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Discussion Starter #1
I am looking to change my wheels from the standard '04 STi 18, i believe these are 18x7.5 PCD 100 ET 48.

If for example i go for a Volk CE28N 19x8 i know i still need to specify PCD 100,

BUT

will the ET48 still be relevant or is it totaly dependant on the wheel stlye?

Thanks in advance.
 
G

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Discussion Starter #2
Also any advice on tyre size -
235 35 19

225 35 19

235 40 19

225 40 19

???

Car is fitted with ap 6 pots ( 7740 ) and soon to have AST adjustable coil overs fitted.
 

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Registered
Joined
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4,130 Posts
the ET 48 figures both wheel width, tire size, and tire width into the equation really. The 48 is offset, and offset is what keeps your wheel (tire) from rubbing on the inside of the wheel well, or on the strut. Offset also figures into brake clearance...so if you have a SG6, you'll need to make sure the wheel will clear those huge brakes.

Offset and wheel fitment is pretty simple, yet it seems to be the most asked question on every car board. I'm going to put together a pictorial and some text about wheel fitment- hopefully it can get stickied here for future reference.

regards,

_D
 

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No more Foz !
03 Impreza Sti
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1,912 Posts
Simon - have you seen this ?


http://www.miata.net/garage/tirecalcold.html

From a match to your original wheel/tyre size which I think is 225/45/18 same as mine the best match would be a 225/40/19 although I think I would be tempted to go for a 235/40/19 just because of the greater tyre width plus your speedo would be 1.7% too slow which if anything like mine which reads about 7% too fast would not be an issue..
Also need to check what tyres are available in those sizes as you may be restricted for choice on certain ones..
Have you had a look at GTrydaz ? There's quite a few guys over there running Foresters on 19"s and bigger who could prob offer more advice..
 

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Mr. November 2008
2015 BMW 335d xDrive GT Auto
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969 Posts
My FSTi speedo matches GPS exactly at all speeds I've tested it to up to, ehem 70. I believe the speedo might read slightly high beyond that. That's at a steady speed, and to the resolution of the dial. This means that I can go to tyres which give a smaller overall diameter (and then it will over-read like most cars do anyway) but I can't easily go to a tyre with even a slightly larger size without it under-reading.

Unless the speedo indication is adjustable in software - I don't know what they do to make it go from km to miles anyway - is that a little box of tricks inserted somewhere ?
 

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Premium Member
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726 Posts
N.B.

The Miata calculator is a bit of a rough guide as the actual tyre overall diameter can vary between Make & Model of tyre for a given profile.

You need to get the real data for the actual tyre you are interested in from the Manufacturers website.

Miata suggests a 55 profile tyre to go from Geolander 215/60/16 to 225s on a 17" wheel on my XT.

Checking the stock Geolander O/D on the Yokohama website against a 17" x 225 Falken ZE512 O/D shows that the best match is a 50 profile not a 55.

Ian
 

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Premium Member
'09 STI
Joined
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4,128 Posts
PSi3 said:
I am looking to change my wheels from the standard '04 STi 18, i believe these are 18x7.5 PCD 100 ET 48.
If for example i go for a Volk CE28N 19x8 i know i still need to specify PCD 100,
BUT
will the ET48 still be relevant or is it totaly dependant on the wheel stlye?
Thanks in advance.
Offset is offset. It simply refers to where the wheel mounting surface is in relation to the center of the rim. In this case 48mm offset from the middle of the rim towards the outside. Wheel style only matters when it comes to brake clearance due to the shape of the spokes. You may need to go with a lower offset if you go with a 8" or wider for strut clearance. 235 is a better match for an 8" wheel. I wouldn't get too caught up in worrying about your speedo- if you keep the overall diameter the same it doesn't matter. As you should to match the gearing.

You read about people trying to get perfect speedo readings and fixing wheel well gap when they are buying tires and wheels. Nothing could be more incorrect! You pick wheels and tires for performance and intended use. Wheel gap should be addressed via suspension lowering. If accurate speedo readings are important than get it recalibrated. Choosing tire diameters to correct your speedo is not right.:confused:
 

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Premium Member
'09 STI
Joined
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4,128 Posts
So how much clearance do you have with the new C/Os? If you stayed with the stock +48 and went to an 8" wheel, you can estimate that the extra 1/2" in width split in half which is 6-7MM added on either side.

This doesn't take into consideration the extra tire width but it gives you an idea of what to expect. I doubt the CE28 spoke style will clear your brakes as I don't think the +48 clears on an WRX/STi. Possibly a +43.
 
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