speedo and new wheels

Reply Subscribe

Thread Tools

Search this Thread

Apr 23, 2008 | 10:06 PM

Banananutz

Thread Starter

Junior Member

Joined: Nov 2002

Posts: 28

Likes: 0

From: Pa

speedo and new wheels

i have a 91 5spd rs, and i want to put some new wheels and tires on it, will changing the overall tire diameter change the reading on the speedo??

Apr 24, 2008 | 07:38 PM

Ozz1967

Supreme Member

iTrader: (4)

Joined: Dec 2005

Posts: 4,795

Likes: 15

From: St. Cloud, MN

Car: 1984 Trans Am

Engine: LS1383 in work

Transmission: Magnum F - to be installed

Axle/Gears: Zexel Torsen 3.73, 28-spline mosers

Re: speedo and new wheels

Quote:

Originally Posted by Banananutz

i have a 91 5spd rs, and i want to put some new wheels and tires on it, will changing the overall tire diameter change the reading on the speedo??

Yes, if you change your tire size, gear ratio, wheel diameter, you could possibly effect your speedo reading.

If your stock tire is a 15" wheel with say, 265/55/R15 and you upgrade to a 17"wheel but don't get a smaller sidewall tire (Making your overall wheel/tire combo larger), then your speedometer will actually read slower than your true speed. This happened on my 67 Camaro when I swapped the original 14" wheels for 15" wheels. At 70mph my speedo read 55....

Apr 24, 2008 | 08:46 PM

Banananutz

Thread Starter

Junior Member

Joined: Nov 2002

Posts: 28

Likes: 0

From: Pa

Re: speedo and new wheels

fudge... any easy ways to correct for the different diameters?

Apr 24, 2008 | 11:57 PM

Kevin91Z

Moderator

iTrader: (1)

Joined: Jul 1999

Posts: 10,950

Likes: 26

From: Orange, SoCal

Car: 1990 Pontiac Trans Am

Engine: 355 TPI siamesed runners

Transmission: Tremec T56

Axle/Gears: 12-Bolt 3.73

Re: speedo and new wheels

Yes, swap the drive or driven gears in the tailshaft. There is a sticky post at the top with links on how to figure out what speedo gears you need based on your tire size.