tire size vs. speedometer accuracy
Thread Starter
Drifting
Joined: Sep 2004
Posts: 1,532
Likes: 4
From: Fairview Heights Illinois, near Saint Louis MO, STL C3 Shark
tire size vs. speedometer accuracy
My speedometer is off a tad, well maybe more than a tad. When driving this past weekend, speedometer said 51, and the trailer/police radar deal said 61. I can only assume that the rear end in my car is original and is still the 3.70:1, 4 speed manual, so 4th gear is 1:1. The tires I have on it are 255 60 15's. Are these different enough diameter than the originals to make this kind of mismatch at the speedometer? I still think I have the 3.70:1 rear ratio as It raps up to about 3500 rpms on the interstate to "blend" in with folks in the 65 mph zone - they're at least going 70mph. Any help would be great,
Thanks,
Jeremy
Thanks,
Jeremy
Race Director
Joined: Feb 2005
Posts: 16,100
Likes: 17
You can possibly start here:
http://richmondgear.com/101032.html
I have 255/60/15's and mine is not that far off from the old 225/70/15's.
http://richmondgear.com/101032.html
I have 255/60/15's and mine is not that far off from the old 225/70/15's.
Thread Starter
Drifting
Joined: Sep 2004
Posts: 1,532
Likes: 4
From: Fairview Heights Illinois, near Saint Louis MO, STL C3 Shark
TTT
Anyone know the diameter of whatever the stock size would be for a 76. I'll look and see if my manual has what the original tire size was. Im sure it wasn't 255 60 15.
rihwoods, I'll measure diameter ofmy tires tonight and plug it into that website.
I guess my real goal is to figure out if I really have 3:70.1 or something that is just off a bit, or if the gear in the transmission is the culprit, or if the tires are the culprit.
Anyone know the diameter of whatever the stock size would be for a 76. I'll look and see if my manual has what the original tire size was. Im sure it wasn't 255 60 15.
rihwoods, I'll measure diameter ofmy tires tonight and plug it into that website.
I guess my real goal is to figure out if I really have 3:70.1 or something that is just off a bit, or if the gear in the transmission is the culprit, or if the tires are the culprit.
Pro
Joined: Sep 2003
Posts: 511
Likes: 4
From: Phoenix AZ
Try checking your odometer. If its the speedo gears in the trans they will both be off the same. Go run 10 miles on a freeway will resonable mile markers and see what you get. Try to stay away from mile markers that are near interference (bridges, on ramps, etc.) they have a tendency to be off a bit.
My .02
My .02
Race Director
Joined: Feb 2005
Posts: 16,100
Likes: 17
Originally Posted by ruby76
TTT
Anyone know the diameter of whatever the stock size would be for a 76. I'll look and see if my manual has what the original tire size was. Im sure it wasn't 255 60 15.
rihwoods, I'll measure diameter ofmy tires tonight and plug it into that website.
I guess my real goal is to figure out if I really have 3:70.1 or something that is just off a bit, or if the gear in the transmission is the culprit, or if the tires are the culprit.
Anyone know the diameter of whatever the stock size would be for a 76. I'll look and see if my manual has what the original tire size was. Im sure it wasn't 255 60 15.
rihwoods, I'll measure diameter ofmy tires tonight and plug it into that website.
I guess my real goal is to figure out if I really have 3:70.1 or something that is just off a bit, or if the gear in the transmission is the culprit, or if the tires are the culprit.
