I’ve just changed the tyres on my 2007 TDV8 from 275/40/20 to 255/55/20 much better ‘off-road’ and a little more comfy on road, I’ve noticed that it now appears to ‘hang on’ before changing up gears and changes down down earlier, the MPGs also dropped from 28 to 20, does this hanging on have any ill effect? do I need to ‘tell it’ the tyre size is bigger?
Is there a re map I should consider?
Not to worried about MPG but have had 2 coolant leaks since, just wondering if everything is working harder??

that tyre change shouldnt have effected any thing ..check your hoses ... - .- -.




Y. O. L. O.
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Cheers Stan I’ve found the leaks guess they could just be age related, was just concerned that everything was working harder since the change and if I should address it

sorry , i meant your turbo hoses, they tend to get splits ... ... - .- -.




Y. O. L. O.
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Would they only affect the MPG?

There's a thread somewhere on here where somebody had changed their tyres from 255 50 to 255 55 and was having similar issues.

a loss of 8 mpg shouldn't happen..coincidence, but i reckon it's the turbo hoses.. ... - .- -.




Y. O. L. O.
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There was a chap on here who was saying that when he switched to 255 55 tyres on his supercharged it rarely ever went into top gear afterwards hence had a similar drop in fuel economy.

I had a quick look for the thread yesterday but couldn't find it. It was within the last month or 2.

Page 2....
http://www.fullfatrr.com/forum/post460980.html#460980

he says its holding gears and not going into 6th but i thought that was all related to the engine rpm..even at a steady 50mph the auto box should go into top gear .. ... - .- -.




Y. O. L. O.
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Putting on bigger tyres simply ups the gearing and as you can see by the photo that chap has posted, brand new 55's are a lot taller than worn out 50's

The rpm probably isn't going up high enough to get into top gear.

this is all beyond my knowledge level but i thought that even at low speed [50mph?] the auto box should go into its highest gear.. ... - .- -.




Y. O. L. O.
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going from a 40 to a 55 in tyre wall height will most definitely effect the speedo reading pal , you can get away with 5 either way without it effecting it but going 15 will defo upset it , as for the MPG thing , reckon its mechanical as the others have already suggested

andy's '40' profile is wrong for the FF anyway, it should be '45'...... ... - .- -.




Y. O. L. O.
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oh right