Overdrive range

[Gray]

I was wondering at what speed the transmission shifts into 5th gear overdrive on most trucks here which still have the original tire size. On this PF it seems like it goes in at about 60 kms/hr // 37 mph but will then stay in OD till the speed drops to about 53 kms/hr // 33 mph, so cruising around the city if I bring the speed up to 60 kms until in OD I can then back off the speed slightly and still stay in OD on flat streets and get fairly good economy cruising along at about 1100 rpm.

Reason I'm asking about this is I was wondering how a change to taller tires would affect where the bottom end of the OD range is. Thanks.

Interestingly from looking through the manual it says that the transmission won't go into OD until the truck is up to operating temperature.

.