I will be replacing my stock 16" 235's with new 255's will I need to change anything and will there be any change in my speed or gas milege?

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I went from 255's to 275's and lost a little lowend and the speedo is about 3mph off at 60mph (reads 60 while doing 63)
However the truck looks MUCH better
Rides better too.
Well worth it IMHO.

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Truck Pictures

99 XLT 5.4L Regular Cab 4x2 120" Wheelbase 4 wheel disc brakes/ABS 5 star larait style wheels Toreador Red/Silver 3.55 gears 275/70/16 Micheln LTX Delta toolbox, Ford Running Boards, Ventshades, Bugflector, Bullrings, Donnelly compass mirror, 2" Rear drop.
Eclipse 5340 cd player
Memphis ARCS50 component speakers w/tweeters mounted flush in the door panels (excellent sound)powered by a Sherwood 35x2 RMS amp
Kicker ZR360 for the 2 Audiobahn AWC10 subs
54regcab@ifreedom.com

 

oops

[This message has been edited by Red BullSr (edited 08-14-2000).]

 

oops

[This message has been edited by Red BullSr (edited 08-14-2000).]

 

foots,

The 235mm is 9.25" wide (section, not tread width). The 255mm is 10.0" wide (sec width). What you're doing is increasing rolling resistance when you go w/wider tires. However, by only increasing the width of the entire tire by 3/4 of an inch, you won't feel too much drag... maybe when you let off the gas pedal at highway speeds, but no economical differences.

A few things to consider:
gears, auto/manual, Liter engine, 4x4?
Also, if you just got new tires w/only section width differences, then expect what was written above. If your tires you changed look like 235/70R16 (29.0x9.25) to 255/70R16 (30.5x10.0), then you may incur a slight HP loss (2 or 3, 5-max depending on drivetrain). Highlight slight... because, again, your change is not very drastic.

Again, lacking your drivetrain specs, I'll assume you have average:
99 4.6, auto, X-Cab, 2WD, 3.55 gears
there will be, again, slight changes in speedometer reading (you'll need to buy new speedo gear and computer readjusted from auto shop or dealer. I have trained myself to know how fast I'm going). I changed from your stock tire to a 32x11.50. My speedo reads 63 and I'm really going 75. New gears won't be required. Any other modifactions to drivetrain will not be required. If any skepticism rises of HP loss, you can easily fix that w/new gears (3.55 to 3.73 or 4.10 (probably overkill) 2WD - $450, 4x4 - $950), performance computer chip, better air flow in/out of engine.
[img]//albums.photopoint.com/j/View?u=1035764&a=7645316&p=26012800&Sequence=0[/img]

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1999 Red F150 4x4 5.4L XLT X-Cab
Towing Pkg
Corporate 9.75 Rear Axle, 3.55 LS
Corporate 8.8 Front Axle, 3.55 Open
K&N Generation II
JET Chip
32x11.50 Super Swamper SSR
-coming soon
JBA Headers
40-Series Flomaster exhaust

 

foots, did that tire change on my 97 f150. Only a couple of miles off on the speed o. Not enough to go through the trouble of correcting. If your speed o shows 55, your actually doing 57.

good luck.

 

I changed from your size (235 70r16) to 265 75r16s. speedo is off 8%. MPG averaged over several tanks dropped from 17 to 16.6 (after compensating for 8%) power feels about same. Ride and looks are MUCH better.

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97 F150 4x4 SC 8' box, 5.4l auto 3.55LS.