Quick question?? I have a 1998 F-150 4x4. I've purchased and installed a few after market goodies. They are super-chip, exhaust system, K&N intake system and a few other goodies. My question is this. Do bigger tires make you speedometer read fast or slow? I'm not sure what the size of the stock tire was. I do know I installed the biggest BFG's that I could without lifting it. I know I've lost some towing power. I had saved up to have the gears changed, but spent the money on a new stereo for my boat. I wanted 4.10 gears, but I don't have $1300.00 laying around. Anyway back to my main question. Is my speedometer reading slow or fast. I drove next to anothe vehicle today and here is what I found. The other vehicle said 70 and my truck was reading 76. I was told this could not be possible. What do you think?

 

Your speedo will read slow. For instance, with my 35" tires, when I was going 70 mph, my speedo used to read 61 mph. You have a '98, so all you need to do is swap a gear in the tailshaft of the tranny and you'll have the speedo fixed. I went from a stock 20 tooth to a 17 tooth. It takes about 5 minutes to change it, but you need to know whether the splines go right to left or left to right with the "tip" up.

Lok

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1997 F-150 Supercab 4X4,Royal Blue,4.6 V-8, Tow Package,3.55 LS,
K&N FIPK,Performance Accessories 3" body lift,Superchip,
Gibson Supertruck Exhaust,Smitty Nerf Bars,
16X10 Eagle 589's, 315/75-16 A/T's,
Alpine CD,Alpine 5 Channel Amp,PPI 5 X 7's,
Boston 10" Sub.



Pics at: http://www.f150world.com/loknload/

 

I went from stock 255/70/16 to BFG 285/75/16 tires and my speedo is almost exzactly 5 mph slower now. ( 65 on speedo = 70 mph on GPS)

I use my GPS on the Highway to keep myself from going to fast.




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Y2K F150 4x4 XL Med Torredor Red
4.2 5 speed,AIRAID, SuperCHIP,
3.55 LS, Leer camper shell, bedrug,
Ranchhand Rover Brushguard with 6 LIGHTS and
Wireless remote switch Tint/alarm/ aftermarket keyless entry/locks
2m/10m/11m/12m radios, Scanner
LT285/75/16 BFG All Terrains
regulator@f150driver.com