Posted: 12/3/2010 2:43:33 PM EDT
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I have a spare set of 18x8 wheels. I'd like to put a wide tire on them, but I don't know if it will fit the wheel. According to this, the 275/40-18 tire size is ok for my car, but I don't know if it will fit on a 18x8 wheel (stock size is 235/50/17). It also looks like 265/40-18 will fit the car, but I don't know if it will fit the width of the wheel. The guys at Discount Tire told me that the 275's would fit the 8" wheel, but TireRack seems to recommend a 9.5" wide wheel. In case it matters, the new 18" wheels have a +40mm offset, and the stock 17" wheels have a +33mm offset. Does anyone have experience with either of these tires/wheel sizes? Basically I just want to put the widest possible tire that will fit. These are going to be my autocross tires. Thanks!  (Figured I would get more responses in GD than the car forum) |
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Answer: 275 mm = 10.8267 "
Dimension Tire A: 275/40 R 18 Tire Width 10.83" (275.00mm) Sidewall height 4.33" (110.00mm) Overall height 26.66" (677.20mm) Circumference 83.76" (2127.49mm) On an 8" rim your sidewall is going to have to absorb almost 3 inches of "deflection" with just over 4 inches of sidewall to do it in. In other words your tire profile will be mushroom shaped. On my truck, I run 12.5" wide, 60 series tires on 10" rims, and they are a complete motherFer to mount, and really pooch out, and in my case, 7.5" of sidewall only has to deal with less than 3" of deflection. Dimension Tire A: 325/60 R 15 Width 12.80" (325.00mm) Sidewall height 7.68" (195.00mm) Overall height 30.35" (771.00mm) Circumference 95.36" (2422.17mm) You could make it work, but you might end up having to tube the tires to keep them inflated and the autocriss handling would be beyond miserable due to so much sidewall roll. If you find a talent tire shop that manages to get these mounted without destroying the tires, you will be REALLY unhappy with the performance. So, Either get a tire that will fit your rims and go 1 or 2 steps stickier than you were planning, or get wider rims. |
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Quoted: Answer: 275 mm = 10.8267 " Well, that's the tread width, but what I'm concerned about is the part that actually touches the rim. My current wheel size is 17x8", with a 235x50 tire. 235 millimeters = 9.252 inches These are not going to be tires that I drive on daily, only for track use. Only reason I didn't go with a wider rim, is these 18's were free from a friend.  |
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Quoted: Sorry, I hit submit too early, I was still composing. No prob. After some more research, it looks like I'll be going with 255/45 or 255/50 sized tires. The wheels currently have 245's, and tire rack says that 255's will fit an 18x8" rim. Thanks for the help  |
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A LOT depends upon the tire. Also, one mfr's "275" may be the same width as anothers "235". There is no "spec" ruler used to define tire sizes from mfr to mfr. Most radial street tires will stretch an amazing amount and will work fairly well even when stretched so. Bias ply tires do not like undersized wheels. R-compound DOT-approved tires have stiffer carcasses and will be harder to mount, but will still generally fit on undersized wheels. I have seen 225 Hoosiers squeezed onto 5" wide wheels, and it worked well for the car & driver. The ideal of course is to properly match tire width to wheel width. |