Min Tire Pressure for 40-series without Beadlocks (1 Viewer)

[AlexJet]

What is minimum Tire Pressure can be run on FJ40 with 35s MT tires on 17" rims (315/70-R17)?
What would be recommended tire pressure?

I have been searching the web and forums, but what I get allot is recommendations for Jeeps on 15" rims. Many runs 10-12 psi on 31s and 33s with 15" rims on Jeeps. Some extreme drivers use 8-10 psi, but state they tend to loose beads sometimes on rocky terrain. I also read that running bigger rims can raise the min tire PSI.

40-series is weighting close to the Wrangler (CJ/YJ). Using that logic, would it be 15psi for safe off-road drive? I usually wheel on rocky and mud ruts terrain.

How many run 17" wheels on their 40-series and how low have you personally going when off-roading without beadlocks?

 

[shawnfj40]

I have never lost a bead at 15 and I have lost a couple at 10.

 

[JohnnyC]

On my old stocker 15" rims I ran 15psi regularly without issue

On my 16" I used to go down a lil further to 12psi ... but they are split ring rims

 

[lc69hunter]

I run 12 lbs on my 33X9.50 on stock 15 in rims

 

[vfrer]

How wide are your rims? It will have an impact on the beads holding. I run 36x12.5's on 15x8" rims. The narrow rim relative to a wider tire helps hold the beads. I run ~8psi and have not lost one yet.

 

[White Stripe]

If you air down without beadlocks, the rim can spin in the tire. This will ruin the balance and you will have to get the tires balanced again. I tested it once by marking my tires to wheel relationship with tire chalk. By the end of the trip, the Marks were 180 degrees apart. When you have 5 ounces or more weight on the wrong side of the wheel, it can be felt pretty bad at highway speed. I got tired of balancing my tires all the time, I have beadlocks now.

 

[AlexJet]

How wide are your rims? It will have an impact on the beads holding. I run 36x12.5's on 15x8" rims. The narrow rim relative to a wider tire helps hold the beads. I run ~8psi and have not lost one yet.

I run 315/70-R17 (35×12.5-R17) MT tires on 17x9 rims.

 

[AlexJet]

If you air down without beadlocks, the rim can spin in the tire. This will ruin the balance and you will have to get the tires balanced again. I tested it once by marking my tires to wheel relationship with tire chalk. By the end of the trip, the Marks were 180 degrees apart. When you have 5 ounces or more weight on the wrong side of the wheel, it can be felt pretty bad at highway speed. I got tired of balancing my tires all the time, I have beadlocks now.

I'm aware of this concern as well as possibility of loosing a bead especially on front tires at the obstacles. This is why I'm trying to get an opinion of what could be the safe minimum pressure 35s on 17" can be run with, hoping to get people first hand opinion and personal experience.

 

[White Stripe]

I'm aware of this concern as well as possibility of loosing a bead especially on front tires at the obstacles. This is why I'm trying to get an opinion of what could be the safe minimum pressure 35s on 17" can be run with, hoping to get people first hand opinion and personal experience.

In my experience 12 is pretty safe. 8psi is a little sketchy. Tire construction plays a fair amount into it. Also if the tire is pretty wet it's more likely to loose a bead, especially in the single digits.

 

[76 PTO]

I run 6psi on 15 x 8 with 33 x 13.5 ltbs in the sand. I use bead glue, and have to watch it carefully.

 

[reddingcruiser]

FWIW, I usually run in the 10 - 12 psi range, but have run 8 - 10 psi with no problems. A lot has to do the weight of my rig and the trail. Fully loaded with a weeks worth of stuff for the Rubicon, around 10. Empty day runs, <10.

 

[TCinVA]

Before I had beadlocks I would run 10 psi, never had a problem. With some heavy boggers I ran 8 psi.

 

[pjohnson]

As mentioned, the width of the wheel vs tire is important. But also important is the height of the sidewall. The more sidewall, the more flex. A 37 on a 15" wheel will flex a bit more than a 37 on 17" wheel. I think more tire flex is better but could be wrong.

I run 37x12.5 on 15x8 wheels at 8 -10 psi with no issues.

 

[Tin basher]

The style of safety bead on the rim effects how well the tire stays on with lower pressure too
Some 17 rims take little effort to break the beads
With a tire machine and others are a battle to break
Range Rover factory rims are a bitch to break down

 

[AlexJet]

The style of safety bead on the rim effects how well the tire stays on with lower pressure too
Some 17 rims take little effort to break the beads
With a tire machine and others are a battle to break
Range Rover factory rims are a bitch to break down

I have Procomp 7015 17x9 (-12 Offset) rim with 315/70-R17 Procomp Xtreme MT tires