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  1. #1
    Sr. Apprentice GeorgiaZ71's Avatar
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    Loganville, GA
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    Default New tires - is a speedo adjustment necessary?

    Hi All,

    I tried using the search function, and I didn't find anything. So sorry if this has been asked a thousand times!

    So within a 2 weeks of getting my 2014 (150 miles on her), I had the level kit and bigger Wrangler Duratracs put on.

    My question is, going from a 265/60/18 to a 275/70/18 - is my speedometer / odometer off you think? I guess I could download some GPS app on my phone and test it...but thought I would ask here first.

    If it is - what's the recommended point for getting the old tune and reflashing the ECM? If the speedo is off by just a little - would you still recommend? (Obviously if it's like 7+mph off, I think I would... but what if it's only 2-3mph off?)

    Thanks!
    2014 Chevrolet Silverado Z71 4x4 | 2.5" level/lift | 275/70/18 Goodyear Wrangler Duratrac

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  3. #2

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    Quote Originally Posted by GeorgiaZ71 View Post
    Hi All,

    I tried using the search function, and I didn't find anything. So sorry if this has been asked a thousand times!

    So within a 2 weeks of getting my 2014 (150 miles on her), I had the level kit and bigger Wrangler Duratracs put on.

    My question is, going from a 265/60/18 to a 275/70/18 - is my speedometer / odometer off you think? I guess I could download some GPS app on my phone and test it...but thought I would ask here first.

    If it is - what's the recommended point for getting the old tune and reflashing the ECM? If the speedo is off by just a little - would you still recommend? (Obviously if it's like 7+mph off, I think I would... but what if it's only 2-3mph off?)

    Thanks!

    There are a couple of reasons you would want to have the Trucks Computer Re-Programmed to Correct your Speedometer Readings,
    which will Be Off with this change in Tire Size(As Shown Below).....as the Vehicle’s Computer Calculates your Speed based on the Diameter of the Stock Tires, and with this Change in Tire Size, the Vehicles Computer doesn’t know how Fast your Vehicle is going......also with this change in Tire Size, your Transmission may Not Shift Correctly......

    Most Hand-held Programmers have the feature of Correcting the Speedometer Readings, when there's a Change in Tire Size and/or Change in Gear Ratio.



    Here are the Specs for Both Tire Sizes you've mentioned

    Typical Weight ~ 26 lbs / 12 kg ~ 18 lbs / 8 kg
    Tires: Tire 1 Tire 2
    Tire size 265/60-18 275/70-18
    Section width 265 mm (10.4'') 275 mm (10.8'')
    Sidewall 159 mm (6.3'') 193 mm (7.6'')
    Tire Diameter
    775 mm (30.5'') 843 mm (33.2'')
    68 mm (8.8%) taller.
    Rim sizes 18x7.5 to 18x10 18x7.5 to 18x10.5
    Circumference 2434 mm (95.8'') 2647 mm (104.2'')
    Revs per mile 661.3 608
    Speedometer Assuming that this is OEM tire and speedometer readings are correct >>> Speedometer reads 60mph actual speed will be 65.3mph 8.8% faster.

    Edit:....IMO....you should have the Speedometer Corrected, for this Change in Tire Size.

    Last edited by 99'HEARTBEAT; 11-21-2013 at 05:33 PM. Reason: Added some more Infor.

    MIKE


    99"SILVERADO
    5.3 l 3.73 l G80
    BLACK BEAR CUSTOM TUNE
    SNUGTOP l COLORMATCH l KATZKIN










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  5. #3

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    GPS tells you how fast, you are going! If not, GPS model? Yes.. Get a "SCT" programmer, http://www.sctflash.com/index.php I am not a rep, just a Owner of their product.
    2010 GMC SIERRA CREW CAB (Silver) 4x4, ReadyLift 2.5" Level Kit, 305/60/18 Dick Cepek Mud Country, Go Rhino Nerf Bars, Husky Liners front and rear, Bushwacker Bed Rail Caps, Custom tuned. 4:11's

  6. #4

    Default

    Sounds like an excuse for a custom tune with a diablo tuner from @06MonteSS to me!! There are a bunch of satisfied customers of his here.

    1995 Silverado 4x4
    6" BDS Suspension Lift-3" Body Lift-Add A Leaf in rear -Trailmaster SSV Shocks-Duel Steering Stabilizer Kit -AirAid Cold air intake-
    4.56 Gears with Detroit Auburn Locker-Pro-Comp Traction Bars with duel shocks-Aluminum Skid Plate Kit-38.5" x 16.5" Mickey Thompson Baja Claws-Constant Dropping fuel gauge

    2005 Yukon XL Jet Power Programmer, Bilstein Shocks, Bilstein rear springs, Helwig Anti-sway bars, EGR Window Visors, EGR Hood Shield, Denali Headlights, Headlight harness upgrade, GE NightHawk Bulbs, White Night Rear lighting system, Russell Braided SS brake lines, PowerStop Brake pads, PowerStop cross drilled and Slotted Rotors, http://www.gmtruckclub.com/forum/sho...5-GMC-Yukon-XL
    2002 Silverado ext cab 2wd (Sold)
    2003 Yukon XL (Totaled)

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  8. #5

    Default

    Quote Originally Posted by Pikey View Post
    Sounds like an excuse for a custom tune with a diablo tuner from @06MonteSS to me!! There are a bunch of satisfied customers of his here.
    I second the tune from Lew. My truck is a beast since he's been working on it. And we're not yet done! For the price you can't beat it!

    2011 Chevrolet Silverado 5.3L LT
    Line-X bed--Line-X Aries Step Bars--Blacked out bow ties--Flowmaster exhaust--Black low-profile UWS toolbox--Weathertec floor mats--5% tint all around--2" leveling kit--Removed front air dam--K&N 77 Series CAI--Diablo Trinity--Diablew custom tune...

  9. #6
    Sr. Apprentice GeorgiaZ71's Avatar
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    Loganville, GA
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    Default

    Quote Originally Posted by JimmyA View Post
    GPS tells you how fast, you are going! If not, GPS model? Yes.. Get a "SCT" programmer, http://www.sctflash.com/index.php I am not a rep, just a Owner of their product.
    Well, I just use my Chevy MyLink system for Navigation now... and sometimes my phone. But now that you mention it, my old TomTom GPS did give me a speed readout. But the current system doesn't display my actual speed. I will check into both an SCT or Diablo Tuner. I was thinking about exhaust and CAI...I might as well order it all with the tuner. Shopping time! Thanks everyone!

  10. #7

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    There are some iPhone / Android apps that will give you your speed and other driving information as well, they can be very useful in helping to determine how much off you are.

    Steve
    10 Chevy Traverse LT AWD
    02 Chevy Trailblazer LS (110K+ miles - loaded except for 4WD - WRECKED!)
    99 Chevy Cavalier LS (105K+ miles - commuter car)
    78 Chevy Suburban Silverado (454, 3/4 ton)
    62 GMC 3/4 ton Pickup (350 police interceptor)

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