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18-02-2014, 10:15 AM
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66 Mustang
Join Date: Jan 2009
Location: Townsville, QLD
Posts: 206
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My AU 2 XR8 (Auto - 3:45 LSD) has 235/45 17 tyres on it but the speedo is 4-5% slow ie. sit the speedo on 104-105, car is doing 100.
As most 75% of my driving is on the highway in 100 zones, it is quite frustrating. I was thinking I could use a speedo corrector, ie. like the jaycar one, or change the speedo gear to one for a 3:23 ratio auto. But... Running 235/50 or 245/45 tyres could fix the problem and give a slightly better ride. I had 235/50 tyres on the other AU ute and the speedo was spot on, I have 245/45 on the back of that one now and the car does 98-99 when reading 100 on speedo, which I'm cool with... What are your thoughts? |
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18-02-2014, 01:43 PM
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Next upgraded Mk1 Leopard
  
Join Date: Jan 2005
Location: Sydney, in the burbs
Posts: 4,903
 
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I know everyone like a 'low look' but everyday drive I'd take the better ride path.
UK
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Plastic Surgery 1 AUII Monsoon Blue How 2's: Change rear view mirror, Install backfire valve, Change foam front seats, Install auto transmission cooler, Replace Trans Shift Globe, Remove front door Trim, Paint AU headlights, install door spears, Premium Rear Parcel Shelf, go here...
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18-02-2014, 05:08 PM
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CNC fixer guy
Join Date: Sep 2006
Location: Melbourne Vic
Posts: 609
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I had 235 45 r17 all round on 3.23:1 fairlane, the speedo was like yours (a few km out).
I ended up fitting 255 45 r17 (not such a common size) to fill the rear guards a bit (max legal width tyre for an 8 inch wide 17 inch diam rim). The speedo is now spot on with the gps. 245/45 would be good, go for it.
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Weekend Toy: S1 AU Fairlane V8 with LTD bits, Tickford 17" wheels, front and rear chin spoilers, series 2 front brake conversion with Super pro bushes, Pacemaker headers, rear muffler removed, Kings/Pedders lowered suspension, Koni adj rears, painted headlight bezels, HR 2300kg hitch, 2 stage shift kit, trans cooler, reverse cam and media player. Wife unit's : 2010 update FG XR6, reverse cam, HR 2300kg Hitch, German Maestro speakers, parcel shelf sub, trimmed mudflaps, batman stickers. |
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19-02-2014, 01:13 AM
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Miami Pilot
 
Join Date: Jan 2005
Location: ACT
Posts: 21,701
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245/45 is what is standard for commodores, I think, so would be cheaper than a 235/50, and would give the same overall diameter.
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The Hammer: FG GTE | 376rwkw | 1/4 mile 11.793 @ 119.75mph 1.733 60' (4408lb) 1 of 60 FG MK1 335 GTEs (1 of 118 FG Mk 1 & 2 335 GTEs). Mods: Tune, HSD/ShockWorks, black GT335 19” staggered replicas with 245 & 275/35/19 Michelin Pilot sport 5s Daily: BF2 Fairmont Ghia I6 ZF, machine face GT335 19” staggered Replicas with 245s and 275s, Bilsteins & Kings FPV 335 build stats: <click here> Ford Performance Club ACT |
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19-02-2014, 05:31 AM
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66 Mustang
Join Date: Jan 2009
Location: Townsville, QLD
Posts: 206
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Fg started with 235/50, changed to 245/45 in 2010/2011.
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19-02-2014, 06:20 PM
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5.6L x 2 pilot
Join Date: Dec 2009
Location: Canbra
Posts: 14,897
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104 at 100 I have found to be pretty standard. So to bring the speedo down, you will need a larger rolling diameter.
This site might help. http://tire-size-conversion.com/tyre-size-calculator/ Cheers Stu
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2002 AU II LTD 5.6L 342ci T3 Short, AFR165 heads, Comp XE270HR-12 Cam, Brembo 4/4s(355/330), T3 5 spokes, LC-1 wideband, Whiteline HD swaybars, TCE 3K Hi Stall, PWR Auto Trans Cooler, Koni shocks, King Low Springs, Hurricane headers, 100 cpsi cats, Twin 2.5" exhaust. Quarter Mile: 13.73 @ 105.86mph Runner Up NA/DA to BF Fairlane/LTD Geelong AFD 2024  2002 XR8 pursuit 250 Custom twin 2.5" exhaust w Herrod modifed extractors, Tuned with Moates QH
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19-02-2014, 07:34 PM
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Next upgraded Mk1 Leopard
Join Date: Jan 2005
Location: Sydney, in the burbs
Posts: 4,903
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Quote:
 UK
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Plastic Surgery 1 AUII Monsoon Blue How 2's: Change rear view mirror, Install backfire valve, Change foam front seats, Install auto transmission cooler, Replace Trans Shift Globe, Remove front door Trim, Paint AU headlights, install door spears, Premium Rear Parcel Shelf, go here...
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19-02-2014, 10:19 PM
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CNC fixer guy
Join Date: Sep 2006
Location: Melbourne Vic
Posts: 609
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If you cant be bothered with metric to imperial conversion then you can try this one too:
http://www.willtheyfit.com It also has a handy visual reference in regards to wheel widths and offsets. Cheers.
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Weekend Toy: S1 AU Fairlane V8 with LTD bits, Tickford 17" wheels, front and rear chin spoilers, series 2 front brake conversion with Super pro bushes, Pacemaker headers, rear muffler removed, Kings/Pedders lowered suspension, Koni adj rears, painted headlight bezels, HR 2300kg hitch, 2 stage shift kit, trans cooler, reverse cam and media player. Wife unit's : 2010 update FG XR6, reverse cam, HR 2300kg Hitch, German Maestro speakers, parcel shelf sub, trimmed mudflaps, batman stickers. |
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Changing tyre size on XR8 - 17 inch.
Linear Mode
