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Old 12-17-2008, 04:05 PM   #1
tazswing
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Default Off-set question

So, I can't wrap my brain around this. I am looking at some 17x8.5 Enkei RPF1s 5x114.3 +38 for my 08STI for sale by a local. Tirerack has these for sale for this car but the off-set is +45. That seems like a substantial difference in off-set and I am inclined to say that the +38 will not work.

Any tips on making this determination aside from fitting them up?

Thanks.
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Old 12-17-2008, 04:16 PM   #2
tsispyder97
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really? less than 1cm change wont work?

seriously, get your damn tape measure out and look.

its a 7mm difference in outer positioning. not rocket science
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Old 12-17-2008, 04:44 PM   #3
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Ah, your right. It's not rocket science, it's wheel off-set science.

I don't have the rims, I am contemplating purchasing them making using a measuring tape difficult.

08 STi comes with a 18X8.5 rim and these are 8.5 meaning that YES, a "1cm change" might make a difference.

I guess dealing with people like you is still better than crawling back to a seller saying will they give me my money back for making a mistake.
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Old 12-17-2008, 04:56 PM   #4
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tirerack will typically recommend a "safe" offset, almost guaranteeing that you won't rub. +38 is more aggressive than +45, and will probably look better. However, those 7mm might cause rubbing on the body depending on suspension mods, alignment, and tire size.

All in all, 8.5" +38 isn't THAT aggressive for a STI... Heck, I'd run that on my wagon, but I have stiff suspension and adjustable camber...
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Old 12-17-2008, 04:57 PM   #5
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http://www.1010tires.com/WheelOffsetCalculator.asp

With the same width rim, I am looking at moving the rim location out by 17mm. Tirerack shows a +45 but with a 8" rim (for the same model rim) which translates into extending the rim out by only 4mm and gaining 16mm from the strut housing. So back to the tape measure above, I am going to assume if I add 17mm to the location of the stock wheel, that is where I can expect the the 8.5 by +38 to land the tire.
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Old 12-17-2008, 04:59 PM   #6
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Quote:
Originally Posted by dantastic View Post
tirerack will typically recommend a "safe" offset, almost guaranteeing that you won't rub. +38 is more aggressive than +45, and will probably look better. However, those 7mm might cause rubbing on the body depending on suspension mods, alignment, and tire size.

All in all, 8.5" +38 isn't THAT aggressive for a STI... Heck, I'd run that on my wagon, but I have stiff suspension and adjustable camber...
Thanks for that. Now I need to look up the handling benefits/compromises of moving the location of the tire in relation to the suspension.
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Old 12-17-2008, 05:19 PM   #7
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Quote:
Originally Posted by tazswing View Post
Thanks for that. Now I need to look up the handling benefits/compromises of moving the location of the tire in relation to the suspension.
....not a direct answer to your application but perhaps a good starting point to get the noodle thinking about various aspects:

http://www.miata.net/garage/offset.htm

It doesn't really discuss the benefits or drawbacks but it may help open some doors to finding answers during your research.
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Old 12-17-2008, 05:29 PM   #8
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aren't the RPF1s a 17x8.5 +40mm?

the wheel tire rack shows is the 17x8 +45mm.

reason being is the +40mm will rub unless the proper modifications are done to the rear fenders and ride height matters as well.

where as with the +45mm 8" wheel there aren't any issues with a 225/45/17.

as for the 8.5" +40mm you can get away with a 245/45/17 on an 08 most likely but you do run the risk of rubbing on the rear fenders depending on your ride height.

if these are for winter wheels going a little narrower wont hurt performance and you'll gain some well needed clearance.

when looking at wheel size you can't ignore the tire. 90% of the time the tire is wider than the wheel.

some good articles here.

http://t3hclap.com
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Old 12-17-2008, 05:29 PM   #9
tazswing
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Quote:
Originally Posted by Kean View Post
....not a direct answer to your application but perhaps a good starting point to get the noodle thinking about various aspects:

http://www.miata.net/garage/offset.htm

It doesn't really discuss the benefits or drawbacks but it may help open some doors to finding answers during your research.
Thank you. "scrub radius" is a new term for me. I am familiar with the term and concept of scrubbing speed when it come to racing. Seems though that unless someone has really done the math with the suspension geometry of a given application you can really only tell if a different offset/rim width will fit vs. adding/take away performance.
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Old 12-17-2008, 05:47 PM   #10
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Quote:
Originally Posted by tazswing View Post
Thank you. "scrub radius" is a new term for me. I am familiar with the term and concept of scrubbing speed when it come to racing. Seems though that unless someone has really done the math with the suspension geometry of a given application you can really only tell if a different offset/rim width will fit vs. adding/take away performance.
there are ranges of what fits and what doesn't, those also concern Scrub radius.

in short if you have to do Excessive work to make it fit and you have more room between your strut/tire then you did before you could've made a better choice.
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Old 12-17-2008, 06:39 PM   #11
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not sure all the different variations. They are advertised as 17x8.5 with +38 and after PMing with the person they said that info was taken off the rim so I have to believe it is correct. This webpage has that size listed minus the off-set: http://wheelweights.net/

Quote:
Originally Posted by WRX8XB View Post
aren't the RPF1s a 17x8.5 +40mm?

the wheel tire rack shows is the 17x8 +45mm.

reason being is the +40mm will rub unless the proper modifications are done to the rear fenders and ride height matters as well.

where as with the +45mm 8" wheel there aren't any issues with a 225/45/17.

as for the 8.5" +40mm you can get away with a 245/45/17 on an 08 most likely but you do run the risk of rubbing on the rear fenders depending on your ride height.

if these are for winter wheels going a little narrower wont hurt performance and you'll gain some well needed clearance.

when looking at wheel size you can't ignore the tire. 90% of the time the tire is wider than the wheel.

some good articles here.

http://t3hclap.com
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Old 12-17-2008, 10:17 PM   #12
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the +45 hit the calipers

the +38 dont
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Old 12-18-2008, 12:31 AM   #13
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Quote:
Originally Posted by Uncle Scotty View Post
the +45 hit the calipers

the +38 dont
Thanks! I miss read the post, and the offset is 30 which is a little too much for me. 38 and would have made an offer
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Old 12-18-2008, 12:58 AM   #14
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the 45's clear the 'subaru' 4-pots but not the brembo's
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