I put the fabtech 3.5" spindle lift on my truck, and then went with 33" tires. According to my calculations, this dropped my effective gear ratio to a 3.08. (It's a 3.55 stock) My mileage has not increased at ALL! (may'be even went down slightly) I sure know I lost some power, so shouldn't I be getting better gas mileage with a lower gear ratio? Any ideas?

Thanks,
Chris

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1998 F-150 Standard Cab/Long Bed 4.2L V6

• Fabtech 3.5" Spindles
• 2" Rear blocks
• BFGoodrich 295/75R16 AT's
• Rancho RS 9000's
• Rhino Bedliner
• 3.55 Gears
• Changed pinstripes to gray (come on Ford, did purple pinstripes really look good on ANY truck?
• Limo Tint
• Pioneer P-6000 Head Unit, 4 Pioneer 3-Way 6x9's, 800 watt Pioneer Amp, 2 12" Pioneer Subwoofers
• PIAA High-Intensity Driving Lights mounted in bumper
• Updated front end to 2001 Black Grille w/ honeycomb, 2001 Chrome bumper, 4x4 Valance w/ fog lights & Tow hooks
• Clear corners and tail lights
• 2001 XLT 60/40 Seat

 

don't forget that your engine now has to work harder to turn those bigger tires (it's all about torque).

and then again, you have increased wind resistance from the added height of the truck.

------------------
"flexible hips mean higher steps"

2001 F-150 Supercab XLT 4x4 5.4L Auto
optional equipment: carpet delete, tow package, power adjustable pedals, "man"ual 4wd shift lever, law enforcement scanner, CB w/PA, spray-in Speedliner, Streamlight Stinger, Graco infant car seat
visit http://quickdraw.f150online.net/ to see my F-150

 

Maybe on the highway......since your rpms will be down.......MAYBE...but you got to remember around town in stop and go traffic you are using more power to get started..and our trucks arent exactly areo dynamic..especially when we put them higher into the wind.......HEY BUT WE LOOK GOOD.....Dave

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1998 F-150,4x2,4.6 AUTOMATIC, XLT

FABTECH LIFT 6.5
BODY LIFT 3IN (6"11 1/2")
LIFT LIPS
315 GEOLANDERS
EAGLE 143 16X10s
SUPERLIFT TRACTION BARS
NERF BARS
F&R LUMI LOGOS
SUPERCHIPPED
FLOWMASTER 40
CB (TX CHAPTER MUST)
CLEAR CORNERS
IMAGE COVERS BACK LIGHTS
COVERKING DASH COVER
SNUG LID
BEDLINER AND MAT
EGR FENDER FLARES
CLASS III HITCH
STROBES
PAINTED MOTOR
AIRAID KIT W/PREFILTER
BUG SHIELD AND RAIN GUARDS
6 DISC CD CHANGER
BLUE LIGHTS UNDER TRUCK
MUTH MIRRORS

San Antonio
DWESSELS89@AOL.COM

FUTURE MODS
4.56 GEARS
SUPER CHARGER
HEADERS

 

It's kinda like pushing an even taller brick wall through the air.

 

Don't forget to factor in the odometer reading difference when figuring the mpg. If you just use the odometer reading as is (less miles than actually travelled!) without adding the appropriate percentage for your bigger tires it will definitely look bad! My mileage actually increased about 6%... still not great, but better!

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-JonC-
*Silver 2000 4x2 F150 Supercab
*4.6L Triton V8
*315/75/16 Pathfinder ATR's
*16 x 8 Panther Custom 108's
*K&N GenII FIPK
*Custom Cat-back w/ Flowmaster 50 Series
*Fabtech 6.5" "Ultimate" suspension lift
*Smittybilt nerf bars
*Extang Black Max soft tonneau
*Stull billet grille
*Clear corners
*Heckethorn steering stabilizer

 

how do you figgure out the correct mileage with bigger tires? I never thought about how it is affecting the miles traveled also. I was getting pissed because my truck is getting about 200 miles to a tank. thats about 10 mpg right? So actually I have gone alot more than that, but how do you figgure out how much more? Thanks

