SDRs or Formels?

[sperry]

Holy crap!

Man, if those Formels came in 18" gold, I'd sell my SubZeros and get some!!

[ArthurS]

I know. They look sick. I am trying to find a set of Golds on a car, but it seems no one has put them on yet. I am going to talk to Oakos Automotive http://oakos.com/ and see if they can get the gold in for me.

If they can, I might deal with the extra pounds on the rim. Someone mentioned in another thread that the 17's only weight around 17.8.

[ArthurS]

Looks like I may be going SDR's since everyone is selling out of the Formels with polished lip.

Oh well, SDR's still look damn good IMO.

[ArthurS]

Question:

Carson Subaru said that once you get bigger rims and tires, that your speedometer goes off. It will show that you are going faster then you actually are and would need to be adjusted. Is this true? They said they aren't aloud to do it there either way, so that makes me feel like the aren't trying to just sell me. Have any of you with rims adjusted this?

[sperry]

Originally Posted by ArthurS

Question:

Carson Subaru said that once you get bigger rims and tires, that your speedometer goes off. It will show that you are going faster then you actually are and would need to be adjusted. Is this true? They said they aren't aloud to do it there either way, so that makes me feel like the aren't trying to just sell me. Have any of you with rims adjusted this?

It has to do with the overall diameter of the wheel, not just the rim. If you go to a larger rim, but have a lower profile tire, the overall diameter changes very little. This is called "plus-sizing" your rims. If you look at the tire rack specs for each tire, the last column is the revolutions per mile (or something). As long as this number is pretty close (like +/- 10) you won't notice any issues with your speedo or odo.

When I put rims on my TBird, the overall diameter of my tires was almost an inch smaller. This gave the car better acceleration, but caused my speedo to read lower than my actualy speed. Austin did the math for me.. it was something like 70mph on the speed0 = 65 in real life, and 105 on the speedo (the speed limiter) was only 95 in real life.

I am actually planning on reducing my overall diameter when I get some autocross rims and tires, since that will help the acceleration of the car. Remember, on AWD cars, all 4 tires *must* have the same overall diameter or you'll cook a differential or two! So, no mixing and matching tires unless they're the same size!

One more thing, if you were to get bigger rims, and keep the same profile on the tire, say a 225/65/17 or something, it would simply be too big to fit under the wheel well.

One more, one more thing... Carson *sells* cars with aftermarket rims.. I saw a few WRXs with Prodrive P7s on the lot when I was in there a year+ ago for my clutch replacement, so I dunno wtf they're talking about with the "we can't do rims" thing.

edit: Oh, I get it, they can't adjust the odometer... yeah there's laws against that... the speed sensor is linked to the odometer, so "adjusting" it is against the law to prevent odometer fraud.

[ArthurS]

No they said they would be happy to help with the rims, they just can't adjust the speedometer if the rims, like you said, create to bad of a offset. They said I would have to go to a shop or something.

Well, I plan on getting ROTA's, 17" x 7.5" and the Kuhmo ESCTA Supra 712's , but I forgot the siz the recommended. 215/75/17 or something like that.

[AtomicLabMonkey]

Originally Posted by sperry

I am actually planning on reducing my overall diameter when I get some autocross rims and tires, since that will help the acceleration of the car.

Yeah, like Scott said the overall diameter of your tires is part of the overall gear ratio between the engine and where the rubber meets the road. Reducing the overall diameter gives you a shorter (numerically higher) ratio, and increasing it gives a taller (numerically lower) ratio. So if you put some bling bling 20"s on the car or something and the overall tire diameter goes from 25" to 28" for example, then the car is gonna accelerate slower. Just something to think about when buying rims/tires since we usually want the cars to go faster instead of slower. So just throw some teeny little 10" diameter rims on there and you'll be super-fast, hehe.

[sperry]

Originally Posted by ArthurS

Well, I plan on getting ROTA's, 17" x 7.5" and the Kuhmo ESCTA Supra 712's , but I forgot the siz the recommended. 215/75/17 or something like that.

Stock re-92's are 205/55-16's (829 revs per mile)

The tires for a Subaru on a 17x7.5 rim should be 225/45-17 (829 revs per mile). This is known as "+1 sizing" your rim. One inch bigger rim diameter, same overall diameter.

I'll be getting 235/40-17's (840 revs per mile) for autocross, since they'll be a bit wider, and a little quicker. I'm not sure that 235's will fit on a wagon since the wagon doesn't have the fender flares.

[dknv]

My bf showed me this website last year when I was tire shopping ---

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

Enlightening.

[ZER026D]

I have heard that on the sedan we can use up to 245 with a little rolling of the fenders I think I might go for it.

[sperry]

Originally Posted by ZER026D

I have heard that on the sedan we can use up to 245 with a little rolling of the fenders I think I might go for it.

Good luck, you're going to have to roll the fenders ($500+ if there's any paint damage), install ride height adjustable coil-overs ($2000), and get very specifically sized rims, like Volk CE-28N's ($1600). So, expect to drop like $4000. Whereas you could get some 235's on Rotas for $1000, and not have to roll the fenders. Is that 1cm of width really worth $3000 and possibly having to paint the fenders?

Here's a pretty good discussion about running 245's and all the work required to get them to fit:

http://forums.nasioc.com/forums/show...hreadid=282620

But it can be done, with minor rubbing: