Changing wheel size question
11-22-2005, 11:45 AM
#3
MF Moderator
Join Date: Mar 2005
Location: Missouri
Posts: 3,441
RE: Changing wheel size question
angcobra is somewhat correct.
If you change tires / wheels... you will need a tuner to reset the Speedo to account for the difference.
There is a formula, where you measure the total height, calculate the revolutions per mile and then use the tuner to set the computer.
In the case of the Preditor...
To calculate your revolutions per mile, measure your tire diameter in inches and use it in the following formula.
Example: 20168 divided by tire diameter = revs per mile Ex 20168/26 = 775 rev/mile
The stock gear ratios on the 2005 mustang are 3.31:1 for the automatic transmission cars and 3.55:1 for the manual transmission
cars. If you have changed your rear differential crown and pinion gears, (select the appropriate ratio using this parameter to
correct your speedometer and shift points). Use this parameter to select the appropiate ratio to correct the gear ratio.
You make the change under the tune your running - parameters - axel ratio - Tire Revs Per Mile.
If you change tires / wheels... you will need a tuner to reset the Speedo to account for the difference.
There is a formula, where you measure the total height, calculate the revolutions per mile and then use the tuner to set the computer.
In the case of the Preditor...
To calculate your revolutions per mile, measure your tire diameter in inches and use it in the following formula.
Example: 20168 divided by tire diameter = revs per mile Ex 20168/26 = 775 rev/mile
The stock gear ratios on the 2005 mustang are 3.31:1 for the automatic transmission cars and 3.55:1 for the manual transmission
cars. If you have changed your rear differential crown and pinion gears, (select the appropriate ratio using this parameter to
correct your speedometer and shift points). Use this parameter to select the appropiate ratio to correct the gear ratio.
You make the change under the tune your running - parameters - axel ratio - Tire Revs Per Mile.
11-22-2005, 12:29 PM
#4
4th Gear Member
Join Date: Nov 2004
Location:
Posts: 1,724
RE: Changing wheel size question
How was I only somewhat correct?
There was no mention of diff gear change.
Wheel change by itself does not change tire diameter. The key as we both pointed out was the total diameter (heigth) of the tire. As the diameter changes so does the cirumference, circumference determines the distance traveled per revolution of the tire.
There was no mention of diff gear change.
Wheel change by itself does not change tire diameter. The key as we both pointed out was the total diameter (heigth) of the tire. As the diameter changes so does the cirumference, circumference determines the distance traveled per revolution of the tire.
ORIGINAL: Professor Wizard
angcobra is somewhat correct.
If you change tires / wheels... you will need a tuner to reset the Speedo to account for the difference.
There is a formula, where you measure the total height, calculate the revolutions per mile and then use the tuner to set the computer.
In the case of the Preditor...
To calculate your revolutions per mile, measure your tire diameter in inches and use it in the following formula.
Example: 20168 divided by tire diameter = revs per mile Ex 20168/26 = 775 rev/mile
The stock gear ratios on the 2005 mustang are 3.31:1 for the automatic transmission cars and 3.55:1 for the manual transmission
cars. If you have changed your rear differential crown and pinion gears, (select the appropriate ratio using this parameter to
correct your speedometer and shift points). Use this parameter to select the appropiate ratio to correct the gear ratio.
You make the change under the tune your running - parameters - axel ratio - Tire Revs Per Mile.
angcobra is somewhat correct.
If you change tires / wheels... you will need a tuner to reset the Speedo to account for the difference.
There is a formula, where you measure the total height, calculate the revolutions per mile and then use the tuner to set the computer.
In the case of the Preditor...
To calculate your revolutions per mile, measure your tire diameter in inches and use it in the following formula.
Example: 20168 divided by tire diameter = revs per mile Ex 20168/26 = 775 rev/mile
The stock gear ratios on the 2005 mustang are 3.31:1 for the automatic transmission cars and 3.55:1 for the manual transmission
cars. If you have changed your rear differential crown and pinion gears, (select the appropriate ratio using this parameter to
correct your speedometer and shift points). Use this parameter to select the appropiate ratio to correct the gear ratio.
You make the change under the tune your running - parameters - axel ratio - Tire Revs Per Mile.
11-22-2005, 11:14 PM
#5
1st Gear Member
Join Date: May 2005
Location: Bradenton, Florida
Posts: 78
RE: Changing wheel size question
Angcobra, you said that wheel change alone does not change tire diameter. But that is not true.
