157dB

Put some 16.5 tires on 16 rims before. He he he.
I used a 1/4" spacer all the way around.

Ford has a re calibrator but its for gear changes, not tire diameter changes.
A Tuner is the only way to compensate for larger tires.
You wont notice a small change.

235/50R18 STOCK
9.251" WIDE
27.251" TALL
85.641" ROUND
740 REVS / MILE

245/50R18
9.645" WIDE
27.645" TALL
86.851" ROUND
729 REVS / MILE

255/50R18
10.039" WIDE
28.039" TALL
88.088" ROUND
719 REVS / MILE

265/50R18
10.433" WIDE
28.433" TALL
89.325" ROUND
709 REVS / MILE

245/45R18
9.645" WIDE
26.681" TALL
83.821" ROUND
755 REVS / MILE

255/45R18
10.039" WIDE
27.035" TALL
84.934" ROUND
746 REVS / MILE

265/45R18
10.433" WIDE
27.389" TALL
86.047" ROUND
736 REVS / MILE

255/40R18
10.039" WIDE
26.031" TALL
81.780" ROUND
774 REVS / MILE

265/40R18
10.433" WIDE
26.346" TALL
82.769" ROUND
765 REVS / MILE

275/40R18
10.826" WIDE
26.661" TALL
83.759" ROUND
756 REVS / MILE

waykooljr

255/45-18's are approximately the same height as stock, so if the speedo hasn't been calibrated for the tires you have, there shouldn't be a need to re-calibrate.

BAB GT

My current 'stang has stock tire and wheel size, but the speedo is about 5% high vs. GPS. On other vehicles that I have changed tire/wheel diameter, I have just used my GPS for correction. I find the GPS speed much easier to read at a glance and I assume more accurate than even the OEM speedometer with OEM diameter.