Here is my question, I ordered my F40 with the 4.88 gears, it comes with the 19.5 rims and not sure what size tire, as I see it, the RPMs will or should be lower than my 2005 F350 KR with 4.30 gears and 17" rims.

Am i missing something?

Do they go with the larger wheel and tire to bring the RPMs down?

 

The larger wheels and tires allow the 450 to carry more weight and have bigger brakes.

If you want to know how it all shakes out driveshaft speed wise between the the 2 trucks you might be able to find the tire revolutions per mile for each size tire at www.tirerack.com or similar site and do the math.

 

That I understand, but it should also lower the RPMs, right? if the truck had the 17" rims with the 4.88 gears I would think the engine would tack out at a very low speed.

at least in theory

 

The factory tire size on your F-450 (and on F-550s) is 225/70R19.5. Height-wise, it is almost exactly the same overall diameter as your 17s on your '05. Just FYI.

Heather

 

you need to look up the tire revs per mile or overall diameters for each size as some tires are low profile with short sidewalls and some are larger diameter with taller sidewalls.

 

All 19.5" commercial-grade tires have an aspect ratio on 70 so it is a somewhat lower profile tire than most light truck tires.