changing tire size

[Heartbeatracing]

I have a 2000 E350 superduty with an Auto tranny. It runs down the highway at 70 at 2400 RPM and is getting right at 13.5 mpg has anyone put taller tires on one of these to lower the RPMs to get better mileage...right now it has 215/85-16 and that is the stock size....thanks

[strokin_early_99]

You need to drop it to around 2K for the best economy. Do you have 3.73 or 4.10 gears?

[silverF250]

Yeah I don't know a whole lot about the vans, but you should be able to fit some 225's on it possibly 235's. That should help lower the rpm's.

[Heartbeatracing]

I meant F350...although I do have an E350 boxvan that we race moto out of, but im phasing that out because i bought a toybox trailer

[strokin_early_99]

Is it a dually? That is not the standard size tires on a singel rear wheel. Single Rear wheel come with 265-75-16

[silverF250]

Okay you have an F350 big difference. There are guys on here running 265's without spacers in the rear. That should really drop your rpm's and get you better mileage.

[Heartbeatracing]

265/85s? or 75s and ya its a dually

[silverF250]

265 75 16 is about all your going to fit on a dually without spacers. If you had a single wheel you could do up to 305's without a problem.

[GoldieStroker944]

i have an f-250 and i got 315/75-16s on it and they look awesome and do a little better on fuel but it is a single rear wheel

[D-man]

Originally Posted by GoldieStroker944

i have an f-250 and i got 315/75-16s on it and they look awesome and do a little better on fuel but it is a single rear wheel

I asked about mileage with 315's on another post. Most claim a loss in mileage due to the need for more power to turn the tire. I'm sure that is true
for a stock truck. But i've got a well modded truck. What was the difference you saw between the stock tires and the 315's?
Thanks, D