Tire Diameter question
Thread Starter
Safety Car
Joined: Sep 2003
Posts: 3,692
Likes: 5
From: Hayward CA
Tire Diameter question
I'm thinking about getting some new wheels 18x9.5-f & 18x10.5-r
What size tires would I need in order to maintain the same diameter (as to not throw off the speedo). I'm currently running 17x9.5 with 275-40-17 all around.
THANKS!!!
What size tires would I need in order to maintain the same diameter (as to not throw off the speedo). I'm currently running 17x9.5 with 275-40-17 all around.
THANKS!!!
Team Owner
Joined: Dec 2000
Posts: 90,675
Likes: 304
From: SE NY
Cruise-In II Veteran
Re: Tire Diameter question (TM-96CE)
Go to http://www.tirerack.com/ and check out the diameter of the new tire of choice vs your current rear tire.
Just ratio the new tire size by the old and multiply by 60 to see how far off you speedo would be.
My stock GY Eagles are 25.6" dia so, for example, if I install a 26.0" dia tire my speedo will read 60mph at true 61mph.
Just ratio the new tire size by the old and multiply by 60 to see how far off you speedo would be.
My stock GY Eagles are 25.6" dia so, for example, if I install a 26.0" dia tire my speedo will read 60mph at true 61mph.
Drifting
Joined: Jul 2003
Posts: 1,613
Likes: 0
From: Orlando FL
Re: Tire Diameter question (Curveit)
this topic bothers me. my 85 has the standard wheels/tires right now...i bought the AFS Zr-1 wheels...9.5 in the front and 11 in the rear on 17 inch rims. i'm looking at 275/40 for the front and 315/35 for the rear....is my speedo going to be off now? it better not be. :mad :banghead:
Safety Car
Joined: Sep 2003
Posts: 4,504
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From: Charleston SC
Re: Tire Diameter question (Orlando85UCFvette)
Stock 255/50 16 = 799 rev's per mile, 315/35 17's roll 811 revs per mile so your speedo will read 1.5% slower then your going. At 67 your speedo will read 66.
Melting Slicks
Joined: Feb 2003
Posts: 2,770
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From: Construction Sucks! MI
Cruise-In V Veteran
St. Jude Contributor '03 & '05
Re: Tire Diameter question (Orlando85UCFvette)
Orlando, you'll be running about 1 MPH slower on the expressway. no big deal.
255/50-16 = 26.04" diameter
275/40-16 = 25.66" diameter
315/35-17 = 25.68" diameter
RPM / Gear Ratio / Diff Ratio * 60 * Wheel diameter in miles
If you have a 4+3 with 3.07 diff, at 2000 RPM's in 4OD you'll be going 75.3MPH on a stock tire. You'll be doing about 74.3 on a ZR1 rim.
Auto w/ 3.07 @2000 RPM's - stock=72.1, ZR1=71.1
Auto w/ 2.73 @2000 RPM's - stock=81, ZR1 = 80
255/50-16 = 26.04" diameter
275/40-16 = 25.66" diameter
315/35-17 = 25.68" diameter
RPM / Gear Ratio / Diff Ratio * 60 * Wheel diameter in miles
If you have a 4+3 with 3.07 diff, at 2000 RPM's in 4OD you'll be going 75.3MPH on a stock tire. You'll be doing about 74.3 on a ZR1 rim.
Auto w/ 3.07 @2000 RPM's - stock=72.1, ZR1=71.1
Auto w/ 2.73 @2000 RPM's - stock=81, ZR1 = 80
