wheel sizes
Thread Starter
Racer
Joined: Oct 2006
Posts: 354
Likes: 0
From: Stilwell OK.
wheel sizes
Hi guys, bored to death with the weather here, just came through an ice storm that they say is a record for Oklahoma. Any way my question is on a 1989 the wheels were 17", but when I bought the car it has 255/50/16's on it. Will my speedometer be off, and by how much ? Thanks Bill.
Race Director
Joined: Dec 2002
Posts: 13,348
Likes: 233
From: SCMR Rat Pack'r Charter Member..Great Bend KS
Find out the stock size tires. Go to Tirerack and find out the percentage difference in circumference between the stock and your present tires.
That will be the percentage your speedo will be off.
Larry
code5coupe
That will be the percentage your speedo will be off.
Larry
code5coupe
Team Owner
Joined: Dec 1999
Posts: 34,873
Likes: 487
From: Lacey WA RVN 68-69
NCM Sinkhole Donor
The 89 and later 275/40-17 tire and the 84-87 (and base 88) 255/50-16 tires are actually very close in diameter given the same make and model of tire. I don't think that the Tire Rack tire specs show circumfrence, only diameter.
I run both sizes on my 87; 275/40-17 on AFS 9.5x17 wheels for track days and summer street use and 255/50-16 on stock 9.5" wide wheels for winter driving. I have not noticed any real difference in the speedometer readings.
How did the car wind up with a 255/50-16??
The 89's came stock with 275/40-17 on 9.5x17 wheels. By 89, the standard front rotors were 12" and some of the early 16" wheels would not clear the calipers.
In addition, the early 16" wheels had a 38mm offset while the 17" wheels used a 56mm offset.
I run both sizes on my 87; 275/40-17 on AFS 9.5x17 wheels for track days and summer street use and 255/50-16 on stock 9.5" wide wheels for winter driving. I have not noticed any real difference in the speedometer readings.
How did the car wind up with a 255/50-16??
The 89's came stock with 275/40-17 on 9.5x17 wheels. By 89, the standard front rotors were 12" and some of the early 16" wheels would not clear the calipers. In addition, the early 16" wheels had a 38mm offset while the 17" wheels used a 56mm offset.
Team Owner
Joined: Dec 2000
Posts: 21,094
Likes: 282
From: Phila., PA burbs
According to this site
http://www.miata.net/garage/tirecalcold.html
"Speedo reading will be 1.5% too fast. When your speedo reads 60 MPH you'll actually be traveling 59.1%"
Close enough for gov't work
http://www.miata.net/garage/tirecalcold.html
"Speedo reading will be 1.5% too fast. When your speedo reads 60 MPH you'll actually be traveling 59.1%"
Close enough for gov't work