Wheel diameter change:
You have to change the tire size when you change the wheel diameter. This creates a larger or smaller tire diameter on the vehicle. Which could create the need for a tune change. The only exception is when a the width and aspect ratio difference between the old and new tires creates an identical total tire diameter.
Wheel width change:
If you change the width of the wheel enough while keeping the the wheel diameter the same you will have to change the tire width to fit the wheel. The tire width will change the tire sidewall heigth. This changes the overall tire diameter.
The question that I have is how much of a overall diameter change constitutes a need to retune the vehicle?
Wheel diameter change:
You have to change the tire size when you change the wheel diameter. This creates a larger or smaller tire diameter on the vehicle. Which could create the need for a tune change. The only exception is when a the width and aspect ratio difference between the old and new tires creates an identical total tire diameter.
Wheel width change:
If you change the width of the wheel enough while keeping the the wheel diameter the same you will have to change the tire width to fit the wheel. The tire width will change the tire sidewall heigth. This changes the overall tire diameter.
The question that I have is how much of a overall diameter change constitutes a need to retune the vehicle?
11-23-2005, 02:11 PM
#7
4th Gear Member
Join Date: Nov 2004
Location:
Posts: 1,724
RE: Changing wheel size question
You said I was wrong and then you went on to say I was right. When I change wheel size on a car, I make a point to choose a new tire that keeps the same overall size, so wheel change does not change tire diameter.
Some of you guys need to get off of telling folks they are wrong. You should better understand the issue yourself so you can recognize a correct response.
Some of you guys need to get off of telling folks they are wrong. You should better understand the issue yourself so you can recognize a correct response.
ORIGINAL: Hammermill
Angcobra, you said that wheel change alone does not change tire diameter. But that is not true.
Wheel diameter change:
You have to change the tire size when you change the wheel diameter. This creates a larger or smaller tire diameter on the vehicle. Which could create the need for a tune change. The only exception is when a the width and aspect ratio difference between the old and new tires creates an identical total tire diameter.
Wheel width change:
If you change the width of the wheel enough while keeping the the wheel diameter the same you will have to change the tire width to fit the wheel. The tire width will change the tire sidewall heigth. This changes the overall tire diameter.
The question that I have is how much of a overall diameter change constitutes a need to retune the vehicle?
Angcobra, you said that wheel change alone does not change tire diameter. But that is not true.
Wheel diameter change:
You have to change the tire size when you change the wheel diameter. This creates a larger or smaller tire diameter on the vehicle. Which could create the need for a tune change. The only exception is when a the width and aspect ratio difference between the old and new tires creates an identical total tire diameter.
Wheel width change:
If you change the width of the wheel enough while keeping the the wheel diameter the same you will have to change the tire width to fit the wheel. The tire width will change the tire sidewall heigth. This changes the overall tire diameter.
The question that I have is how much of a overall diameter change constitutes a need to retune the vehicle?
11-23-2005, 03:59 PM
#8
5th Gear Member
Join Date: May 2005
Location: S.burbs Chicago
Posts: 4,793
RE: Changing wheel size question
question wasnt specific enough. Everones right! Thats me tryin to keep the peace
What size tire are you planning to go?
heres a nifty site that will help you out if changing tire size.
http://www.miata.net/garage/tirecalc.html
What size tire are you planning to go?
heres a nifty site that will help you out if changing tire size.
http://www.miata.net/garage/tirecalc.html
]
11-23-2005, 11:02 PM
#10
1st Gear Member
Join Date: May 2005
Location: Bradenton, Florida
Posts: 78
RE: Changing wheel size question
Sorry to offend you but you did state"Wheel change by itself does not change tire diameter" That is an absolute statement which is not correct. That is why I stated "But that is not true" No need to get mad. Maybe I should have not been so picky and you should have not made an absolute statement. I apologize. 
I will say this though. Its hard to get tires that do exactly match each other in diameter when you change wheel diameter. They are typically off by some amount. That's why I asked "The question that I have is how much of a overall diameter change constitutes a need to retune the vehicle?" Can someone answer that question please?
I will say this though. Its hard to get tires that do exactly match each other in diameter when you change wheel diameter. They are typically off by some amount. That's why I asked "The question that I have is how much of a overall diameter change constitutes a need to retune the vehicle?" Can someone answer that question please?