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  1. #1
    Jr. Apprentice
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    Default Can installing larger tires really improve a trucks performance?...

    OK, so this past weekend, after installing the 285's on my 2002 Z71 4x4 I ran the truck up to Reno and back (round trip 199 miles) and ended up putting 10.7 gallons in it when I got back to top it off. That averages out to 18.59 mpg. The drive to Reno has a lot more hills and turns and braking than the drive to LA, (before I put on the bigger tires I ran an average of 18.6 mpg to LA) so i'm figuring that I may have actually improved my mpg by putting these larger tires on. Also, and many of you may think I'm way off here but I SWEAR to this, my truck handles BETTER after turning up the torsion bars. It take the mtn roads better and my power band also changed. Where I was lagging and my truck was up and down shifting randomly at around 60 to 65 mph (around 2000 rpm), it now runs at 72 mph at 2000 rpm and when I step on it it seems to downshift faster and pull better. Can putting larger tires on and cranking up the torsion bars really do ALL that at once? It feels like a different truck...a BETTER truck.
    Last edited by BigBill; 02-15-2011 at 03:59 PM.

  2. #2
    Jr. Engineer racekid91's Avatar
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    Default

    For better MPG, it's going to take more power to turn over 285's. It's a larger tire, it takes more effort to turn them over. How are you figuring out your MPG?

    And for the torsion bars, did you crank a lot?

    1995 Chevy Tahoe

  3. #3
    Legend

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    Default

    Usually wider tires hurt FE.
    Taller tires COULD IN THEORY improve FE, by lowering RPMs, but usually it is a wash-the taller tire lowers the RPMs, but it increases aero drag, so it evens out.
    Wider tires-same tread- always should decrease FE-increased Rolling resistance and increased aero drag.
    Maybe the thread are lower RR or maybe you have more pressure in them, or maybe you caught favorable winds.
    Out west the wind is a BIG deal in respect to FE.
    Either way 18 mpg is pretty decent for a 4x4 in a hillly area.
    Charlie
    Charlie
    1998 suburban-
    1/2 ton

    199500 miles
    River
    Ridge,LA

  4. #4
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    Not sure what size your previous tires were, but when I went from 265s to 285s, it also had an effect on my speedometer...which in turn threw off the odometer. If I remember correctly, at 60mph, it was reading 57mph...this will give you the illusion of increased mileage since your truck thinks you are going further on a tankful of gas than you actually are.


    Mike (Denver, CO) - 2008 Sierra 1500 Z71 SLE 5.3L 4WD

    SUSPENSION: Rancho 4" Suspension Lift; Rancho RS9000XL Shocks; Rancho Skid Plates; Rancho MyRide Wireless Shock Controller;
    TIRES:
    BFG All Terrain KO 315/70/17
    DRIVE TRAIN: 4.56 Gears; Detroit TrueTrac Differential; True Cool 40k Transmission Cooler
    PERFORMANCE: DiableSport Predator Tuner; Custom Tuned by Diablew; Magnaflow Exhaust; AFE Cold Air Intake
    ELECTRONICS: Kenwood DNX6180 Touchscreen; Subthump box w/10" Kicker; Driver Information Center (DIC); Rear View Camera
    ACCESSORIES: Westin Brush/Grill Gaurd; Westin Nerf Bars; Truxedo Tonneau; 20% Tint; Tow Mirrors w/Heat & Signals

  5. #5
    Jr. Engineer racekid91's Avatar
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    Quote Originally Posted by mfleetwood View Post
    Not sure what size your previous tires were, but when I went from 265s to 285s, it also had an effect on my speedometer...which in turn threw off the odometer. If I remember correctly, at 60mph, it was reading 57mph...this will give you the illusion of increased mileage since your truck thinks you are going further on a tankful of gas than you actually are.
    x2 on what I was thinking.

    1995 Chevy Tahoe

  6. #6
    Legend

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    Usually bigger tires give the illusion of DECREASED MPG.
    You odometer says you went 57 miles, but you actually went 60 miles. You'll figure you traveled 228 miles when you actually went 240 miles(for example)
    You will divide the 10 gallons into 228 miles and get 22.8 mpg- when you actually got 240/10= 24 mpg.
    Your odometer reads wheel turns, or transmission exit shaft turns or driveshaft turns or whatever.It doesn't know you have a 33.5" tire instead of the 32" that came stock(just a guess the 285 might be even taller).
    With bigger tires you are actually going father and faster each wheel turn, but your "COMPUTER " doesn't know that.
    Charlie
    1998 suburban-
    1/2 ton

    199500 miles
    River
    Ridge,LA

  7. #7
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    stephan's Avatar
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    Quote Originally Posted by mfleetwood View Post
    Not sure what size your previous tires were, but when I went from 265s to 285s, it also had an effect on my speedometer...which in turn threw off the odometer. If I remember correctly, at 60mph, it was reading 57mph...this will give you the illusion of increased mileage since your truck thinks you are going further on a tankful of gas than you actually are.
    You wrote this right for going to bigger tires, but it is the opposite effect of what you explained Mikey. With taller tires it doesn't put as many miles on the odometer as what you've actually traveled (just as you stated), so it would show worse mpg than what you're actually getting.


