Tire Size Questions
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October 2009 ROTM
October 2009 ROTM
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Joined: Nov 2007
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From: Eastern PA,
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Not sure if it will help but the numbers mean something. 245/50/16
First number 245 MM wide tread (or 9.65")
Second number is a ratio of width to side wall height. Since the above is 50 or 50% that would be 245 X 50%=122.5 MM (4.82" tall side wall).
You can use above to calulate the diameter of the tire 16+4.82+4.82= 25.64 Dia. Compare that to your current setup to check to see how far the computer will be off. As you go wider you want a lower percentage of side wall to keep your diameter close so you do not need to update your computer.
First number 245 MM wide tread (or 9.65")
Second number is a ratio of width to side wall height. Since the above is 50 or 50% that would be 245 X 50%=122.5 MM (4.82" tall side wall).
You can use above to calulate the diameter of the tire 16+4.82+4.82= 25.64 Dia. Compare that to your current setup to check to see how far the computer will be off. As you go wider you want a lower percentage of side wall to keep your diameter close so you do not need to update your computer.
I was thinking about this too a while back and was using the same calculations to figure how close I could get to the same height with a wider tire.
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Overdrive Member
Joined: Nov 2006
Posts: 4,042
From: IL
Well, I think you have to qualify that, since with a larger contact patch you get worse traction on snow, ice, etc. My application here is all season in the midwest, so I am sure your comment didn't apply to this...
Dry may be fine, though.
Local tire shop said the difference between V6 stock and the Z28 size ends up being ~ 1.3 something Mph difference, so the speedo shows you're going faster than you are...
Dry may be fine, though.
Local tire shop said the difference between V6 stock and the Z28 size ends up being ~ 1.3 something Mph difference, so the speedo shows you're going faster than you are...
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Overdrive Member
Joined: Nov 2006
Posts: 4,042
From: IL
So there is a nationwide backorder on the BF Goodrich Z rated tires till January, so I went with Michelin Pilot Sport A/S Plus tires Z/W rated, 245/50/16. Much better. 
FYI, those wondering about tire sizes and speedometer calculations like Gorn was talking about, there is a free calculator HERE:
Tire Dimensions Made Simple - Discount Tire
Oh, I also learned my chrome wheels are peeling under where the tire sits too, so air leaks are likely -- damn midwest salt! So looks like I need to start hunting new wheels as well...
FYI, those wondering about tire sizes and speedometer calculations like Gorn was talking about, there is a free calculator HERE:
Tire Dimensions Made Simple - Discount Tire
Oh, I also learned my chrome wheels are peeling under where the tire sits too, so air leaks are likely -- damn midwest salt! So looks like I need to start hunting new wheels as well...
Last edited by libertyforall1776; Dec 12, 2011 at 08:14 PM.
2nd Gear member
Joined: Jul 2010
Posts: 493
I compared 235/55/16 to 245/50/16 on the calculator, and it shows if your speedometer reads 100 you're actually going 97.97. So to correctly figure your mileage you'd have to subtract 2.03 miles for every hundred, or .0203 for every mile correct?
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