Correct tire pressure

[Chipe]

Put Michelin Defender LTX M/S 295/70r18's on my Sahara, with 1 5/8" spacers and 2" Mopar lift. I just checked the tire pressures for the first time and the dealer has them at 50psi. Max for this tire is 80

My question: shouldn't they be at the pressure that is on the door frame? Thanks!

Sponsored

 

[Uhdinator]

Door jam spec is for stock tires with max capacity (4 passengers and lists the weight)
32-34 is a good guess to start depending on load/weight.
https://www.4wd.com/article/content.jsp?childEventId=jeep-parts-resource-jeep-tire-pressure

 

[Chipe]

Did the chalk test at 45psi, which seemed reasonable, and had about an inch of chalk left on the outside edges of the tires, which means to me that it is still overinflated a little bit. I will let out about 3psi and try it again after dinner.

 

[blnewt]

I'd fast forward to the 34 psi range like Uhdinator mentioned, JLs just aren't that heavy vs. the typical weight the tires are designed for.

 

[Chipe]

Will try it out!

 

[Chipe]

I'd fast forward to the 34 psi range like Uhdinator mentioned, JLs just aren't that heavy vs. the typical weight the tires are designed for.

Went to 35 but till have a bit of chalk at the very outside edges of the tires on two of them. I think it will be fine for now.

 

[Chipe]

I'd fast forward to the 34 psi range like Uhdinator mentioned, JLs just aren't that heavy vs. the typical weight the tires are designed for.

One last question: Will I have to recalibrate my speedo again with the TazerJL due to pressure changes?

 

[Uhdinator]

You need to measure actual height with load on tires with a tape.....Mfr size/spec is unmounted tire size.
Set Tazer for actual tire height/diameter. My 305/65 tires are @ 30 cold. They warm up to 33 psi (10% change). You'll find the ride much nicer. Keep in mind the factory PSI is designed to be a compromise of MPG vs Tire life. I prefer to be on the lower side that favors ride/tire wear over MPG. Rim width effects Psi also. An 8" rim with an 11-12" wide tire will require a little less psi than a 9 or 10" rim to have the tread flat and not rounded in the center.

 

[Chipe]

You need to measure actual height with load on tires with a tape.....Mfr size/spec is unmounted tire size.
Set Tazer for actual tire height/diameter. My 305/65 tires are @ 30 cold. They warm up to 33 psi (10% change). You'll find the ride much nicer. Keep in mind the factory PSI is designed to be a compromise of MPG vs Tire life. I prefer to be on the lower side that favors ride/tire wear over MPG. Rim width effects Psi also. An 8" rim with an 11-12" wide tire will require a little less psi than a 9 or 10" rim to have the tread flat and not rounded in the center.

Thank you. I will measure tomorrow morning!!

 

[Chipe]

You need to measure actual height with load on tires with a tape.....Mfr size/spec is unmounted tire size.
Set Tazer for actual tire height/diameter. My 305/65 tires are @ 30 cold. They warm up to 33 psi (10% change). You'll find the ride much nicer. Keep in mind the factory PSI is designed to be a compromise of MPG vs Tire life. I prefer to be on the lower side that favors ride/tire wear over MPG. Rim width effects Psi also. An 8" rim with an 11-12" wide tire will require a little less psi than a 9 or 10" rim to have the tread flat and not rounded in the center.

Ok, so I measured it exactly at 33.8125 inches. Set that in the TazerJL, and was still off by about 2 mph (slow). So I set the tires to 34.19 something, and now the speedo is spot on.

 

[roaniecowpony]

You need to measure actual height with load on tires with a tape.....Mfr size/spec is unmounted tire size.
Set Tazer for actual tire height/diameter. My 305/65 tires are @ 30 cold. They warm up to 33 psi (10% change). You'll find the ride much nicer. Keep in mind the factory PSI is designed to be a compromise of MPG vs Tire life. I prefer to be on the lower side that favors ride/tire wear over MPG. Rim width effects Psi also. An 8" rim with an 11-12" wide tire will require a little less psi than a 9 or 10" rim to have the tread flat and not rounded in the center.

Ok, so I measured it exactly at 33.8125 inches. Set that in the TazerJL, and was still off by about 2 mph (slow). So I set the tires to 34.19 something, and now the speedo is spot on.

If you jack the vehicle and measure the circumference of the tread at the outer edge, the tire will not change circumference with pressure. It will change circumference a bit in the middle of the tread as it crowns from pressure. But that won't matter if you lower the pressure to allow the edge of the tread to contact the road. Lower pressure than that won't change the distance the vehicle moves with each revolution. Otherwise a M1 tank would only move 12 feet for every track revolution.

Sponsored