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Discussion Starter · #1 ·
I am thinking of upgrading to 18in wheels and I just need some info (I will probably forget it when I hear the exact prices but I already have a rough idea).

The wheels I am thinking of are 18inx8 and I need to know the following:
The C/bore is I assume 67.1mm on the E6?
I also assume the offset won't need to be changed? (ET38)

What tyre size do you recommend, the obvious is 235/40 but that makes an overal 11mm diameter difference whereas 225/40 only makes a 3mm difference. Will 225/40 be suitable on a 18inx8 wheel? Will an 11mm overall tyre diameter increase make a noticeable difference if I use 235/40?
Will 18inx8 wheels with these tyres cause any clearance problems (standard suspension, maybe lowered later)?

Sorry for so many questions, especially as I may not go ahead with it but any help would be appeciated :D
(and theres me thinking all those people who bought larger wheels were possers ;))
 
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Discussion Starter · #2 ·
225*40/18 is the right size. Any larger and the wheels will touch in the wheelarches and you need body mods.

Larger wheels are only an improvement if they are lighter or if you need them to fit a brake upgrade.
 
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Discussion Starter · #3 ·
HH6,

I'm in the same situation as you.

I also believe 225/40 18 is the right size. A change of 3mm in overall diameter (645 vs 642mm) will change final gear ratio in less than 0.5% (almost nothing). Deformation at incorrect pressure or even tire wear will account for more than that. I got the number from Michelin data sheets, and I'm sure other manufacturers specs will differ from those numbers.

According to Michelin, the ideal wheel for this size is 18x8, but the min. and max. range they recommend is 18x7.5 and 18x9.

Can anyone confirm if 38mm is the correct offset for 18x8 wheels? Which manufacturers are currently selling this size and offset?

What does 'C/bore' mean?

Thanks, and also sorry for posting so many questions and few answers.
 
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Discussion Starter · #4 ·
AFAIK - 67.1mm is the correct centre bore for all Evos, Starions, EX2000, VR4's.

Stud pattern is usually 114.3mm (4.5 ) 4stud pre evo3, 5stud evo4 on.

For tyre widths - rule of thumb is plus 1 to the wheel width and multiply by 25 - then pick nearest size.

8 wheel 8|PLS|1|EQU|9*25 |EQU| 225
8.5 8.5|PLS|1|EQU|9.5*25|EQU|237.5 - and amp;gt;235
9 9|PLS|1|EQU|10*25 |EQU| 250 - and amp;gt;245
 
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Discussion Starter · #6 ·
Thanks people.
I was confused as I worked out that 225/40 would be a better size than 235/40 (see the tyresize link below) yet blade had whacked 235/40 on his beastie (with 18inx8.5 rims). I assumed that the rim width was a factor in his selection and thanks Lightspeed for confirming it, I just didn't know what the ideal tyre width to rim width was and hence whether 235 was necessary.

Lightspeed,
I have just found (helps to read up on it!) that the rim width should generally be 90% of the tyre width for road use. I like your calc better though :D
I assume the offset can remain at |PLS|38mm for 8in rims (and likewise for 8.5in rims for Rallyman) with no clearance or other problems?
On a seperate note, I have filled in a load more stuff on your spreadsheet but I have not finished yet, I will send it back when done.

Claudius,
The only reason for going for 18in's is that the 18in's rims I am thinking of getting are the same price as the 17in's so it seems silly not too ;)
I have no performance reasons for going for 18in's only practical ones, in fact I may still go for 17in's or when I see the prices the whole idea may not seem so practical after all!

Rallyman,
The centre bore is the diameter of the centre of the rim to allow the best centring fitment on the hub. Not many people quote it so note it down - 67.1mm, saves the old tape measure :)

Some useful links that I think Chunky originally posted on here years ago (been in my favourites ever since ;))
http://www.tyresave.co.uk/tyresize.html
http://www.tyresave.co.uk/choose.html
http://www.tyresave.co.uk/fitment.html
 
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Discussion Starter · #7 ·
HH6

Why not fit 235 /35/18 tyres which will not only give you a better match on the rolling diameter but in my opinion will also look better :)
 
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Discussion Starter · #9 ·
Quite a few brands manufacture wheels with the right offset, PCD, central bore and width (8 or 8.5 ) in 18 diameter, but I'm afraid many of those wheels will not fit in the Evo VI due to size of the front Brembo calipers.

I have received a suggestion by a manufacturer to fit spacers welded to the wheel. I don't like the arrangement for several reasons, and one of them is that even if the wheel's original offset is the correct 38mm, after fitting the spacer it would be altered. Could I fit a 1 cm spacer and chose the same rim in 28mm?

I was also against fitting 18 whels at first, but I'm seriously thinking about it now. As I see quite a few members of the forum are using 18 already, can you explain what fittings and brands are you using?
 
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Discussion Starter · #10 ·
Madevelopment,
Hmmm....the last thing I want to do is fit spacers. I have never been convinced by them. Hopefully the ones I am going for won't need them but if they do then I will forget about it. Thanks for that.

Daved6,
235/35 18 does actually have a worse rolling diameter difference (-12mm) compared with 225/40 18 (|PLS|3mm) unless my maths is wrong somewhere. You are right though, I bet they look good :)
 
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Discussion Starter · #11 ·
HH6

I would rather have the smaller dia , ie more clearance / lower gearing than increase the diameter which will have the opposite effect.

I have used 235/35/17 on the std rims for trackdays in the past and you can feel the difference , the car feels much liver / quicker of the line with sharper steering.
 
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Discussion Starter · #12 ·
Original Post:
Claudius,
The only reason for going for 18in's is that the 18in's rims I am thinking of getting are the same price as the 17in's so it seems silly not too ;)
I have no performance reasons for going for 18in's only practical ones, in fact I may still go for 17in's or when I see the prices the whole idea may not seem so practical after all!
In fact, if you do not modify anything else but the wheels and tyres, ie if you do not get a brake upgrade, you will lose brake performance. The only time I will get 18 inch wheels will be when I decide to fit AP 362mm. But my brake setup is ok for the power (or rather the lack of power) I have right now.
 
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Discussion Starter · #13 ·
255/35R18 is closest - 0.2% difference don't know whether those arches can handle the width though - would be looking at 8.5x18s or 9x18s. Also might catch on the suspension arm or something

Well I dont even have an Evo, so who am I to comment ? :D
 
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