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NEW TRUCK!
00 f150 ext. cab 4x4 ORP w/5.4/auto, black! Tan buckets, expy center console, tinted windows, westin nerf bars, flowmaster 40 series, remote start/alarm/keyless entry, headlight/taillight covers, Lund wiper cowl, vent visors, tono cover
5" RCD lift, 3" body lift, 35" pro comp ats on eagle 589s

old truck
99 black f150 4x2 ext. cab sport w/4.6 V8. external mods. include:
3" body lift, 3.5" fabtech lift, airaid FIPK, JBA headers, Superchip headlight/taillight covers, wiper schroud, shadeblade, ventshade, bug deflector, bed liner, tonno cover, and custom duel exhaust out the sides with 3.5" chrome tips and NO muffler. Tires: Mickey Thompson Baja HP 35 12.50 17 internal mods. include:
Pioneer indash cdplayer, 2 12" subs, 400 watt amp, remote start, and aftermarket alarm
http://www.4tssinc.com/truck

 

the hard but accurate way:
5280 feet in a mile. 5280 / circumference of old tire (go out and measure it with a flexible measuring tape OR measure your diameter with a yardstick and * by 2) = # revolutions required for one mile (i'll call this "rev")

rev * circumference of new tire (hand measure this--a 35" tire isn't really 35" tall) = total feet travelled in one mile on your odometer (i'll call this "odo")

odo / 5280 = "ratio"

this ratio is useful because if you multiply the ratio by your speedo you'll know how fast you are really going (eg 60 * 1.1 = you're really going 66 mph when your speedo says 60) or you know how many miles you really travelled on a tank of gas (e.g. 1.1 * 200 miles (trip odometer from fill up to empty) = you really drove 220 miles)

the easy way:

to get the ratio described above: divide your new tire diameter (or radius) by your old tire diameter (or radius) this is a lot easier. if you had 31" tires and upgraded to 35" tires: 35/31=1.13 your speedo is off by about 113% and so is your odometer

[This message has been edited by quickdraw (edited 04-19-2001).]

 

I had 3.55 gears. With truck stock with 265/75-16 tires and travelling 60%HW/40%City, I got 17.5-18 mpg.

Now adding 5" RCD lift, 3" PA Body lift, 315/75-16's, and 4.10 gears. I now get 15 mpg. I did change my speedo gear to correct speedo within 1 mph.

 

LOL
Like it has already been pretty much stated it takes more power off the line to get those bigger meats turnin and the aerodynamics is diffently changed. I once helped lower a Mazda 4x2 and it was like adding another engine to the truck. So wind resistence does play a big part.
On another note can anybody tell me how I can add a pic to my profile/signature so it will show up on all my posts?

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97 Ford F150 XLT 4wd 4.6L auto, Std cab/Long bed 2 tone royal blue w tan bottom, PW,PL, and PM, captian chairs w/arm rests

Current Mods
K&N Filter
Xact Plug Wires- 8mm
Ventshade side window deflectors,read window deflector, bug guard, headlight and taillight blackouts
custom hand painted Ford emblems on door jamb guards and under hood on plastic intake cover
plastic mud guards
custom 4x4 off road graphics
Ford hitch cover and license plate frame
Custom carpet liner (protects factory carpet)

 

The biggest thing that'll make a difference is that you have affected the trucks optimal RPM range. Because the truck has a "lower ratio" technically, it is having to use higher RPMs to get it up to speed. You'll notice the transmission tends to shift quicker when you give it gas and jumps into the higher rpm range sooner, where as, it used to stay in gear and slowly climb rpms. This increase in RPMs means gas! My truck has its bad spot right around 70mph. If i give it any gas it'll jump from 4th to 3rd and rpms will fly up to around 2500 until i let off the gas again, where it'll go back down to about 1800 rpms. Overdrive is probably the most effected gear, and that is the most gas-efficient too, so by eliminating the sustained use of this gear, you will hurt your mileage. Around town i get about 9.5-10 and on the highway i get around 12.5-13! Fun huh? And i'm pretty careful on the accelerator...if your used to getting off the line a little quicker, than i can imagine its hurting you even more. But like the others said, you should probably add about 10% to your mileage travelled because with 35s mine's about 18-20% off, so i must add those to the odo. That'll make it seem a little more reasonable...if you're getting 200 on a tank that means you are really probably going about 225 miles at least. But i'm assuming you're not draining the tank...when i get close to E i usually fill up but realize i has about 3-4 gallons left, so i add about 40 miles...if you do the same, than i image you could get about 275 at least out of yours. If you have the 25 gal. tank than that avg. to about 10.5 mpg...if you have the smaller tank, than youre getting about 11.5-12.5...anywayz... Hope this helps.

