tire width/dia
Thread Starter
Racer
Joined: Jun 2006
Posts: 461
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From: ilion ny
tire width/dia
hello i have an 84 with all 4 rims being 16 inch by 9.5 with the stock 255/50VR16 tires on them. i want to go to a wider tire thinking 285/50/16 in back and maybe front. my ? reguards tire dia more then the width. i need to know what is the widest tire i can get while keeping the same overall dia tire so i am not messing with my speedo? i am not sure how to figure out which series tire is what i need for the 285 width tire. i read that the 50 series and such tires dia is determined by a percentage of the width of the tire. not sure so i figured id ask before i ordered something
Race Director
Joined: Oct 2005
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From: Rolla Missouri
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Here is a formula to calculate overall tire diameter. Different brands use slightly different sizes, meaning that one manufacturers 285/50 16 might be slightly different diameter than another manufacturers.
Formula:
((2 x Tire Size x Aspect Ratio) / 2540) + Rim Diameter
Using the above formula for the sizes you listed:
((2x255x50) / 2540) + 16 = 26.039 inches diameter
((2x285x50) / 2540) + 16 = 27.220 inches diameter
As you can see, the 285 tire in this case will be 1.181 inches taller. This is enough that it will affect the accuracy of your speedometer.
The ideal size would be a 285/45 16 which would be 26.098 inches. Much closer and within the limits of accuracy. Notice I dropped the aspect ratio a size (50 series down to 45 series). This is what kept this 285 width tire close to your original tire diameter.
HOWEVER, you may not find any tires this size. I just looked at Tirerack and didn't see any listed.
16 inch tires are not as popular as the newer 17 - 19 inch sizes, so you might have some trouble.
Formula:
((2 x Tire Size x Aspect Ratio) / 2540) + Rim Diameter
Using the above formula for the sizes you listed:
((2x255x50) / 2540) + 16 = 26.039 inches diameter
((2x285x50) / 2540) + 16 = 27.220 inches diameter
As you can see, the 285 tire in this case will be 1.181 inches taller. This is enough that it will affect the accuracy of your speedometer.
The ideal size would be a 285/45 16 which would be 26.098 inches. Much closer and within the limits of accuracy. Notice I dropped the aspect ratio a size (50 series down to 45 series). This is what kept this 285 width tire close to your original tire diameter.
HOWEVER, you may not find any tires this size. I just looked at Tirerack and didn't see any listed.
16 inch tires are not as popular as the newer 17 - 19 inch sizes, so you might have some trouble.
Burning Brakes
Joined: Feb 2001
Posts: 769
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From: Granbury TX
I believe "The Tire Rack" has a calculator on their web siteand most local dealers list tires by their diameter. I've found most dealers very willing to help with this type concern.
Generally the middle number in the tire size is the tred width to wall hight ratio and can get you close. For example the 255/50v16 means the wall hight (from wheel bead to tred hight) is 50% of the 255 mm of tred width (127.5 mm). A 285/45v16 may yield a simular wall hight (45% of 285mm = 128.25mm) This info will get you close.
Generally the middle number in the tire size is the tred width to wall hight ratio and can get you close. For example the 255/50v16 means the wall hight (from wheel bead to tred hight) is 50% of the 255 mm of tred width (127.5 mm). A 285/45v16 may yield a simular wall hight (45% of 285mm = 128.25mm) This info will get you close.
Team Owner
Joined: May 2002
Posts: 24,337
Likes: 25
From: San Diego , CA Double Yellow DirtBags 1985..Z51..6-speed
Just multiply the tread width (255) by the section height (50). As long as this number is close to your stock number, and you're not changing rim size, you'll be fine.
The actual tire width and section height can differ from this, but the overall diameter is usually dead nuts accurate using the two numbers together.
Safety Car
Joined: Sep 2002
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From: The reason time exists is so everything doesn't happen at once
Thread Starter
Racer
Joined: Jun 2006
Posts: 461
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From: ilion ny
thanx alot guys this helps alot i was kinda figuring like rolla said and going to a 45 series just wasnt sure how far to go 45 40 or what. that gives me what i needed and ill check out the tire calculator as im calling looking for tires. thanx
Race Director
Joined: Sep 2000
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From: The Top of Utah
Originally Posted by Strike3
For example the 255/50v16 means the wall hight (from wheel bead to tred hight) is 50% of the 255 mm of tred width (127.5 mm).
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