Hello All,
It's been a while since I've been a regular on the boards, and I know this question has been asked to death, but here goes: I have a '98 F150 Lariat 4x2 SuperCab with a 4.6/5-speed/3.55non-LS; I am about to change my tire size from the 'standard' 30" tires to 28.5" tires (265/55R17 Firestone Firehawk GTA's); this essentially changes my gearing from a 3.55 to a 3.73, a 5% drop; here's the question, finally; does my truck use a 'speedo gear' in the tranny or an electronic sensor in the rear end to monitor speed/distance? The local Ford place says a '98 uses the electronic sensor, but I could've swore I remembered that '97's and '98's used the gears. If it is a gear, where can I get one? It should only have to have one more tooth than what I've already got (assuming I'm gearing it). Thanks for the assistance.

P.S. Anybody have any comments on the tires I'm installing? I've got the 17x7.5 'sawblade' rims. Thanks again.

 

if your truck has a digital odometer, the speedo must be corrected using a chip, programmer, or computer.... If you odoeter is not digital, (analog) your speedo must be corrected using a speedo gear.

 

well i have a 99 with a digital odometer and i watched the ford dealer plug in to the obd II and use the ford computer to change my tire size to correct my spedo, you can get a gear at the dealer they should also have a chart to tell u what gear to go withn for what rear end and tire/rim size, if u have the digital as long as the dealer has a good drivability mechnIC he will know about changing the tire sixe on the comp.

 

These tires get very low marks on tirerack.com owner survey.

http://www.tirerack.com/tires/tires....irehawk+GTA+02

If you are concerned about your speedometer reading being accurate after the tire swap, you may want to take your truck to a speedometer shop or check the actual speed of your truck with the new tires yourself. You can do this with a handheld GPS or by putting a stopwatch on the Interstate mile markers.

There is a pretty good chance your current speedo reading is say, +/- 3% accurate anyway.

So you may end up more accurate than before with the new tires, or you could ask the Ford tech to put in the proper tire diameter that will get your speedo spot-on.

Is your goal to lower your truck by 3/4" ?

Scott D