18 inch to 20 inch Tire Pressure

[johncode]

I upgraded my factory 18 inch tire and wheels to 20x9 with 285/60r20. After the change my tire pressure reads low in the front and says inflate to the factory 55 psi. Discount tire says it works itself out but it’s been about 100 miles so far and still reads low. I googled and searched and just saw that factory is around 39-40psi but not a solution to my issue.

 

[Ramjack]

55 psi? Isn't 36 psi the factory spec? How low are they reading?

 

[johncode]

For reference just 0 offset 20x9 wheels

 

[johncode]

55 psi? Isn't 36 psi the factory spec? How low are they reading?

40 all around. Says fill front to 55

here’s a pic of the sag at contact

 

[Daverous]

That's the correct factory spec. You'll need to adjust it in the bcm, it will not self adjust those peramitors. Alfaobd is a good option for this. Or perhaps try a dealer.

 

[johncode]

That's the correct factory spec. You'll need to adjust it in the bcm, it will not self adjust those peramitors. Alfaobd is a good option for this. Or perhaps try a dealer.

Dealer said they were looking into it. Have an oil change due in about a month so may just do it then. Just thought it was odd I couldn’t find anything mentioning the issue.

 

[clazer]

Open the door, look at the plate. That’s what the truck cares about- it will give low pressure warning unless you’re within 5psi of that number. Since you had 18’s, you door plate says 55 front (engine weight) and 45 rear (for empty ride quality).

 

[johncode]

Open the door, look at the plate. That’s what the truck cares about- it will give low pressure warning unless you’re within 5psi of that number. Since you had 18’s, you door plate says 55 front (engine weight) and 45 rear (for empty ride quality).

Yes but wouldn’t 20 inch wheels have lower pressure?

 

[Ram1500rsm]

They’ll take more psi to maintain the same weight support. You have less sidewall with 20” so you need more air. What’s the factory tire and load rating on the Rebels? I’m surprised with RAM factory psi values. 2020 Tundras take 30 front 33 rear. 17 Tacoma’s are 29/29. In my truck factory was 39/39. I’m running my 315/70/17 tires at 35 and that exceeds what the factory calls for in my placard. Ran 37x12.5x17 at 30psi for 15k miles. Hate to run pumped up tires especially on something E rated. Is like driving on damn rocks

 

[johncode]

They’ll take more psi to maintain the same weight support. You have less sidewall with 20” so you need more air. What’s the factory tire and load rating on the Rebels? I’m surprised with RAM factory psi values. 2020 Tundras take 30 front 33 rear. 17 Tacoma’s are 29/29. In my truck factory was 39/39. I’m running my 315/70/17 tires at 35 and that exceeds what the factory calls for in my placard. Ran 37x12.5x17 at 30psi for 15k miles. Hate to run pumped up tires especially on something E rated. Is like driving on damn rocks

55 front/45 rear. I do like the feel of 40 all around though.

 

[bwsRam19]

 

[SD Rebel]

55 psi? Isn't 36 psi the factory spec? How low are they reading?

55 psi front and 45 psi rear is the stock psi on the Rebel 33" Duratrac tires. Because he went aftermarket and is using a different psi than stock, he is getting a warning from the computer that his pressure is too low.

The only way he can fix it is to get a tuner that allows him to adjust the PSI warning system down to his new pressures. He can also raise them and try running 50F/40R and see if that's also acceptable. That's about as low as you can go on a Rebel without getting a psi warning.

 

[SD Rebel]

They’ll take more psi to maintain the same weight support. You have less sidewall with 20” so you need more air. What’s the factory tire and load rating on the Rebels? I’m surprised with RAM factory psi values. 2020 Tundras take 30 front 33 rear. 17 Tacoma’s are 29/29. In my truck factory was 39/39. I’m running my 315/70/17 tires at 35 and that exceeds what the factory calls for in my placard. Ran 37x12.5x17 at 30psi for 15k miles. Hate to run pumped up tires especially on something E rated. Is like driving on damn rocks

May have to do with the spec of Duratrac the Rebel runs? I have run them at 55/45 and 50/40 on the street and they feel smooth and supple, which is surprising to me as someone who is use to 35 psi A/T settings on the street in previous vehicles.

I do run them at about 25 psi for hard/pack sand off-roading at my local trail.

 

[johncode]

May have to do with the spec of Duratrac the Rebel runs? I have run them at 55/45 and 50/40 on the street and they feel smooth and supple, which is surprising to me as someone who is use to 35 psi A/T settings on the street in previous vehicles.

I do run them at about 25 psi for hard/pack sand off-roading at my local trail.

Yeah I’m going to up the psi tomorrow and see how she goes. Too wet to do a chalk test.

 

[Ram1500rsm]

May have to do with the spec of Duratrac the Rebel runs? I have run them at 55/45 and 50/40 on the street and they feel smooth and supple, which is surprising to me as someone who is use to 35 psi A/T settings on the street in previous vehicles.

I do run them at about 25 psi for hard/pack sand off-roading at my local trail.

I checked tire rack and found the factory size for you guys is LT 275/70/18
So given those specs the OP only needs to add 2 psi to the factory psi on the new size LT 285/60/20 So 47/57.
I prob wouldn’t change a thing an keep them at 45/55 given the difference will be peanuts.

 

[Booch]

Air them up to what the load vs inflation table says as compared to the LT275/70R18 at 55/45. It's probably a little higher as stated above since the 285/60/20 has a lower load rating. LT tires have a wider band of pressures/loads as opposed to P tires, and the Rebels are one of the few (if not the only) 1/2 tons that come with LT tires. You could lower them a bit when empty as those pressures are to handle a full payload.

Then give them a 1000 miles or so to break in, they'll soften up a bit.

 

[johncode]

I’ll see how the settle at factory psi. I know water isn’t as good as chalk testing but looks like it’s a little over inflated