I thinking about going up to a 235/85/16. I realize that the first number is the width of the thread and the second is the ratio of the thread width. I was just wondering what the circumference difference was on average. I realize that every manufactors sizes aren't the same. I was just wondering if the 235 had like a 10% more circumference then the 215 or what. Since that would help my highway rpms while not towing but hender while towing. Or would I even notice a diffence.

[LatahF250PSD]

The difference in diameter roughly one inch.

[Willie]

Won't a 235 width be too wide for DW on the rear ??

[Mr_Roboto]

Lots of people have used 235's on their duallies.

You do need to keep them aired all the way up to keep them from "kissing" under load. 4x4 duallies came with rims with a little different offset to get the tires further apart.

You probably won't even notice the power / gearing difference between the tires.

Your other option is to get a set of 7.50R16's. They are "100 series" tires that are as tall as a 235/85 but narrower. They are a little hard to find, but they ARE available. 7.50x16 (bias ply) was what duallies used back in the 70's and early 80's.

[classy_gene]

So are you saying that all of the dually rims don't have the same offset? The guy at the tire shop told me that according to his computer the duallys either came with 215's or 235's. It would just affect my spedo. I just don't to pay $145 each for six tires and not like them for 40k miles, if you know what I mean. Maybe I will just stick with the size that I got and suffer with the higher rpm's. If only I could buy a Gear Vendor.

[tomshep]

I can't give you a specific answer for your 94 model. But, for the 99+ models the XL duallie comes with the 215s standard. When you upgrade to XLT or Lariat you get 235s. So, on the later models they easily fit. I would think they would work on your 94 as well.

Tom

[Westro]

Tomshep is correct.

My 2000 Lariat came with 235/85 R16s stock. With my 3.73 rear end I am at about 2000 rpm's slightly below 70mph.