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i'll just stick with the ones i have..oh well..18's maybe next year
#0009
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Joined: Jun 2002
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Originally posted by Troll Pete:
Chris,
You are right and wrong, as are Mike and I. But Mike and I are more correct than you are. While width does effect sideall height, the 2nd number (aspect ratio) effects the sidewall height twice more than the width.
225 x 0.45 = 101.25
215 x 0.45 = 96.75
4.5mm difference
225 x 0.45 = 101.25
225 x 0.40 = 90.00
11.25mm difference
Therefore the common belief and used practice is to increase or decrease the 2nd number (aspect ration) to determine sidewall size.
In addition, it's smarter to change sidewall size.
Why? Because you do not sacrifice width for height. By doing so you get less rim protection on your wheels, increasing the chances of damaging/bending a wheel - especially "curb rash".
The common practice is to increase wheel size while maintaining as close to the original diameter as stock unless one is willing to have the speedometer recalibrated.
example:
stock SVT
Wheel: 16"x6.5"
Tire: 215/50-R16
Width: 215mm (8.464567")
Sidewall: 4.232283" (50% of width 215mm)
Diameter: 24.46457" (sidewall x 2 + 16" wheel)
+1 (upgrade from 16" to 17")
Wheel: 17"x7"
Tire: 215/45-R17
Width: 215mm (8.464567")
Sidewall: 3.809055" (45% of width 215mm)
Diameter: 24.61811" (sidewall x 2 + 17" wheel)
+2 (upgrade from 16" to 18")
Wheel: 18"x7"
Tire: 215/40-R18
Width: 215mm (8.464567")
Sidewall: 3.385827" (40% of width 215mm)
Diameter: 24.77165" (sidewall x 2 + 18" wheel)
On the same car all of the above combos will look pretty much exactly the same when it comes to wheel gap weather the car is lowered or not. The only difference will be the decrease in sidewall/wheel size, the diameter will remain basically the same. With that you get improved performance/handling but less comfort as the smaller sidewall will create a harsher ride. Now if you don't mind a change in speedometer reading then people will increase the sidewall persentage to help close the wheel well gap. However if you venture off the +1, +2, +3 rule of thumb you will change the diameter of the tire and change the output of your speedometer.
If you can handle more width you can also adjust tire size to near the same diameter by playing with larger width tires and different aspect ratios. A safe bump in this direction has been proven to be the 225mm tires in all sizes.
example:
tire: 225/50-R16
width: 225mm (8.858268")
sidewall: 4.429134" (50% of width 225mm)
diameter: 24.85827" (sidewall x 2 + 16" wheel)
difference between 215/50-16 & 225/50-16
width: 0.393701"
diameter: 0.393698"
A little over 3/8" in diameter and not enough to make a big change in speedometer reading so a safe upgrade in most cases. Note: in the above example a bump to a 235mm tire from 215mm would need a change in aspect ratio to 45% and the difference in overall diameter would be around 1/8". Nothing to worry about IF you can handle the width.
same goes with the 18's 215/40-18 & 225/40-18
tire: 225/40-R18
width: 225mm (8.858268")
sidewall: 3.543307" (40% of width 225mm)
diameter: 25.08661" (sidewall x 2 + 18" wheel)
difference between 215/40-18 & 225/40-18
width: 0.393701"
diameter: 0.314964"
less then 3/8" in diameter...again nothing to worry about.
It's all very simple...just do the math.
1st convert "width" mm to "inches" (215mm = 8.464567", 225mm = 8.858268", 235mm = 9.251969")
2nd multiply "width" x "aspect ratio" (50 =.50, 45 =.45, 40 =.40)
sum = "sidewall" (1/2 overall)
3rd multiply "sidewall" x 2 + "wheel diameter" (16", 17", 18")
sum = "tire diameter"
This will get you in the ballpark 99.9% of the time. If you don't care about all this stuff then put on whatever you want to get the look you like. Just be prepaired to get your speedometer recalibrated or face a speeding ticket for not knowing how fast you are going 
Scott
2000 Contour SVT #1464
Mustang Dyno: 171.6hp/145.3lb
Dynojet Dyno: 171.1hp/148.9lb
1989 20th Anniversary Turbo T/A "Indy 500 Pace Car"
#1376 of 1550 All Original, 46k with a few mods
2002 F150 SuperCrew
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Joined: Apr 2001
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Originally posted by scottd60:
If you don't care about all this stuff then put on whatever you want to get the look you like. Just be prepaired to get your speedometer recalibrated or face a speeding ticket for not knowing how fast you are going
I'll not care because it's easier than reading your post! 
