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    Thread: Choosing the right offset (ET)

    1. #1

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      Choosing the right offset (ET)

      Dear GH experts,

      I have pretty much understood the tyre bible except choosing the right offset (ET). I had upgraded to 175/70 R13 for my A-Star as opposed to the stock (155/80 R13) and still running on the stock rims (R13 * 4.5j). My next upgrade would be using the plus size concept to 185/60 R14 which would match the stock specs exactly.

      Now the important aspect is to choose right alloys with the right PCD and offset so that we do not end up with scary fouling issues. When we upgrade, should the offset match the original spec? If not, What is the allowed variance of the offset? When the tyre width increases, the offset should be reduced? I am confused. Is there a technical math around this? Please provide your expert opinion. Thanks!


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      Can someone please provide an answer? Appreciate your inputs!
      It's what you learn after you know it all that counts.

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      I take the liberty to provide an answer to my own query since I went thru this exercise. Experts, please correct me if I am wrong.

      I noticed the mostly people focus on the PCD values. Offset (ET) does play a big role in choosing the right alloys.

      When selecting aftermarket wheels, a wheel with too little positive offset will be closer to edge of the fender, and one with too much positive offset will tuck inside the fender and be closer to the suspension components.

      For A-Star:-

      Stock Offset = 38mm
      Stock Tyre width = 155mm


      Offset of alloys=35mm
      Upgraded Tyre width = 175mm

      The edge of the new tyre will be (175-155) / 2 - (38 - 35) = 7mm closer to the inside of the wheel well and suspension components, and (175 - 155) / 2 + (38 - 35) = 13mm further out from the edge of the bodywork. From this, we could notice that there won't be any fouling issues with the upgraded alloy/tyre combination.

      A simple thumb rule could that choose any alloys with an offset of {stock offset (+/-) 4 } to ensure no fouling issues after the upgrade.

      References to understand more:-

      Car Bibles : The Wheel and Tyre Bible Page 3 of 4

      Wheel Offset: Why It Matters, Look Cool Without Being A Dummy

      Measuring and Defining Wheel Offset

      http://en.wikipedia.org/wiki/Offset_(wheel)
      Last edited by revfriendly; 9th May 2011 at 15:41.
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      Astar Alloys

      Hey Bro... Thanks for the information.. Ive been asking everyone right from Maruti Service Executive to Mechanics.. None of them had a clue about the Correct Offset.. How did you find it out? Im Planning for an upsizing with 14" Rims and 175/65/R14 tyres... Whats your opinion on that.. Did you upgrade to R14? Did you notice any tightness in your steering wit your tyre change?

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      Quote Originally Posted by SoulCollector View Post
      Hey Bro... Thanks for the information.. Ive been asking everyone right from Maruti Service Executive to Mechanics.. None of them had a clue about the Correct Offset.. How did you find it out? Im Planning for an upsizing with 14" Rims and 175/65/R14 tyres... Whats your opinion on that.. Did you upgrade to R14? Did you notice any tightness in your steering wit your tyre change?
      I did not upgrade to 14 rims. I switched back to stock size (155/80 R13) with Stock A-Star alloys. They are doing great. I would suggest you to get stock alloys. Clocked 30k odd kms with stock alloys. Pristine condition.
      It's what you learn after you know it all that counts.

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