Not the usual tyre question

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Roders1

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Barnsley
just upgraded ( I think? ) from 97 disco 1 300tdi ES to a 99 disco 2 td5 ES. It is currently sat on 255/65/r16's on steel rims with a slightly deeper offset ( than normal ). Now although I like the look of the stance I don't like the look of the centres, as in able to see hubs & standing proud wheel nuts. So I have bought a set of alloys ( no tyres ) which are 7 1/2 J18" so with standard height suspension & body what size tyre would usually go on 18" rims on a disco 2 ?
 
Ooh, think I've just discovered how to add a picture
 

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Ooh, think I've just discovered how to add a picture

Tidy enough looking D2! :)
Sorry, but no idea what tyres you need, when I bought mine it had 18" wheels, I took it straight up the breakers and swapped em for a set of standard alloys with 235 75 R16. Cant remember what was on the 18s, but they were very wide, and only about a 45 ratio! :D
Quite like those steels, I would have got them if I had seen any, better for a working vehicle.
 
They're all the usual tyre questions!

First of all, I would check that those new alloy rims you've bought are going to fit, the stud layout isn't what you might call standard.
Looking at the owner's handbook, the only 18 inch wheel/tyre arrangement for the Disco2 is shown as 255/55R18, but that's for an 8Jx18 alloy rim, 7 1/2J isn't even mentioned.
The next down is for a 7Jx16 rim.
 
They're all the usual tyre questions!

First of all, I would check that those new alloy rims you've bought are going to fit, the stud layout isn't what you might call standard.
Looking at the owner's handbook, the only 18 inch wheel/tyre arrangement for the Disco2 is shown as 255/55R18, but that's for an 8Jx18 alloy rim, 7 1/2J isn't even mentioned.
The next down is for a 7Jx16 rim.

Think mine had fake RRS wheels when I bought it, the tyres were mahoosively wide, steered like a pig! :eek: :D

 
OK that's the first test done.
Working it all out, The 8J tyre width is 255mm and the 7J tyre width is 235mm, you don't have to be Steven Hawking to work out that the tyre width for 7 1/2 J needs to be somewhere between them, say 245mm.
Now the next bit is some calculating and it all works out around the diameter or as the tyre people say the standing height. It's the aspect ratio which sets the tyre wall height. An aspect ratio of 60 for a 245mm wide tyre will give a tyrewall height of 147mm.
Anyway, it all works out that to a diameter of 29" for a 255/55R18 and in your case, a tyre of 245/60R18 has a diameter of 29.5"
So the next problem is yours, find four tyres sized 245/60R18 but do check with your tyre fitter before you part with money.
 
Cheers Brian, so in your example would the + .5" higher or lower the gear ratio. Just trying to keep it somewhere near where it should be
 
With a difference of .5 inches in the diameter, the difference in the rolling circumferance will be .5x3.14159 inches which is 1.5707 inches.
this means that a 245/60R18 tyre is going to go an inch and a half further per revolution than a 255/55R18 tyre. IMHO such a "huge" difference just isn't worth getting all in a lather about.
 
Looks nice. But I bet you notice a difference in ride quality. For some reason D2's always ride firm and a bit more bumpy on 18's vs 16" rims.
 
Suspect that is probably down to the tyre tread more so. But if you are happy with it, that's all that really matters.
 
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