T20Driver

iTrader: (3)

Am looking to upgrade to 18" rims given that the Toyo T1Rs get me all over the place on my std 17" rims ... yet people rate them on 18's.

Sorry to be a dunce on this, but what are the critical dimentions I need to know when looking out for new wheels given that the car is an MY05 JDM Sti and has 235/45 R17s tyres on at the moment (.. as per the original RE070's ... which are fine on the 17" rims on the track, but I don't like their tramlining, uncomfortable ride or grip in the wet for every day use).

I've see things like 7, 8 and 8.5 inch widths ... I pressume this is about the width of the wheel, but as 235cm is c.9.25 inches I am confused as to whether 8.5 inch wheels are wide enough.

And then there are 'offsets' ... what is that all about ?

And how do I know whether the wheel stud pattern will be the same .... or that they will fit over the 4 pot brembros ?

As I stated earlier .. apologies for being a little slow on this, but would appreciate your inputs.

weemac2000

Ok here goes.

The '235' is the overall section width of the tyre, face to face, this is a bit wider than the actual width of the tread, since the tyrewall follows a curve and is rounded at the shoulderes of the tread The bit where the tyre actually fits into the wheel rim is the 'bead' If you took a measurement from the inside of the wheel, where the tyre bead fits, to the same place on the other side of the wheel, you get the wheel width. Since the tyre beads are closer together than the section width, then a 235 section tyre fits nicely onto a 71/2" or 8" wide wheel. The stated diameter of the wheel is the diameter at this same point.
Where the wheel bolts onto the hub isnt always exactly in the middle of the inner and outer extremities of the wheel. the difference is called the offset.
If you imagine a wheel bolted on to the car, if you could push the whole wheel in to the car , then you'd be increasing the offset of the wheel. Subies like an offset of 53 or so on a 8" rim. If you increase rim width, its best to keep the offset the same, moving the inner rim inwards and the outer rim outwards by the same amount, but eventully you'll run out of space on the inside, so you have to decrease offset a wee bit.
As a rule of thumb, you can increase section width by 10 or every 1/2" extra rim width. BUT for every 20 or 30, you need to drop 5 on the profile, so as to make the diameter of the wheel the same. If you increase rim diameter by 1" you need to drop another 5 on the profile.
Basically, for an 18" wheel you'll need 8.5" or 9" width with an offset of 45-48 and a tyre size of 255/35 x 18 or 265/35 x 18
Most 18s will fit over the brembos ok, not many 17s will tho. the wheel manufacturer can confirm.
Wheel stud pattern for Subies is 5 studs on a pcd of 100mm BUT!: MY05 and 06 STIs (Including JDM IIRC)have a stud pattern of 5 x 114.3 meaning that most 'Subaru' fitments wont be suitable. There are loads of wheels out there for Evos, and skylines which WILL fit this pcd. Not all wheel dealers are aware of this.
Hope this helps

ricardo

Big list here with other info about weights and offsets:
http://forums.nasioc.com/forums/showthread.php?t=448097

(US stuff, but many of those wheels are available here).

I'd be interested to know what you mean about the Toyo's - are they too squirmy in that size for that power, or do you mean a lack of grip ? Might be worth getting the alignment checked by Curtis before spending too much ?

T20Driver

iTrader: (3)

Thanks weemac and recardo .... looks like I've got some reading and mental agility exercises to do !!

Recardo .. yes .. had thought of giving Curtis a ring as he put the ASTs on and did the alignment .. but that was when I was on RE070s rather than the T1Rs so don't know whether that has made the difference.

I found RE070s really good for high speed cornering as they just didnt move, the T1Rs sidewalls however seem to suddenly 'buckle' as I don't think they are loosing grip.

Anyway .. thanks for the responses peoples

ps you got those ASTs sorted on your Forrester yet Recardo ?

ricardo

Getting some non-inverted ones like on the Type20/25 (but 30mm longer), Curtis is expecting them from AST next week. That should put paid to the stiction that I'm getting on the inverted ones.