Changed tires and redid REV/MILE with SCT, but??

[F350CCFX4]

So, had the stock 265/75/16 on the truck, but moved up to the 275/70/18 which are damn near 2 inches taller. So did the calculations to see what the Revs/mile difference was.

637 vs 608.34 So I got out the SCT and looked at what could be done with it and set it too 610, because my other choice was 605 since it only seems to go in 5 count increments. Is that the only amount it can be adjusted by?

Seems I am getting worse mileage with the taller tires and I am assuming it's because of the mass of the tires. They weigh more, but I haven't had a chance to weigh each of them too see the difference.

So, I have a few questions and of course these are more personal opinions then anything, so here goes...

Should I change the tune so it is set to 605 Revs/mile?

The speedo is corrected with the tune correct?

Does this affect my gauge in the truck for Avg miles/gal?

Anyone else done this swap and what did your mileage do?

[jello]

from what I've heard the speedo isn't corrected with x-cal.

[PSDPlayer]

The speedo isn't corrected but the trans is. The issue is that the speedo information is gathered by the ABS module and then is transmitted over the network for the cluster. Only way to change the speedo is to adjust the ABS module or get a tru-speed.

[nummit]

The speedo isn't corrected but the trans is. The issue is that the speedo information is gathered by the ABS module and then is transmitted over the network for the cluster. Only way to change the speedo is to adjust the ABS module or get a tru-speed.

Please tell me more about ABS module adjustment.
Is this a change that can be done at home or is it a dealer item?

[PSDPlayer]

Dealer item. Its in the configuration on the WDS, PDS, or IDS. I have heard some rumors amongst my technician friends that the late 05s and 06s have issues. But I did it to my 05.