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Joined: Jun 2002
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Hard-core CEG\'er
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Hard-core CEG\'er
Joined: Jun 2002
Posts: 1,423 |
Originally posted by Troll Pete:
Originally posted by scottd60:
If you don't care about all this stuff then put on whatever you want to get the look you like. Just be prepaired to get your speedometer recalibrated or face a speeding ticket for not knowing how fast you are going
I'll not care because it's easier than reading your post!
time to go to bed
later 
Scott
2000 Contour SVT #1464
Mustang Dyno: 171.6hp/145.3lb
Dynojet Dyno: 171.1hp/148.9lb
1989 20th Anniversary Turbo T/A "Indy 500 Pace Car"
#1376 of 1550 All Original, 46k with a few mods
2002 F150 SuperCrew
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Joined: Feb 2001
Posts: 1,756
Hard-core CEG\'er
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Posts: 1,756 |
Originally posted by Shawnb:
Who is running 17x7.5s?
I currently am.
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Joined: Feb 2001
Posts: 1,756
Hard-core CEG\'er
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Hard-core CEG\'er
Joined: Feb 2001
Posts: 1,756 |
Originally posted by scottd60:
It's all very simple...just do the math.
1st convert "width" mm to "inches" (215mm = 8.464567", 225mm = 8.858268", 235mm = 9.251969")
2nd multiply "width" x "aspect ratio" (50 =.50, 45 =.45, 40 =.40)
sum = "sidewall" (1/2 overall)
3rd multiply "sidewall" x 2 + "wheel diameter" (16", 17", 18")
sum = "tire diameter"
Not as simple as using an online tire calculator  .
http://www.1010tires.com/tiresizecalculator.asp?action=submit
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Joined: Apr 2002
Posts: 1,616
Hard-core CEG'er
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Hard-core CEG'er
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Originally posted by 1314:
Originally posted by Shawnb:
Who is running 17x7.5s?
I currently am.
Me too. I've run 17x7.5 Kosei, 17x7.5 FSVT, and am currently running 17x7.5 ATS Comp Lites, all with 215/45/17's. Tho when I switch back from my winter set-up (nasty 205/60/15's on ASA's) I'm gonna run 225/45/17's (in Falken Ziex 512 flavor).
Oh...none of the 215/45/17's rubbed, probably because the extra .5" stretched out the tire and reduced the over-all height of the tire.
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Joined: Jun 2002
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Hard-core CEG\'er
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Hard-core CEG\'er
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Originally posted by 1314:
Originally posted by scottd60:
It's all very simple...just do the math.
1st convert "width" mm to "inches" (215mm = 8.464567", 225mm = 8.858268", 235mm = 9.251969")
2nd multiply "width" x "aspect ratio" (50 =.50, 45 =.45, 40 =.40)
sum = "sidewall" (1/2 overall)
3rd multiply "sidewall" x 2 + "wheel diameter" (16", 17", 18")
sum = "tire diameter"
Not as simple as using an online tire calculator .
http://www.1010tires.com/tiresizecalculator.asp?action=submit
There you go...awesome, I'll add that to my other online performance calculators 
Scott
2000 Contour SVT #1464
Mustang Dyno: 171.6hp/145.3lb
Dynojet Dyno: 171.1hp/148.9lb
1989 20th Anniversary Turbo T/A "Indy 500 Pace Car"
#1376 of 1550 All Original, 46k with a few mods
2002 F150 SuperCrew
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Joined: Apr 2001
Posts: 5,975
Hard-core CEG'er
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Informative and that's it. No chance I would actually use that to determine what size tire to put on. 
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 I did. When I was trying to decide between a 225/45 or a 235/40, I wanted to be as close to stock in diameter as possible. That calculator showed that the stock diameter of a 215/50 16 is 24.46. The 225/45 is 24.97 and the 235/40 is 24.40. The 235's were closest and that's what I went with and haven't had a single problem.
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