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11-08-2010, 11:07 AM | #1 |
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245 or 255 Square for Auto-X?
Just bought a new set of wheels, 18x8.5 et 42 on all 4 corners. Which tire size would you recommend for auto-x? I was thinking 245 would be the ideal with but that'd require a 35 profile which then puts me lower than stock. I know a 255 will fit w/o rubbing based on others' reporting but I'm worried that it might be overkill for the front?
This is a non-m coupe, on stock oe sports suspension. |
11-08-2010, 09:17 PM | #3 |
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thanks man, i'm thinking the same...
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11-10-2010, 09:02 AM | #5 |
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agreed but also considered the min difference bet 245 vs 255, given the increased weight of larger tires and the slower turn-in...
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11-10-2010, 06:57 PM | #6 |
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I don't think you will really notice the decreased turn in and that even if their is any. The only way I think your going to get slower turn in is if the larger tires is to big for the rim or it has a larger side wall. A 255 should be okay on an 8.5 rim especially if i am running a 255 on a 8" rim. In addition if you run a 255/35/18 you have less side wall which should help turn in. I am going off an R888 here because it what I know best but the 255/35/18 is .4 of an inch wider then the 245/40/18. In addition because of the smaller side wall it weighs in at 25.8 pounds compared to the 26 pounds of the 245/40/18. Lastly toyo lists the 255/35/18 as being able to fit on the 8.5 rim. So not only is it wider with less side wall flex but it is also lighter. Seems like a no brainer for me
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11-11-2010, 12:24 AM | #7 |
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18x8.5 et42 with 255 will touch the front strut.
I am running 18x8.5 et38 with 245 and the inside clearance is only about 7mm, so your et42 will reduce the clearance to 3mm, don't think you can use 255 without spacer in the front. |
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11-11-2010, 10:57 PM | #8 | |
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Quote:
http://www.e90post.com/forums/forumdisplay.php?f=12 i put in oem settings of: 8.0", et 50, 225/40/18 new wheel: 8.5", et 42, 255/35/18 and it spits out: "2mm MORE clearance on the strut side, and the outside edge of the wheel will EXTEND an extra 14mm" |
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12-28-2010, 09:33 AM | #9 |
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They'll fit. I run 285-30 Hoosier A6s square on my M coupe with stock wheels. I need a 5mm spacer in the back for wheel well clearance. The front fits fine.
Shorter tires are typically better for autocross. You get better acceleration because of the gearing advantage, and you lower the car. If you're in stock class, shorter tires are the only legal way to lower the car. |
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12-28-2010, 04:25 PM | #11 |
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Yup. Only works with Hoosiers though. You could never get a 285-30 street tire on an 8" wide wheel. You can't even get Kumho V710s in that size on an 8" wheel without some radical methods. Hoosiers pop right on.
Also, remember that this is a kludge forced by SCCA rules. You would not want to run a tire that wide on a wheel that skinny if you were allowed wider wheels. |
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12-30-2010, 10:06 PM | #12 |
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Wider tire = a more ovaly contact patch that has pressure more evenly distributed throughout. The key to grip is to have the largest, most homogeneous contact patch possible. A wider tire helps with the latter. This means more grip. A wider tire will also generally reach peak grip at a smaller slip angle because of increased lateral stiffness (hence the concept of wider tires breaking away more suddenly) which means BETTER turn in (assuming identical side walls). You will have to fight it more (i.e. heavier steering), but that shouldn't be an issue with power steering.
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08-05-2012, 01:15 AM | #13 | |
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Quote:
For example you put OEM setting 8", et 42, 225/40/18 New super wide tires (on the same wheel) 8" , et 42, 295/30/18 It says "same clearance" which is WRONG. We know the tire width will extend more to both inside and outside , but formula ignores the tire width and only reported the tire diameter effect. |
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08-05-2012, 05:20 AM | #14 | |
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Quote:
The only dimensions it's calculating for tires is the diameter and it's using that to calculate speedometer error. |
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08-05-2012, 09:30 AM | #15 |
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I am running a square 275/35/18 set up currently for my track set up. It took a couple minor mods to make them fit but nothing too serious
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08-05-2012, 09:06 PM | #16 |
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R-Comps and Street Tires are 2 different enemies.
R-Comps you can get more tire on a wheel. Like said earlier, it's not abnormal to see +30mm of tire on a wheel with R-Comps versus STs. I run 235s on a stock wheel up front. If you run 245s on a 18x8 wheel, you'll actually lose speed. It's too much tire for that wheel. Given a 1/2 inch is 12mm, I'd only suggest going 245s on the 18x8.5 wheel. With 255s, you'll be putting too much tire on that wheel, and the tire itself will roll too much across the wheel and you'll loose alot of turn-in. Again, from personal experience. I still don't know how you guys are getting that much tire in front (and rear). I'm close the the strut in the front with 235s + 5mm spacers. In the rear I rub with 265s. With a 5mm spacer it's better, but I'm convinced I rub in hard corners. These are with RS3s |
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