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  1. #1
    Jr. Mechanic b-radical's Avatar
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    Default How to get right gears for my tires and adjust transmission

    I have been running my 265/70/16 tires on my silverado since I got it. The truck is supposed to have 235/75/16 tires. I would like to change the gears in the diff to fit the tires I have, and put in a g80 rear locker at the same time. How do I go about finding the right gears?

    I would also like to adjust the transmission to run properly with the bigger tires. I think the shift point would be adjusted but I'm not sure.

    Can anyone help with this?
    Thanks.


    2000 Silverado, 4.8L, LS
    3" Dynomax cat back exhaust
    Drop-in K&N air filter
    200 amp Nations alternator
    KYB GR2 Shocks
    Bluetooth OBD2 adapter with Torque App on Samsung Note 2
    Custom Stereo System l Pioneer/ Boss door Speakers l 1200 watt Performance Teknique amp l 1 farad capacitor l 2 12" kicker comp subwoofers
    Slider rear window l Locking tailgate, de-baged l 265/75/16 Bridgestone Dueler H/L tires l Fully synthetic oil l Tinted windows
    4l65e upgrades - five pinion planetaries l HD sun shell l high performance band

  2. #2

    Default

    Regarding gear ratio:
    You'll need a hand-held programmer that's capable of adjusting gear ratio size so that after you've got the new gears into the vehicle you aren't throwing error codes/idiot lights. You might as well make sure that tuner will also allow you to adjust your shift points. You can do it, yourself, or if the tuner you get is a Diablosport then you can work with someone like Diablew (a site sponsor, here) to get a custom tune. Lew sells bundles (i.e. device + custom tune) and his pricing is very reasonable for his services ... especially if bundled, so you might reach out to him if interested. He goes by @06MonteSS, here.

    Now, as for the gear ratio choice, you will need to convert your new and old tire sizes from metric to inches. Here's a tool that'll help: http://www.miata.net/garage/tirecalc.html

    From there you can eyeball the proper ratio using a Jeep chart like this one, with the understanding that this chart assumes a manual transmission with a 1:1 ratio (i.e. no overdrive engaged) at 65mph:
    Click image for larger version. 

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    You can do more precise, Chevy-specific calculations, using tools here: http://www.4lo.com/calc/gearratio.php

  3. #3

    Default

    thats not that much of a tire size change between the two sizes. dont know which axle you have, but i would see if i could find a axle in a junk yard that had close the right gear ratio, correct the speedo, and be done with it. to put a set of custom gears in and buy a G80 wouldnt be cheap.

    I cant see a junkyard axle costing much more then $250, and if you find the right one, it should bolt right in, dont know how mechanically inclined you are, but it is something u could do in your driveway.

    Alex


    2011 GMC Sierra SLE 5.3 Z71 4X4 Stealth Gray Metallic / 2004 Chevy Impala LS 3.8 Cappuccino

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  4. #4

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    Yeah sierra is right. Your diameter difference is only like 7/10 of an inch larger on the 265 tires. its only throwing your spedometer off like 2mph at 65. Here is the formula though to figure out your gearing for different size tires.
    To bring your truck back to stock performance, it is important to re-gear the truck accordingly. A simple calculation will tell you what gear ratio would get you back to your stock equivalent. The calculation is your new tire diameter in inches, divided by your old tire diameter in inches, multiplied by your old axle ratio, will equal your new axle ratio (new tire diameter/old tire diameter x current axle ratio = new axle ratio).

    Your stock tire diameter is 29.9 inches and your larger tire diameter is 30.6 inches. Not sure what gear ratio you have but I think this info will tell you what you need to know.




    2011 Silverado CrewCab 5.3L*Ram Air Look Cowl Induction Reflexxion Hood*6" Pro Comp Lift*Flowmaster Dual exhaust*Perfect Launch Rear Diff. Cover*Led Smoke Taillights*L.E.D.Smoke 3rd Brakelight*60" L.E.D. Tailgate Bar*Rearview Mirror Reverse Camera and Sensors*Smoke Headlight Covers*Front Bumper Grill Insert*Deezee Black Alum. Diamond Rail covers*20" Ultra Motorsports Rims wrapped with 35.5"B.F. Goodrich Tires*Inchannel Raingaurds*CAI*Bullydog GT Tuner*Alpine Amp*Boss 6x9's*Boston Acoustic Subs*Terrantula Tweeters*Custom Sub box*Red Led Interior Accents*5% Ultimacool duo tint rear window and doors, 20% front doors*Custom Vinyl Graphics*Demolded*Debadged*Painted drums and calipers*
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  5. #5

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    I personally wouldn't regear for that small a change in tire sizes, either. But hey, some people do...

  6. #6
    Jr. Mechanic b-radical's Avatar
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    Default

    Thanks for all the good feedback guys. I don't think ill be going through with the gear change considering all the suggestions. However, I will be putting in a G80. I vaguely remember a link for a website than allows you to put in your vin # and get all the stock equipment your truck came with. Does anyone have that link?

    Thanks again,
    Brad


    2000 Silverado, 4.8L, LS
    3" Dynomax cat back exhaust
    Drop-in K&N air filter
    200 amp Nations alternator
    KYB GR2 Shocks
    Bluetooth OBD2 adapter with Torque App on Samsung Note 2
    Custom Stereo System l Pioneer/ Boss door Speakers l 1200 watt Performance Teknique amp l 1 farad capacitor l 2 12" kicker comp subwoofers
    Slider rear window l Locking tailgate, de-baged l 265/75/16 Bridgestone Dueler H/L tires l Fully synthetic oil l Tinted windows
    4l65e upgrades - five pinion planetaries l HD sun shell l high performance band

  7. #7
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    mfleetwood's Avatar
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    Default

    Here are a couple of links that will help....also, if you have a 4wd, just make sure the gears in the G80 you are getting are the same ratio as your current set up or you will need to change the ones in the front diff to match.

    http://www.compnine.com/vid.php?vin=&x=22&y=6
    http://www.decodethis.com/
    Last edited by mfleetwood; 06-08-2012 at 10:43 AM. Reason: added additional link


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

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  8. #8
    Jr. Mechanic b-radical's Avatar
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    Default

    sweet , Thanks!


    2000 Silverado, 4.8L, LS
    3" Dynomax cat back exhaust
    Drop-in K&N air filter
    200 amp Nations alternator
    KYB GR2 Shocks
    Bluetooth OBD2 adapter with Torque App on Samsung Note 2
    Custom Stereo System l Pioneer/ Boss door Speakers l 1200 watt Performance Teknique amp l 1 farad capacitor l 2 12" kicker comp subwoofers
    Slider rear window l Locking tailgate, de-baged l 265/75/16 Bridgestone Dueler H/L tires l Fully synthetic oil l Tinted windows
    4l65e upgrades - five pinion planetaries l HD sun shell l high performance band

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