F550 gear change -- which one?

[Srpat]

2012 F550 6.7 diesel shuttle bus. I am getting 42" Continental MPT tires and dbl design wheels in the next week or two. I am taking it to my mechanic later this week to get the gears changed. Currently has 4.30 gears with a limited slip in the rear.

5.38 is what I am planning on getting. But I know some of you have researched this extensively and have a lot more knowledge than me on which gears work best. 4.88 gears will save me about $1,000 according to the mechanic. I want to get something that is a good fit for the bus, and something that will keep me in the "almost teens" for gas mileage on the highway.

Bus is about 16,000 lbs, give or take. Any opinions?

 

[mog]

I can't speak to 'Ford' gearing specify as I have a C4500 on 42s, but with the factory 5.13 gearing around town and 'accelerating/hills I need to run it with the electronic overdrive 'off'. Then at highways speeds flat/semi-flat, I can engage the OD and run about 1700-1900 rpm (8.1L Vortec, Allison 1000) at 65-70 mph. It actually works very well as it accelerates 'normal' (as if it had factory tiny-tires) in the OD off mode.
MPG, ha! 8.1 Vortec in a 12k truck on 42s = B17 with flak holes in the wings (actually about 8-11 mpg, highway 60ish, much lower at 75mph)

BTW the guys at Nitro Gears are great (https://www.justdifferentials.com)

 

[FordGuy1]

Make sure you use Spicer gear sets, regardless of the ratio.

 

[Buliwyf]

I drove a stock F550 7.3 DRW with little DRW tires. It had 4.56 gears and did fine. So that would put me firmly in the 5.13+ camp.

Stick to your plan. Sounds like you have it figured out well. I don't think 4.88 will be nice, but may be acceptable. Don't fear the gear.

 

[cph05a]

Are you doing the 335/80r20s? That's the most common size and they're more like 41inches tall (the DBL design website is wrong).

FWIW I have the 335/80r20 MPT 81s on ours and we're still on the stock 4.30 gears and it works surprisingly well. We're weighing in at about 12,500lbs fully loaded. The 4.88s would be fine for 335/80r20 unless you want to have a huge camper and tow a boat.

Our mileage is usually between 11 and 12mpg. We have a 6.0 powerstroke and a pop up so we're lower profile on the road than you will be.

 

[Srpat]

Are you doing the 335/80r20s? That's the most common size and they're more like 41inches tall (the DBL design website is wrong).

FWIW I have the 335/80r20 MPT 81s on ours and we're still on the stock 4.30 gears and it works surprisingly well. We're weighing in at about 12,500lbs fully loaded. The 4.88s would be fine for 335/80r20 unless you want to have a huge camper and tow a boat.

Our mileage is usually between 11 and 12mpg. We have a 6.0 powerstroke and a pop up so we're lower profile on the road than you will be.

Yeah. Went with the 335/80/20s. They are sitting in the driveway now. Bus is at the shop getting the new gears put in. 5.38 should be very close to stock gear ratio. Should be a good fit. Like you said, the bus has a huge frontal area and it is fairly heavy.

 

[MTVR]

What size are your stock tires?

What terrain? Be specific.

Comparing other engines, transmissions, tire sizes, and vehicle weight/profiles to yours, is going to be just this side of meaningless...

 

[MTVR]

Are you doing the 335/80r20s? That's the most common size and they're more like 41inches tall (the DBL design website is wrong).

I concur- the theoretical height of a 335/80R20 tire is 41.10"...

 

[Letsgomoreplaces]

Been Running 5.38 with 335/80R20 for Several years now. The goodyears are 10x better than the continentals. I've got over 30K on them and hardly worn. The conti's were done after 20k. We stock the gears etc as well.

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