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-Brandon Warford
97 F150 4x4 Sport Brt. Red SuperCab
4.6l Triton V8
3.55LS Rear-end
MECHANICAL MODS:
3" Performance Acc. Body Lift & lift lips
1-1.5" torsion bar adjust. so it sits level
Clear Corner Lenses
315/75R16 Yoko. Geolander MTs
American Racing Atlas 16x10
True Dual Exhaust
--(2) 3 Chamber Flowmasters (Exits like the Lightning)
FUN MODS:
Pioneer 8000 3D series
Boston Acoustic 5x7s
Sony Xplode 4ch Amp
(2) 8" RF XLC Subs
Custom 4x4 Sticker
Viper Alarm
FUTURE MODS:
4.56 gears
Repaint around Headlights where clearcoat is coming off >=(
Fix ding in tailgate
Skidplate
New pinstripe
Heckethorn or Rancho Steering Stabilizer
Rancho RS9000 Shocks & Control System
Thats about it for now!
Check out my NEW WEBSITE:
****BigBadRed's Website****
Killintime4fun@aol.com
"F-150: The other woman!"

"...the road curves to the right and there are a lot of signs that say you cannot turn left...TURN LEFT."

 

Thanks for the help guys!

To those who changed their gear ratio:

I have been contemplating getting 4.56 gears, which would equal out to a 3.73 with the bigger tires. The reasoning behind this is because I figure it will add a little more torque but not totally KILL my gas mileage. Since you guys were talking about it taking more power to get off the line with the stock gears, would the gear swap actually somewhat "help" gas mileage when in town? Either way could you give my an "estimate" of how my mileage will be affected by this swap, assuming my driving is about 70% in town/30% highway driving?

Thanks in advance,

Chris

------------------
1998 F-150 Standard Cab/Long Bed 4.2L V6

• Fabtech 3.5" Spindles
• 2" Rear blocks
• BFGoodrich 295/75R16 AT's
• Rancho RS 9000's
• Rhino Bedliner
• 3.55 Gears
• Changed pinstripes to gray (come on Ford, did purple pinstripes really look good on ANY truck?
• Limo Tint
• Pioneer P-6000 Head Unit, 4 Pioneer 3-Way 6x9's, 800 watt Pioneer Amp, 2 12" Pioneer Subwoofers
• PIAA High-Intensity Driving Lights mounted in bumper
• Updated front end to 2001 Black Grille w/ honeycomb, 2001 Chrome bumper, 4x4 Valance w/ fog lights & Tow hooks
• Clear corners and tail lights
• 2001 XLT 60/40 Seat

 

This is probably not as accruate, but will get you a better idea of what your speedo/odomerter is doing. On the highway, use the mile markers to check what your odometer is reading. Just note the 1/10 reading as you pass the first post. Keep going until you find that you are exactly 1/10 off and note how far you have gone (how many mile posts did you pass), then multiply the # of mile posts by 10. This is how many miles you travel while losing 1 mile on the odometer. For example, I did this and found I lose 1/10 every two miles. 2x10=20, so for every 20 miles on the odometer, I have to add one mile (5%). 200 miles on the odometer, means the truck has gone 210 actual miles. You can use the percentage to figure how off your speedo is too. 60mph x .05 = 3, so you are really going 63mph when your speedo shows 60.


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1997 F150 4x4 Off Road, SuperCab, Short Box, 5.4, Royal Blue/Silver, K&N, Gibson SS, LT265/75/16 Wild Country APT's

 

Here is something to think about, we had a expedition in for a fuel consumption concern and one of our Training People had the vehicle at the Ford Training center. He drove the vehicle for a month or so and found that he got better fuel economy with the overdrive switched off. The engine was higher in the RPM band but it was breathing better and took less torque to move it down the road. The fuel injector pulse width was lower at this higher RPM at steady throttle cruise. Less pulse width is less fuel. If you install a vacuum guage, in general..the higher your vacuum the less fuel you are using. These trucks use a Mass air flow sensor as opposed to a MAP [manifold absolute pressure] [vacuum] sensor to meter fuel but it still has the same effect. sometimes the lower rpms run the engine at a higher load which burns more fuel, expecially on slight grades or towing.
Dave