factory wheel sizes and axle ratios

[crunchiespg]

can anyone explain to me why if you select the 3.55 axle on a F350 SRW lariat diesel it forces you to choose 20 inch wheels.

the 18's are a slightly smaller overall size. so the 3.55 would help for highway cruising over the 3.73..

it seems odd to me that the 20 inch wheels will lower the revs, and you can select an even lower gear ratio. but not with the 18's..

why is this?

i would like the 18's as i dont like the 2011 20 inch wheels, but i also want the 3.55 as i want the fuel economy and lower revs..

[jasonmt]

With the 6.7 and SRW you have the choice of either 3.55 or 3.31 gears with 18" tyres.

[crunchiespg]

Originally Posted by jasonmt

With the 6.7 and SRW you have the choice of either 3.55 or 3.31 gears with 18" tyres.

you're right. stupid me. i saw it said 3.73 as standard. i didnt notice the axel was listed under the diesel engine, not in the axel section...

that makes more sense now.. it all seemed backwards before.
thank you.