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Rvlegaleagle · 03-04-2017, 05:51 PM

An option for the new Ford F-550 chassis “rear axle ratio” has several selection options from 3.73 to 4.88 with non-limited slip axle (3.73, 4.10, 4.88) to limited (4.30 or 4.88) or Electronic locking axle (3.73 or 4.30). How does this factor into a good RV chassis? Aside from the general idea that lower ratio gets better gas millage, any other practical reasons to get one or the other for an RV?

Unplanned Tourist · 03-04-2017, 06:30 PM

Limited slip is like the old posi-traction. If 1 wheel is on ice, the other side will grab and get you going. Non limited is I'm guessing an open diff where if 1 wheel is on ice and spinning, that's as far as you are going without putting chains on. The electronic locking diff is like an open diff until you switch it to lock, then both wheels will turn, as they are locked together.
Hope that helps. Maybe someone with similar set-up will chime in with ratio ideas. Good luck.

ps. diff ratios are often referred to as lower when the actual numbers are higher and higher when the numbers are lower.

Confusing, but think of it like low gear vs high gear. Low may be 4 to 1 and high may be 1 to 1.

garys 68 · 03-06-2017, 11:37 AM

Lower numeric ratio will get slightly better mileage at lower rpm, but wont accelerate, go uphills as well, or tow as much weight. You can probably find a recommended ratio for your expected CGVW. Go higher if you're going to be towing a toad.
Non limited is an open rear, just like most cars...only one wheel does the driving.
Limited transfer a percentage of power to both wheels. Great for mud, grassy areas, dirt, snow/ice, etc.
I'm only familiar with aftermarket E-lockers or air-lockers. They're pretty much all 100% locked rear. You would only use in extreme offroad or towing a boat up a slippery ramp. Not much other use in an RV. You wouldn't want to use above 10mph.