Has anyone seen the specs on the tow ratings for 3.55 gears, auto trans, and the 6.4?

 

Same as for 3.73 gears I believe.

 

Correct... 3.55's carry the same tow ratings as 3.73's.

 

I'm sorry but I just don't see how you could try to tow 15,000+ lbs with 3.55 rear end on anything but flatlands. This would struggle fully loaded in the mountains. I had a tricked out 7.3 with 4.10 pulling almost 14,000 lbs and I had a tough time in the mountains of the east!

 

I could see the ratings being the same. The off the line acceleration will suffer, but you will have more useable gears at highway speeds.

 

Ford appears quite confident in the 3.55 gears. For the '09 model year, the only way you can get a F-250/350 SRW 6.4L with 3.73's is by either ordering it with a 6-speed manual and/or 20" wheels. 3.73's are forced with both options. Other than that, 3.55's are your only choice...

When you take overall tire size into consideration, 3.73's with 20's and 3.55's with 18's or 17's endup with nearly the same effective ratio.

 

I think one would have to tow with it before dissing it. My friend has the 3.55s and we tow over Donner summit all the time (7200' extreme grades). No problemo.

My truck has effectively taller ratio with the bigger tires, I think it comes in at 3.6x ratio, plus the extra weight of the tires to spin, plus I'm down 80 lb ft of torque vs. a 6.4, and I can accerate at will on the steepest grades at that elevation with 19K GCW (a slide-in camper is not exactly aerodynamic at 65mph either).

as an aside I was looking for this info, but maybe someone on the thread can tell me: was the 3.73 also re-rated to what the old 4.10 was before the 6.4? Can you get a 3.73LS with a widetrack front end? (thinking of an '09 order here and dealer says no)

 

Power stroke, I am a little confused, what does the size of the rim have to do with anything? Isn't it the outside circumference of the tire that is the real factor? If these are the same outside diameter of the tire on the 20's or the 18's it would be the same ratio wouldn't it? And I am just asking because this does not make sense to me.

 

Your thinking is correct (the actual wheel has nothing to do with it) and that is why I said overall tire size. 17's are approximately 32", 18's are approximately 33" and 20's are approximately 34".

 

Thanks for restating, I skipped the last sentence of your post. I wonder why Ford only offers it on the 6 speed or 20" rims when this is the case. Another weird deal that Ford has done. I have 37" tires on my truck so I am just fine with the 3.73 setup. 3.55 would not get me going even slower.