Wheel size/speedometer question..
Thread Starter
Racer
Joined: May 2014
Posts: 361
Likes: 34
From: Central MA
Wheel size/speedometer question..
If I change from stock wheel sizes 17" front, 18" rear to 18"/19", how much does this affect actual speed reading? Is there any way to adjust or compensate for this? I'm assuming its just minor and I probably shouldn't care.
Drifting
Joined: Apr 2008
Posts: 1,510
Likes: 15
From: Ga
Drifting
Joined: Mar 2011
Posts: 1,412
Likes: 15
From: Richardson TX
The PCM doesn't automatically adjust for different wheel sizes. It does "automatically adjust" for rear end/transmission gear ratios, because it pulls the car speed from the wheel sensors, and not from the transmission.
Different sized tire heights will affect the speedometer.
If you're getting new wheels, the tires on them will probably be around the same overall diameter as the stock tires. Bigger wheels = smaller tires.
TL;DR -> No, your new wheels should not affect the speedometer.
Different sized tire heights will affect the speedometer.
If you're getting new wheels, the tires on them will probably be around the same overall diameter as the stock tires. Bigger wheels = smaller tires.
TL;DR -> No, your new wheels should not affect the speedometer.
Race Director
Joined: May 2003
Posts: 14,137
Likes: 2,985
From: Iowa
St. Jude Donor '03 thru '26
The PCM doesn't automatically adjust for different wheel sizes. It does "automatically adjust" for rear end/transmission gear ratios, because it pulls the car speed from the wheel sensors, and not from the transmission.
Different sized tire heights will affect the speedometer.
If you're getting new wheels, the tires on them will probably be around the same overall diameter as the stock tires. Bigger wheels = smaller tires.
TL;DR -> No, your new wheels should not affect the speedometer.
Different sized tire heights will affect the speedometer.
If you're getting new wheels, the tires on them will probably be around the same overall diameter as the stock tires. Bigger wheels = smaller tires.
TL;DR -> No, your new wheels should not affect the speedometer.
I run 18" and 19" wheels and speedo is not affected (or is it effected 
)
Racer
Joined: Nov 2013
Posts: 332
Likes: 41
From: Mesa, AZ
Bought an '04 coupe in Oct13 with original '03 date code GY run flats still mounted. Purchased a used set OF ICONZ wheels with V12 tires mounted here off the forum. New set is 19" all four corners. Original rear tire diameter is 26.7". The 305/30/19 currently on the rear diameter measurement is 26.3".
According to the Garmin 2598, actual speed is one MPH slower than posted on the speedometer.
Not that they affect speedometer accuracy but the fronts are 275/30/19 at 25.6" diameter.
I would believe overall tire diameter is the more determining factor rather than wheel diameter.
Chas
According to the Garmin 2598, actual speed is one MPH slower than posted on the speedometer.
Not that they affect speedometer accuracy but the fronts are 275/30/19 at 25.6" diameter.
I would believe overall tire diameter is the more determining factor rather than wheel diameter.
Chas
Last edited by chasb4570; Feb 15, 2015 at 12:52 PM. Reason: added
Melting Slicks
Joined: Jul 2004
Posts: 3,092
Likes: 120
From: orlando florida
St. Jude Donor '15
Its not rim diameter it is overall tire diameter that affects the speedometer.
275/40-18
285/35-19
325/30-19
All three tires have the same overall tire diameter of 26.7" tall. Zero affect on speedometer.
275/40-18
285/35-19
325/30-19
All three tires have the same overall tire diameter of 26.7" tall. Zero affect on speedometer.
Last edited by mrr23; Feb 15, 2015 at 01:23 PM.
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Melting Slicks
Joined: Jul 2004
Posts: 3,092
Likes: 120
From: orlando florida
St. Jude Donor '15
Last edited by mrr23; Feb 15, 2015 at 01:17 PM.
Drifting
Joined: Apr 2006
Posts: 1,936
Likes: 13
From: Redding California
Here is a tire/wheel size calculator.
Type in your current rear tire/wheel size, then type in your proposed new rear tire/wheel size. The speedometer chart will show the difference in speedometer reading.
http://www.tacomaworld.com/forum/tir...0r18-325-35r19
.
Type in your current rear tire/wheel size, then type in your proposed new rear tire/wheel size. The speedometer chart will show the difference in speedometer reading.
http://www.tacomaworld.com/forum/tir...0r18-325-35r19
.