Any correalation between tire size and the infamous Ford clunk????

[David Johnson]

Ok this might sound silly to some of you gearheads but here goes. I discovered my speedo was reading faster than i was actually going with my stock tires 235/70/16s. These were the stock size according to the sticker on the door jamb. I cant figure this out unless my 2000 F150 was actually calibrated to have 255s on it. I just recently replaced the stock tires with LT265/75/16s and now based on the guy with the digital speedo driving next to me today, i noticed that my speedo is now much closer to reading correct. I have also noticed that that infamous clunk i have had since day one is not as apparent now with the larger tires. The clunk usually sounded when letting off the accelerator and a downshift takes place. This tranny has already been rebuilt once at 31000 miles. Could the slower spinning of the driveline with the larger tires made a difference with the clunk or the lower rpms of the motor made a difference with the clunk? Could the wrong calibration of the computer mated with the wrong tires ( driving with 235s on a computer calibrated for 255s) and the shift points being different or something like that caused my clunk. I do definatley notice that the clunk is not near as apparent as it was when the truck downshifts now with the larger meats on it. Is this all in my head or what? Thanks all you gearheads in advance for any replies. Dave 2000 F150XL SC 4x4 4.6L 3:31

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