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| Crafty1980 Member Since: 21 Jul 2014 Location: Norfolk Posts: 74  
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I've just been reading this months LRO mag and the first article about the black TD5.
He's put on cooper discovery SST tyres at 285/75 R16... But my standard tyres on my XS are 235/85 R16... So doesn't that mean he's put on smaller diameter wheels that standard?!? They look much bigger than standard on the pics in the magazine! ...or am I a nonce and getting something wrong?? |
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5th Oct 2014 11:30am |
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| AndrewS Member Since: 10 Apr 2007 Location: Hereford Posts: 3707 
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To keep the rolling radius as close as possible to the original spec, the side wall dimension is reduced as the tyre width increases.
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5th Oct 2014 1:06pm |
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| Crafty1980 Member Since: 21 Jul 2014 Location: Norfolk Posts: 74
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Oh it's a PERCENTAGE! DOH. For some reason I always thought the 75/85 etc was the actual depth of the wall. i.e. 75mm 85mm etc... That explains a lot!
Everyday is a school day!   |
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5th Oct 2014 2:47pm |
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| munch90 Member Since: 26 Oct 2013 Location: guildford Posts: 3558 
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if you need to different check sizes etc there are quite a lot of tyre websites that have tyre calulators on them , put old size and new size and its gives you rolling radius , height & % etc etc
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5th Oct 2014 2:56pm |
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| NJSS Member Since: 26 Aug 2014 Location: Catherington Posts: 30
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This site may help:-
http://www.alloywheels.com/Tyre_Calculator NJSS 2016 Discovery 4 Landmark 2011 Mercedes Benz SL350 (R230) 1973 MG B GT V8 - 3.9L John Eales engine, 5 speed R380 gearbox, since 1975. 1959 MGA roadster - 1.9L Peter Burgess Engine - 5 speed gearbox Past LRs - Multiple FFRs, Discos & a Series I - some petrol, some diesel, none Electric yet. There are 10 types of people in this world: Those who understand binary, and those who don’t. |
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5th Oct 2014 2:57pm |
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| Crafty1980 Member Since: 21 Jul 2014 Location: Norfolk Posts: 74
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Ok, so the guy in the magazine has increased his overall tyre size quite a bit then by all accounts.
So what happens then with things like VOSA? MPH gauge? He's going to increase the amount of power needed to push off from first gear too I'm guessing? Or is it so negligible that there's no need to worry about it? |
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5th Oct 2014 3:46pm |
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| munch90 Member Since: 26 Oct 2013 Location: guildford Posts: 3558
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they say you shouldn't go above 2.5% difference , if you use a tyre calculator it will tell you the % gain or loss , yes if you go up or down in tyre size diameter gearing will change (bigger tyre diameter slower pull away higher top speed (if engine will pull the higher gearing ) smaller diameter faster pull away , slower top speed
235 85 16 is a tall ish tyre anyway as standard profile is 80 sometimes marked as 235/16 or 235/80/16 there difference is 3.47% (that's if his standard tyre was a 235/85/16 and new was 285/75/16 ) so really a bit over what they recommend , but maybe he has altered speedo ratio to suit each tyre size if fitted as standard will have its own speedo ratio unless they all come out same diameter |
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5th Oct 2014 6:26pm |
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| blackwolf Member Since: 03 Nov 2009 Location: South West England Posts: 16879 
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I run 285/75 R16 BFG KMII Muds and the speedo is now spot on when checked with a Home Office approved device. All vehicles have speedos which over-read (indicate a higher speed than you are travelling at) by design. Larger tyres often compensate for this.
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5th Oct 2014 9:13pm |
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| dorsetsmith Member Since: 30 Oct 2011 Location: South West Posts: 4554 |
land Rover 90/110 speedo drive gears
Colour: blue/20 teeth - Part number: FRC3310 - Tyres: 7.50/16 or 235/85/16 Colour: green/21 teeth - Part number: FRC3311 Colour: yellow/22 teeth - Part number: FRC3312 - Tyres: 205/16 tyres Colour: red/24 teeth - Part number: FRC3313 |
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5th Oct 2014 9:30pm |
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| Crafty1980 Member Since: 21 Jul 2014 Location: Norfolk Posts: 74
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Is the speedo on new Pumas still analogue gears? Or are they now controlled as part of the ECU?
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6th Oct 2014 8:28am |
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| carrotbay Member Since: 18 Aug 2013 Location: Northants, UK Posts: 695 
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Ashcroft do a 'speedo correction kit' for Puma Defenders. This would solve the problem, although I found that running 285/65 18s my speedo is now spot on rather than slightly optimistic as standard.
http://www.ashcroft-transmissions.co.uk/sp...n-kit.html 2008 Defender 110 XS SW - M57N2 / 6HP28X |
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6th Oct 2014 8:50am |
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