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Discussion Starter #1
I had 20x8 inch wheels all around factory with PSI 32 per door.

Bought new rims, 20x8.5 front, and 20x10 on the back .

Also bought new tires, mickey thompson street comp 255/35/20 front, and 275/40/20 on the back.

My question is this... What is the PSI i should use on daily driving ? Do i stick to what my door tells me even though i am using new rims and tires which are different kind than my factory rims and tires ?

Also since the backs are wider, do they need to have a different PSI than my front?

Last but not least, on the track do you lower the PSI to about 20 on the back for traction? What about the fronts at the track ?
 

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Dazed & Confused
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I've got 245/45/20 w/9" rims on the front and 275/40/20 w/10" rims on the rear running Nitto Invo's. My paperwork from Discount Tire said 32 psi on the front and 29 psi on the rear. Not sure if your's would be similar or not.
 

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Dash Cam Guy
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I have 275's on the rear of mine and I run around 32psi. It is higher now since it has warmed up. Yesterday they were at 36psi so I have to let some out. Next time I go to the track I am going to try 40psi up front and 25psi for the rears.
 

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Discussion Starter #4
Called Mickey Thompson tech and they told me to use 41 front and 29 in back to even out all 32 PSI factory ? I don't think that is right, and talking to dodge sales/tech , they mentioned just to keep 32 on all 4 tires even with aftermarket rims and tires even if size is different now.
 

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Premium Member
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I have been running about 40 psi for the street it is a bit harsh so I might back it off to 37 .

For the road track you will want as much pressure as possible for corners, so the side wall stays stiff and solid, not sure on the drag strip
 

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Look at the tires or the manufacturer specs and make note of the minimum and maximum tire pressures. The ideal pressure depends on what you intend to accomplish. Under inflated tires tend to run on the outside edges of the contact patch and over inflated tires tend to run on the center.

This being said, at the track where you want less friction from the front tires, ,run higher pressure in them so there is less contact patch. Don't exceed the maximum recommended, but I'd say air them up to the max.

For the rears you have to remember that heating the tires increases the pressure, so run them just slightly below best contact patch. And you may be wondering how you get the best contact patch, well back in the day we did it with a piece of chalk and some dry flat ground. Set your air pressure and then chalk line the tread area all the way across the tire in several places. Roll the car forward and make a note if the chalk is rubbing off evenly. If it isn't, adjust the air pressure (down to make the edges contact and up to make the center contact). Remark the lines and try again. This should be done in a straight line as cornering forces make it a whole other story.

It is possible to have 4 different pressures to have maximum contact at the 4 corners. It is also possible that a full contact patch will not be obtainable due to suspension geometry, but you can still get the maximum contact available for your car with this method.
 

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I have been running about 40 psi for the street it is a bit harsh so I might back it off to 37 .

For the road track you will want as much pressure as possible for corners, so the side wall stays stiff and solid, not sure on the drag strip
Try using the method I just described and then take the car around the track. Let me know if your times improve. It's not maintaining sidewall strength that is the ultimate goal. If the tire is on a properly sized rim it shouldn't have a problem staying on the rim.

Grip is more important than sidewall lean. At least that is how it used to be back in the day.
 

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Discussion Starter #8
Look at the tires or the manufacturer specs and make note of the minimum and maximum tire pressures. The ideal pressure depends on what you intend to accomplish. Under inflated tires tend to run on the outside edges of the contact patch and over inflated tires tend to run on the center.

This being said, at the track where you want less friction from the front tires, ,run higher pressure in them so there is less contact patch. Don't exceed the maximum recommended, but I'd say air them up to the max.

For the rears you have to remember that heating the tires increases the pressure, so run them just slightly below best contact patch. And you may be wondering how you get the best contact patch, well back in the day we did it with a piece of chalk and some dry flat ground. Set your air pressure and then chalk line the tread area all the way across the tire in several places. Roll the car forward and make a note if the chalk is rubbing off evenly. If it isn't, adjust the air pressure (down to make the edges contact and up to make the center contact). Remark the lines and try again. This should be done in a straight line as cornering forces make it a whole other story.

It is possible to have 4 different pressures to have maximum contact at the 4 corners. It is also possible that a full contact patch will not be obtainable due to suspension geometry, but you can still get the maximum contact available for your car with this method.
I thought i had to deflate the tires down to like 20 so it would be more on the ground when taking it to the drag track ? Your saying go higher ?
 

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I thought i had to deflate the tires down to like 20 so it would be more on the ground when taking it to the drag track ? Your saying go higher ?
You want the least rolling resistance on the front tires. So air the fronts all the way up. That will make it roll on the center of the contact patch and give the least rolling resistance. Do this on the front tires only.

On the rears you want more contact patch to get better traction. Air them down about 1 pound under best contact patch as I described. By the time you heat them up with a burn out, they should be just about right.
 
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