I was reading the service manual for my 06 TJ and came across this:
“For speeds up to and including 120 km/h (75 mph), tires must be inflated to the pressures shown on the tire placard. For continuous speeds in excess of 120 km/h (75 mph), tires must be inflated to the maximum pressure specified on the tire sidewall.”
I’m running street tires that have a max PSI of 51 on the sidewall. Is it seriously suggesting I inflate to 51 PSI if I’m driving over 75 mph for a long time? Or am I missing something here? The door placard says 33 PSI for all tires.
Lower pressure causes tires to heat up more due to flexing, which can lead to damage like delamination. The manual is probably just being cautious to avoid liability. It’s a good idea to air up when driving long distances on the road after off-roading.
Driving a TJ over 70 mph feels wild! Even in my '95 YJ, hitting 70 feels like the world might explode. I’ve heard if a YJ or CJ or TJ hits 88 mph, they go back in time.
Jai said:
Driving a TJ over 70 mph feels wild! Even in my '95 YJ, hitting 70 feels like the world might explode. I’ve heard if a YJ or CJ or TJ hits 88 mph, they go back in time.
Do YJs drive differently from TJs? I haven’t driven a YJ, but a TJ with worn suspension feels terrifying.
@Koa
My wife says her teeth feel loose when riding in our YJ! Leaf springs are something else. I got my YJ as a project, and it’s mostly original. I’ve replaced so many parts on it. The TJ’s coil spring suspension is better, but it’s still sketchy over 70 mph, just less “we’re going to die” than the YJ.
You’re all soft. I drive my ‘97 TJ with a rough 4-inch lift and 33-inch tires at 85 mph on highways without any issues. Sure, a breeze can nudge it, but it handles fine otherwise.
How often are you even driving a TJ at 75+ mph? 70 is my limit with all-new front-end parts. Chalk the tires to find the right pressure for your setup.
Toby said:
How often are you even driving a TJ at 75+ mph? 70 is my limit with all-new front-end parts. Chalk the tires to find the right pressure for your setup.
70 is my max too. I replaced almost every suspension and steering part this year except the steering box. This reminds me of the guy asking about panic stopping at 80 mph in traffic with a TJ!
Toby said:
How often are you even driving a TJ at 75+ mph? 70 is my limit with all-new front-end parts. Chalk the tires to find the right pressure for your setup.
Mine feels okay at those speeds, like an old truck from the '90s. A friend compared it to driving his dad’s old Ranger. Being stock probably helps.
The pressure on the sidewall is what the tire is made for, while the door placard is based on the stock tire size. Remember the Ford Explorer-Firestone tire issues? Ford recommended 26 PSI, but the tires were rated for 35 PSI. They failed a lot in high-heat areas because the pressure was too low, leading to more contact and overheating.
Think of the air in the tire as a way to manage heat. Higher pressure keeps the tire cooler at high speeds. It’s common to increase pressure when hauling loads to reduce heating from flexing.