Where RV Now? Super-Duty Differences

Super-Duty Differences	Saturday, 22 May 2004
	written by Sterling

I've frequently heard from GVWR-apologists some bilge along the lines of "The only difference between a 350 and a 450 is the wheels". So out of curiosity, I once scrounged through the Specifications section of Ford's Truck Body Builder's Guide to nail down just what the real distinctions are between an F-350 and its bigger siblings. Here's what I found:

Frame – F-350 has a section modulus (essentially sectional volume of steel) of 8.7 cubic inches, F-450/550 have 10.1. The 450 and 550 also have straight frames, while the 350 pickup's has a "hump" over the rear axle.
Front Axle - All have a Dana 60 front differential, but while the F-350 has a rating at the ground of 5200 lbs, the F-450/550 have 6000 lbs.
Rear Axle - F-350 uses a "Ford Standard" axle with a rating at the ground of 9750 lbs, F-450 has a Dana 80 rated at 11,000; F-550, a Dana 135 at 13,500 lbs.
Brakes - F-350 uses 13.03" diameter discs in the front, 12.83" rear. F-450/550 have 14.53" front, 15.55" rear. Note that these larger discs won't fit a stock 350 because of...
Wheels - the F-350 runs 16" wheels rated at 2600 lbs each, F-450/550 use 19.5" wheels rated for 3750.
Tires - for the F-350 it's LT235/85R16, E load rating (note the "LT" for Light Truck); the F-450/550 come with 225/70R19.5 tires (no LT) in an F load rating, and if that's not enough, G-rated tires are readily available for these wheels.
Steering - the F-550 comes stock with a steering stabilizer, which neither the F-350 or 450 do.
Springs - Lots of options here, and the highest rated F-350 front spring set equals the F-450/550 at 6000 lbs. In the rear, though, the F-350 goes no higher than 9750 lbs rating (total thickness 3.89"), while the F-450 has 11,000 (5.68") and the F-550 is at 13,500 lbs (6.66").

In short: very different trucks, deserving of their very different weight ratings.

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