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Old 02-03-2001, 03:52 PM   #1
ImprezaL
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Lightbulb Changing tire size- ? for RS guys-

Well, I just had a thought for all you RS owners that stay with stock rims, but go to better tires- I've noticed a lot of you stay with the stock tire sizes...why do you stay with 205/55-16? Why not go to 205/50-16? Wouldn't a smaller rolling diameter help a bit with acceleration? I only ask because I'm running 205/50-16 on 98 RS rims, because I have to (diameter is almost identical to my old tires), but I would think more people would go to smaller tires if they were going to change them anyway.
What gives?
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Old 02-03-2001, 06:08 PM   #2
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I wanted to go with the smaller side wall but was told that it would change the speedo calibration. I was told that if I went to a 225/50 I could get a wider bigger tire without messing up the speedo.
Well needless to say i went with that. i love the look they handle really well, but they do rub on harsh dips and bumps. This was not what I had wanted when I asked about different tire size. the place I had this done said they were going to measure out all of the clearances to make sure no rubbing would occur. I took them at there word and did not have any tire rubbing until allmost two weeks later to late to change them out so I will just deal with the slight rubbing until I go with bigger rims.
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Old 02-03-2001, 07:09 PM   #3
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<FONT face="Comic Sans MS">I put 50 series tires on my 16" tires too, mostly because that's what was available when I bought them. Most people are concerned with messing up the speedo, and don't change the stock tire size unless they plus size the wheel. Go figure. My new tires will be 215 40 (or 45) 16's.

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Old 02-03-2001, 09:01 PM   #4
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sspriest-

Are you running a stock suspension? I was thinking about running 225/50-16's on my stock rim, but I don't want them to rub. They'd be on the P1 suspension by the way. Also, why does the 225/50-16 rub, when the stock 205/55-16's don't seems strange, b/c they are almost the same diameter.
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Old 02-03-2001, 10:04 PM   #5
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205/50s are like a well-kept secret. Everybody who's tried them loves them, but there is apparently a big crowd of owners out there who have a fierce and utterly undeserved loyalty to the stock profile. 3% speedo error is not a big deal guys. It's not even a little deal.
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Old 02-04-2001, 10:08 AM   #6
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when i still had 16's i ran 205/50 kumhos and was very happy with them.
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Old 02-04-2001, 10:44 AM   #7
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225/50-16's run because they are wider. That's it.
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Old 02-04-2001, 02:50 PM   #8
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When I agreed on getting the 225/50 tires the tire shop told me the size difference was minor to none. Not sure exactly where they are rubbing. I see no signs of wear anywhere on the tires. They only seem to rub in the rear. All of this Is on stock suspension. Found no problems with the front.
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Old 02-05-2001, 12:00 AM   #9
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205/55-16: d=24.88" rc=79.2 <--- stock
205/50-16: d=24.07" rc=76.6 e=+3%
215/50-16: d=24.46" rc=77.8 e=+2%
225/50-16: d=24.85" rc=79.1 e=+0%
215/40-16: d=22.77" rc=72.3 e=+9%
215/45-16: d=23.62" rc=75.1 e=+5%
215/50-17: d=25.46" rc=81.0 e=-2%
215/45-17: d=24.62" rc=78.2 e=+1%
where 1"=25.4cm, pi=3.1415, d=diameter to 2 places, rc=rolling circumference (not counting for inflation variances) to 1 place, and e=difference in 1 percent intervals. The smaller the E value, the more acurate your speedo and odo will be. -% means slower acceleration, higher top speed (well, if not drag limited) and lower miles registering. +% means the opposite.

The 3% isn't bad, but why not cut it down to 2% and add a little bit of tread width? I don't think I've heard anybody rubbing with 215/50-16s.

Yes, I like numbers.

OK. While 3% isn't a big deal, it can add up. In your 3000 mile oil change that adds up to 90 miles (no biggie). In a 200,000 lifetime it'll add up to 6000 miles, or two extra oil changes.
To whoever was looking at the 40 series 16's... I dunno, that's almost a mile for every ten you roll. After 100,000 miles that's an extra 9,000 miles. You'll get the shaft when it comes time to sell, with the car reading lots more miles than it really has on it.

EDIT: adding stuff, correcting mistakes, checking work.
REEDIT: correcting my math. Jeez. Don't you guys check people's work?

Last edited by CosmoTheCat; 06-26-2001 at 05:53 PM.
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Old 02-05-2001, 08:23 AM   #10
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Truely how big of a difference can there be in a 205/50 -vs- 205/55?? plus the speedo is off so you'll actually be fooled into being slower than you actually are.

