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Discussion Starter · #1 ·
So, I am considering upgrading the rims on my R/T to 20s. I got to think what effect this would have on the rest of the car. A question that has come to mind is this. Does changing out the rims and tires have an effect on the low tire pressure indicator sensor? Where is the sensor installed?
 

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The sensor is the valve stem, which you should be able to switch to the new wheels with no issues...just keep the overall diameter within .2 of an inch and you would not have to flash the computer...
 

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Discussion Starter · #3 ·
Ok, that makes sense. Thanks.
 

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chargershed said:
just keep the overall diameter within .2 of an inch and you would not have to flash the computer...
Actually you need to keep the size of the tire within +/- 3% of the original size to not affect the speedo. This is industry standard.

The .2 of and inch is not accurate.
 

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autoguy said:
Actually you need to keep the size of the tire within +/- 3% of the original size to not affect the speedo. This is industry standard.

The .2 of and inch is not accurate.
You are both correct and wrong all in the same post. I have also heard of the plus/minus 3% to be within margins for the speedo. However, any change WILL have an affect on the speedo if they are not the same diameter as the computer is set for. For example, the Daytona's 235/55R18 are 28.17" in diameter. Even one percent larger will have you doing more than 60MPH with it only indicates you doing 60MPH. It is just that the difference is so small as to not really worry about. So yes you are right that the plus/minus 3% is a "guide" to go by when trying to decide on new tires. That is unless you want a specific tire and are willing to have the computer reset to the new size.

You are wrong however that .2" plus/minus is not accurate. Using your own 3% guide, the Dayona's 28.17" can go between 29.01" and 27.32" in diameter to fall within your guide range. 28.17" plus/minus .2" is 28.37" and 27.97". Well within your guide range and is in fact only plus/minus 0.7%. The overall variance of 1.69" in your guide will give all sorts of strange readings on the speedo the farther you get from OEM size.

After doing some extensive spreadsheet analysis researching these differences in tire sizes, I found that to keep the speedo anomolies to a bearable difference you have to stay within a plus/minus .8% of OEM diameter. chargershed's suggestion of .2" is very valid and quite acurate in my opinion.
 

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I guess what I was trying to say is that you can go UP TO 3% larger or smaller without having an adverse affect on the functionality of the ABS, engine control systems, etc.

Yes, if you put it in a spreadsheet, you can analyze it to death. If you want to get really technical, keep the EXACT same size as OE and then there will not be any problems.

Think about the tires wearing, if you really analyze it, the size actually changes as the tire wears.

Another thing you will see is that different manufacturers have different size specs for the same size tire.
 

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autoguy said:
I guess what I was trying to say is that you can go UP TO 3% larger or smaller without having an adverse affect on the functionality of the ABS, engine control systems, etc.

Yes, if you put it in a spreadsheet, you can analyze it to death. If you want to get really technical, keep the EXACT same size as OE and then there will not be any problems.

Think about the tires wearing, if you really analyze it, the size actually changes as the tire wears.

Another thing you will see is that different manufacturers have different size specs for the same size tire.
Yes, 3% is a good casual guide. Going beyond it will get you into speedo differences that are more than just a mile or two off and can get you into trouble, or at the minimum have you putting more mile on than you really are.

Yes, I do analysize things to death, I like things in detail so that I know fact from fiction and to judge where I draw the lines of acceptability. If you or others choose to go casual, that your choice.

Correct, as tires wear, it does affect your the size of your tire, but from brand new tread to worn out tread (the 3/32" basis for when to change rubber) we are still talking only about .2 or .3 inches in difference.

I based my calculation of the diameter on the formula for tire ratio and wheel diameter, not on manufacturer's specs. I would assume that there would be some variance between manufacturers, but only slight ones that are within acceptable ranges.
 

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I just had a local shop install my Davin 22s and I guess they did not transfer this across. They said to go to the local dealership and have the computer reset to not recognize the sensor or something. What are your suggestion or shoul I have them remount with the valve stem or whatever will make the blinking light go away.... :confused: This was the first charger they did and said they did not know of the issue. Oh well it can always be fixed?!?!
 

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maximus said:
I just had a local shop install my Davin 22s and I guess they did not transfer this across. They said to go to the local dealership and have the computer reset to not recognize the sensor or something. What are your suggestion or shoul I have them remount with the valve stem or whatever will make the blinking light go away.... :confused: This was the first charger they did and said they did not know of the issue. Oh well it can always be fixed?!?!
The shop is just inexperienced, there is a reset code for al vehicles with Tire pressure sensors, some dealerships arent to friendly when giving up that information due to their loss in aftermarket sales, if you can PM and let me know where you bought your davins. Call dodge and see if they will give you the reset code, if they do dont be alarmed when they tell you to turn the lights on and off 3 times and turn the key to on and put the parking brake on, it sounds weird but thats how many computers are reset today. Goodluck!
 

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I actually got the wheels from a rep then had a local shop install them. I would have assumed they would have know this since they deal with high end cars all the time.

As far as the dealer.. I went to the dealer and they said they could not do anything. They said just get them remounted and have the sensors installed. I guess I will when i have time.. At this point the light just flashes randomly and not enough to bother me. I even have kind of forgotten about it.
 
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