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Author Topic: just fitted 18" and mpg reading on display has dropped by 10mpg  (Read 3612 times)

Offline rugbymad

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just fitted 18" and mpg reading on display has dropped by 10mpg
« on: 10 February 2009, 14:42 »
just fitted my alloys on fri and now my mpg disply has dropped by 10mpg. it was around 47 ish now at 35 ish, will these wheels make a big difference? do i need to adjust anything in vagcom

thx in advance

steph
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Offline DJGTi

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Re: just fitted 18" and mpg reading on display has dropped by 10mpg
« Reply #1 on: 10 February 2009, 17:06 »
Ideally, you should have lower profile tyres on to keep the rolling radius the same. Even if you haven't, there shouldn't be that big a difference (maybe 2-3mpg). What size tyres did you have, and what are they now?
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Offline rugbymad

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Re: just fitted 18" and mpg reading on display has dropped by 10mpg
« Reply #2 on: 10 February 2009, 17:11 »
i had 205/55/16 and now have 225/45/18 . i checked the tyre pressure today they were down at 30 psi now at 35.  i need my mpg back lol
steph

ps the wheels are now on another thread to view
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Offline Egbutt Wash

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Re: just fitted 18" and mpg reading on display has dropped by 10mpg
« Reply #3 on: 10 February 2009, 18:20 »
Queer as hairy eggs.
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Offline rugbymad

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Re: just fitted 18" and mpg reading on display has dropped by 10mpg
« Reply #4 on: 10 February 2009, 19:23 »
i know i'm gutted
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Offline bobbarley

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Re: just fitted 18" and mpg reading on display has dropped by 10mpg
« Reply #5 on: 10 February 2009, 19:25 »
Correct me if I'm wrong, but you should be using 225/40/18's?  :undecided:
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Offline bacillus

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Re: just fitted 18" and mpg reading on display has dropped by 10mpg
« Reply #6 on: 10 February 2009, 19:33 »
Quote from: bobbarley on 10 February 2009, 19:25
Correct me if I'm wrong, but you should be using 225/40/18's?  :undecided:
You are correct!
The tyres he's using have a greater circumference than standard and will alter speedo speed and mpg readings.
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Offline bobbarley

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Re: just fitted 18" and mpg reading on display has dropped by 10mpg
« Reply #7 on: 10 February 2009, 19:34 »
Thought so.  You're going to need 4 new tyres  :embarassed:
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Offline rugbymad

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Re: just fitted 18" and mpg reading on display has dropped by 10mpg
« Reply #8 on: 10 February 2009, 19:41 »
what size should i have then? how much will my speedo be out by
thx
steph
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Offline bobbarley

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Re: just fitted 18" and mpg reading on display has dropped by 10mpg
« Reply #9 on: 10 February 2009, 19:42 »
You need 225/40/18 more often than not.
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