    Big Bill, Cranking your T bars up has made the suspension stiffer & is why your truck handles & corners so much better now. I think this was a win-win for you
    1988 Chevy C-3500 2wd (no pic)
    350 c.i. 5.7 L Stock Block, 4 Bolt Mains
    L-31 Vortec Heads, Edelbrock Cam & Intake,
    Holley 650, Flowtech Headers, Magnaflow exh.
    Jet Trans 700R4, B&M Ratchet, 4:10 gears,
    3" susp. lift kit "shadetree"
    No rev limiter, No speed limiter lol


  8. #8

    Default

    If vehicle MPG's could be improved by simply putting bigger tires on. Gm would have done that. The best tire size for your vehicle for best mpg's is the size the manufacturer puts on the vehicle.

    As stated above. Changing tire size caused your speedometer to be inaccurate.

    IF your stock tire size was 265/70/17 and you went to 285/70/17 your speedometer would be off 3.490% too slow. If you were actually going 60 mph your speedometer would read 57.9 mph.
    Last edited by 1flyfisher; 02-15-2011 at 06:58 PM.
    2010 GMC Savana AWD
    Silver Metallic, 5.3L, 3.73 Gears and G80 Heavy Duty Locking Rear Differential, American Racing Off Road Series ATX Chrome Assaults 17X8, BFG T/A KO's 245/70/17 (Stock Size).
    Alpine ida-x303 head unit, Alpine Power Pack, Alpine SPS-600 Speakers
    Viper 350HV car Alarm
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  9. #9
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    mfleetwood's Avatar
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    Default .......................

    Quote Originally Posted by stephan View Post
    You wrote this right for going to bigger tires, but it is the opposite effect of what you explained Mikey. With taller tires it doesn't put as many miles on the odometer as what you've actually traveled (just as you stated), so it would show worse mpg than what you're actually getting.
    Yeah,yeah...you guys are right...my bad. I knew it was something like that. However, I forgot to mention that I spent the majority of my time on ice driving uphill, thus my tires were spinning faster than I was going. I guess I left that critical piece of information out.


    Mike (Denver, CO) - 2008 Sierra 1500 Z71 SLE 5.3L 4WD

    SUSPENSION: Rancho 4" Suspension Lift; Rancho RS9000XL Shocks; Rancho Skid Plates; Rancho MyRide Wireless Shock Controller;
    TIRES:
    BFG All Terrain KO 315/70/17
    DRIVE TRAIN: 4.56 Gears; Detroit TrueTrac Differential; True Cool 40k Transmission Cooler
    PERFORMANCE: DiableSport Predator Tuner; Custom Tuned by Diablew; Magnaflow Exhaust; AFE Cold Air Intake
    ELECTRONICS: Kenwood DNX6180 Touchscreen; Subthump box w/10" Kicker; Driver Information Center (DIC); Rear View Camera
    ACCESSORIES: Westin Brush/Grill Gaurd; Westin Nerf Bars; Truxedo Tonneau; 20% Tint; Tow Mirrors w/Heat & Signals

  10. #10
    Jr. Apprentice
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    Default

    Quote Originally Posted by 1flyfisher View Post
    If vehicle MPG's could be improved by simply putting bigger tires on. Gm would have done that. The best tire size for your vehicle for best mpg's is the size the manufacturer puts on the vehicle.

    As stated above. Changing tire size caused your speedometer to be inaccurate.

    IF your stock tire size was 265/70/17 and you went to 285/70/17 your speedometer would be off 3.490% too slow. If you were actually going 60 mph your speedometer would read 57.9 mph.
    Then DAMN I was going WAY too fast! I was figuring I was going around 72 mph to 75 mph the whole trip...no wonder everyone was going so dang slow. OK, so if my speedo was reading 72 mph I was roughly going approx 75 mph. So, if I was going 75 to 79 mph the whole trip and traveled 200 miles according to the ODO (which is actually approx 207 miles) then dang, this truck isn't doing too bad.

    As far as the wind, it typically blows from the south most of the trip which would have hit me on the passenger side on the way up and drivers side on the way down...except for over Donner Pass where it's a headwind when your going down the slope on the way up to Reno and when you're pulling the slope back to California you don't get any wind except from the south again (the two directions of the highway are divided by a mountainside). My point is that the wind isn't favorable for driving the majority of the time.

    I'll need to check around town mileage in another 100 miles to get an average. I'll repost the results here...

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