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Old 02-05-2001, 08:46 AM   #11
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I was gonna stay with stock size tires on my 16" wheels to mantain my ground clearance(bad excuse), as well as for the speedo error. I recently picked up a set of gold 17" Speedline SuperTurismos w/ 215/45/17 Yoko A520s. The shorter sidewall and the wider tire make the car feel totally different. The grip and improved feel is excellent.

horatio102, if you do a search on The Tirerack for a 215/50/16 you will come up with three tires. I have seen limited reviews on the board for these tires. The BFG g-Force T/A KDW in this size is standard on SVT Contours and seems to be a pretty good tire. But in the end, there is a better variety in the 205/50/16 and 205/55/16 sizes.

db
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Old 02-05-2001, 09:21 AM   #12
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Glad someone mentioned the odometer difference, not just speedo.
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Old 02-05-2001, 03:46 PM   #13
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omahasubaru - About 2.5" per rotation.
And stock = 800 RPMile
205/50 = 827 RPMile
I'm really quite sleepy so my mind isn't working properly, but I keep coming up with a number like 167 feet/mile difference.
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Old 02-05-2001, 03:50 PM   #14
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Oh yeah...
Dustin - That's a totally valid point. But if I were looking to replace mine I'd go for the 215/45-17's. I'm no expert on tires or anything, but I'd like to keep my speedo and odo as accurate as possible.
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Old 02-06-2001, 05:37 AM   #15
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accuracy is key!
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Old 02-06-2001, 09:25 PM   #16
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Omaha - I believe your speedo/odo can be recalibrated by someone with the Subaru Select Tool... this is an unconfirmed rumor for me since I have never plugged my RS into the Select Tool, but perhaps someone else can substantiate.

The problem with 215/50s is that they are rare and most of the good tires we like aren't made in that size. Also, increasing the section width to 225 is pointless - you don't get more contact patch, you only change its shape, and to boot you introduce rubbing in the rear. If it were such a good idea Subaru would do it on the STi WRX... they don't.
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Old 02-06-2001, 10:58 PM   #17
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PK - the 225's should increase the tread width, but to take advantage of it a wider wheel is probably mandatory. The stock wheel is what, 7 inches wide? The 205s are about 8.4 inches, while the 225s are 9.2" 2 inches wider than the wheel. Yeah.. new rim time.
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Old 09-04-2005, 01:16 AM   #18
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I have done the math and these are the results, but first let me just state my current assumptions. first, i assume that tires are gears in this situation which they are. secondly i assumed that gear reduction any where in the chain has the same effects at the end as long as it is expressed in precentages (in otherwords i did not account for the differential gears) however these are in precentages so the should remain accurate to tire rotation. This strictly address the radius and not the rotating mass issue. ofcourse since the tires are all smaller you would benift by reducing moving inirta.

the RA gear kit reduces the size of gears giving you a better machanical advantage. For the 02 wrx second gear ratio is reduced 86.82% and 3rd is reduced 83% for all intents and purposes. since tires are gears and gears are nothing more than round levers; smaller tires should help acceleration however i can not conferm this with someone that has tested it.

so here is the good stuff: how far will it drop the car and then the % smaller than stock 205/55-16
lower the car % smaller
205/50-16 .81 inch 96.7
215/45-16 .63 inch 94.85
205/45-16 1.08 inch 93.48
215/40-16 1.06 inch 91.52
205/35-16** 1.6 inch 86.8

**In order to acheve RA gearing you would have to move to a 205/35-16
i have a friend with the RA kit he said he tops out at 130mph my math with the 205/35 says it topspeed should be about 136. but 5th gear is a diffrent ratio but i am 6mph over so that balances out properly.

So in short you will want an odomerter correction for some tire changes and definatly for others** the % elso represents milage change (for every 86.8 miles you drive your odometer will add 100 miles)but of course that is proportional to engine wear. Please correct me if this seems inaccurate.
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Old 09-04-2005, 11:03 AM   #19
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yeah i have 205-45-16's on my stock wheels and you can tell a difference with mileage. The accleration is exactly the same, so you won't get any noticable difference there. As far as i can see there has been absolutely no benefit to going to smaller tire. The tires are Kumho ASX's for reference.

Last edited by rbehny; 09-04-2005 at 11:11 AM.
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Old 09-04-2005, 11:39 AM   #20
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i have 225/50/16 pirrelli pzero nero

had to use a 3mm spacer to kep it off the strut however they've been great. floats a little but grips pretty well in return (for an all season). however that would be a charecteristic of the tire
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