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Model specific boards => Golf mk5 => Topic started by: rugbymad on 10 February 2009, 14:42

Title: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: rugbymad 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
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: DJGTi 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?
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: rugbymad 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
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: Egbutt Wash on 10 February 2009, 18:20
Queer as hairy eggs.
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: rugbymad on 10 February 2009, 19:23
i know i'm gutted
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: bobbarley on 10 February 2009, 19:25
Correct me if I'm wrong, but you should be using 225/40/18's?  :undecided:
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: bacillus on 10 February 2009, 19:33
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.
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: bobbarley on 10 February 2009, 19:34
Thought so.  You're going to need 4 new tyres  :embarassed:
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: rugbymad on 10 February 2009, 19:41
what size should i have then? how much will my speedo be out by
thx
steph
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: bobbarley on 10 February 2009, 19:42
You need 225/40/18 more often than not.
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: rugbymad on 10 February 2009, 19:44
can this be changed via vag com?  gotta be cheaper than 4 tryes?
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: bobbarley on 10 February 2009, 19:45
I don't think so, as the tyres are throwing your speedo out as well.
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: rugbymad on 10 February 2009, 19:46
sorry just checked the tyres they are 225/40/18 and not the 45> thank f***.

still that aint helped really lol

steph
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: pazz on 10 February 2009, 20:15
sorry just checked the tyres they are 222/40/18 and not the 45> thank f***.

still that aint helped really lol

steph

Just about to say 225/45/18s are way out! And I'm assuming you mean 225/40/18.

Could be a lot heavier wheels, but 10mpg heavier - wouldnt really think enough to make that big a difference
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: Egbutt Wash on 10 February 2009, 22:22
205/55/16 gives a diameter of 16" (40.64 cm) + (20.5x0.55)x2 = 63.19cm, Circumference = 198.5 cm
225/40/18 gives a diameter of 18" (45.72 cm) + (22.5x0.4)x2 = 63.72cm, Circumference = 200.2 cm

So the new rubbers are just 0.8% bigger than the old ones. 

47 mpg would be 46.6 mpg.

35 mpg suggests you are feeling good about the new wheels and driving with some verve.
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: rugbymad on 10 February 2009, 22:29
LOL :grin: :grin: :grin: DO YOU KNOW I WISH I HAD BEEN TANNING IT BUT DECIDED TO KEEP SAFE DUE TO NEW WHEELS AND ROAD CONDITIONS SNOW ICE ETC.
but thanx for the calculations . by the looks of it it shouldnt make that much difference..

in my hyundai coupe i used to reset the ecu by disconnecting the batt and pumping the brakes to dischare any juice left, and when reconnected it would learn your drive style and resort to that. i.e if you drive like a nutter it put more juice in and reflects on the dash but if you drive carefully ..

can this be done on a mk5?

Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: winrya on 10 February 2009, 22:36
The rolling radius is exactly the same so should see no difference at all.  If they are genuine monza's they should be extremely light as they are made using a new bbs hollow technology.
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: No Golf Clubs at all on 10 February 2009, 22:49
How many miles had you driven before you arrived at the new figure and did you rely on the onboard computer or did you brim it and do the manual thang?
 
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: rugbymad on 10 February 2009, 23:44
those figs were off the computer but it always been at 47 ish, just brimmed it today so will run her dry to see what i am getting.
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: pw motorsport on 11 February 2009, 08:25
As suggested above, the weight of the wheels will affect performance and fuel economy.

I use a A6 2.0 TDI for long trips through Europe, I run a light 18" wheel. A few months back I sold the demo wheels and fitted some old 19" reps that I had.
The MPG was reduced from 48/50 mpg to 40/42 mpg. Plus it was a lot slower.
Title: Re: just fitted 18" and mpg reading on display has dropped by 10mpg
Post by: 2007GTI on 11 February 2009, 09:22
the fuel computer will need to settle down for a few days, so dont panic.