I have a 1994 F-350 with the indirect injection 7.3L diesel engine (turbo) (Not Power Stroke). I am upgrading to a newer 5th wheel, a 35 ft. Montana Mountaineer. Had a 1990 29ft Alpenlite. The trailer is going to be heavier than the alpenlite and I have been told I can increase torque by going to a smaller aspect ratio tire, so long as the weight rating stays high.

What size tire should I look for? I thought of changing out the differential but it is way to expensive and heard its not such a good idea anyway.
Thanks....

 

Your going to have problems with pin weight, if your single rear wheel drive. You will need to load the trailer as you would for camping(propane,water,clothes,food,utensils, folding chairs, blocking,etc). Full fuel and passengers in the truck and weigh the truck and trailer together. Hopefully with readouts for truck front axle, truck rear axle, and trailer axles. I think you will be right at or over on the rear axle rating with stock tires (235/85/16E).

If your truck is a dually, you can go down to 215/85/16E and gain a little gearing advantage.

For more power, you can put on an ATS upgrade kit (ATS and Ford worked together to make your turbo system). Which includes exhaust compressor housing, larger exhaust, and directions for turning up the injector pump, and advanced timing. It makes a big difference.

Good luck

 

Thank you very much... I've started to check into the ATS "kit" and hope its something I can install myself. Definitely on a limited budget...

There's really only one hill I'm worried about over at the coast and even with the Alpenlite I'd have to gear down turn up the heater and open the windows! So maybe this kit will help ease us over the top with the new trailer.

I didn't quite get what you were saying about wheels. I heard that if I can reduce the over-all diameter of the wheel somewhat that would also help. I don't have a dually and your right I've got the 16 inch rims. Its not a 4x4, either. Crew cab.

Thanks again!

 

a 2wd wouldnt be as bad to swap gear ratio in then, without having to worry about the front end, you might be able to find a better geared rearend cheap on craigslist or somewhere like that, and its a 'simple' swap, might be worth looking into

c.f.moore - how would him going to a skinnier tire help hime with gearing if he keeps stock height, unless are you referring to less width so less contact = less stress

 

Found a 4.10 geared rear end out of a 92.... Would that fit my 94?

Yes, about the tires, I would just want to reduce total diameter without losing sidewall strength... I think...

 

What gears you have now, 3.55s? Those 4.10s you found will help out for sure, I'm actually kinda surprised that your truck being a crew-cab ain't got those from the factory. Going with numerically-higher gears makes for less load on the engine which translates into more pulling power, which is why most 1-ton dually trucks with that engine seemingly got the 4.10s, and the larger F-Superduty (basically an old F450) being rated at higher GVWR got 4.88 and 5.13 gears.

On the tires topic, the problem with smaller tires is that their load capacity is also lower. Take the all-season BFG Commercial T/A tires for instance, their 215/85-16E size (what I should be using on my dually if I cared for factory recommendations) is rated at 2680 lbs, their 235/85-16E size (what I actually have on my rear axle) is rated at 3042 lbs, and their 265/75-16E size (what I have on my front axle, same diameter as the 235s but wider) is rated at 3415 lbs. See where I'm going with this? What you gain in pulling power by going with a smaller size tires is negligible compared to the load capacity (and therefore safety) you lose. In your situation I'd go for a set of nice 265/75-16E tires for their higher load ratings, and also swap in the numerically-higher gears to help the engine out some. I understand you're on a budget, we all are, but when it comes to pulling big trailers safety is what should come first...

 

Its not a dually, but you're right, I don't actually know what ratio is in there now. Not sure how to find that out. The 4.1 is listed as "available" on some site I found that lists 350 specs for 1994. I also would need to make sure the 92 rear end will fit the 94...

And THANKS for the run down on the tire issue. First time I'm getting the concepts on that one. One of those turbo upgrade kits would be nice but they look like they cost around 2k... And you're absolutely right on the safety issue so I'll do what I need to do. The newer, aluminum trailers are lighter than the old ones and so maybe I'm going to come in pretty close all things considered.
Cheers.

 

I know it ain't a dually, I just gave the tire size an example why going up is better than going down in size. You should probably go with 265/75-16 tires, they are as tall as the 235s you have now but they are about an inch wider and most importantly they can haul 400 lbs more each.

The $2k turbo kits are the complete setups for adding a turbo on a naturally-aspirated engine - you already got the ATS turbo from the factory, the upgrade kit for that was less than $600 last time someone price-checked it on the diesel forum.

How to check you gear ratio - on the door jamb sticker that has your VIN and also axle ratings and GVW and such, there is a little srction that lists a code for the axle - find that number or letter or combination of both and post it here, we'll decode it for you. Also on the differential cover one of the bolts has a steel tag attached to it, the tag will read something like 3 55 or 3L55 or 4 10 or 4L10 - these would be 3.55 open diff, 3.55 limited-slip, 4.10 open diff, and 4.10 limited-slip respectively.

 

Wow. Really? $600. I can swing that. And does it will really make a difference? Looks like combined weight of trailer and truck (crew cab, long bed) will be around 17-18k loaded, so maybe going to the tire you mention would also help. The truck is in the repair shop (that darned ignition switch problem which I see is an official recall, so I might see if Ford is still replacing that for free...), so can't check the door tag. But when I do I'll send along. Will be interested to know what ratio they put in there. Thanks again. I'm learning a lot fast.